Solar Program Overview: Fiscal Years 2002 & 2003 (Brochure) · 2 • Solar Program Overview FYs...

PHOTOVOLTAICS SUBPROGRAM

Fundamental and Exploratory Research . . . . . . . . . 6

❂ Achieved a 36.9%-efficient triple-junction terrestrial concentrator cell

❂ Demonstrated a 19.2%-efficient CIGS thin-film cell

❂ Gained approval for design of Science and Technology Facility

❂ Provided measurements and characterization support to more than 70 organizations.

Advanced Materials and Devices . . . . . . . . . . . . . . . 13

❂ Achieved 12.8%-efficient CIS module

❂ Received R&D 100 award with First Solar, Inc., for manu-facturing of CdTe PV modules

❂ Established Thin Film Module Reliability National Team to coordinate research on reliability of thin-film modules

❂ Decreased costs by more than 55% for participants in PV Manufacturing R&D projects

❂ Readied new subcontracts for award under PV Manufac-turing R&D—Large-Scale Module and Component Yield, Durability, and Reliability

❂ Reported long-term exposure data on 20 CIS modules to manufacturers to help improve module durability

❂ Created an educational industry-interactive Web site titled Cadmium Use in Photovoltaics.

Technology Development . . . . . . . . . . . . . . . . . . . . . 21

❂ Increased sources of data for reliability database

❂ Approved engineering designs for prototypes under High-Reliability Inverter Initiative

❂ Transferred dark I-V testing to PowerLight Corporation to aid quality measurement during production

❂ Supported inclusion of PV systems on the Rural Utility Service’s approved list of materials and within the National Voluntary Practitioner Certification Program and the Navajo Electrification Demonstration Program

❂ Conducted the Solar Decathlon, American Solar Challenge,and Renewable Energy Academic Partnership Conference.

SOLAR THERMAL SUBPROGRAM

Concentrating Solar Power . . . . . . . . . . . . . . . . . . . 26

❂ Developed prototype parabolic trough collector with Solargenix Energy. Tests at the National Solar Thermal Test Facility (NSTTF) at Sandia validated optical accuracy and thermal performance

❂ Developed and operated the Mod 1 prototype of the Advanced Dish Development System (ADDS) with Stirling Energy Systems with 91.4% availability during field tests at the NSTTF

❂ Demonstrated closed-loop tracking and automated opera-tion in grid-connected mode of the Mod 2 10-kW dish

❂ Demonstrated PV as receiver (dense-packed array) in dish concentrator with tests at the High-Flux Solar Furnace at NREL

❂ Formed the 1,000 MW CSP Project Team in response to Congressional interest to stimulate the deployment of CSP in the Southwest.

Solar Heating and Lighting . . . . . . . . . . . . . . . . . . . 30

❂ Provided testing and analysis to solar water heating indus-try to identify and solve problems, such as corrosion, occurring in the field

❂ Began field tests of two designs for low-cost solar water heating systems using polymer materials

❂ Began tests of a prototype hybrid solar lighting concept.

Cover photos (from right to left): With a combined output of 354 mega-watts, the Solar Electric Generating Systems’ CSP facility in southernCalifornia constitutes the world's largest solar power plant (Sandia,SNL1428-5); The owners of this Colorado home take advantage of asolar water heating system on the roof (Industrial Solar TechnologyCorp., PIX12964); 30,000 square feet of PV panels grace the roof of the Moscone Convention Center in San Francisco (PowerLight Corp.,PIX13340; A PV system is integrated into an awning over a back porchin California (AstroPower, PIX12345); Crowds flocked to the SolarDecathlon, an event that showcased solar homes designed and built by college students (Warren Gretz, NREL, PIX11779); Two megawattsof utility-scale PV generation are located at the Prescott, Arizona, air-port (Arizona Public Service, PIX13338)

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Solar Program Overview FYs and •

TTHHE SSOLLAARR EENERRGYY TTECHHNOLLOGIES PPRROGRRAAMTTHHE SSOLLAARR EENERRGYY TTECHHNOLLOGIES PPRROGRRAAM

T he sun’s energy holds tremendouspotential to diversify our energy supply, reduce our dependence on

imported fuels, improve the quality of the airwe breathe, and stimulate our economy bycreating jobs in the manufacture and instal-lation of solar energy systems. To reap thesebenefits for our nation, the U.S. Departmentof Energy (DOE) manages a Solar Energy Tech-nologies Program directed toward specific,measurable results. In partnership with universities and industry, the Solar Program conducts research and analysis to make solarenergy a greater part of our nation’s economy.

Here we report some of the impressive resultsof fiscal years (FYs) 2002 and 2003, both toaccount for taxpayer resources invested andto outline the continuing activities necessaryto reach our goal of having cost-effectivesolar energy technologies in widespread usethroughout our nation.

Essential to carrying out a complex researchand development (R&D) program is carefulplanning. In FY 2003, we drafted the firstSolar Energy Technologies Program Multi-YearTechnical Plan, which charts a five-year plan-ning cycle for Program activities and high-lights how a systems-driven approach isbeing used to achieve short- and mid-termresults and set the research direction forachieving long-term goals. This document,along with information about Program activi-ties and about solar energy technologies ingeneral, can be found on the Solar ProgramWeb site (www.eere.energy.gov/solar).

We manage the activities of the Solar Programthrough the efforts of staff at DOE and itsnational laboratories, including the NationalRenewable Energy Laboratory (NREL), SandiaNational Laboratories (Sandia), Oak RidgeNational Laboratory (ORNL), and BrookhavenNational Laboratory (BNL). This talentedgroup of scientists, engineers, and managerswork together in organizational structures we call virtual laboratories. Through coopera-tion, communication, and teamwork among

their many participants, the National Centerfor Photovoltaics (NCPV) serves as the virtuallaboratory for the Photovoltaics Subprogram,and Sun♦Lab is the virtual laboratory for theConcentrating Solar Power Subprogram. Foreach virtual lab, a single team of managers

from NREL and Sandia directs day-to-day program activities. Together with DOE man-agers, they formulate a long-term vision forthe programs, develop yearly operating plans,and negotiate cooperative agreements withthe Solar Program’s industrial partners.

This solar-powered house was designed and built by students from the University of Missouri-Rolla forthe Solar Decathlon competition in Washington, D.C., in fall 2002. This event, sponsored by the SolarProgram and others, showcased the ingenuity of U.S. college students in applying renewable energyand energy efficiency technologies for living and working environments.

With improved technology supported by DOE, the cost of solar energy in the United States has declinedsteadily. The projected costs (shown as dotted lines in the graph) are based on continuing the proposedbudget support for the Solar Program.

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• Solar Program Overview FYs and

We are witnessing yet another year of dra-matic growth in the worldwide solar energyindustry. In 2003, annual revenues from solarpower equipment and installation reached$4.7 billion. This impressive growth is found-ed on decades of research and developmentat our universities, laboratories, and in indus-try. Yet to make a bigger difference to ournation’s energy economy, we can and mustdo so much more. To this end, the SolarProgram is mobilizing the nation’s resourcesto develop a portfolio of reliable and afford-able solar energy technologies in line withguidelines in the President’s National EnergyPolicy (May 2001).

Our integrated research program works forthe wider use of photovoltaic (PV) and solarthermal approaches to solar energy conver-sion. PV and solar thermal power have manycommon challenges in entering markets anddeveloping cost-competitive applications, sys-tems, and subsystems. For example, all solartechnologies that are integrated into buildingroofs or installed on roofs have commonchallenges in satisfying builder and ownerpreferences and in interconnecting with thebuilding’s energy system.

To understand these challenges and to identi-fy the most important research required tocreate effective systems, the Solar Programuses a systems-driven approach that relatesmaterials, processes, components, products,applications, data from fielded systems, andmarkets for the technologies.

The overriding benefit of the systems-drivenapproach is the ability to see how changes inone component might affect the applicationor market for the entire system. For example,when we develop a new low-cost polymer forsolar water heaters, we open up completely new markets for the systems. On the other

hand, changes in a market can change com-ponent requirements. For example, newnational interconnection standards maychange requirements for components of PVsystems supplying power to the utility grid.Our systems-driven approach to planningand managing the Solar Program helps iden-tify common elements that impact R&Dactivities. This management style, driven by results rather than by processes, is key to building on the accomplishments of our program reported here.

Raymond A. SutulaRaymond A. Sutula, ManagerSolar Energy Technologies Program

The systems-driven approach is being used throughout the SolarProgram. At the technology level, this approach can help identify common research concerns, avoid duplication of effort, and explorehow advances in an area such as subsystems might change theassumptions or requirements for systems, applications, or markets.

A MESSAGE FROM THE PROGRAM MANAGER

The goals of the Solar Program align directlywith the National Energy Policy goals. As partof the DOE Office of Energy Efficiency andRenewable Energy (EERE), the Solar EnergyTechnologies Program works with other federal institutions to develop PV and solar thermal energy technologies. The SolarProgram works with the U.S. Department of Agriculture, Department of Defense,Federal Emergency Management Admini-stration, Office of Homeland Security, andothers. For example, in early 2004, theDefense Advanced Research Projects Agencyawarded a contract for basic research todevelop new materials for hybrid PV cells.The U.S. Army Soldier Systems Center, NREL,and other PV Subprogram subcontractors willparticipate in these efforts. By working with

other government institutions, the SolarProgram conveys and collects valuable infor-mation about how solar technologies canmake the best contribution to our nation’senergy portfolio.

The Solar Program also works closely withother DOE efforts to achieve EERE goals. For example, the Solar Heating and LightingSubprogram performs R&D and works closelywith the Building Technologies Program toovercome barriers to acceptance of solar ther-mal technologies and to increase their deploy-ment. Solar water-heating systems and PVsystems have been installed by some teamsparticipating in the Building TechnologiesProgram’s Zero Energy Buildings and BuildingAmerica activities. These teams have been

supplying valuable feedback on product specifications includ-ing pricing, aesthetics,and installation prac-tices. In other work, cooperative research is also under way through hybrid solar

lighting, with the Energy Efficiency ScienceInitiative and the DOE Fossil Energy Program.

An important part of the Solar Program is itsrelationship with industry. Through competi-tive solicitations, cooperative research anddevelopment agreements (CRADAs), confer-ences, and publications, the Solar Program brings the perspectives and resources of thesolar industry into the planning and imple-mentation of the R&D activities.

The highlights presented in this report are a sample of the accomplishments of the previous two fiscal years. They indicate thebreadth and depth of the activities underway and explain our optimism for evengreater accomplishments in the years ahead.


Through improved technologywe can ensure that America will lead

the world in the development of clean, natural, renewable and alternative

energy supplies. – President’s National Energy Policy

AMBITIOUS GOALS, STRONG WORKING RELATIONSHIPS

NCPV Director Larry Kazmerski (left) presents the 5th NCPV PaulRappaport Award to the 2002 Solar Decathlon. Accepting theaward, on behalf of the hundreds of students who participated inthis event, are DOE Solar Program Manager Ray Sutula and DOEPV Team Leader Richard King.

At the Solar Program Review Meeting in 2003, Frank Wilkins(left), Team Leader of the Solar Thermal Subprogram,

recognized Hank Price of NREL for his work in analyzing parabolic trough systems. Scott Jones (not shown) of Sandia

was honored for contributions to power tower systems.

Warren Gretz/PIX12514


T here is more than enough energyfrom the sun falling on the UnitedStates to meet our electricity needs.

Each hour, enough sunlight strikes the earthto meet the world's energy needs for anentire year. We can tap this solar energyusing photovoltaics (PV), the direct conver-sion of sunlight to electricity using semicon-ductor materials. Rooftops on existing build-ings and homes offer ideal locations for PV.

Since 1953, when the first practical solar cellproduced a few thousandths of a watt ofpower with a conversion efficiency of about5%, PV cells and modules have become afamiliar part of our lives, powering every-thing from homes, to satellites, to emergencyroadside telephones. This progression fromlaboratory to spacecraft to roadside began in the 1970s, when the federal governmentstarted working with universities and indus-try partners to harness PV for energy needson earth. The goal of the federal program hasalways been to increase the conversion effi-ciency and reliability of solar cells in order to reduce the cost of electricity generation. In addition to research to improve cells madeof silicon, the past 30 years have seen discov-eries in thin-film materials—amorphous sili-con (a-Si), copper indium diselenide (CIS),and cadmium telluride (CdTe). In the 1990s,III-V multijunction devices took center stagewith their champion efficiencies. All of thesetechnologies have been incorporated in someof today’s commercial products.

By 2003, commercial PV cells averaged 15%to 20% conversion efficiency, and ourresearchers demonstrated a laboratory cellwith nearly 37% efficiency. With improve-ments in technology and manufacturing, the cost of PV modules has dropped from$55 per watt in 1973 to $3 to $4 per watt in 2003 (2003 dollars). Annual production of PV cells in 2003 rose to about 744 mega-watts (MW) of power capacity.

Despite this progress, costs must come downeven more before PV can make a significantcontribution to our energy economy. A majorgoal of the Solar Program is to reduce thecost of electricity from PV systems fromabout $0.25/kilowatt-hour (kWh) in 2003 to$0.18/kWh in 2005. To bring costs down, theProgram conducts an aggressive R&D effortaimed at increasing efficiencies, improvingreliability and system life, and improvingmanufacturing processes.

PV SUBPROGRAM STRUCTURE

The PV Subprogram carries out these activitiesthrough the National Center for Photovoltaics

(NCPV), an alliance of organizations workingwith the U.S. PV industry to maintain ourglobal leadership position. Several nationallaboratories—NREL in Golden, Colorado;Sandia in Albuquerque, New Mexico; andBNL in Upton, New York—are key partici-pants in these efforts.

Our PV Subprogram, in conjunction with theNCPV, supports world-class scientists at thenational laboratories with the latest equip-ment, performing research aimed at our national energy goals. We use efficiency—the percentage of energy from sunlightfalling on a PV device that is converted to


UUSING PPVV TTECHHNOLLOGYY TO MMAAKE EELLECTRRICITYYUUSING PPVV TTECHHNOLLOGYY TO MMAAKE EELLECTRRICITYY

RICHARD KING, TEAM LEADER, PHOTOVOLTAICS SUBPROGRAM

The primary purpose of the DOE Photovoltaics Subprogram is to accelerate the developmentof solar electricity as a national and global energy option. In 2002 and 2003, we saw con-siderable progress. The market for PV grew by 30% for the third and fourth years in a row,and, for the first time, sales of systems for connection to the utility grid equaled sales forremote power applications. This growth and the impressive advancements in manufactur-ing and R&D are in line with the strategy and goals of the U.S. Photovoltaic IndustryRoadmap developed in 1999.

The PV Subprogram has met or exceeded the goals and milestones set by our annual andmulti-year planning process for FYs 2002 and 2003. These accomplishments include newrecord efficiencies: 36.9% for the triple-junction terrestrial concentrator cell and 19.2% for a CIGS thin-film cell. These laboratory records and the increased understanding of solar cell processes down to the atomic level led to improvements in the efficiencies ofmodules and cells coming off the manufacturing line. At the same time, module-manu-facturing costs have decreased by 55% for participants in the PV Subprogram’s PV Manu-

facturing R&D Project. Building on these accomplishments, we will work aggres-sively to meet our planned goals and milestones in FY 2004.

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electricity—as one measure of our progresswith materials, devices, and systems. Thechampion efficiencies result from materialsand devices made in the laboratory where the very latest equipment and highly trained personnel control every step of every process.

Developing PV products that can compete withother forms of electric generation begins with basic research in the laboratory, then exam-ines advanced materials and devices, continuesthrough manufacturing R&D, and extends to technology development and the market-

place. Once in the mar-ket, information about performance and relia-bility provides impor-tant feedback to all theprevious activities.

TEAMS, PEER REVIEW,AND PUBLICATIONS

Some of the researchactivities are coordi-nated by nationalteams composed of in-house researchersfrom NREL and San-dia, U.S. industrial partners, and univer-sity researchers withexpertise in a specificPV material. Industrypartners first suggestedthis approach, whichwas adopted in 1993.Teams are added astechnologies or issuesarise. About 40researchers are on each team, doing theresearch and reportingon it about every ninemonths. In FY 2003,there were researchteams for CdTe mate-

rials, CIS materials, a-Si and thin siliconmaterials, environmental safety and health,and thin-film module reliability. The PVnational teams include the nation’s bestresearch and engineering talent drawn from industry, universities, and the nationallaboratories.

Peer review of research results and manage-ment strategy is basic to the PV Subprogram,and we continue to receive high marks forour efforts. In 2003, an independent panelselected by DOE conducted a formal review

of the PV Subprogram. The reviewers includedrepresentatives from the National Aeronauticsand Space Administration, National Instituteof Standards and Technology, Electric PowerResearch Institute, Rutgers University, andUniversity of Massachusetts at Amherst. Toquote from this report, “The Thin Film Part-nership and Systems Reliability researchefforts examined during this review are out-standing accomplishments for DOE that areemblematic of the high standards and excep-tional capabilities that the panel found dur-ing the peer review of the entire program in 2001.”

Cooperation with other institutions and pro-grams maximizes the impact of our results by moving discoveries and developments tothose who can make best use of them. Forexample, papers published by NCPVresearchers in refereed journals, such asApplied Physical Letters, Solar Energy Materialsand Solar Cells, Journal of Physical Chemistry,and others demonstrate the high caliber ofwork and level of influence the PV Subpro-gram is having on the field. In the last sixmonths of FY 2003, the NCPV had more than 500 publications in journals and confer-ence proceedings. In addition, staff membersmade 92 presentations at technical meetings,including 26 invited talks.


A solar electric system includes several key components that work together to deliver electricity to the user. Cells are composed of layers of semicon-ductor and other materials that produce electric current in response to sunlight. Individual cells are connected in strings to make up the PV module that is sealed from the weather with encapsulants. Module elec-trical wires are connected by electrical junction boxes. PV modules gen-erate direct current (DC) electricity that can be stored in batteries. Chargecontrollers keep batteries from overcharging or undercharging. If alternatingcurrent (AC) is needed, such as for conventional appliances or for intercon-nection to a utility grid, an inverter or power conditioner is necessary.

The primary purpose of theDOE Photovoltaics Subprogram is to accelerate the development of PV as a national and global

energy option.


PV FUNDAMENTAL AND EXPLORATORY

RESEARCH: PUSHING THE FRONTIERS

The PV Subprogram supports fundamentalresearch to understand the limitations of current and next-generation PV technology.Building on this understanding, researchersthen work to push PV technologies to thelimit. They conduct exploratory research toidentify strategies to “leapfrog” or jump overand avoid protracted R&D to completely newtechnologies. These breakthrough technolo-gies could make a dramatic impact on energymarkets.

The PV Subprogram supports two main areasof basic research. The first explores defectsand structures of electronic materials anddevices to discover ways to increase efficien-cies and to validate novel fabrication tech-niques. The second applies material anddevice-processing science to develop newtools for deposition, processing, and charac-

terization of electronic materials. These toolswill allow us to integrate processes and diag-nostics in any number of ways, thus provid-ing the opportunity to study research prob-lems that were previously difficult or evenimpossible to pursue. Both areas involveclosely coordinated efforts among scientistsat the national laboratories, at universities,and in industry.

BASIC AND UNIVERSITY RESEARCH: ORGANIC

SEMICONDUCTORS, NANOTECHNOLOGY, THIRD-GENERATION SOLAR CELLS, AND CREATIVE

STUDENTS

To help stimulate creative ideas and movethem into the development process, the PVSubprogram has awarded contracts under the

Future Generation PV and PV Beyond the Horizon projects. Beginning in 1999, contracts to 29 univer-sity teams and four companies have explored new concepts to better understand their potential. These efforts have sparked the interest of industry,and some subcontracts have resulted in start-up companies.

This effort to explore unconventional ideas for converting sunlight into electricity has met and exceeded its overallgoals and objectives by

identifying a number of very promising newapproaches to solar cells. Results have beenpresented at two conferences sponsored byDOE and NREL in FYs 2002 and 2003, FutureGeneration Photovoltaics and Photovoltaicsfor the 21st Century II. At these conferences,international experts and the DOE contrac-tors presented research on new materials orprocesses for generating electricity from thesun. Peer reviews of research results ensuredhigh-quality contract performance.

The approaches explored under basic anduniversity research include high-efficiencyconcepts for which costs need to be reduced—or low-cost concepts for which efficiencyneeds to be increased. Projects have also con-tributed to some of the more mature tech-nologies in the PV Subprogram. For example,several universities have worked to under-stand the Staebler-Wronski effect in amor-phous silicon and develop ways to ameliorateit. Three projects explored innovative deposi-tion techniques that can be used for thin-filmPV modules, and at least one subcontractormay bring its idea to commercial realitythrough subcontracts in other parts of thesubprogram such as PV Manufacturing R&D.

Organic and Nanotechnology Solar Cells

One approach addressed by six DOE-fundedprojects explores using organic semiconductorsin solar cell technology. Organic semiconduc-tors, recognized in the 2000 Nobel Prize forChemistry, hold promise as building blocksfor organic electronics, displays, and solarcells. In conventional PV technologies (siliconand thin-film materials), light creates separatedelectrons and holes that are swept away byan internal electric field produced by a p-nsemiconductor junction. In an organic solarcell, light creates a bound electron-hole paircalled an exciton, which separates into anelectron on one side and a hole on the otherside of a material interface within the device.

This effort to explore uncon-ventional ideas for converting sun-light into electricity has met and

exceeded its overall goals…

An NREL research team holds the world efficiency record for a cadmium telluride PV cell. Innovations include a CdSn transparent conducting oxidelayer (for superior conductivity, strong optical transmittance, and a smoothersurface) and a ZnSn buffer layer (for improved performance and repro-ducibility). Shown above are Xuanzhi Wu (left) and James Keane.

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One result of this different process is thatorganic solar cells can be about 10 timesthinner than thin-film solar cells, which arethemselves about 100 times thinner thancrystalline-silicon solar cells. Organic solarcells could be manufactured in a processsomething like printing or spraying the mate-rials onto a roll of plastic. Consequently,organic solar cells could lower costs in threeways—low-cost materials, reduced materialuse, and high-volume production techniques.

The PV Subprogram has funded work onorganic solar cells at a variety of universities,including early efforts at the University ofCalifornia at Berkeley and Vanderbilt Uni-versity for quantum dots (a nanotechnology)embedded in an organic polymer. Later proj-ects included work on heterojunction small-molecule solar cells at Princeton University,liquid-crystal (small-molecule) cells at theUniversity of Arizona, polymer cells at the

University of California Santa Cruz and NREL,and small-molecule chromophore cells atJohns Hopkins and North Carolina StateUniversity. Work will be completed in

FY 2004 with the goalof increasing the effi-ciency of organic solarcells to 4%. New effortsare planned to begin in 2004 to increase theefficiency from 4% to7.5% by 2007.

Nanotechnology for PVis exciting because theoptical and electronic


This graph of measured solar cell efficiencies reflects the significant progress that has been made in fabricating devices from 1975 to the present.

A schematic of a dye-sensitized solar cell, which uses nanoparticles of titanium dioxide as the semiconductor, is shown above. A group from the California Institute of Technology is working on an all-solid-state device to overcome problems associated with a liquid electrolyte.

Researchers at Vanderbilt University are investigatingPV photosystems based on semiconducting nano-crystals. The size-tunable bandgap, large absorptioncoefficient, intrinsic electron-hole-pair separation,long exciton lifetime, and chemical robustness makethese nanocrystals an ideal PV material.


properties of the materials can be tuned bycontrolling particle size. This novel class ofsemiconductor material, including quantumdots, lies between the single-atom and solid-state forms of matter. Nanostructured solarcells are likely to be extremely thin becausethey are also excitonic. They may be easy tomanufacture when the nanoparticles are pro-duced by means of chemical solution.

Dye-Sensitized Solar Cells

Dye-sensitized solar cells have foundations inphotochemistry rather than in the solid-statephysics that support research in today’s sili-con or thin-film solar cells. In these simplecells, titanium dioxide (TiO2) serves as aporous matrix holding organic dye mole-cules. The dyes are sensitive to the solar spectrum and after the dye absorbs photons,electrons are injected into the TiO2. Dye-sensitized solar cells are extremely attractivebecause of their near 11% conversion effi-ciency and the low cost of the constituentmaterials; TiO2 is a common material used in paints and toothpaste. In addition, themanufacturing process could be quite simplecompared to other PV technologies. At thePhotovoltaics for the 21st Century II confer-ence, more than a dozen experts favorablyassessed progress on this technology by theDOE Solar Program. Work on dye-sensitizedsolar cells will continue at NREL and atselected universities in 2004.

A direct result of work supported by the PVSubprogram is the commercialization effortof a new U.S. company, Konarka. Havinggathered investor support, the companybegan developing the dye-sensitized solar cell technology for use on flexible substratesin 2003. Work supported by DOE in 2004 at several universities will help Konarka byincreasing the understanding of transparentconducting coatings for their cells andexploring a new version of their dye cell thathas an organic electrolyte.

Continued progress in basic research and technology development demands a good

supply of talented new scientists coming from our universities. To provide research

experience and to spark the interest of talented students, the Solar Program helps

sponsor several projects for undergraduate and graduate students in the field of solar

energy. The most visible of these projects was the 2002 Solar Decathlon, a challeng-

ing competition for college student teams to design, build, and operate a small home

powered only by solar energy systems. Students in many academic disciplines

worked together on each team to bring their houses to the competition on the

National Mall in Washington, D.C. All of the houses in this Solar Village showcased

the latest energy-saving products, advanced building techniques, and renewable

building materials. All houses used both photovoltaic and solar thermal technologies.

Plans for the next Solar Decathlon, to be held in the fall of 2005, are under way,

with 19 teams selected and briefed on the contest procedures.

Once again, in the summer of 2003, the nation was intrigued by the American Solar

Challenge, an intercollegiate competition to design, build, and race solar-powered

cars across the United States. NCPV staff has helped organize this biennial competi-

tion since its inception in 1990.

Another important project to encourage students to study solar energy is the DOE-

NREL HBCU (Historically Black Colleges and Universities) Photovoltaic Research

Associates Program, which includes the Renewable Energy Academic Partnership

(REAP). Begun in 1995, this program reached out to students in colleges with large

populations of minority students, who are typically underrepresented within science

careers. A variety of research projects in PV have been funded at these schools, many

of them linked to different parts of the Solar Program. The annual REAP Conference

in 2003 featured presentations on the most recent research projects of these students

and their professors. Twelve students from these schools worked on a variety of PV

projects at NREL as summer interns in 2003. In FY 2003, the Minority University

Research Associates (MURA) program was announced to more than 250 minority-

serving institutions. This is a successor to, and expansion of, the HBCU Program and

will run through 2004 and beyond.

The projects of the Solar Energy Technologies Program further benefit students

through the efforts of the national laboratories, including NREL, Sandia, and ORNL.

These organizations all have agreements with universities to employ students on

research projects funded by DOE and others.

THE SOLAR PROGRAM INSPIRES OUR YOUTH


Third-Generation Solar Cells

Researchers around the world are looking forideas with the potential of converting solarenergy into electricity with efficienciesbetween 60% and 85%. Referred to as “third-generation PV” by Martin Green, who devel-oped the highest-efficiency crystalline siliconsolar cells in the 1980s, many of these ideashave been around for decades but lackedenabling technologies to move beyond theory.For example, the idea of a multijunction solar cell that is sensitive to several differentcolors of the solar spectrum was made possi-ble years after its inception by a technologybreakthrough in the 1980s. The resulting

high-efficiency III-V solar cells (referring toelements in groups III and V of the periodictable) have demonstrated efficiencies todayapproaching 37%.

The PV Subprogram has been contributing tothis search by funding universities to conduct fundamental and exploratory research tobring theories closer to the reality of mate-rials and devices that can be tested in thelaboratory. One success story has been thework of several universities to explore newIII-V compounds (particularly GaInNAs as a potential third-junction material) for evenhigher four-junction solar cell efficiencies.

Several of these projects explored fabricatingmultijunction III-V solar cells on cheaper sub-strates. Successes of this work were continuedby other elements of the PV Subprogram,such as the High-Performance PV Project (seepage 10). In 2004, a new university projectwill explore a different third-generation con-cept for getting multiple charge carriers perphoton, this time in an organic solar cell.

In FY 2003, a request for research proposalsfrom universities under the Future Gener-ation PV Project attracted an exciting groupof proposals for research into high-efficiencyorganic solar cells, third-generation concepts,high-efficiency III-V solar cells on low-costsubstrates, and innovative crystalline siliconconcepts. Some of this work may begin in FY 2004.

MEASUREMENTS AND CHARACTERIZATION:TRACKING OUR PROGRESS

Every activity of the PV Subprogram relies tosome extent on the resources of the NCPVmeasurements and characterization effort atour national laboratories—NREL, Sandia, andBNL. These measurements and characterizationteams help researchers measure progress andbetter understand the behavior of materialsand devices. Measurements include electro-optical characterization, microscopy, surfaceanalysis, and more. The teams also developand implement new and specialized measure-ment techniques, allowing researchers to testand analyze thousands of materials and devicesamples each year. This effort also helpsdevise diagnostic tools to advance manufac-turing R&D.

The measurements and char-acterization activity cuts across all

strata of the PV Subprogram from basicR&D to module and system performance

to solar resource assessment and characterization of materials

and devices.

In July 2003, 20 teams of college students put theirdesign and engineering skills to the test by entering

their PV-powered cars in the American Solar Challenge. This 10-day “road rayce” traversed

more than 2,200 miles on historic Route 66 from Chicago, Illinois, to Claremont, California,

encountering a variety of climates, topography, and road conditions along the way. The University of Missouri-Rolla was the overall winner and North Dakota State University won the Stock Class. But in a sense, everyonecame away a winner. The students celebrated a well-earned sense of accomplishment and the media and public saw that solar power

was up to the task.

Photos courtesy of the American Solar Challenge.


The measurements and characterization activ-ity cuts across all strata of the PV Subprogramfrom basic R&D to module and system per-formance to solar resource assessment andcharacterization of materials and devices. InFY 2003 alone, the NCPV measurements andcharacterization effort provided support tomore than 70 participants in industry, uni-versities, and national laboratories.

HIGH-PERFORMANCE PV: RECORD

EFFICIENCIES, LOWER COSTS, AND NEW

PROTOTYPES

The High-Performance PV Project explores theultimate performance limits of existing PVtechnologies, seeking to nearly double theirsunlight-to-electricity conversion efficienciesduring its course. This work includes bringingthin-film tandem cells and modules toward25% and 20% efficiencies, respectively, anddeveloping precommercial multijunction con-centrator modules able to convert more thanone-third of the sun’s energy to electricity.

High-performance PV with concentrators isbeing developed for markets at least 10 yearsin the future. One attraction is the possibilityof generating low-cost electricity by usingsmall, highly efficient solar cells with large,inexpensive concentrating lenses or mirrors.The PV Subprogram awarded 2-year subcon-tracts under the High Performance PVProject, “Identifying Critical Pathways,” in FY 2001. These contracts to university andindustry contractors complemented work byNCPV in-house scientists in the areas of thin-film multijunction cells and high-efficiencyIII-V multijunction cells.

Multijunction solar cells achieve higher effi-ciencies by using a broader portion of thesolar spectrum and by achieving more effi-cient conversion of individual photons. Therefore, research is aimed at improvingmaterials and processes to maximize per-formance and offer low-cost manufacturingpotential.

Moving toward the goal of higher efficiencies,the new world-record conversion efficiency(36.9% at up to 600 suns concentration) wasachieved under a High-Performance PV sub-contract by Spectrolab, Inc. This result buildson the NREL-patented two-junction devicelicensed to Spectrolab. The company modi-fied the two-junction device into a triple-junction solar cell. The champion cell,

measuring about one-quarter of a square centi-meter in area, was fabricated and tested atSpectrolab and then measured at NREL understandard reporting conditions. Adding anotherjunction (the third of four junctions) to thisdevice using material with a bandgap of 1 elec-tron volt (eV) would raise the theoretical efficiency to 50%. Cells such as these coulddramatically reduce the cost of generating

From Atoms and Molecules to Processes and Products

In current research programs, resources to conduct fundamental research, applied

research, prototype manufacturing, and full-scale manufacturing are separated, both

physically and organizationally. This arrangement has limited the rapid movement of

research technology and relevant intellectual property from R&D to U.S. industry. The

planned Science and Technology Facility is designed to speed the transition from

fundamental R&D to full-scale manufacturing by adding laboratories for process-

integration research, diagnostic development, and process simulation right next to

existing research capabilities of the Solar Energy Research Facility at NREL. After

construction in FY 2006, the new laboratories will be used for work on PV, energy

sensors, and energy storage. However, the flexible design of the facility means that

laboratories can be converted quickly and at minimal cost to conduct R&D in new

areas, as required by the U.S. energy research programs.

THE SCIENCE AND TECHNOLOGY FACILITY


electricity from solar energy. Another High-Performance PV subcontractor, Amonix, Inc.,is working to integrate these high-efficiencycells into a Fresnel-lens-based, high-concen-tration module.

A promising approach to increasing efficiencyand lowering the cost of solar cells made frompolycrystalline thin films involves combiningmaterials in monolithic two-terminal tandemcells. Researchers at the NCPV demonstrateda prototype tandem arrangement using Si asthe bottom absorber and CuGaSe2 (CGS) asthe top-cell absorber. The CGS top cell wasgrown by elemental evaporation followingthe NREL-patented 3-stage process. The inter-connect junction consisted of an n+ intercon-nect transparent oxide, and initial measure-ment showed excellent voltage addition ofabout 1.3 V and efficiency of about 5.1%.With an improved CGS top cell, the nextresearch step will examine an all-thin-filmpolycrystalline Si/CGS tandem combination

that could offer a via-ble route to a low-cost,high-voltage cell.

Obtaining high-bandgap top-cell materials is critical to the development of tandem PV cells.The Institute ofEnergy Conversion at the University ofDelaware developedone such potential top cell based onCIGS, with the bestperformance obtainedfor low-S and high-Gacontents. Cells weretested with an anti-relective coating atNREL and were >10% efficient.

In FY 2003, the PV Subprogram made 3-yearsubcontract awards under the High-Perform-ance PV Project, “Exploring and AcceleratingPathways Toward High-Performance PV.“Forty-six letters of interest were received, and from these, 14 organizations including universities and companies began work in FY 2004. Seven of the subcontracts involvepolycrystalline thin-film tandem cells, andthe other seven concern III-V multijunctionconcentrators.

CRYSTALLINE SILICON: INSIGHTS, NEW

PROCESSES, AND ENHANCED ANALYTICAL TOOLS

Crystalline silicon, the first material used tomake commercial solar electric devices, is stillused in nearly 90% of the PV systems beinginstalled today. Nevertheless, there is muchmore to learn about the basic science of sili-con as it relates to solar cells. In keeping withthe PV Subprogram strategy of peer reviewand developing a coordinated researchapproach, about 40 scientists from universi-ties, NCPV, and industry perform sharedresearch important to the future of this tech-nology. These researchers explore defects andstructures of electronic materials and devicesto discover ways to increase efficiencies andto validate novel processing techniques. Theyalso apply material and device processing science to develop new tools for deposition,processing, and characterization of electronicmaterials.

In 2003, three universities, NREL, and repre-sentatives from the PV industry joined theNational Science Foundation Silicon WaferEngineering and Defect Science (SiWEDS)consortium. Originally created for the inte-grated-circuit industry to conduct exploratoryresearch into crystalline silicon, SiWEDS isgenerating information on research topicsthat are also relevant to the PV industry.

The DOE-funded University Center of Excellence in Photovoltaics at the Georgia

Institute of Technology has contributed to the understanding of silicon-based solar

electric cells since 1992. The faculty and students at Georgia Tech have fabricated

devices that set several world records for conversion efficiencies. In addition, Georgia

Tech works with industry to improve manufacturing techniques. For example, the

rapid thermal processing methods they pioneered are faster than conventional

furnace diffusion and oxidation of silicon wafers by a factor of five or more.

GEORGIA INSTITUTE OF TECHNOLOGY—CENTER OF EXCELLENCE

Subcontracts issued under the new solicitation, “Exploring and Accelerat-ing Pathways Toward High-Performance PV,” investigate these pathways to high efficiency for thin-film polycrystalline tandem cells.


CRYSTALLINE SILICON UNIVERSITY RESEARCH

PROJECT

To integrate industry research needs with theexpertise at our leading research universities,the PV Subprogram initiated the CrystallineSilicon University Research Project in 2001 toinvolve university teams in topics of concernto the PV industry. Subcontracts were awardedto seven universities; they included collabora-tion with industry wherever appropriate. The contractors formed teams to explore four topics identified by industry: mechanicalstrength and yield; the production of bettermaterials; hydrogen passivation and siliconnitride coatings; and contacts and selectiveemitters.

As part of the PV Subprogram’s results-orientedapproach, a review panel was convened toassess the impact of these university/industrycollaborations after the first two years ofeffort in 2003. With one year left on most ofthese projects, the review panel applaudedthe work so far as providing necessary tools,analysis, and diagnostics that are very rele-vant to industrial concerns. Six of the ninereviewers were from the PV industry.

Facilitating exchange of research results, DOEsponsored the 13th Workshop on SiliconSolar Cell Materials and Processes in 2003.More than 100 scientists and engineers fromaround the world attended the conference,including representatives from 22 companiesand 22 research institutions. Presentationsand discussion sessions addressed crystalgrowth, new cell structures, new processesand process characterization techniques, andcell-fabrication approaches suitable for futuremanufacturing demands. Ongoing collabora-tions such as these are crucial to the designand conduct of the DOE PV Subprogram.

A major objective of the PV Subprogram is tomove research procedures and tools to indus-try as quickly as possible. A prime example of

the effective use of the patent, license, andtechnical-assistance strategy of the program is the transfer of the PV Reflectometer. Thisreflectometer, developed and patented atNREL, measures surface roughness, thicknessof antireflective coatings, fraction and heightof metallization, wafer thickness, and reflec-tance of back surfaces in less than one secondwithout ever touching the materials. Anequipment manufacturer, GT Solar Technol-ogies, has licensed the PV Reflectometer andplans to commercialize the technology,which is perfectly suited for the characteriza-tion of photovoltaic materials and finishedsolar cells in a production-line environment.

Another tool developed in the PV Subprogramand licensed to GT Solar Technologies is PVSCAN (photovoltaic scanner), a high-speed, optical scanning system designed for the characterization of PV materials and finished solar cells. This tool won an R&D100 award in 2001 from R&D Magazine asone of the 100 best R&D advances for theyear. GT Solar Technologies will market PVSCAN to help crystal growers achieve ahigh-quality (low defect density) material. The tool can also help solar cell process engineers develop fabrication processes forhigher-efficiency devices.

Additional Achievements in Photovoltaics R&D

Organization Achievement Significance

NREL Completed experiments using Rapid exploration of materials forcombinatorial materials science device structures

NREL Identified signature for minority- Possible third junction in a four-junc-carrier lifetime defect in GaInNAs tion device aimed at 40% efficiency

goal

Rutgers University/ Detected novel properties in Hybrid organic-inorganic superlattice NREL ZnTe/tetracene structure could be useful in solar cells and

LED devices

University of Toledo Used ZnO to fabricate a Major improvement in efficiency;14%-efficient, all-sputtered sputtering technique could expandCdS/CdTe cell the range of material options for

tandem cells

Unisun Developed a process for non- Complements a complete nonvacuumvacuum transparent conducting CIGS solar cell process cofunded by coating California Energy Commission

NREL Demonstrated a mechanical Highest efficiency for this structurestack with CGS on CIS, 9.5% efficiency

Princeton University Achieved 3.6% organic solar cell Higher efficiency is critical to the and published results in Nature future of organic solar cells

Ohio State University Developed a SiGe buffer layer Permits deposition of III-V solar cells on Si substrate on low-cost Si

NREL Identified a hole barrier preventing Explained why polycrystalline CIGSrecombination at CIGS grain works better than single-crystalboundaries material

Sandia Developed and patented maskless Increases cell performance over plasma texturing using reactive untextured or planar and wet-texturedion etching for multicrystalline cells by up to 6% silicon cells


PV ADVANCED MATERIALS AND DEVICES

Once record conversion efficiency is achievedin the laboratory, the next step is to explorehow this improved material or device can beproduced outside of the laboratory. Takingtechnology from the laboratory to the pro-duction line falls under the AdvancedMaterials and Devices element of the PVSubprogram.

THIN FILMS: HIGHER EFFICIENCIES, RECYCLING,NEW NATIONAL TEAM

Making PV devices by applying thin layers ofsemiconductor material to an inexpensivesubstrate holds great promise for reaching thelong-term goal of cost-competitive electricityfrom PV. Over the past decade, the work ofscientists at the NCPV in collaboration withuniversities and industry in the Thin Film PVPartnership has steadily driven up the effi-ciency of thin-film devices. Better still, thisthin-film PV technology has recently enteredthe marketplace.

However, to reach our cost goals, issuesremain of increasing device efficiencies,increasing module reliability, and developingdeposition and manufacturing capabilities forlarge-scale production. The PV Subprogramhas focused the efforts of the Thin Film PVPartnership, the NCPV, and the nationalteams on these issues for four of the mostpromising thin-film technologies—copperindium diselenide, cadmium telluride, amor-phous silicon, and thin-film silicon. An addi-tional national team was started in 2002 toaddress thin-film module reliability issues.

Copper Indium Diselenide (CIS)

Copper indium diselenide thin-film manufac-turing benefits from economies of scale, tech-nology improvements, and having fewer spe-cial handling requirements than the processfor making PV modules from silicon. Forthese reasons, CIS may one day undercut the

cost of production for silicon PV. Achievinghigher efficiencies for thin-film solar cellsand translating these results to large-scaleproduction of modules is a major planninggoal of the PV Subprogram.

In FY 2003, Shell Solar Industries achieved twomajor planning goals as part of its subcontractwith the Thin Film PV Partnership. Whiledoubling production capacity from one totwo MW, the company also achieved a newworld-record efficiency for a thin-film CIS-based module. The 46.5-W power modulemeasuring 4 ft2 (3626 cm2) was 12.8% efficient as verified at NREL. Optimizing eachlayer of the module and improving fabricationprocesses resulted in this record efficiency fora monolithically integrated thin-film module.

Higher efficiencies and lower costs for CISwith added gallium (CIGS) are possible with a fabrication technique called evaporation.Using this technique, a new world-record efficiency for CIGS thin-film solar cells,19.2%, was verified at the NCPV in FY 2003.The improved efficiency is the result ofmastering the composition controland uniformity of the films,improving the CdS and ZnOprocesses, engineering band-gap at the absorber inter-faces, and improving anti-reflective coating and grids. The improved effi-ciency is the latest result of careful and rigorousresearch by the NCPV CISNational Team to achieve amajor planning goal.

Lightweight, flexible PV moduleshave many applications. Global SolarEnergy (GSE), in a joint venture with TucsonElectric Power and ITN Energy Systems, set a record in 2003 by delivering a module toNREL that tested at a record 9.2% efficiency.This met a major milestone of the Solar

Program to move toward more-efficient devicesfor this application. The device structure isITO/CdS/CIGS/Mo/SS, and the CIGS isdeposited by the physical vapor depositionmethod. GSE supplies these lightweight, flexi-ble solar power packs to the U.S. Army andthe Marine Corps.

In some cell designs, a layer of cadmium hascontributed to the efficiency, but another goal of the program is to develop high-effi-ciency cells that do not include cadmium. The CdS window layer also limits the currentthat can be collected in the solar cell. In2003, NREL researchers fabricated a cadmium-free CIGS device with a record measured effi-ciency of 18.6%. This work was conducted incollaboration with Aoyama Gakuin Univer-sity in Japan. Future work with industrialpartners will translate this important result to large-scale U.S. production of more-effi-cient modules.

Shell Solar installed this 245-kW thin-film CIS PVsystem on its factory in Camarillo, California. Theaverage aperture-area efficiency of the modules is between 11% and 11.5%.

Shell Solar/PIX13329


Cadmium Telluride (CdTe)

Cadmium telluride thin-film material has theadvantage of a bandgap that is well matchedto the solar spectrum and a high absorptioncoefficient such that even one micron of theabsorber film is sufficient for solar cell fabri-cation. Several U.S. manufacturers haveapplied the development work performed incollaboration with the PV Subprogram to the manufacture and sale of products using this technology.

A key challenge for industry is to develop andimplement manufacturing techniques for this promising material. The PV Subprogramand a subcontractor, First Solar, Inc., wererecognized for achievement in this area byR&D Magazine, which presented the presti-gious R&D 100 award to the team as one ofthe top 100 R&D achievements of the year.

The award was for the continuous-feed, auto-matic, nonstop produc-tion line for manufac-turing CdTe PV modulesdeveloped by First Solar(Toledo, OH) with fund-ing from the Thin Film PV Partnership. This is the 18th R&D 100 awardassociated with the PVSubprogram over theyears. In addition toreceiving the award, FirstSolar has applied results of its research subcontract,“High-Rate Vapor Trans-port Deposition for CdTePV Modules,” awarded by the Thin Film PV Part-nership to reduce the price of its product by

30%. Such cost reduc-tion of commercialmodules is an impor-tant milestone for thePV Subprogram.

A new approach toimproved manufactur-ing and lower cost hasbeen developed atNREL to prepare CdTecells on low-cost commercial soda-limeglass/SnO2 substrate.The best cell so far had an efficiency of14.4%. The newprocess takes advan-tage of two patentedfilms. The NREL teamhas begun collabora-tion with First Solar to demonstrate thenew process in a man-ufacturing setting.

Licensing and technical assistance will followif the process is adopted for production ofCdTe modules.

Recognizing the challenges presented by theroutine use of cadmium, the PV Subprogramhas invested considerable resources andworked with BNL to develop safe proceduresand information for decision makers abouthandling cadmium for solar cells. In 2003,this information was consolidated in a newWeb site, Cadmium Use in Photovoltaics(www.nrel.gov/cdte), which serves as a clear-inghouse and forum for discussing relatedenvironmental issues.

The PV Subprogram recognizes that recyclingmaterials is an important way to increase theenvironmental benefits of PV. With technicalassistance from the subprogram, First Solar,the largest producer of cadmium telluride PV modules, now recycles all of its cadmiummanufacturing waste at its Perrysburg, Ohio, plant, including modules that do not meetproduct specifications. With assistance fromDOE, BNL, and NREL, the company adopted

First Solar, Inc., and NREL, through the Thin Film PV Partnership, earnedan R&D 100 award in 2003 for a faster, less costly process for manufac-turing CdTe PV modules. Shown above (from right) are Ken Zweibel, aproject leader who manages the Thin Film PV Partnership along with Harin Ullal and Bolko von Roedern.

Tucson Electric Power’s 3.4-MW Springerville solar field is the fourth largestinstallation of PV modules in the world. Using $6 million per year from a pro-vision of Arizona’s Environmental Portfolio Standard (which requires utilities to install more renewable energy systems such as solar), Tucson Electric buysPV systems made of crystalline silicon and promising thin-film technologies. In addition to generating electricity, the Springerville solar field also serves as a useful laboratory for identifying ways to improve thin-film module design.

Jim Yost/PIX13218

Tucson Electric Power/PIX13327

an aggressive approach to cadmium handling,which minimizes all aspects of exposure andany related environmental, safety, and healthissues. Much of the waste cadmium is reusedin the manufacture of NiCd batteries. Recy-cling is cheaper than disposal at a hazardouswaste site.

Amorphous Silicon (a-Si)

Amorphous silicon PV modules accounted forabout 10% of the PV market in 2003. Com-mercial modules of a-Si average about 7%efficiency, yet they are competitive with crys-talline silicon modules in some applicationsbecause of lower manufacturing costs. Oneway to reduce the cost of electricity for a-Simodules is to increase cell and module effi-ciency; another is to increase deposition rates of PV materials during manufacture.

These ways to reduce costs could result fromeffective research in nanocrystalline materials.Prior to 2002, nanocrystalline solar cell device work was making news in Germany,Switzerland, and Japan. In 2002, the a-SiThin Film National Team added thin-film

silicon activities to its agenda. By the close of 2003, many devices had been tested in the United States, and efficiencies matchingthose achieved abroad were reported.

The most recent researchresults were reported at the16th meeting of the Amor-phous Silicon/Thin FilmSilicon National Team. Thefirst day was devoted to thin-film Si solar cells, whichoften feature nanocrystallineSi made by low-temperature deposition using techniquesdeveloped for a-Si. One com-pany, United Solar, incorpo-rated nanocrystalline cellsinto multijunction structuresthat have an a-Si top and a nanocrystalline bottom. These cells achieved initialefficiencies up to 13%.

Another company, MVSystems, reportednanocrystalline thin-film Si cells that were7% to 9% efficient using plasma-enhancedvapor deposition, which holds the promise of increased deposition rates without reduc-tions in material quality.

For several years now, another approach tohigh deposition rates, hot-wire chemicalvapor deposition (CVD), has been developedand applied at NREL and the Institute ofEnergy Conversion (IEC) at the University ofDelaware. This rapidly maturing technologywas the focus of the Second InternationalConference on Hot-Wire CVD hosted byNREL in 2003. More than 100 scientists fromaround the world exchanged detailed infor-mation on processes and discussed solutionsto deposition-related processing issues. Thehighlights of this technology continue to bedeposition at high rates and at a temperaturethat does not damage substrates.


The Institute of Energy Conversion (IEC), University of Delaware, has been a DOE

University Center of Excellence in Thin Films since 1992. IEC continues to provide

cutting-edge equipment and expertise to the PV research and development commu-

nity. For example, in 2003 researchers contributed to achieving a key milestone of

the High-Performance PV Project by developing a potential wide-bandgap cell

based on Cu(InGa)(SeS)2; the best performance was obtained with low-S and high-

Ga content. Cells were tested with an antireflective coating at NREL and were greater

than 10% efficient, an important milestone for the PV Subprogram. IEC will continue

its work under the next phase of the High-Performance PV Project on research to

develop a wide-bandgap solar cell in the thin-film tandem structure. This has been

identified as the single most critical issue for developing very high efficiency thin-

film tandem solar cells as a follow-on to today’s single-junction thin-film PV. IEC’s

best CIG-alloy cell has a verified efficiency of 17%. In addition to such efforts to

increase cell efficiencies, IEC will support other subcontractors by preparing and

providing CIGS films and devices for testing and characterization.

INSTITUTE OF ENERGY CONVERSION—CENTER OF EXCELLENCE

The outdoor test facility at the Florida Solar Energy Center providesvaluable data to the Solar Program about PV array and system performance under hot and humid operating conditions.

FSEC

/PIX

1333

4


In other work on a-Si, the University of Toledoachieved a cell with 10.4% stabilized efficiencyusing a new p-layer with a single-junction a-SiGe cell. Researchers there also measuredan a-Si/a-SiGe tandem cell with 12.5% initialefficiency.

Module reliability has been identified as animportant research issue by the thin-filmnational teams. As a result, a new team wasassembled in 2002 to discuss and proposeresearch in this area. The Thin-Film ModuleReliability National Team with about 60members had met three times by the close of2003. On recommendations of the nationalteam, the Thin Film PV Partnership shiftedsome of its FY 2004 funding toward resolvingmodule-level reliability issues. For example,two contracts were awarded for outdoor test-ing and monitoring of new thin-film moduletechnologies in hot and humid climates toidentify and fix durability issues before themodules are commercialized on a large scale.All major U.S. companies manufacturingthin-film modules supplied modules with

their most advanced packaging designs fortesting. The results of these tests will helpguide any product revisions to improve reliability.

PV MANUFACTURING RESEARCH AND

DEVELOPMENT

Since Congressional funding for the PV Man-ufacturing R&D Project began in 1991, theDOE PV Subprogram has conducted R&Dprojects in partnership with the U.S. PVindustry. Over this period, the PV Manufac-turing R&D Project has issued seven solicita-tions for partnerships that have resulted inmore than 50 subcontracts, including 10 that were active at the close of FY 2003.Between 1992 and 2002, these cost-sharedR&D projects have increased productioncapacity among the 15 U.S. participants more than 16-fold and have reduced thedirect manufacturing cost of PV modules for participants by more than 55%.

By comparing customer savings to the gov-ernment investment and comparing manu-facturer savings to their cost-share invest-

ment, an analysis of the PV ManufacturingR&D Project showedthat these investmentshave more than paid for themselves by reduc-ing costs to consumersand expanding the U.S.industrial base. In fact,according to an analysisof data submitted byparticipants, the recap-ture of the public’sinvestment in thisresearch by the close of 2002 stood at 355%since the project’sinception.

The U.S.-based PVindustry is planning fora domestic industry that

can meet a significant portion of the nation’selectricity needs. In 2001, the first U.S. Photo-voltaic Industry Roadmap set a goal to scale upU.S. PV manufacturing capacity to 7 gigawattsby 2020. Manufacturing capacity in 2002 was270 MW, so making this goal a reality willdemand continued investment in manufac-turing R&D.

The PV Subprogram’s continued manufactur-ing R&D will help make the national goal ofplentiful, low-cost PV a reality. The latest procurement is focused on increasing yield,durability, and reliability and will furtherreduce costs and improve manufacturingprocesses so that increased capacity will follow. The PV Manufacturing R&D Projectissues competitive, cost-shared contracts toindividual manufacturers for research thatbuilds on their own unique approaches tomanufacturing. Projects address promising PV technologies and include research on crystalline silicon, thin-film devices, and concentrator technologies. Research is con-ducted to increase module reliability and toimprove integration, manufacturing, andassembly of systems; balance-of-systems com-ponents; packaging of systems and systemcomponents; and methods for quality con-trol and storage of components.

At the close of FY 2003, major technical pro-gress was reported on the first phase of con-tracts awarded for the solicitation, In-LineDiagnostics and Intelligent Processing, which isaimed at larger and more accelerated scale-upof manufacturing, as well as the other objec-tives of the PV Manufacturing R&D Project.For contractors to continue through the threephases of their projects, tasks and milestonesfor each phase must be completed. Somehighlights of the Phase I review follow.

Under its subcontract, Energy ConversionDevices explored possible process improve-ments for a 30-MW amorphous silicon man-ufacturing facility at lower-tier United Solar

PowerLight Corporation installed the largest roof-mounted system in theUnited States, nearly 1.2 MW in size, at the Santa Rita jail in California. The system comprises mainly crystalline silicon modules, which are tied to the electric grid through four large inverters. This large system uses several different module materials and thus provides an excellent oppor-tunity to compare the long-term reliability of different PV technologies. NCPV engineers collected baseline performance data on all 12,244 PV modules soon after installation.

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Ovonic Corporation. The work developedcontrol, monitoring, and diagnostic systemsthat allow quality assurance and quality con-trol during production of each of nine layers of the PV device. For example, Energy Conver-sion Devices developed a closed-loop thick-ness control system for the deposition ofZnO, ITO, and a-Si layers within the UnitedSolar Ovonic production line. Application of a PV capacitive diagnostic system allowed themeasurement of the current-voltage (I-V)characteristics of component cells in thetriple-junction device. Improvements incleaning processes applied to the substrateincreased production yield. With theseadvancements in place, the company willbegin Phase II work in FY 2004.

Energy Photovoltaics, Inc., also makes amor-phous silicon thin-film PV modules. Duringits subcontract, the company has increasedthe stabilized power output of its modules by 10% and reduced the cost of modules by20%. These results meet or exceed the goalsof the subcontract, so the company willbegin work on the next phase of the sub-contract in FY 2004.

ITN Energy Systems, Inc., is performing man-ufacturing R&D to support the CIGS produc-tion systems of Global Solar Energy. Under its subcontract, ITN has developed diagnostictools for use in the processing line at GlobalSolar Energy to assess the relationship betweenprocessing conditions and the properties ofthe resulting products. Using a combinationof in-line sensors and process controls, thecompany demonstrated process improve-ments, which increased the uniformity, yield,and throughput of CIGS deposition. Forexample, the company reduced variability in the thickness of the copper layer by 71%.Manufacturing technology for ultra-thin multi-crystalline silicon solar cells is being devel-oped by BP Solar. Under its subcontract, thecompany increased its ingot size from 250 kg

to over 300 kg, which increased yield andreduced casting cycle time by 14%. Materialuse was improved when the wire sawsreduced saw-room losses by 30%. Work continues to develop equipment fordemounting and subsequent handling of very thin silicon wafers and to help increaseproduction capacity of the silicon industryfor lower-cost solar-grade silicon feedstock.

RWE Schott Solar, Inc., cuts wafers from sili-con material produced in the unique edge-defined, film-fed growth (EFG) system, whichproduces a thin-walled octagonal cylinder ofcrystalline silicon material. The cylinders are6.5 meters long and have a face width of 10 cm. These faces are cut with lasers to makesilicon wafers for manufacturing PV modules.Under its PV Manufacturing R&D Project sub-contract, the company completed design andprototypes of a module that replaces a frac-tion of the solar cells with lower-cost reflect-ing materials. This reflector-module conceptcould reduce the cell area required by 40%.

Evergreen Solar has developed an innovativeand unique approach to manufacturing crys-talline silicon wafers through the string- ribbon growth process. Under its subcon-tract with the PV Manufacturing R&DProject, the company moved a dual-ribbongrowth system, known as Project Gemini,from R&D concept to pilot phase to produc-tion. This system produced cells with prom-ising efficiencies, the best measuring 14.6%.One element of the system, a new contact-printing machine, increased yields by 3% and throughput by 70%. Work will continueto demonstrate reliability of the frameless,monolithic modules produced with thismaterial.


The PV Subprogram’s continued manufacturing R&D will

help make the national goal of plentiful, low-cost PV a reality.

Since 1992, production capacity of participants (13 companies with active manufacturing lines in 2003)in the PV Manufacturing R&D Project has grown from 13 to 201 megawatts. And direct productioncosts (in 2003 dollars) decreased from $5.47 to $2.49 per peak watt.


PowerLight Corporation incorporates crystal-line silicon or thin-film PV components intoits PowerGuard® roofing tiles. In FY 2003, the company installed more than 1.5 MW ofthis product, which provided valuable feed-back to the work conducted under a PV Manufacturing R&D Project subcontract. For example, with improvements in overall factory quality control, the company delivered 4,664 tiles to a customer, and all performed at or above specification. One element of this quality control establishedunder the subcontract is testing PV modulesbefore they are integrated into the roofingproduct. This and other efforts have reducedcosts by 18%.

Under a PV Manufacturing R&D Project sub-contract, Sinton Consulting, Inc., developed an in-line monitoring tool that measures minority-carrier lifetime during manufactureof single-crystal and polycrystalline wafersand cells. To date, PV manufacturers havepurchased six of these WCT-100 tools. TheWCT-100 in-line diagnostic equipment meas-ures minority-carrier lifetime as an indicatorof cell performance and serves as a qualitycheck. Unacceptable materials are pulledfrom the manufacturing line before incurringthe expense of converting the wafer to a cell,thus substantially increasing cell yield. Earlyfeedback from industry to Sinton Consulting

suggests that the equipment saves enough topay for itself in less than one month.

The materials that encapsulate PV modules toprotect them from the outside elements mustbe especially durable to ensure continuedhigh performance of PV systems. As a primeexample of the systems-driven approach toresearch in the Solar Program, SpecializedTechnology Resources, Inc., under a PVManufacturing R&D Project subcontract, isworking closely with PV module manufac-turers including BP Solar, Energy Photo-voltaics, Inc., and Shell Solar Industries todevelop encapsulants for specific moduletypes and end-use applications. In FY 2003,the company performed interfacial character-ization of the glass surfaces to which theencapsulants must bond. To address issues of cost, Specialized Technology Resources,Inc., investigated ways to optimize extrusiontechniques for large-scale manufacturing ofencapsulants based on ethylene vinyl acetate(EVA) that cure fast and are flame retardant.As this work progresses, the company willcontinue work with manufacturers to testmaterials on specific module types for targetedend-use applications.

The PV Subprogram issued a request forLetters of Interest for the next solicitation, PV Manufacturing R&D—Large-Scale Moduleand Component Yield, Durability, and Relia-bility. The 29 responses from industry repre-sented a 30% increase versus responses to previous solicitations. The subcontract awards will be divided into two categories: PV System and Component Technology, and PV Module Manufacturing Technology.Awards are expected in FY 2004 for researchextending over three years and will be cost-shared with industry.

PV manufacturing processes in the United States havegrown increasingly sophisticated since the PV Manu-facturing R&D project commenced in 1991. Thesephotos show (a) AstroPower’s production line, (b)amorphous silicon deposition machine, built forUnited Solar Ovonic by Energy Conversion Devices,and (c) RWE Schott Solar’s system for producing octagonal cylinders of crystalline silicon materialfor slicing into wafers.

(a)(a)

(b)(b)

(c)(c)

Energy Conversion Devices/PIX13342

AstroPower

RWE Schott Solar/PIX13343

PV MODULE PERFORMANCE AND RELIABILITY

To reach the PV Subprogram goal of cost-competitive products with a 30-year servicelife, PV systems must withstand year-roundweather conditions including intense sun-light, high humidity, driving rain, snow,wind, and hail, as well as temperatures rang-ing from well below zero to midday summerheat. During years of exposure to these con-ditions, consumers reasonably expect mod-ules to generate the same amount of elec-tricity each year with few, if any, unexpectedmaintenance costs or down-time events.

To help manufacturers and system designersmeet these consumer expectations, the PV Subprogram provides a unique combination of testing and analysis services for prototype and commercial PV modules and systems. With data from these tests, PV manufacturers can pinpoint problems and build on strengths.When overriding issues emerge, the PV Sub-program may sponsor targeted research toadvance the industry as a whole. This activityto measure and improve the performance andreliability of commercial PV systems relies onthe specialized testing and analysis capabilitiesat NREL, Sandia, the Southwest TechnologyDevelopment Institute (SWTDI), the FloridaSolar Energy Center (FSEC), and the PVTesting Laboratory at Arizona State Univer-sity. Because no single manufacturer couldinvest in such comprehensive testing equip-ment and expertise, this is an important way that the Solar Program accelerates thedevelopment of reliable PV systems.

Tracking Long-Term Durability

After years in the field, one effect of long-termexposure to weather can be the intrusion ofmoisture into PV module and cell structures.If moisture makes its way into a module, itcauses current drain and/or corrosion of sol-der joints, which reduces the electrical effi-ciency of the PV system. To learn more aboutwater intrusion and other processes that

reduce the electrical efficiency or cause com-plete failure of PV systems, the PV Subprogramhas conducted reliability tests since 1991.

In 1997, the Module Long-Term ExposureProject was initiated in cooperation with PV manufacturers. Under this project, morethan 80 modules from five manufacturershave undergone initial baseline testing atSandia and have then been installed at FSECand SWTDI to undergo monthly measure-ments during operation outdoors. Thesemeasurements can be very helpful to manu-facturers. For example, in 2003, a group of 20 modules made from CIS thin-film mate-rial was returned to the manufacturer for in-depth analysis. After three years of exposure,performance of these modules had decreasedmore than predicted. In 2002 and 2003, morethin-film modules were installed at FSEC,after baseline testing at Sandia, to measureany effects of operation in the hot andhumid environment of the FSEC test center.

At NREL, seven grid-tied, 1- to 2-kilowatt (kW)systems are maintained to test module made of varied materials for long-term performanceand reliability. To expand understanding oflong-term exposure to weather and ultravio-let light, and new long-term test programbegan in 2003.

Verifying Performance

Consumer confidence in the projected elec-trical output of PV systems is an important element to be cultivated in the growing market for PV systems. Aside from the continuous work of NCPV staff to fine-tune national standards and certi-fication programs, the PV Subprogram’s

testing facilities generate unbiased reports onthe electrical performance and reliability ofprototype and commercial PV modules andsystems. These confidential test reports aregiven to manufacturers about their products,but can be released by the companies if theychoose. This work verifies projected electricaloutput and annual energy production.

Module performance can be measured in several ways. At NREL, researchers measureperformance outdoors under natural sunlighttests or in the laboratory using solar simula-tors. In 2003, a new pulse-analysis spectro-meter system will allow faster and more accu-rate flash spectrum analysis in the laboratory.

Outdoors, more than 30 modules can be mon-itored over weeks, months, or years; and morethan 50 modules can be tested for short-termperformance under prevailing weather condi-tions. Stand-alone systems for remote homesand streetlights are also being monitored.


NREL's Outdoor Test Facility is used to verify, characterize, and model performance and improve PV performance and reliability. From top: TheOutdoor Accelerated-Weathering Tracking System with Tom McMahonand the High-Voltage Test Bed with Joseph del Cueto.

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Thirty thousand square feet of PV panels grace the roof of the Moscone Con-vention Center in downtown San Francisco. Installed by PowerLight Corpo-ration, this is the first project resulting from two voter-backed initiatives tofinance renewable energy efforts in San Francisco’s commercial, residential, and government-owned buildings. At their peak, these panels will generate 675 kilowatts of electricity. When combined with other newly installed energyefficiency measures, this solar power should save the convention center about$210,000 a year.


At Sandia, module performance measurements,as well as measurements of arrays with severalPV modules, are conducted under actual out-door operating conditions. In 2003, test engi-neers characterized dozens of modules forthree different manufacturers because theaccuracy of their nameplate ratings was indoubt after discrepancies arose among tests at other laboratories.

Predicting performance based on measure-ments can be helpful for system designers.Module performance models have been under development for several years and use a database of measured performance parame-ters being assembled at Sandia. The databasecontained more than 165 commercial mod-ules and arrays at the close of 2003.

Improving Durability: Systems-DrivenApproach

When the testing and analysis activities pointto a common durability issue, the PV Subprogram, through the systems-driven

approach to pro-gram management,responds by initiat-ing research proj-ects to address theissue. In 2002, it became clear that some new thin-film PV products that now represent a significant num-ber of systems in operation were showing signs of wear. Industry rep-resentatives recog-nized that resolv-ing any perform-ance problems early in this mar-ket process would

be crucial to rapid acceptance of the newtechnology, and they asked the Solar Programto work with them to head off problems.

Following the successful pattern of assem-bling national teams, the PV Subprogramresponded to the industry by sponsoring anew Thin-Film Module Reliability National

Team to address module design and reliabilityissues. Cosponsored by the Thin Film PVPartnership and the Systems and ModuleReliability projects, the new national teambrings together more than 60 scientific repre-sentatives from NREL, Sandia, FSEC, industry,universities, and module-packaging experts.The first meeting, held in 2002, began theprocess of recommending activities.

One of the first issues discussed by the Thin-Film Module Reliability National Team wasresearch that had been conducted at NREL inconjunction with BP Solar on the delamina-tion of tin oxide on glass in thin-film mod-ules. The activities to resolve this issue pro-vided a model for the national team effort:identify a problem in the field; analyze andunderstand it in the laboratory; replicate theresult in lab-scale, accelerated tests; designalternative manufacturable solutions; and testsolutions using the lab-scale accelerated tests.

The second and third meetings of the newnational team also drew more than 60 peopleand have set out a detailed research agendafor FY 2004 and beyond.

The NCPV and Sun♦Lab virtual laboratories offer specialized testing facilities for the

solar research and development community. From atomic-level measurements and

analysis to systems-level performance and reliability measurements, the Solar

Program makes these tools available to industry through cooperative agreements

and joint research projects. Test beds are located at NREL, Sandia, Oak Ridge,

Brookhaven, FSEC, SWTDI, at the centers of excellence at Georgia Tech and the

University of Delaware Institute of Energy Conversion, and at research universities

that work with the Solar Program. Technical details on testing is available at the Web

sites of each organization.

SOLAR PROGRAM OFFERS INTEGRATED TEST BEDS

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PV TECHNOLOGY DEVELOPMENT

DOE does not commercialize solar technolo-gies nor sell them in the marketplace. That isthe private sector’s responsibility. When tech-nology reaches the application and marketend of the development framework, the fed-eral research program collects informationand feedback from the private sector to helpguide early stages of new technology develop-ment. An important way the program getsthis feedback is through partnering withindustry and with other government organi-zations such as within the states or otherparts of the federal government. Partnershipsamong industry, government, and othersintegrate all elements of the PV Subprogramthrough the systems-driven approach toimprove performance and reliability of PV systems and to help introduce PV todomestic and foreign markets.

SYSTEMS ENGINEERING AND RELIABILITY

Systems engineering and reliability research ofthe PV Subprogram aims to reduce the life-time costs of the entire PV system, improvethe reliability of systems and components,and verify and improve the performance ofsystems in the field.

An important component of the systemsengineering activity is the collection of dataon the field performance of PV systems,including operation and maintenance (O&M)costs. Now that PV is being considered fordistributed energy generation, it is moreimportant than ever to record maintenanceexperience and identify lifecycle costs and/or levelized energy costs for fielded systems.Understanding these costs and their sourcesis critical to the systems-driven approach inmanaging continued R&D on PV because thisinformation can identify areas for system orcomponent improvements.

The reliability database being developed atSandia is one of the few repositories of O&Minformation for fielded PV systems. In FY2003, data were analyzed from Arizona PublicService Company for PV systems on homesnot connected to the utility grid. For thesehomes, annual O&M costs were between 4% and 5% of the initial capital cost of thePV system. An analysis of water pumping systems in the Northwest Rural Public PowerDistrict showed annual O&M costs of about 4% of the initial capital cost of the PV sys-tem. In FY 2004, cooperative efforts withTucson Electric Power and Arizona PublicService will assemble data for grid-tied PVsystems in both residential and utility-scaleapplications. Additional partners in industryand government, such as the Department ofAgriculture/Rural Utilities Service, will alsoprovide experience data from fielded systemsto guide future R&D in the PV Subprogram.

Inverter R&D: New initiative, valuabletests, enhanced facilities

PV modules work with other components tomake up the system that delivers electricityto the end use, or load. An important compo-nent of most PV systems is the inverter thatconverts dc electricity from PV to ac electric-ity necessary for most appliances and for connecting to the utility grid. System engi-

neers can get valuable information aboutinverters from the unique laboratories of theNCPV. For example, inverter test facilities atSandia can provide surge testing and accel-erated life testing. In one set of accelerated lifetime tests conducted during 2003 atSandia, more than 20 possible problem areaswere located and communicated to the man-ufacturer for consideration. The companyalso got the good news that its approach totransferring heat away from critical compo-nents was shown to be very effective by thermal imaging conducted during tests.

In the past, PV systems designers had to useinverters developed for other industries thatoften did not perform reliably when subjectedto the special demands of PV systems. In2002, the DOE Office of Energy Efficiencyand Renewable Energy launched the High-Reliability Inverter Initiative to fund cost-shared work with three companies to designand commercialize inverters specifically foruse with PV, energy storage, and other distrib-uted energy resource (DER) technologies. By the close of 2003, three subcontractors,General Electric Global Research Center,Xantrex Technology, Inc., and SatConApplied Technology, had completed engineer-ing designs and proposed work to build pro-totype high-reliability inverters in FY 2004.

Arizona Public Service (APS) has installed 2 MW of utility-scale PV generation at the Prescott, Arizona,airport. Sandia is collaborating with APS to assess the field performance, operations and maintenanceexperience, and cost of these systems.

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System Design and Evaluation: Newtechniques and standards

Before a PV module is incorporated into asystem and installed in the field, it is impor-tant to know if it is operating up to specifi-cations. Testing modules is important, andtools that make the process easier and moreeffective are in great demand. Responding tothis need, engineers at Sandia worked withPowerLight Corporation to develop a low-cost procedure, called “dark I-V” testing. Thisprocedure uses a power supply to flow cur-rent through the PV module and generateelectrical parameters. Comparison of actualparameters with the expected performance of the module thus identifies any rejects. Theprocedure also quickly identifies problemssuch as reversed wiring cables from the junc-tion box; any problems with bypass diodes,including polarity; and short-circuited oropen-circuited modules. PowerLight and itsmodule suppliers are using the testing proce-dure to verify the electrical integrity of mod-ules before costly system integration andinstallation in the field.

In the world marketfor PV systems, buyersrely on internationalstandards to assureminimum perform-ance and safety of PVsystems. Now, thanksto years of work bythe NCPV and others,U.S. PV manufacturerscan submit their sys-tems to the same setof testing standards in the United Statesand abroad for stand-alone applications not connected to theelectric grid. A newrecommended prac-tice approved in 2003 by the Institute ofElectrical and Electronics Engineers (IEEE)IEEE-SA Standards Board Review Committeewill be used in the United States. It will alsoserve as the basis for international standard,IEC 62124, Photovoltaic Stand-Alone Systems—

Design Qualification and Type Approval. The new IEEE P1526,Recommended Practicefor Testing the Perform-ance of Stand-AlonePhotovoltaic Systems,contains proceduresfor independent test-ing laboratories toevaluate the perform-ance of stand-alone PV systems. FSEC isauthorized to providecertification testing for PV systems and will use the proce-dures in P1526. Testresults from NREL,Sandia, SWTDI, andFSEC over the past

five years provided the data necessary to validate this recommended practice.

Before standards or tests apply, designers relyon system-analysis tools to model the fea-tures of PV. One such tool, called HOMER,developed in part with PV Subprogram sup-port, can model a wide variety of renewableenergy systems including grid-connected systems. By the close of FY 2003, the HOMERdatabase contained more than 300 users in145 countries. HOMER is a key component of the NCPV’s international technical assistanceprograms in renewable energy in many coun-tries, including Brazil, China, India, Mexico,Philippines, the Maldives, and Senegal.

PARTNERSHIPS FOR TECHNOLOGY

INTRODUCTION

To meet the challenges of increased marketdemand posed by the U.S. PV Industry Road-map, the PV Subprogram conducts analysesand distributes information about PV. Theseanalysis and outreach activities raise theawareness of PV in numerous promising market sectors, including rural America andinternational markets.

As part of its GreenWatts program, Tucson Electric Power partners with local builders to install PV systems such as this one at an Arizona home.

This Distributed Energy Test Laboratory at Sandia was used in 2003 to studythe effects of PV and PV hybrid systems and inverters on electrical utility operation.

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Spreading the Word at Home

A huge potential market exists for PV systemsowned by or financed by the federal govern-ment and other government entities. How-ever, obstacles to wider use of PV in this mar-ket include overly complex procedures forprocuring equipment and the need to be onapproved lists of materials. To get PV systemsonto such lists, experts at Sandia and FSECare working through an interagency agree-ment with the U.S. Department of Agricul-ture Rural Utility Service (RUS). Applyingtheir recent experience in developing theFlorida PV Buildings Program, PV Subpro-gram engineers helped develop acceptancecriteria and review procedures to get com-plete PV systems onto the RUS list of mate-rials. Having PV systems on this list shouldgreatly simplify the process for rural utilitiesto buy and install this equipment. In FY 2004,the RUS list of materials for the first time willinclude grid-tied residential and off-gridwater-pumping PV systems. Work continuesto get all PV applications on the RUS list ofmaterials. This will also facilitate the pur-chase of renewable energy systems by otherfederal agencies and programs such as the

Bureau of Land Management, National ParkService, and Farm Bill. Installed systems willprovide performance and reliability data tothe systems-reliability databases of the SolarProgram.

Making consumers aware of the short- andlong-term value of PV is a goal of the SolarMarket, Policy, and Value Analysis activity.The NCPV’s Value Matrix tool highlights thebest areas of the United States for cost-effec-tive PV installations. Available on CD, regu-lators are using this and other tools devel-oped by researchers to implement portfoliostandards, a very powerful incentive that isencouraging construction of PV generatingsystems in several states. Continuous updatesto this useful tool are planned for FY 2004and beyond.

Inspiring confidence among potential buyersof PV systems, an important goal of the SolarProgram, will be served by the National Vol-untary Practitioner Certification Program.With help from experts at the NCPV, thisprogram to certify installers of PV systems got under way in FY 2003 by developinghandbooks, study guides, and applicationforms. In FY 2004, the first installers willapply for certification, take tests, and receive

The Solar Program has many outreach activities to increase public awareness of renewable energyoptions. One award-winning effort in 2002 and 2003 was the Solar America CD, which features nearly500 photos of solar energy installations in each of the 50 United States, Puerto Rico, and the U.S.Virgin Islands.

This traveling exhibit is used to educate students, teachers, and the community. Curriculum includesmajor renewable energy and efficiency themes researched and developed at NREL and BP America,which sponsored the exhibit. The bus is a teacher resource center, outfitted with electronics, displays,and workstations, whereas the trailer displays actual technology and renewable power generation.

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certificates from the North American Board of Certified Energy Practitioners.

Specialists in the Solar Program often partici-pate in events that educate potential buyersof renewable energy systems. One such eventthat gathers farmers, ranchers, and residentsof rural America each year is the NationalWestern Stock Show in Denver, Colorado,which, in 2003, drew more than 640,000people. For the eighth year, in January 2003,NREL volunteers staffed a booth on renew-able energy at this event. Providing evengreater depth on the subject, volunteers fromthe NCPV staffed three workshops on solarenergy attended by 360 people.

A large potential market, the Navajo TribalUtility Authority (NTUA) had several hun-dred PV systems in place at remote Navajoresidences in Arizona, New Mexico, and Utahby the close of 2003. Engineers from Sandiahave provided technical expertise over theyears with technical training and communityforums to make NTUA the nation’s largest off-grid residential PV program. To take fulladvantage of PV in these homes, a dc refrigerator developed by a former NASA

engineer is being test-ed at a remote home on the Navajo Reser-vation. This newrefrigerator uses about150 watt-hours ofenergy per day, com-pared with a conven-tional refrigerator’s1000 to 2000 watt-hours. To make thebenefits of PV morewidely known tonative communities,Sandia published abook in 2002, TheSolar Way: Photovol-taics on Indian Lands,that showcases uses of PV on tribal landsthroughout the United States.

Solar Electricity Worldwide

To build stronger markets for U.S. PV products,the DOE Solar Program, the Organization ofAmerican States, and the U.S. Agency forInternational Development sponsored a one-day workshop, PV in the Americas, in con-junction with the PV Specialists Conferenceof the IEEE in 2002. More than 70 peoplefrom 10 countries participated in this forumfor suppliers, installers, and researchers to discuss approaches to increasing consumeracceptance of PV technologies in the hemi-sphere. They discussed establishing compo-nent and system laboratories for testing and certification, demonstrating innovativeapplications such as hybrid PV-diesel systems

for rural power, publicizing the success ofsmall-scale business uses in Mexico, and targeting several national rural electrificationprograms.

Introducing U.S. technologies in major mar-kets outside our hemisphere can provideimportant benefits to U.S. companies. DOE and NREL, in collaboration with the SolarEnergy Centre in New Delhi, India, haveinstalled 21 kW of thin-film PV modulesmade of amorphous silicon, CIS, and CdTe.The systems, supplied by U.S. companies, are undergoing tests and data are being col-lected on all aspects of system operation. The Chinese State Development and Plan-ning Commission is working with DOE tohelp design a $240-million rural electrifica-tion program to provide electricity to 1,061townships using only renewable energy tech-nologies (including 20 MW of PV).In 2003, the Navajo Tribal Utility Authority

installed 44 small wind/PV hybrid power systems in Arizona, New Mexico, and Utahunder the Navajo Electrification Demonstra-tion Program.

The electricity from five thin-film PV arrays is being used to power room lights,ceiling fans, computers, water coolers, air conditioners, and data acquisition systems at the Solar Energy Centre in New Delhi, India.

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PV provides high-reliability power for a communications tower in DinosaurNational Monument, Utah/Colorado. Communications facilities can be pow-ered by solar technologies, even in remote, rugged terrain. Also, if a naturalor human-caused disaster disables the utility grid, solar technologies canmaintain power to critical operations.


The Million Solar Roofs (MSR) Initiative, announced in June

1997, seeks to install solar energy on one million U.S. homes

and buildings by 2010. By the close of 2003, more than

300,000 solar roof installations had been made, thanks in

large part to partnerships in states and communities across

the nation. As part of the MSR initiative, the federal govern-

ment is committed to installing solar electric and solar thermal

energy systems on 20,000 federal buildings by 2010.

The technical and analysis staff of the NCPV and the solar

water heating activity of the Solar Thermal Subprogram are

contributing to many of these projects. They are testing equip-

ment, reviewing designs, and collecting performance data.

Some installations feature prototype or early commercial

versions of products from the R&D programs.

The use of renewable and energy efficiency technologies in

detecting, preventing, mitigating, and recovering from both

natural and human-caused disasters is a growing market.

The Solar Program provides technical assistance to the

Federal Emergency Management Administration and the

insurance industry about the advantages of renewable

energy technologies in the face of disasters. Accomplish-

ments and plans have been featured on NREL’s Web site,

Surviving Diaster with Renewable Energy (www.nrel.gov/

surviving_disaster), since FY 2002. By the close of FY 2003,

this site was listed in the Intermediaries and Reinsurance

Underwriters Association Database of Storm and Weather

Catastrophe Web Sites.

SOLAR PROGRAM SUPPORTS DEPLOYMENTJohn Masson/PIX11040


T he Solar Thermal Subprogram com-plements the PV Subprogram withsimilar goals of product develop-

ment, improved manufacturing, and reducedcost. Two key applications are being addressed:Concentrating Solar Power (CSP) and SolarHeating and Lighting (SH&L). The near-termCSP goal is to help industry bring commer-cially proven technologies (trough, dish, andpower towers) to power markets in the UnitedStates and to export CSP technologies toother countries. The long-term goal for CSP is to provide a significant fraction of U.S.power-generation capacity. For SH&L, thenear-term goals are to cut solar water heatingsystem costs in half and to perfect solarhybrid lighting prototypes for transfer to thelighting industry. The long-term SH&L goalsare to develop solar space heating, cooling,and lighting systems that are economicallycompetitive with conventional technologies.

CONCENTRATING THE SUN’S ENERGY

CSP technologies use mirrors to concentratethe sun’s energy up to 10,000 times. Thisconcentrated energy powers conventionalturbines, heat engines, or other devices, suchas PV cells, to supply electricity. These attrib-utes, along with world-record solar-to-electricconversion efficiencies and costs that are pro-jected to decline rapidly when large numbersof systems are deployed, make CSP an attrac-tive renewable energy option.

The Solar Thermal Subprogram is workingwith industry to position several CSP tech-nologies for wider commercial development.CSP technologies, including parabolic troughs,power towers, and dish/engines, can range in size from 10 kW to 10 MW for distributedpower, village power, and grid-connectedapplications. Systems supplying up to severalhundred MW can be used for utility power generation. Some systems use thermal storage

during cloudy periods or at night. Others canbe combined with natural gas, and the result-ing hybrid power plants provide high-value,dispatchable power that can be fed to theutility grid when it is most needed.

1,000 MW CSP PROJECT TEAM

R&D has reduced the cost of CSP technologyby a factor of three since 1985. Future R&Dwill continue this trend. However, an in-depth

study of the technology by Sargent & Lundyin 2003 indicated that more than R&D isrequired if cost goals are to be met. Deploy-ment—the building of projects—is also neces-sary. Deployment contributes to cost reduc-tion in two ways. It enables industry to takeadvantage of mass production and enablesthe building of larger, more-efficient solarpower plants. To address this need for deployment, the Solar Thermal Subprogram

EELLECTRRICITYY AANDD HHEAAT FFRROM SSOLLAARR TTHHERRMAALLEELLECTRRICITYY AANDD HHEAAT FFRROM SSOLLAARR TTHHERRMAALL

FRANK WILKINS, TEAM LEADER, SOLAR THERMAL SUBPROGRAM

The mission of the Solar Thermal Subprogram is to get solar technologies into the marketplace. To do this, we believe it is important to work closely with industry. Ourcollaborations between DOE researchers and industry engineers feed into the systems-driven approach to planning and have resulted in major progress toward our program-matic milestones. We set these milestones based on discussions with industry about top research priorities and the necessary collaborative activities to reach our objectives.

In FYs 2002 and 2003, we made significant progress. For example, we launched thenext generation of parabolic trough collector developed by Solargenix Energy. Weworked closely with Stirling Energy Systems to improve the reliability of its 25-kWdish/engine system. We worked with two industry teams, Fafco and Davis Energy/SunEarth, to develop a new low-cost solar water heater. And, to bring sunlight indoors,in collaboration with the University of Nevada, we began tests of a prototype hybridsolar lighting concept.

During this same period, the CSP activity underwent intense evaluation—first bySargent & Lundy, an engineering company in Chicago, and then by the NationalAcademy. The objective was to get an independent assessment of the potential forachieving trough and power tower cost goals. The report issued by Sargent & Lundy in 2003 estimated trough costs could be reduced to between 4.3 and 6.2 cents/kWh and towers to between 3.5 and 5.5 cents/kWh. To achieve these cost goals, however,required a combination of R&D and deployment. The National Academy verified theseresults, although it expressed doubts that sufficient deployment would take place. Toaddress the need for deployment, we formed the 1000 MW CSP Project Team, which has since discussed the benefits of CSP with several states in the Southwest. These dis-

cussions have created interest in deploying CSP technology and willcontinue in FY 2004. These accomplishments, along with continued

R&D in the years ahead, will help launch the commercial solar products that will enrich our nation’s energy portfolio.

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assembled a 1,000 MW CSP Project Team tomake contacts in the states and to developappropriate information about the benefits and characteristics of CSP projects. The team,

which includes members from industry,Sandia, NREL, and DOE, has made presenta-tions to the Western Governors Association,Western Interstate Energy Board, andGovernors’ offices in Arizona, Nevada, New Mexico, and California. Governor

Bill Richardson (NM) subsequentlyannounced the formation of a solar

task force that is to plan a con-centrating solar plant in New

Mexico. Members of our CSPProject Team are on thattask force. Other south-western states have alsoexpressed an interest inCSP plants, and activitiesare planned for FY 2004that we hope will lead to

1000 MW of new CSPcapacity in the Southwest.

CONCENTRATING TROUGHCOMPONENT R&D

One type of CSP system is the para-bolic trough. These systems, some of which

have been operating for as long as 18 years,are the most commercially mature of all CSPtechnologies. By the close of 2003, more thantwo million square meters of collectors total-ing 354 MW were operating in the UnitedStates. Trough systems use parabolic trough-shaped mirrors to focus sunlight on thermally

efficient receiver tubes containing heat-transferoil. The hot oil is pumped through a series ofheat exchangers, producing superheated steamthat powers a conventional turbine generatorto produce eletricity. The DOE CSP researchprogram is working to improve each compo-nent of trough systems to reduce costs andimprove performance.

The CSP R&D effort is working in partnershipwith industry to develop a U.S. supply of para-bolic trough collector technology. During2002 and 2003, Solargenix Energy (formerlyDuke Solar) developed a new parabolic troughconcentrator under contract to NREL andtested a prototype at the NSTTF at Sandia.This next-generation concentrator uses analuminum collector structure made up ofaccurately manufactured hubs and low-coststruts. The new aluminum design is strongerand stiffer than previous steel structures,which leads to improved optical performanceand the possibility to make larger systems. It should also have relatively lower shippingcosts because it is lighter and more compactthan previous designs. The NSTTF tests in FY 2003 validated the optical accuracy andexpected thermal performance of the prototype.

A key component of the CSP research effort is the Sun◆Lab virtual laboratory. The

expertise of the Sun◆Lab technical staff covers every scientific and engineering field

needed to develop, operate, test, and evaluate complex solar systems and facilitate

their use. The staff has received two recent R&D 100 Awards for work in CSP

research as well as numerous awards for papers and technical accomplishments.

An important feature that makes Sun◆Lab effective is the excellent working relation-

ship between researchers at the national laboratories and test facilities and their

counterparts in the solar industry.

SUN◆LAB

Established in 1976, the National Solar ThermalTest Facility covers 110 acres of land andincludes four distinct test areas: the CentralReceiver Test Facility with a central tower and222 heliostats; the Trough Rotating PlatformFacility; the Engine Test Facility; and theDistributed Receiver Test Facility with two 25-kW parabolic dishes.

This new parabolic trough concentrator devel-oped under contract to NREL was tested on arotating platform at the National Solar ThermalTest Facility in Albuquerque, New Mexico.

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In FY 2004, full-scale field tests of the newcollector will be conducted, and the firstcommercial installations are expected by latein the year. Arizona Public Service will haveSolargenix build a 1-MWe Organic Rankinecycle plant. Solargenix will use this collectordesign for a 50-MWe commercial plant inNevada planned for 2005.

IMPROVING THERMAL ENERGY STORAGE

One long-term development project has beenthe power tower CSP concept, pioneered atSolar One in Barstow, California, in the1980s. A power tower plant has a field ofheliostats (large mirrors) that track the sun toreflect solar energy onto a receiver mountedon top of a tower in the center of the field.Today’s receivers use molten salt as the work-ing fluid and heat exchangers to producesteam. The steam powers a conventionalsteam turbine-generator power block. Themolten salt doubles as thermal storage so that power towers can generate power ondemand to the utility grid up to 24 hours aday. The DOE CSP Subprogram provides tech-nical assistance to manufacturers, who aremarketing these systems in the United States,Spain, and South Africa.

CSP researchers are also exploring thermoclinesystems for reducing the cost of thermal energystorage for power towers and troughs. A ther-mocline system uses a low-cost filler materialas the primary thermal storage medium andmolten nitrate salts as the direct heat-transferfluid. The filler materials displace the bulk ofthe more expensive molten salt. To test can-didate filler materials, a series of isothermaland thermal cycling experiments were con-ducted at the NSTTF. The thermal cycling testran for 14 months (10,000 cycles) at 287° to450°C, simulating a 30-year plant life. Finalchemical analyses will be completed in 2004,but preliminary results indicate that thequartzite rock and silica sand tested are com-patible with the molten salt environment.

CONCENTRATING DISH SYSTEM R&D

Promising dish/engine systems use a trackingparabolic dish to focus sunlight onto a ther-mal receiver. Thermal receivers absorb andtransfer the solar energy to a heat engine-generator where electrical power is generated.The dish-engine systems use kinematicStirling engines. Improving the performanceand reliability of these systems is a goal of theDOE CSP research effort.

The CSP Subprogram has been working withindustry to develop several prototype dishconcentrator systems for commercial appli-cations. About two dozen dish-engine unitshave been built and tested over the last 10 years. The Advanced Dish DevelopmentSystem (ADDS) 10-kW prototypes weredesigned and developed under contract tothe CSP R&D effort by WG Associates. TheADDS system is intended for remote powerapplications. Mod 1 and Mod 2 ADDS proto-types were installed at the NSTFF and operatedsuccessfully in an unattended mode. Forexample, in 2002, the Mod 1 ADDS produced17,133 kWh of electricity (net) and had91.4% availability. In 2003, a second Mod 2system was erected and converted to grid-connected, unattended operation.

The ADDS technology was purchased by Stirling Energy Systems (SES) in 2003 to augment its 25-kW dish/Stirling design. SES plans to bring a dish/Stirling design tomarket as soon as possible. Using ADDS tech-nology, the company improved the controlsystem of the 25-kW system. When deployedat the NSTTF, the modified 25-kW designdemonstrated closed-loop tracking and unattended automated operation. Based onthe success of this cooperation with the CSPteam at Sandia, SES will deploy six new unitsat the test facility in 2004 and 2005. In aunique cost-sharing arrangement, SES willsupport its engineering staff working at theNSTTF and supply the hardware. DOE pro-gram funds will be used to support SES with

in-kind engineering and operational support,facilities upgrades, foundations, and comput-ing resources. This partnership should help reach the Solar Program’s goal of commer-cial deployment of dish/electric technology.

ADVANCED MATERIALS R&D

To improve the efficiency and durability ofCSP systems, the R&D effort is developingand testing advanced reflector materials.Materials must resist corrosion, delamination,and deformation because these events reducethe effective concentration of sunlight on thereceiver. The Optical Materials Team collecteddata on the performance of commerciallyavailable thin-glass mirrors, quantified theimpact of defects, and proposed degradationmechanisms accounting for these defects.After surveying standard mirror painting prac-tices, they devised a large matrix of samplecombinations of paints and adhesives so thata contractor could screen for the 84 mostpromising constructions. This informationwill be passed on to the industry to help com-panies improve concentrator performance.

This 10-kW prototype of the Advanced DishDevelopment System provided valuable test data at the National Solar Thermal Test Facility in Albuquerque, New Mexico.

Sandia/PIX13336


As part of the advanced materials effort ofthe CSP Subprogram, NREL and ReflecTechare developing a low-cost reflector materialfor high-volume production. Early, smallscale samples of the material tested well forreflectance and durability. During 2002,ReflecTech delivered 16-in.-wide by 30-ft-long rolls of several improved reflective films

to NREL for measurement and testing. At theclose of 2003, after two years of testing out-doors, the material showed no significant lossof reflectance. Other accelerated weatheringtests simulating eight years of exposure alsoshowed no significant loss in solar-weightedreflectance. The CSP Subprogram goal of 10-year durability for this low-cost materialseems achievable as tests continue.

In other work on reflector materials, DOEhas been working with Science ApplicationsInternational Corporation (SAIC) in McLean,Virginia, to combine the best of thin-glassand silvered-polymer reflectors. The ultra-thin glass reflector being developed has a

All of the components of CSP dish systems have been under development for many

years within the DOE Solar Program. The same holds true for high-efficiency PV

systems. What hadn’t been done was to take a close look at how advanced CSP

and PV technologies might be used in the same system.

In the next decade, dish concentrators that use a Stirling engine as the receiver may

be commercial if reliability can be improved. PV, which has no moving parts, is also

attractive as a receiver because of its high reliability. So, in FY 2003 engineers who

work on projects in the CSP and PV Subprograms joined forces to conduct proof-

of-concept demonstrations of high-concentration components for PV and solar

thermal systems.

One of the first steps was to fine-tune analytical tools and experimental facilities

to support this work. The High-Flux Solar Furnace at NREL was adapted to

conduct preliminary tests of dense-packed arrays of PV cells from Amonix and

Spectrolab. Amonix uses lenses in its commercial PV systems, but wanted to

test a dense array designed for use with mirror-based systems. Tests of the

Spectrolab dense arrays showed efficiencies slightly greater than 30% (based on

cell area and incident flux at the module plane). This is very close to test results

achieved at ideal indoor laboratory conditions for a single cell. The modified High-

Flux Solar Furnace now serves as a test bed for the solar concentrator industry.

Another step toward developing a prototype concentrating PV system was to modify

the dish concentrator for a PV receiver (the dense-packed array). The dish developed

by Science Applications International Corporation for Stirling engine receivers was

upgraded to provide uniform flux to the focal point. NREL supported this upgrade

with optical characterizations using the SolTrace modeling software in conjunction

with the Video Scanning Hartmann Optical Test, a system designed to measure

optical performance of focusing optics. Dozens of fixed-focal-length mirror facets

were tested for use with the PV receiver array.

After working together in this effort, Spectrolab and Solar Systems, Ltd., will work

with NREL in FY 2004 to integrate III-V high-performance PV cells into Solar Systems’

concentrator systems that currently use silicon PV cells. Spectrolab’s goal is to

surpass 40% cell efficiency and achieve system solar-to-electric efficiencies

approaching 33%.

CSP SUBPROGRAM INVESTIGATES CONCENTRATING PV

This densely packed array of PV cells is seenthrough the secondary concentrator during atest at the NREL High-Flux Solar Furnace inGolden, Colorado. These tests were part of aSolar Thermal Subprogram activity to develop a concentrating PV system.

Sandia/PIX13337


polymer or metal-foil substrate coated with a copper layer, followed by a layer of silver,and topped by an optically transparent pro-tective alumina coating. The goal is toachieve a cost of $10.76/m2 at depositionrates above 40 nanometers per second (nm/s).During 2002, deposition rates for sampleswere increased to 20 nm/s, and preliminarydurability tests in 2003 were promising.

USING THE SUN FOR HEAT AND LIGHT

SOLAR WATER HEATING

Using the sun to heat water is a relativelysimple concept that, if perfected in a low-cost system, could significantly reduce con-sumption of non-renewable energy suppliesin the United States. In 2003, solar heating of swimming pools was a strong commercialmarket, with eight million square feet of collector being installed each year in the

United States, equivalentto 300 megawatts thermal(MWt) in rated capacity.Solar water heating sys-tems are being includedwith some new homes;however, sales have lagged since the federaltax credits expired in the late 1980s. Reducing the costs of these sys-tems is a major goal of the Solar Thermal Subprogram.

Low-Cost Solar WaterHeating SystemsCost seems to be one ofthe biggest obstacles towider use of solar waterheating. In fact, analystshave projected that low-ering the first cost ofinstalled solar hot water

systems to $1,000 could significantly expandthe current market. Much of the expense oftoday’s solar water heaters is the cost of keycomponents made of glass, copper, and

aluminum. As a result, finding and testingalternative materials is a major goal of theR&D effort.

Low-cost polymer-based materials for solarwater heaters have the potential to reducecosts by 50% because of lower material, man-ufacturing, and installation costs. The SolarThermal Subprogram has explored and testedpromising new materials and is working withtwo industry teams to develop low-cost, pas-sive systems with polymer components. Thesame polymer-based technology being devel-oped for low-cost water heaters can also beused eventually to provide space heating,thus reducing consumption of fossil fuels for heating homes and businesses.

Using these new materials, FAFCO, Inc., andDavis Energy Group/SunEarth, in partnershipwith NREL and the DOE Solar Program, aredeveloping unpressurized integral collectorstorage (ICS) system designs. In these systems,fresh water moves through the system when-ever hot water is drawn. The water is heatedin a heat exchanger while it sits in the ICSsystem. These simple systems use no pumpsor motors and are being developed initiallyfor use in freeze-free regions of the country.

The 10-kilowatt High-Flux Solar Furnace, which began operation late in1989, uses a tracking heliostat and 25 hexagonal mirrors to concentratesolar radiation. The furnace can nominally provide flux at 2,000 suns but,when required, can use specialized secondary optics to generate concen-trations greater than 20,000 suns. In addition to testing solar energy sys-tems, this installation is used for applied R&D in advanced materials andprocesses and research on destruction of environmental contaminants.

This prototype roof-integrated thermosiphon system has a very low profile, comparable to a skylight. Thisless obtrusive orientation does not significantly reduce energy production. This prototype is testing theperformance of new low-cost materials that resist corrosion caused by various groundwater conditions.


Sun

Syst

ems/

PIX0

5978


In FY 2003, about a dozen second-generationICS polymer solar water heaters were installedin the field. This controlled field-testing isdesigned to stress the systems until weak-nesses appear. They are carefully monitoredand operate under extreme conditions atlaboratory and university settings in Arizona, California, Florida, and Hawaii.Monitoring data show efficiencies as high as 40%, which is higher than predicted.

The passive solar water heating systems near-ing commercial readiness are appropriate forareas that do not experience hard freezes. InFY 2004, work begins to identify promisingconcepts for cold-climate applications.

Testing Materials for DurabilitySupporting efforts to replace costly materialswith polymer substitutes, the University ofMinnesota Department of Mechanical

Engineering tested and identified promisingpolymers for use as heat exchangers in FY2003. Their recommendations will form astarting point for the cold-climate solar waterheating effort that begins in FY 2004.

In 2003, additional tests at DOE’s acceleratedweathering testing facility in Golden, Colo-rado, showed that Korad, a promising ultra-violet screen coating for low-cost polymerglazings, began to exhibit signs of degrada-tion at about 13 years of equivalent ultra- violet exposure for a 2-mil-thick coating.However, thicker 4- and 6-mil coatings of the same material now being tested lookmore promising. If these coatings provedurable, the polymer glazing underneathshould reach the 20-year life necessary forcommercial success. Testing also showed that neither wet nor dry stagnation shouldcause structural problems for the polymerabsorber materials.

HYBRID SOLAR LIGHTING

Good lighting is essential to health and pro-ductivity in our schools, offices, factories,and stores. Electric lighting also represents30% to 35% of the electricity consumed in atypical school, office building, or retail store.Roughly 10% of the electricity consumption in the United States is used to light commer-cial buildings. Therefore, increases in theenergy efficiency of lighting these spacescould have a significant impact on nationalenergy consumption. In addition, someresearch has credited sunlit indoor spaceswith improvements in human health andperformance versus spaces illuminated withelectric lights. Sunlight indoors has also beenshown to increase product sales in retailstores. Hybrid solar lighting, which combinesnatural sunlight with electric light, is a rela-tively new concept with the potential toreduce energy consumption and improve the indoor environment.

The analysis, testing, and engineering resources of the Solar Thermal Subprogram

help answer the inevitable questions that arise with evolving technology. For example,

the Civano sustainable community in Tucson, Arizona, incorporates active and passive

solar energy, including PV, daylighting, and solar water heating, on about 300 homes.

These homes, which consume far less energy than conventional homes in other

subdivisions, have solar water heating systems that use integrated collector storage

designs from several manufacturers. Each system holds about 40 gallons of water.

About a dozen collectors eventually developed pinholes in the copper tubing and

began leaking. Engineers from Sandia were called in to find out why and to assess

the potential for more problems. Their tests showed that, while all collectors had

some pitting, only a small group of systems were vulnerable to leaking. These were

thin-walled systems that operated at higher temperatures. The analysis concluded

that corrosive elements in the water that attacked copper were responsible for the

holes, rather than manufacturing defects. Fortunately, the Solar Thermal Subprogram,

through Sandia, had been working with the Salt River Project (SRP) utility and a

manufacturer, Energy Laboratories, Inc. (ELI), to develop a solar water heating system

that could operate with the potentially corrosive well water common in the region. The

new design is called the roof-integrated thermosiphon system and uses stainless steel,

instead of copper, on all components exposed to water. Using stainless steel to protect

against corrosive water demanded a new manufacturing method for the collectors.

With help from Sandia and SRP, ELI devised a manufacturing approach and produced

prototype systems that were installed on homes in 2001 and 2002. Data from these

prototypes were used to improve the systems. ELI began manufacturing this new

product early in 2004.

FINDING THE ANSWERS


Hybrid solar lighting now has a greater poten-tial to deliver natural light to interior spacesthanks to new low-cost, flexible optical fibers.Hybrid solar lighting systems use small, track-ing parabolic solar concentrators that focussunlight onto flexible optical fibers. Theseoptical fibers “route” the sunlight inside thebuilding and connect to modified electriclight fixtures that distribute the sunlight andprovide back-up light when needed. Controlsystems using dimmable ballasts adjust thelevel of electric light from fluorescent fixturesto compensate for variations in sunlight andmaintain a constant illumination level.Hybrid solar lighting can deliver the benefitsof sunlight without some of the disadvan-tages of conventional daylighting from sky-lights and windows such as glare, variability,heat gain, and costly architectural designrequirements.

After three years of development, the SolarProgram’s first hybrid solar lighting systembegan testing in FY 2003 at Oak RidgeNational Laboratory. Laboratory experiencesuggested several improvements. For exam-ple, in FY 2004, a second-generation collectorand light distribution design will be testedthat uses a new type of fiber optic bundledeveloped by Advanced Lighting Systems,Inc. The new design will eventually be usedin a stand-alone hybrid lighting system thatcan be integrated with several different elec-tric lamps of differing lumen outputs andused in direct, indirect, task, and general illumination applications. The system isexpected to be complete in 2004 or 2005 and meet a cost goal of $0.12/kWh (level-ized cost of energy).

Key technical challenges for hybrid solarlighting include reducing system complexitywhile improving efficiency. Collectors/con-centrators must be easy to assemble, align,calibrate, and maintain. The mirror and fiber-mounting arrangements must be straightfor-ward for installers, and components (mirrors,motors, and mounts) must be low cost, light-weight, and easy to manufacture. The spec-tral characteristics of the sunlight deliveredindoors must be well matched to the backupelectric lamps. And the clarity and robustness

of fiber optic materials must continue toimprove while costs continue to fall. Theabove challenges form the nucleus of anational R&D agenda that is being system-atically addressed by members of the HybridLighting Partnership and other organizations.As part of the systems-driven approach, datawill be collected at demonstration installa-tions planned for Alabama, California, andTennessee in FY 2004 and used to determinefuture R&D activities.

Hybrid solar lighting (HSL) systems use parabolicsolar collectors, flexible optical fibers, and modi-fied electric light fixtures to “route” sunlight intobuildings: (a) the first prototype HSL system,which was installed on the National TransportationResearch Center at Oak Ridge National Laboratoryin Tennessee; (b) the basic HSL system design;and (c) the University of Virginia’s Solar Decathlonhouse, which boasted the world's first domestic-scale HSL system.

(a)(a)

(b)(b)

(c)(c)

Oak Ridge

Chris Gun/PIX12174

RESOURCES OF THE SOLAR ENERGY TECHNOLOGIES PROGRAM

Labs 41%

Industry33%

State/local13%

University13%

03544311

This pie chart shows the Solar Program’sresearch performers and their share of totalfunding.

Solar Program Web Sitewww.eere.energy.gov/solar

The Solar Program’s support spans partners from industry, universities, and national laboratoriesacross the United States.

The Solar Energy Technologies Programuses partnerships to shorten the timeof project completion and to ensurerapid transfer of the technology fromthe research laboratory to the factoryfloor. Through competitive procure-ments and multi-year funding strate-gies, the Solar Program works closelywith the national laboratories, indus-try, state and local agencies, and uni-versities to leverage their expertise and resources.

http://www.nrel.gov/docs/fy03osti/33586CD.zip

A Strong Energy Portfolio for a Strong AmericaEnergy efficiency and clean, renewable energy will mean a stronger economy, a cleaner environment, and greater energy independence for America. Working with a wide array of state, community, industry, and university partners, the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of energy technologies.

Produced by the

National Renewable Energy Laboratory

Operated for the U.S. Department of EnergyOffice of Energy Efficiency and Renewable Energyby Midwest Research Institute • Battelle

DOE/GO-102004-1938 • June 2004

Printed with biodegradable ink on paper containing at least50% wastepaper, including 20% post consumer waste.

For more information contact:

EERE Information Center1-877-EERE-INF (1-877-337-3463)[email protected] visit: www.eere.energy.gov

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