Final Thesis, Solar Dish Engine System 1 Uet Taxila

DESIGN, FABRICATION AND EXPERIMENTAL

INVESTIGATION OF SOLAR DISH STIRLING

SYSTEM

SESSION 2010-2014

Project Supervisor

Dr. Muzaffar Ali

Submitted by:

Aitazaz Ahsan (10-ME-04)

Naeem Nawaz (10-ME-28)

M. Umer (10-ME-36)

Umair Masood (10-ME-82)

Department of Mechanical Engineering

University of Engineering &Technology, Taxila

DESIGN, FABRICATION AND EXPERIMENTAL INVESTIGATION OF SOLAR DISH STIRLING SYSTEM

1

ABSTRACT

In order to satisfy the rising energy demands of global consumption, a new cleaner and

renewable power source needs to be explored, conceptualized, and developed. Solar energy is a

free and clean energy resource which can be used to generate power without damage to humans or

the local ecosystems. To efficiently capture this solar energy as a feasible power source, a Stirling

engine is developed and will use sunlight as a source via a solar concentrator. This project

intends to utilize methods of gathering solar energy that have not yet been commercially

implemented, and modifications to the external heating of the receiver will be made in order

to maximize the efficiency of solar Stirling engines via hybrid mechanism. These modified

solar Dish Stirling engines can produce power for a wide variety of applications. The nature

of the engine allows for both the scalability to create a solar farm as well as use for producing

power in remote areas and disaster relief. Concentrating solar power (CSP) is a unique renewable

energy technology. CSP systems have the ability to provide electricity, refrigeration and water

purification in one unit. This technology will be extremely helpful in improving the quality of life

for many people around the world who lack the energy needed to live a healthy life.


2

DEDICATIONS

We dedicate this project to all those humble human beings who have aided us in

any way to become what we are today, whose sacrifices seeded us success,

especially our parents who felt our pain beyond us and showered with never ending

prayers and support

We deem them as a divine source of inspiration


3

ACKNOWLEDGEMENTS

First of all thanks to ALLAH ALMIGHTY who has guided us through every step and it is only

because of His blessings that we gathered enough audacity and will to accomplish this project.

Then we would like to thank Dr. Muzaffar Ali for showing us the path of learning. He spread his

valuable time to guide us in the selection and implementation of knowledge to practical work. His

guidance is inevitable part of our successful project. Naturally, we would also like to thank our

family for giving us the gift of education. Finally, we would like to take this opportunity to

express our thanks and gratitude to all the persons who have directly or indirectly availed us in

guiding our project.


4

TABLE OF CONTENTS

1 INTRODUCTION .................................................................................................................................. 11

1.1 Energy Crises in Pakistan: ................................................................................................................ 11

1.2 Causes Of Energy Crises: ................................................................................................................. 11

1.2.1 Aging of the Equipment: ............................................................................................................ 11

1.2.2 Wastage of Energy: .................................................................................................................... 11

1.2.3 High Cost of Fuel: ...................................................................................................................... 12

1.2.4 Mismanagement and Monopoly in Business: ............................................................................ 12

1.2.5 Wastage of Energy: .................................................................................................................... 12

1.3 Motivation and Justification: ............................................................................................................ 12

1.3.1 Energy Mix of Pakistan: ............................................................................................................ 13

1.4 Solar Potential of Pakistan: ............................................................................................................... 14

1.4.1 Government Policy: ................................................................................................................... 15

1.4.2 Annual Insolation: ...................................................................................................................... 15

1.5 Solar Technologies: .......................................................................................................................... 15

1.5.1 PV/Solar Cells: ........................................................................................................................... 15

1.5.2 Concentrated Solar Thermal Power Plants: ........................................................................ 16

2 SOLAR THERMAL POWER TECHNOLOGIES & THEIR SIGNIFCANCE ............................. 18

2.1 Parabolic and Fresnel Trough Technology: ...................................................................................... 19

2.2 Central Receiver Systems: ................................................................................................................ 20

2.3 Dish-Engine Systems: ....................................................................................................................... 22

2.4 Solar Updraft Tower Plant: ............................................................................................................... 23

2.5 Technology Comparison: .................................................................................................................. 24

2.6 Weak Points and Barriers: ................................................................................................................ 25

2.7 Strong Points and Diffusion Factors: ................................................................................................ 25

2.8 Main Drivers Influencing Future Technology Development: ........................................................... 26

2.8.1 Climate Protection: .................................................................................................................... 26

2.8.2 Objective of Security of Supply: ................................................................................................ 26

2.8.3 Enforced Direct Market Support for Renewable Energies (feed-in-laws): ................................ 26

2.8.4 Preferring Non-Intermittent Electricity Suppliers: ..................................................................... 26

2.8.5 Advanced Side Applications and Side Products: ....................................................................... 26


5

2.8.6 Increasing Demand for Local Added Value: ............................................................................. 26

2.8.7 Aiming at Conflict Neutral Technologies: ................................................................................. 27

3 DISH ENGINE SYSTEM PROJECT DESCRIPTION ..................................................................... 28

3.1 Project Background: .......................................................................................................................... 29

3.2 Brief History of Solar Thermal Plant: ............................................................................................... 30

3.3 Previous Work: ................................................................................................................................. 31

3.5 Modern Feats in Solar Dish Stirling System: .................................................................................... 34

3.5 Basic Units of Concentrating Solar Power Dish/Engine System: ..................................................... 36

3.5.1 Solar Concentrator: .................................................................................................................... 36

3.5.2 Power Conversion Unit: ............................................................................................................. 36

3.5.3 Advantages: ................................................................................................................................ 37

4 LITERATURE REVIEW OF RESEARCH PAPERS ....................................................................... 38

5 STIRLING ENGINE/ RECEIVER ...................................................................................................... 46

5.1 Brief History: .................................................................................................................................... 46

5.2 Study of Stirling Engine Components and Functional Description: ................................................. 49

5.2.1 Heater / Hot Side Heat Exchanger: ............................................................................................ 49

5.2.2 Regenerator: ............................................................................................................................... 50

5.2.3 Cooler / Cold Side Heat Exchanger: .......................................................................................... 50

5.2.4 Heat Sink: ................................................................................................................................... 51

5.2.5 Displacer: ................................................................................................................................... 51

5.2.6 Power Piston: ............................................................................................................................. 51

5.2.7 Crank Shaft: ............................................................................................................................... 51

5.2.8 Connecting Rod: ........................................................................................................................ 51

5.3 Basics of Stirling Engine: ................................................................................................................. 51

5.3.1 The Stirling Engine Cycle: ......................................................................................................... 52

5.3.2 Isothermal Expansion (2-3): ....................................................................................................... 52

5.3.3 Constant Volume Heat Rejection (3-4): ..................................................................................... 52

5.3.4 Isothermal Compression (4-1): .................................................................................................. 52

5.3.5 Constant Volume Heat Addition (1-2): ...................................................................................... 52

5.5.1 Increase Power Output in Stage One: ........................................................................................ 54

5.5.2 Decrease Power Usage in Stage Three: ..................................................................................... 55

5.6 Stirling Engine Configurations: ........................................................................................................ 56

5.6.1 Alpha Stirling Engine: ............................................................................................................... 57


6

5.6.2 Beta Stirling Engine: .................................................................................................................. 57

5.6.3 Gamma Stirling Engine:............................................................................................................. 57

5.7 Solar Stirling Engine: ........................................................................................................................ 59

5.7.1 Lubricants and Friction: ............................................................................................................. 59

5.7.2 Pressurization: ............................................................................................................................ 60

5.8 Comparison of Stirling Engine with an Internal Combustion Engine: ............................................. 60

5.8.1 Advantages: ................................................................................................................................ 60

5.8.2 Disadvantages: ........................................................................................................................... 60

5.9 Design and Analysis of Stirling Engine: ........................................................................................... 61

5.9.1 Non Dimensional Parameters Used in the Analysis: ................................................................. 61

5.9.2 Beale Number Bn: ...................................................................................................................... 63

5.9.3 Estimating Stirling Engine Power Using Bn: ............................................................................. 64

5.9.4 West Number Wn: ...................................................................................................................... 64

5.9.5 Estimating Stirling Engine Power Using Wn: ............................................................................ 65

5.10 Online Design Calculations: ........................................................................................................... 65

5.11 Final Calculated Results Achieved From Engine Calculations: ..................................................... 66

6 SOLAR CONCENTRATOR ................................................................................................................ 67

6.1 Parabolic Dish Design: ..................................................................................................................... 69

6.2 Parabolic Dish Calculator: ................................................................................................................ 72

6.3 Parabolic Trough: .............................................................................................................................. 73

6.3.1 Parabolic Trough Design: .............................................................................................................. 74

7 SOLAR RADIATION STUDY OF TAXILA ...................................................................................... 76

7.1 Method of Calculations: .................................................................................................................... 76

7.1.1 Prediction of diffuse solar radiation: .......................................................................................... 76

7.1.2 Results and Discussions: ............................................................................................................ 77

7.1.3 Diffused Solar Radiation:........................................................................................................... 77

7.1.4 Sky Condition at Taxila: ............................................................................................................ 77

7.1.5 Statistical Distribution: .............................................................................................................. 77

7.1.6 Variation of Direct and Diffuse Solar Radiation: ...................................................................... 78

8 FABRICATION OF SOLAR DISH STIRLING SYSTEM ............................................................... 81

8.1 Theoretical Part: ................................................................................................................................ 81

8.2 Concentration Ratio: ......................................................................................................................... 82

8.3 Optical Energy Absorbed by the Receiver: ....................................................................................... 84


7

8.4 Experimental Work: .......................................................................................................................... 85

8.5 Gamma Type Stirling Engine Receiver: ........................................................................................... 86

9 PROJECT INNOVATION ................................................................................................................... 88

9.1 Hybrid Mechanism: .......................................................................................................................... 88

9.2 Why Solar Generator: ....................................................................................................................... 89

9.3 Aim of Our Project: .......................................................................................................................... 89

9.4 Research & Development/Constraints: ............................................................................................. 90

9.5 Experimental Setup: .......................................................................................................................... 91

9.5.1 Coil:............................................................................................................................................ 91

9.5.2 Temperature Sensor: .................................................................................................................. 92

9.5.3 The Battery: ............................................................................................................................... 92

9.5.4 Charge Controller:...................................................................................................................... 93

9.5.5 Primary Dish Engine System Setup: .......................................................................................... 94

9.5.6 Hybrid Setup: ............................................................................................................................. 94

9.5.7 Results: ....................................................................................................................................... 95

APPENDEX A ........................................................................................................................................... 96

DETAILED ENGINEERING DRAWINGS OF ALL PARTS AND PRO-E ANIMATIONS ...... 96

APPENDIX B .......................................................................................................................................... 107

DEFLECTION ANALYSIS OF PARTS ................................................................................... 107


8

TABLE OF FIGURES

Figure 1.1 Pakistan's Direct Normal Solar Radiation (Annual) .................................................................... 14

Figure 1.2 Anatomy of Solar Cell ................................................................................................................. 16

Figure 1.3 Working of PV Cell ..................................................................................................................... 16

Figure 2.1 Schematic illustration of the component parts of solar thermal power plants ........................ 18

Figure 2.2 Parabolic Trough System............................................................................................................ 19

Figure 2.3 Fresnel Trough ........................................................................................................................... 20

Figure 2.4 Central Receiver System ............................................................................................................ 21

Figure 2.5 10 MW PS10 central receiver plant in Spain .............................................................................. 22

Figure 2.6 Solar Dish Engine System ........................................................................................................... 23

Figure 2.7 Solar Dish Engine System Prototype (25 kW) ............................................................................ 23

Figure 2.8 Solar Updraft Tower Schematic ................................................................................................ 23

Figure 2.9 Solar Updraft Tower ................................................................................................................... 24

Figure 2.10 Technology Comparison .......................................................................................................... 24

Figure 2.11 Strong and Weak points of Solar Thermal Technology ............................................................ 25

Figure 3.1 Dish Engine Systems .................................................................................................................. 28

Figure 3.2 Dish Engine System Schematic ................................................................................................. 29

Figure 3.3 Pifre's 1878 Sun-Power Plant Driving a Printing Press ............................................................... 30

Figure 3.4 Basic Configuration of Dish Engine System ................................................................................ 31

Figure 3.5 Schematic of Solar 1 ................................................................................................................... 32

Figure 3.6 Concentrator Assembly for Receiver 1 ...................................................................................... 33

Figure 3.7 Receiver Assembly for Solar 1 .................................................................................................... 34

Figure 3.8 Stirling Energy Systems Stirling Power Units ............................................................................. 35

Figure 3.9 Stirling Engine System - SunCatcher .......................................................................................... 35

Figure 3.10 Dish Engine Power Plant .......................................................................................................... 36

Figure 5.1 The Original Stirling Engine Patent of 1816 ............................................................................... 46

Figure 5.2 Automotive Stirling Engine ........................................................................................................ 47

Figure 5.3 Brayton Rotating Unit (BRU) ...................................................................................................... 48

Figure 5.4 Stirling based Fission Surface Power System ............................................................................. 48

Figure 5.5 Cut-away diagram of a rhombic drive beta configuration Stirling engine design ..................... 49

Figure 5.6 Ideal Stirling Cycle ...................................................................................................................... 53

Figure 5.7 Operation of Ideal Stirling Cycle Engine (Displacer at lower dead centre) ................................ 53

Figure 5.8 Operation of Ideal Stirling Cycle Engine (Displacer at lower upper dead centre) ..................... 53

Figure 5.9 Expansion Driving the Power Piston Upwards ........................................................................... 55

Figure 5.10 Transfer of warm gas to the upper cool end ........................................................................... 55

Figure 5.11 Contraction (Driving the Power Piston Downward) ................................................................ 56

Figure 5.12 Transfer of Cooled Gas to the Lower Hot End) ........................................................................ 56

Figure 5.13 Alpha Stirling Engine ................................................................................................................ 57

Figure 5.14 Beta Stirling Engine ................................................................................................................ 57

Figure 5.15 Gamma Stirling Engine ............................................................................................................. 58

Figure 5.16 Gamma Stirling Engine ............................................................................................................. 58

Figure 5.17 Solar Stirling Schematic .......................................................................................................... 59


9

Figure 5.18 Non-dimentional output power, LSmax* as a function of non-dimentional engine speed,

nmax*.......................................................................................................................................................... 62

Figure 5.19 Non-dimentional engine speed, nmax* as a function of non-dimentional non-dimentional

engine specification, S* .............................................................................................................................. 62

Figure 5.20 Online Design Calculations 1 .................................................................................................. 65

Figure 5.21 Online Design Calculations ....................................................................................................... 66

Figure 6.1 Solar Concentrator (Dish Type) ................................................................................................ 67

Figure 6.2 The ANU 400m2 Solar Concentrator Dish .................................................................................. 68

Figure 6.3 The Focus of ARUN160 on focus plate at the receiver mouth .................................................. 69

Figure 6.4 ARUN160, installed at Latur for milk pasteurization - June 2005 .............................................. 69

Figure 6.5 Parabolic Dish Schematic ........................................................................................................... 70

Figure 6.6 Parabolic Dish Schematic Showing the Design Terms ............................................................... 71

Figure 6.7 Parabolic Dish Calculator ........................................................................................................... 72

Figure 6.8 Parabolic Trough Schematic ....................................................................................................... 73

Figure 6.9 SGES(Solar Energy Generating Systems) Plant in California ...................................................... 73

Figure 6.10 SGES(Solar Energy Generating Systems) Plant in California .................................................... 74

Figure 6.11 Parabolic Trough Design .......................................................................................................... 74

Figure 6.12 Parabolic Trough Animation .................................................................................................... 75

Figure 7.1 Statistical Distribution of Global Solar Radiation ....................................................................... 78

Figure 7.2 Input parameter for estimation of monthly Global Solar radiation at Taxila, Pakistan (Table-1)

.................................................................................................................................................................... 78

Figure 7.3 Calculated Solar radiation data for Taxila .................................................................................. 79

Figure 7.4 A plot of the monthly variation of total direct and diffuse solar Radiation for Taxila, Pakistan

.................................................................................................................................................................... 79

Figure 7.5 Shows the variation of direct and diffuse radiation for Taxila, Pakistan ................................... 80

Figure 7.6 Behaviour of the cloudiness index Kt,D/H and D/H0 during a year for Taxila, Pakistan. .......... 80

Figure 8.1 Parabolic Geometry ................................................................................................................... 81

Figure 8.2 Fabricated Model of Dish Engine System .................................................................................. 86

Figure 8.3 Fabricated Gamma Type Stirling Engine .................................................................................... 87

Figure 9.1 Multi Mirror Collectors .............................................................................................................. 90

Figure 9.2 Coil for Circulating Hot Fluid (Hybrid Mechanism) .................................................................... 92

Figure 9.3 Temperature Sensor .................................................................................................................. 92

Figure 9.4 Battery to Provide Electricity during the Night ......................................................................... 92

Figure 9.5 Charge Controller ...................................................................................................................... 93

Figure 9.6 The Project Setup ....................................................................................................................... 94

Figure 9.7 Parabolic Trough Setup .............................................................................................................. 94

Figure 9.8 Project Schematic ...................................................................................................................... 95

Figure 9.9 Relationship between Time of the day & Rpm .......................................................................... 95

Figure: Dish Engine System Animation on Pro-E ...................................................................................... 106

Figure: Parabolic Trough Animation on Pro-E ......................................................................................... 106

Figure: The resulting deflection from the expected loading on the hot endof the engine. The highest

level of deflection is expected to be 11.7 m. .......................................................................................... 107

Figure: The resulting deflection from the expected loading on the body of engine. The highest level of

deflection is expected to be 3.0 mm ........................................................................................................ 108


10

Figure: The resulting deflection from the expected loading on the base of the displacer piston. The

highest level of deflection is expected to be 1.8 mm. .............................................................................. 108

Figure: The resulting deflection from the expected loading on power piston rod for the engine. The

highest level of deflection is expected to be 26 m ................................................................................. 108

Figure: The resulting deflection from the expected loading on displacer piston rod for the engine. The


Figure: The resulting deflection from the expected loading on the crankshaft for the engine. The


Figure: The resulting deflection from the expected loading on engine bolts/ linear shaft. The highest

level of deflection is expected to be 45 m .............................................................................................. 108


11

1 INTRODUCTION

1.1 Energy Crises in Pakistan: An adequate and reliable supply of energy is a prerequisite for development. The energy demand

is expected to grow rapidly in most developing countries over the next decades. For Pakistan,

population and energy demand has been increasing day by day. Most of the power generation of

Pakistan is based on fossil fuel sometimes which is playing a negative impact on finance in the

long run operation. The burning of fossil fuels has given rise to global warming with the increasing

amount of greenhouse gases. For meeting the expected energy demand as the population will rise

and to sustain economic growth, alternative form of energy renewable energy needs to be

expanded. In future fossil fuel will not be able to supply the electricity to the user as it will be

finished & not environment friendly also.

Owing to the existing energy crises, incorrect energy mix and the aging of the equipment it has

become important that we change our energy system and move towards sustainable renewable

energy sources. Solar power is perceived as an environment-friendly, low-cost source of electricity

that relies on proven technology. In order to satisfy the rising energy demands of global

consumption, a new cleaner and renewable power source needs to be explored, conceptualized,

and developed. Solar energy is a free and clean energy resource which can be used to generate

power without damage to humans or the local ecosystems.

1.2 Causes Of Energy Crises: Energy is now the talk of town in Pakistan. Starting from house wives, traders, businessmen,

students, ministers all the victims of the shortage of energy. Karachi the biggest city experiencing

up to 12 hours load shedding in peak hot weather and during the board exams are on the way.

Everybody now became the expert of energy and all the figures are on finger tips, sometimes the

shortage is 200 MW sometimes 2500 MW.

1.2.1 Aging of the Equipment:

One very important reason attributed to this energy shortage is the aging of the generating

equipment which could not develop the electricity as per the design requirement. This is the

responsibility of continuous updating the equipment and keeping the high standard of maintenance.

we sincerely think a serious thought should be given for general overhaul and maintenance of

existing equipment to keep them in good working order. Due to aging of equipment change over

in energy system is required towards a more sustainable system.

1.2.2 Wastage of Energy:

So far energy conservation is limited to newspaper ads lip service in seminars. No serious thought

is being given to utilize the energy at the optimum level. A new culture need to develop to conserve

energy. Some times on government level illiteracy is blamed for the failure of the energy

conservation program. this is not true,. Maximum energy is consumed by elite class which have

all the resources of knowledge and communication. But for their own luxury they themselves

ignore the problem. Government should seriously embark on energy conservation program.


12

1.2.3 High Cost of Fuel:

The cost of crude has increased from 40 $ to 140 $/barrel. It means the generation from thermal

units are costing exorbitant price. WAPDA and KESC when purchasing electricity on higher cost

are not eager to keep on selling the electricity on loss. Therefore they do not move on general

complain of load shedding. One simple solution is to increase the energy cost. Again the theft of

electricity from the consumers adding the misery of common citizen who wants to pay the bills

honestly, the problem of the energy losses is being discussed for more than a decade and in spite

all efforts no solution has been found.

1.2.4 Mismanagement and Monopoly in Business:

WAPDA and KESC are two generation and dispatch units in Pakistan. Although NEPRA is a

government authority to settle the tariff issues but the fact remains that once the question of

WAPDA comes the authority has a very little influence. This is suggested that private sector should

be allowed to install power plant and settle the electricity to consumers. Once the rates are settled

on competitive basis and the service and uninterrupted power supply will be insured then

consumers will be benefited.

1.2.5 Wastage of Energy:

So far energy conservation is limited to newspaper ads lip service in seminars. No serious thought

is being given to utilize the energy at the optimum level. A new culture need to develop to conserve

energy. Some times on government level illiteracy is blamed for the failure of the energy

conservation program. This is not true. Maximum energy is consumed by elite class which have

all the resources of knowledge and communication. But for their own luxury they themselves

ignore the problem. Government should seriously embark on energy conservation program.

Technical and economic constraints, political issues, incompetent and discontinuity of energy

policies, international embargoes, depletion of fossil fuels like natural gas etc. are other causes for

the energy crises.

1.3 Motivation and Justification: The political, economical, environmental concerns over traditional fossil fuel power generation

have led to an overwhelming amount of innovation and research into cleaner renewable sources.

The Islamic Republic of Pakistan currently gets 63% of our energy through fossil fuels and less

than and very little from renewable energy (Systems, Technology, 2009). It is in the nations best

interest to invest heavily in renewable energy so that we could reap the benefits to the

economy, environment, politics, and human health.

Of the existing sources of renewable energy, the most promising is the sun. It is the most abundant

source of energy on the planet and it is a phenomenal source of light and heat. Scientific American

magazine states, The energy in sunlight striking the Earth for 40 minutes is the equivalent to

global energy consumption for one year. (Systems, Technology, 2009). Therefore, it behooves

engineers to design way of capturing this incredible natural resource for use in power generation

as an alternative to other methods such as fossil fuels.

During a national disaster Pakistan has a difficult time quantifying the exact number of lives that

are lost in nature disaster. Perhaps more surprising is not the amount of death that occur from


13

46.50%

27.50%

11.60%

7.50%

Energy Consumption Share of Pakistan

Domestic Users

Industrial Users

Agriculture Sector

Commercial Sector

natural disasters, but the deaths that occur after disaster hits. The lack of clean water, food,

and electricity can sometime cause more deaths than the actual disastrous event. Creating

a technology that provides power to such disastrous areas can provide much needed clean

water, and desperately needed electricity for life saving operations such as medical equipment,

communications, and food preparation. Remote power can provide a real survival opportunity

for disaster victims who have been left without a home, food, water, or power.

1.3.1 Energy Mix of Pakistan:

Total installed capacity of electricity :22477MW

Total production of electricity : 11362 MW

Total Demand of electricity : 16814 MW

Shortfall :5000 6000 MW (approx.)

Thermal Installed Capacity (Fossil Fuels) : 15000MW (approx.) : 62% share. (Oil 35.1% & Gas 27%)

Hydropower : 6595MW (33% share in summers) and 2300 MW in winters

*(In 1995 the energy mix of hydro-thermal was 50-50%)

Nuclear : 462 MW (3.9% share)

Coal : 0.16 MW

Renewables: 42 MW (Solar/Wind)

Annual Increase in demand 8 10%

*These figures are not exact and may vary depending upon season and energy demand, policies


14

Figure 1.1 Pakistan's Direct Normal Solar Radiation (Annual)

The energy consumption share pie chart shows that 46.5% of the users are domestic putting a

significant amount of load on the national grid so it is important to use decentralized energy for

domestic use so that the load on the national grid can be reduced and more share can be given to

industrial sector contributing in national development.

1.4 Solar Potential of Pakistan: Pakistan being in the sunny belt is ideally located to take advantage of the solar energy

technologies. This energy source is widely distributed and abundantly available in the country.

During last twenty years Pakistan has shown quite encouraging developments in photovoltaic

(PV). Currently, solar technology is being used in Pakistan for standalone rural telephone

exchanges, repeater stations, highway emergency telephones, cathodic protection, refrigeration for

vaccine and medicines in the hospitals etc. The Public Health Department has installed many solar

water pumps for drinking purposes in different parts of the country. Both the private and public

sectors are playing their roles in the popularization and up grading of photovoltaic activities in the

country. A number of companies are not only involved in trading photovoltaic products and

appliances but also manufacturing different components of PV systems. They are selling PV

modules, batteries, regulators, invertors, as well as practical low power gadgets for load shedding

such as photovoltaic lamps, battery chargers, garden lights etc.

PCRET and other public and private organizations have developed the know-how and

technology to fabricate solar cells, modules, and systems. In addition to generate electricity,

thermal energy can also be used for desalination of saline water.


15

1.4.1 Government Policy:

Raja Pervaiz Ashraf, the then Federal Minister of Water & Power has announced on July 2, 2009

that 7,000 villages will be electrified using solar energy in the next five years Chief Ministers

senior advisor Sardar Zulfiqar Khosa has also stated that the Punjab government will begin new

projects aimed at power production through coal, solar energy and wind power; this would

generate additional resources.

The Government of Pakistan has allowed the provincial government of Sindh to conduct research

on the feasibility of solar power. The government is planning to install a water filtration plant to

make the seawater sweet through solar energy, said Sindh Minister for Environment and

Alternative Energy, Askari Taqvi.

1.4.2 Annual Insolation:

Insolation is very high in Pakistan, at 5.3 kWh/m/day.

Pakistan has also set a target to add 5% approximately 10,000 MW electricity through renewable

energies by year 2030 besides replacement of 5% diesel with bio-diesel by year 2015 and 10% by

2025.

1.5 Solar Technologies: There are two types of solar technologies used for power generation:

PV Cells. Concentrated Solar Thermal Power Plants.

1.5.1 PV/Solar Cells:

Photovoltaic energy is the conversion of sunlight into electricity. A photovoltaic cell, commonly

called a solar cell or PV, is the technology used to convert solar energy directly into electrical

power. A photovoltaic cell is a non mechanical device usually made from silicon alloys. Sunlight

is composed of photons, or particles of solar energy. These photons contain various amounts of

energy corresponding to the different wavelengths of the solar spectrum. When photons strike a

photovoltaic cell, they may be reflected, pass right through, or be absorbed. Only the absorbed

photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the

material (a semiconductor), electrons are dislodged from the material's atoms. Special treatment

of the material surface during manufacturing makes the front surface of the cell more receptive to

free electrons, so the electrons naturally migrate to the surface.

When the electrons leave their position, holes are formed. When many electrons, each carrying a

negative charge, travel toward the front surface of the cell, the resulting imbalance of charge

between the cell's front and back surfaces creates a voltage potential like the negative and positive

terminals of a battery. When the two surfaces are connected through an external load, electricity

flows.


16

Figure 1.2 Anatomy of Solar Cell

Figure 1.3 Working of PV Cell

Photons in the sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon.

Electrons (negatively charged) are knocked loose from their atoms allowing them to flow through the material to produce electricity.

An array of solar cell converts solar energy into usable amount of DC electricity.

1.5.2 Concentrated Solar Thermal Power Plants:

Using concentrating systems solar power plants produce electric power by converting the sun's

energy into high-temperature heat. The heat is then channeled through a conventional generator.

The plants consist of two parts:


17

1. That collects solar energy and converts it to heat, and

2. That converts heat energy to electricity.

Concentrating solar power systems can be sized from (10 kilowatts up to hundreds of megawatts).

Some systems use thermal storage during cloudy periods or at night.

Others can be combined with natural gas and the resulting hybrid power plants provide high-value, dispatchable power.

Concentrating solar power plants generate their peak output during sunny periods when peak electricity demand occurs as air conditioning loads are at their peak.


18

Figure 2.1 Schematic illustration of the component parts of solar thermal power plants

2 SOLAR THERMAL POWER TECHNOLOGIES & THEIR

SIGNIFCANCE

Solar thermal power generation systems capture energy from solar radiation, transform it into heat,

and generate electricity from the heat using steam turbines, gas turbines, Stirling engines, or

pressure staged turbines.

The four main types of solar thermal power plants developed and tested so far are:

Parabolic trough and Fresnel trough technology Central receiver system (also called power tower or solar tower) Dish-Stirling system Solar updraft tower plant

Parabolic and Fresnel trough, central receiver, and dish-engine systems concentrate the sunlight to

gain higher temperatures in the power cycle. The primary resource for concentrating solar power

(CSP) technology is the direct solar irradiance perpendicular to a surface that is continuously

tracking the sun (direct normal irradiance, DNI). CSP systems have their highest potential in the

"sun belt" of the earth, which is between the 20th and 40th degree of latitude south and north. Solar

updraft towers do not concentrate the sunlight. They use the direct fraction of the sunlight as well

as the diffuse fraction. As a consequence, the working temperature is much lower than those of

concentrating systems, and thus the efficiency.

The electricity is produced by different ways:


19

Figure 2.2 Parabolic Trough System

Troughs and central receivers usually use a steam turbine to convert the heat into electricity. As heat transfer fluids oil, molten salt, air, or water can be used. Central

receivers can achieve very high operating temperatures of more than 1,000 C enabling

them to produce hot air for gas turbines operation combined with downstream steam

turbine operation resulting in high conversion efficiencies.

Dish-Stirling systems can use an engine at the focus of each dish or transport heat from an array of dishes to a single central power-generating block.

Solar updraft towers work with a central updraft tube to generate a solar induced convective flow which drives pressure staged turbines.

2.1 Parabolic and Fresnel Trough Technology: Parabolic trough systems consist of trough solar collector arrays and a conventional power block

with steam turbine and generator. A heat transfer fluid, currently synthetic thermo oil, is pumped

through the collector array and heated up to 400 C. This oil is used to produce steam in heat

exchangers before being circulated back to the array. The steam is used in a conventional steam

turbine-based power plant.

In general, parabolic trough systems using thermo oil can be considered as most mature CSP

technology. Further developments of the original system are aiming at the replacement of the

synthetic heat transfer oil with direct steam or with molten salt. Direct steam generation (DSG)

allows the collection of energy at higher temperatures as well as the elimination of one heat

exchange step which increases the overall efficiency of the plant. Furthermore it avoids the need


20

Figure 2.3 Fresnel Trough

to replace the heat transfer fluid as it is necessary in case of thermo oil and it avoids the use of

energy intensive manufactured and toxic oil. Both improve the plants economic and ecological

balance. The first DSG plant commercially being built will be the 50 MW project Andasol 3 in

Spain. The utilization of molten salts as primary fluid shows similar advantages like the increase

of the solar field operating temperature and therefore a better efficiency, and the elimination of the

heat exchanger in case of using a molten salt storage system. On the other hand, the solar field and

the heat transfer fluid require continuous heat tracing to avoid refreezing of the salt. Currently

there are only few studies concerned with this innovation.

The Fresnel trough simplifies the concentration system by using a plain surface of nearly flat

mirror facets, which track the sun with only a single axis and approximate the classic parabolic

mirror. The efficiency is smaller than with a classic parabolic mirror. The idea is that the lower

costs over-compensate the energy losses in the final economic assessment.

2.2 Central Receiver Systems: Central receiver (CR) systems consist of a field of heliostats (almost plane mirrors), a tower, and

a receiver at the top of the tower. The field of heliostats all move independently to one another and

beam the solar radiation to one single point, the receiver. Heliostat fields can either surround the

tower or be spread out on the shadow side of the tower. Two generic approaches to heliostat design

have been used: a plane structure and a "stretched membrane" approach. Major investigations

during the past 20 years have focused on four heat transfer fluid systems: water/steam, molten salt,

atmospheric air, and pressurized air.

Central receivers have the advantage that the energy conversion takes place at a single fixed point,

which reduces the need for energy transport. By the high concentration factor operation


21

Figure 2.4 Central Receiver System

temperatures of more than 1,000 C can be reached. This rises the conversion efficiency and allows

for advanced energy conversion systems (combined cycle instead of steam cycle). Figure 2.2

shows the 11 MW PS 10 tower power system operated near Sevilla. One of the newest

developments is the "beam-down" concept proposed and tested partly by the Weizmann Institute

of Science in Israel. Rather than converting the concentrated solar energy at the top of the tower,

a hyperbolically shaped secondary mirror directs the converging radiation vertically downward to

a focal point at the bottom of the tower.

One of the newest developments is the "beam-down" concept proposed and tested partly by the

Weizmann Institute of Science in Israel. Rather than converting the concentrated solar energy at

the top of the tower, a hyperbolically shaped secondary mirror directs the converging radiation

vertically downward to a focal point at the bottom of the tower.

The largest central receiver solar system formerly realized was the 10 MW "Solar Two" plant in

southern California. In February, 2007 the 11 MW solar thermal power plant PS10 started its

operation in Southern Spain as the first central receiver which has been built for the last years.

Currently being built in Spain is the 15 MW power tower SolarTres equipped with a 16 hours

thermal storage. Worldwide projects with a total capacity of 566 MW are planned, therein the 2 x

20 MW power tower PS20 as a successor of PS10 and a 400 MW power tower announced by

Bright Source Energy for California.


22

Figure 2.5 10 MW PS10 central receiver plant in Spain

2.3 Dish-Engine Systems: Paraboloidal dish concentrators focus solar radiation onto a point focus receiver. Like parabolic

trough systems they require continuous adjustment of its position to maintain the focus. Dish-

based solar thermal power systems can be divided into two groups: those that generate electricity

with engines at the focus of each dish and those that transport heat from an array of dishes to a

single central power-generating block. Stirling engines are well suited for construction at the size

needed for operation on single-dish systems, and they function with good efficiency. Dish-stirling

units of 25 kW have achieved overall efficiency of close to 30%. This represents the maximum

net solar-to-electricity conversion efficiency achieved by any non-laboratory solar energy

conversion technology.

Within this study parabolic dish systems will not be considered further because they are relatively

small power generation units (5 to 50 kW), making stand-alone or other decentralized applications

their most likely market. Figure 2.3 shows a dish-engine system of type EuroDish.

The cost for such prototype unit (25 kW) is about $150,000. Once in production the cost could be

reduced to less than $50,000 each, which would make the cost of electricity competitive with

conventional fuel technologies.


23

Figure 2.7 Solar Dish Engine System Figure 2.6 Solar Dish Engine System Prototype (25 kW)

Figure 2.8 Solar Updraft Tower Schematic

2.4 Solar Updraft Tower Plant: A solar updraft tower plant (sometimes also called solar chimney) is a solar thermal power plant

working with a combination of a non-concentrating solar collector for heating air and a central

updraft tube to generate a solar induced convective flow. This air flow drives pressure staged

turbines to generate electricity. The collector consists of a circular translucent roof open at the

periphery and the natural ground below. Air is heated by solar radiation under this collector. In the

middle of the collector there is a vertical tower with large inlets at its base. As hot air is lighter

than cold air it rises up the tower. Suction from the tower then draws in more hot air from the

collector, and cold air comes in from the outer perimeter.


24

Figure 2.9 Solar Updraft Tower

Figure 2.10 Technology Comparison

Continuous 24 hour operation can be achieved by placing tight water-filled tubes or bags under

the roof. The water heats up during day-time and releases its heat at night. Thus solar radiation

causes a constant updraft in the tower (although this storage system has never been installed or

tested up to now). The energy contained in the updraft is converted into mechanical energy by

pressure-staged turbines at the base of the tower, and into electrical energy by conventional

generators.

An experimental plant with a power of 50 kW was established in Manzanares (Spain) in 1981/82.

For Australia, a 200 MW solar updraft tower, shown in Figure 2.4, was planned but cancelled in

summer 2006. Currently a 40 MW updraft tower project is announced in Spain (Campo3 2006).

Due to the uncertain perspectives of this technology, the absence of a reference project, and

therefore the lack of cost and material data the solar updraft tower is not considered furthermore

in this study.

2.5 Technology Comparison: Here is a brief technology comparison of all solar thermal power technologies:


25

Figure 2.11 Strong and Weak points of Solar Thermal Technology

2.6 Weak Points and Barriers: Solar thermal power plants currently cause high electricity generation costs which have to

be decreased by technological innovations, volume production, and scaling up to bigger

units.

Although there is a huge solar irradiation supply only locations with irradiations of more than 2,000 kWh/m2, y are suited to a reasonable economic solar thermal performance. This

means that Europe (except Mediterranean part) can only benefit from this potential by use

of high voltage direct current lines connecting South Europe and Nord Africa with Central

Europe which raise the electricity costs by 1.5 to 1 ct/kWh.

2.7 Strong Points and Diffusion Factors: An advantage of solar thermal systems is their relatively high energy density. With 200 -

300 GWh electricity produced per km2 land use they require the lowest land use per unit

electricity produced among all renewables.

Solar thermal power plants can store the primary energy in concrete, molten salt, phase change material, or ceramic storage systems and produce electricity by feeding steam

turbines with the stored heat over night. This means that balancing power can be delivered

and therefore solar thermal power plants could be used as a back-up system even for

intermittent photovoltaics and wind energy.

Solar thermal power plants need big areas but there are huge areas available especially in the desert regions of the earth. For example, to meet Europes electricity demand (about

3,500 TWh/a) only by solar thermal electricity, an area of only 120 x 120 km in a North

African desert would be necessary (that means 0.14% of the Saharas area).

Solar thermal power plants can be operated as co-generation plants by using its steam not only for electricity generation but also for steam delivery, cooling, and desalting water.


26

2.8 Main Drivers Influencing Future Technology Development:

2.8.1 Climate Protection:

Climate protection is one of the major drivers for solar thermal technologies, but since it is a

general driver for renewable energies it is only mentioned at this place. The following drivers are

more STP specific ones.

2.8.2 Objective of Security of Supply:

In the technical perspective, the objective of security of supply is a pushing factor for solar thermal

technologies. With the option of thermal storage or hybrid co-firing STP is able to deliver

balancing power. STP thus is a stabilizing factor for the energy supply system. In South European

countries which are highly dependent on fossil fuel imports like e.g. Spain or Portugal, STP

generation is a high potential source for diversifying energy sources and increasing the share of

domestic energy supply.

2.8.3 Enforced Direct Market Support for Renewable Energies (feed-in-laws):

The establishment of preferential market conditions for renewable energies in several countries

world-wide (e.g. feed-in laws in Germany, Spain, Portugal, and Algeria) and obvious resulting

success stories like the wind energy expansion in Germany and Spain turn out as an important

driver for solar thermal power plants. In Spain and Algeria STP technologies were firstly explicitly

included into the support scheme. As a result, the first large-scale parabolic trough plants (3 x 50

MW) after the power plants in Southern California are being setup in Spain.

2.8.4 Preferring Non-Intermittent Electricity Suppliers:

Energy sources with low intermittency mean an economic advantage. STP will be able to offer

balancing power at a competitive price level. By incorporating thermal storages and co-firing

options, it internalizes the costs of compensating the intermittency of the solar energy resource, at

still a competitive price level.

2.8.5 Advanced Side Applications and Side Products:

STP technologies have the capability of co-generation. The joint production of electricity and heat

for operating adsorption cooling facilities and heat for water desalination respectively is the most

interesting application. The concept of solar fresh water production by parabolic trough plants has

been investigated in several studies (Wilde 2005, DLR 2007). Both cooling and fresh water

provision meet pressing demands in sun-rich, arid countries. Their demand appears at the same

time and the same region which are suited to a reasonable economic solar thermal performance.

Other processes are solar reforming of natural gas or other organics, or thermo-chemical hydrogen

production which are partly demonstrated and may open up high potential markets. Sargent &

Lundy state that CSP could thus potentially get a major source of energy in the fuels and chemical

sector.

2.8.6 Increasing Demand for Local Added Value:

Many developing and transitional countries put more and more emphasis on local added value in

investment decisions. They recognize the employment of national workers, the accumulation of

local expertise and a high cope of national supply as a value for development. Moreover, local


27

added value also promotes socio-economic stability. Solar thermal power stations belong to the

technologies with a high potential for local added value. They have a little fraction of high-tech

components, and about 50% of the investment is expended for steel, concrete, mirrors, and labor

which creates high local value.

2.8.7 Aiming at Conflict Neutral Technologies:

The fossil fuel energy supply system and nuclear energy technologies are increasingly involved in

military conflicts and instable political environments. The discussion is concentrated on the

possible transition from peaceful nuclear energy use to the production of weapon relevant material

(Iran). Moreover, proliferation of weapons-grade plutonium is a latent threat. STP technologies do

not incorporate conflict relevant materials. Even more important, the solar resource is abundant

and inexhaustible, and thus wont give rise to conflicts about using rights. This may reveal as an

important pushing factor for STP technologies, even more as STP addresses the same market

segment as fossil and nuclear power plants.


28

Figure 3.1 Dish Engine Systems

3 DISH ENGINE SYSTEM PROJECT DESCRIPTION

A dish/engine system uses a mirrored dish (similar to a very large satellite dish). The dish-shaped surface collects and concentrates the sun's heat onto a receiver, which

absorbs the heat and transfers it to fluid within the engine.

The heat causes the fluid to expand against a piston or turbine to produce mechanical power.

The mechanical power is then used to run a generator or alternator to produce electricity by an electric generator or alternator.

Dish/engine systems use dual-axis collectors to track the sun. The ideal concentrator shape is parabolic, created either by a single reflective surface or

multiple reflectors.

There are many options for receiver and engine type, including Stirling engine and Brayton receivers.

Dish/engine systems are not commercially available, although ongoing demonstrations indicate good potential.

Individual dish/engine systems currently can generate about 25 kilowatts of electricity. More capacity is possible by connecting dishes together. These systems can be combined with natural gas and the resulting hybrid provides

continuous power generation.

The dish-Stirling system works at higher efficiencies than any other current solar technologies, with a net solar-to-electric conversion efficiency reaching 30%.

One of the systems advantages is that it is somewhat modular, and the size of the facility can be ramped up over a period of time.

That is compared to a traditional power plant or other large-scale solar technologies that have to be completely built before they are operational.


29

Figure 3.2 Dish Engine System Schematic

3.1 Project Background: Heat and power production with lower emission, lower fossil fuel consumption and higher

efficiency is one of the most important issues in the energy industry. Electricity generation using

renewable energy sources especially solar energy is getting more popular. On the other hand, using

small-scale energy system in decentralized electric power generation is gaining significance in

electric power industries.

It is well known that dish-engine systems demonstrate the highest solar-to-electric

efficiencies, compared to other solar technologies. High efficiency, hybridization potential,

modularity and low cost potential make them excellent candidates for small-scale decentralized

power generation. A number of units can be grouped together to form a dish-engine farm

and produce the desired electrical output.

Dish-engine uses a collector which technically is a mirror to concentrate direct normal sun

radiation onto a receiver. In most contemporary dish-engine systems, Stirling engines have been

used as the power conversion unit; however, externally fired micro gas turbines (EFGT) are under

development to be operated in such a system as power conversion unit. Using a highly effective

heat exchanger called recuperator in the cycle results in higher cycle efficiency and lower level of

purity requirement for the gas supplied to the combustor. Integrating this system with a solar

receiver can decrease fossil fuel consumption and related environmental emissions. In a

geographical location with enough solar irradiation, solar energy can be used as a heat source when

it is available and biogas can be used as the second fuel in the system.

In this project the receiver operates in parallel or series with the combustor in a conventional micro

gas turbine and increases temperature of the air in order to drive the turbine and compressor

with the maximum possible efficiency. Since dish-engine systems have demonstrated the highest

solar electric efficiency amongst all solar technologies (29.4%).Considering above mentioned

issues, further investigation in this area is necessary.


30

Figure 3.3 Pifre's 1878 Sun-Power Plant Driving a Printing Press

3.2 Brief History of Solar Thermal Plant: Concentrating solar power is a method of increasing solar power density. Using a magnifying glass

to set a piece of paper on fire demonstrates the basic principle of CSP. Sunlight shining on the

curved glass is concentrated to a small point. When all the heat energy that was spread across the

surface of the magnifying glass is focused to a single point, the result is a dramatic rise in

temperature. The paper will reach temperatures above 451oF and combust. CSP has been theorized

and contemplated by inventors for thousands of years. It is possible that as far back as ancient

Mesopotamia, priestesses used polished golden vessels to ignite altar fires. The first documented

use of concentrated power comes from the great Greek scientist Archimedes (287-212 B.C.).

Stories of Archimedes repelling the invading Roman fleet of Marcellus in 212 B.C. by burning

their ships with concentrated solar rays were told by Galen (A.D. 130-220). In the seventeenth

century, Athanasius Kircher (1601-1680) set re to a woodpile at a distance in order to prove the

story of Archimedes. This is considered the beginning of modern solar concentration. Solar

concentrators then began being used as furnaces in chemical and metallurgical experiments. They

were preferred because of the high temperatures they could reach without the need for any fuel.

Further applications opened for concentrated power when August Mouchot pioneered generating

low-pressure steam to operate steam engines between 1864 and 1878. Abel Pifre made one of his

solar engines operate a printing press in 1878 at the Paris Exhibition, but after extensive testing he

declared the system too expensive to be feasible. His press is shown in Figure 1.2. Pifre's and

Mouchot's research began a burst of growth for solar concentrators.

The early twentieth century brought many new concentrating projects varying from solar pumps

to steam power generators to water distillation. A 50 kW solar pump made by Shuman and Boys

in 1912 was used to pump irrigation water from the Nile. Mirrored troughs were used in a 1200

m2 collector field to provide the needed steam [15]. In 1920 J.A. Harrington used a solar-powered

steam engine to pump water up 5 m into a raised tank. This was the first documented use of solar


31

Figure 3.4 Basic Configuration of Dish Engine System

storage. The water was stored for continual use as power for a turbine inside a small mine.

Concentrating technology had made a huge leap from the nineteenth century but was halted by

World War II and the resulting explosion of cheap fossil fuels. The advantages of solar power lost

their luster and the technology would merely inch forward for nearly five decades.

Starting in the late seventies and early eighties, solar power came back to the forefront of

researchers' agendas with oil and gas shortages. In 1977 in Shenandoah, GA, 114 7-meter parabolic

dishes were used to heat a silicon-based fluid for a steam Rankine cycle. The plant also supplied

waste heat to a lithium bromide absorption chiller. The plants total thermal efficiency was 44%,

making it one of the most efficient systems ever implemented. More modern systems like the

Department of Energy's Dish Engine Critical Components (DECC) project, which was built at the

National Solar Thermal Test Facility, consisted of a 89 m2 dish with a peak system electrical

efficiency of 29.4%. This system utilizes the high. The efficiency of the stirling engine to convert

the heat generated into electricity. This efficiency is unmatched by any concentrator that utilizes a

steam cycle, with one or two working fluids.

3.3 Previous Work: An economic solar dish system was built in 2006 by graduate student C. Christopher Newton. This

first dish system built at SESEC, nicknamed Solar 1, attempted to complete the same goal as the


32

Figure 3.5 Schematic of Solar 1

one addressed in this paper, which is to provide 1 kW of electrical energy for an installation cost

of only $1000 dollars. A parabolic concentrator reflected solar radiation to a central receiver. The

receiver produced intermittent steam that was injected into a steam turbine. The turbine was

connected to an electric generator that produced electricity.

The concentrator used was a fiberglass Channel Master satellite dish with an aperture diameter of

3.66 m. Solar 1 pivoted on a steel alt-azimuth type frame. Two independent linear actuators move

the dish throughout the day. The actuators were controlled automatically by a set of photo-sensing

modules. The modules consisted of light sensing LEDs that sent signals to the actuators when the

module was not oriented normal to incoming solar radiation. The power for the sensors and

actuators was provided by 2 small thin film photovoltaic panels, which charged two 24 V deep cell

batteries. The reflective material used to coat the fiberglass surface was aluminized mylar, which

has an optical reflectivity of 76%.

The system utilized an external type receiver that had an absorber diameter of 15 cm. The absorber

was coated with a high temperature black paint, which has an absorptivity and emissivity both

equal to 90%. The receiver was filled with draw salt to act as a heat storage and heat transfer

medium. Draw salt is a 1:1 molar ratio of potassium nitrate and sodium nitrate. The melting

temperature of this eutectic mixture is 223oC.

The heat exchanger in the receiver consisted of an abbreviated water tube boiler, which consisted

of copper tubes coiled around the outer rim of the salt bath. They connected to a water drum in

contact with the flat absorber at the base of the receiver. The steam in the water drum exited

through copper tubes in the center of the receiver. Figure 21 shows the Solar 1 receiver assembly.

The maximum steady state thermal output for the system was 1 kW. The resulting thermal

conversion efficiency was estimated at 9.03%.


33

Figure 3.6 Concentrator Assembly for Receiver 1

To produce electricity, water was held in the receiver where it pressurized and released in intervals

at a 6.67% duty cycle. The maximum electrical conversion efficiency was estimated at 1.94%,

which equated to a turbine efficiency near 15%. The maximum gross electricity production by

Solar 1 was 220 W.

The majority of the thermal losses for Solar 1 are believed to be from three major factors. First,

the concentrator efficiency was extremely poor. The reflected focal area was much larger than the

receiver. Much of the radiation was reflected onto the side of the receiver, which was heavily

insulated and thus lost. Second, the reflective material had incredibly poor weathering abilities. In

the few months before testing the surface was exposed to the elements and pollution in the

atmosphere. During final testing the mylar was visibly cloudy and turning yellow, clearly

indicating a greatly reduced reflectivity.

The last major factor hurting system efficiency was the absorber. The at plat absorber, although

compact, was extremely exposed and lost tons of energy to the environment through convection

and radiation. This type of receiver is extremely sensitive to wind, and the results show dramatic

drops in receiver temperature with any wind at all. These three factors are primarily responsible

for the low thermal conversion energy and must be improved in the second concentrator if it is to

be successful.


34

Figure 3.8 Receiver Assembly for Solar 1

3.5 Modern Feats in Solar Dish Stirling System: Solar Stirling has made a tremendous impact on alternative energy in the certain years with

companies like Stirling Energy Systems (SES) leading the way. This company in partnership with

Sandia National Lab managed to break the world record for solar-to grid conversion efficiency at

an amazing 31.25 % on January 31, 2008. SES Serial #3 was erected in May 2005 as part of the

Solar Thermal Test Facility which produced up to 150kW of grid ready electrical power during

the hours of sunlight. Each dish consisted of 82 mirrors that can focus the light into an intense

beam.

SES solar Stirling engine, named SunCatcher, was awarded the 2008 Breakthrough Award

winner by Popular Mechanics for its role as one of the top 10 world-changing innovations.

The SunCatcher is a 25 kW solar dish Stirling system which uses a solar concentrator structure

which supports an array of curved glass mirror which are designed to follow the sun and collect

the focused solar energy onto a power conversion unit. The diagram below illustrates the workings

of SESs SunCatche.


35

Figure 3.9 Stirling Energy Systems Stirling Power Units

Figure 3.10 Stirling Engine System - SunCatcher


36

Figure 3.11 Dish Engine Power Plant

3.5 Basic Units of Concentrating Solar Power Dish/Engine System: The dish/engine system is a concentrating solar power (CSP) technology that produces relatively

small amounts of electricity compared to other CSP technologiestypically in the range of 3 to

25 kilowatts. Dish/engine systems use a parabolic dish of mirrors to direct and concentrate sunlight

onto a central engine that produces electricity. The two major parts of the system are the solar

concentrator and the power conversion unit. It consists of two basic units:

Solar Concentrator. Power Conversion Unit.

3.5.1 Solar Concentrator:

The solar concentrator, or dish, gathers the solar energy coming directly from the sun. The resulting

beam of concentrated sunlight is reflected onto a thermal receiver that collects the solar heat. The

dish is mounted on a structure that tracks the sun continuously throughout the day to reflect the

highest percentage of sunlight possible onto the thermal receiver.

3.5.2 Power Conversion Unit:

The power conversion unit includes the thermal receiver and the engine/generator. The thermal

receiver is the interface between the dish and the engine/generator. It absorbs the concentrated

beams of solar energy, converts them to heat, and transfers the heat to the engine/generator. A

thermal receiver can be a bank of tubes with a cooling fluidusually hydrogen or heliumthat typically is the heat-transfer medium and also the working fluid for an engine. Alternate thermal

receivers are heat pipes, where the boiling and condensing of an intermediate fluid transfers the

heat to the engine.

The engine/generator system is the subsystem that takes the heat from the thermal receiver and

uses it to produce electricity. The most common type of heat engine used in dish/engine systems

is the Stirling engine. A Stirling engine uses the heated fluid to move pistons and create

mechanical power. The mechanical work, in the form of the rotation of the engine's crankshaft,

drives a generator and produces electrical power.


37

3.5.3 Advantages:

The main advantages of Stirling dish CSP technologies are that:

The location of the generator - typically, in the receiver of each dish - helps reduce heat losses and means that the individual dish-generating capacity is small, extremely modular

(typical sizes range from 5 to 50 kW) and are suitable for distributed generation.

Stirling dish technologies are capable of achieving the highest efficiency of all types of CSP systems.

Stirling dishes use dry cooling and do not need large cooling systems or cooling towers, allowing CSP to provide electricity in water-constrained regions.

Stirling dishes, given their small foot print and the fact they are self-contained, can be placed on slopes or uneven terrain, unlike PTC, LFC and solar towers.

These advantages mean that Stirling dish technologies could meet an economically valuable niche

in many regions, even though the levelised cost of electricity is likely to be higher than other CSP

technologies. Apart from costs, another challenge is that dish systems cannot easily use storage.

Stirling dish systems are still at the demonstration stage and the cost of mass-produced systems

remains unclear. With their high degree of scalability and small size, Stirling dish systems will be

an alternative to solar photovoltaic in arid regions.


38

4 LITERATURE REVIEW OF RESEARCH PAPERS

We went through a series of research papers regarding concentrated solar dish stirling technology

in order to get a grip on latest innovation going on in the field of CSP. Following is a brief overview

of research papers that we went through.

1) Thermal model of a dish/Stirling system:

This research paper represent global model of energy conversion of 10KW of dish/Stirling unit.

Using optical measurements made by DLR, the losses by parabola reflectivity and spillage are

calculated. A nodal method, thermodynamic analysis of solar Stirling engine is made.

Conclusion: Temperature, mass, density of working gas, heat transfers and the mechanical power

are calculated for one Stirling engine cycle of 40 ms and for a constant direct normal irradiation

(DNI).

Reference: F. Nepveu et al. / Solar Energy 83 (2009) 8189

2) Monthly average clear-sky broadband irradiance database for worldwide solar heat

gain and building cooling load calculations:

This paper establishes the formulation of a new clear-sky solar radiation model

appropriate for algorithms calculating cooling loads in buildings. The aim is to replace the

ASHRAE clear-sky model of 1967.New model derived in two step, 1st obtaining a reference

irradiance dataset from the REST2 model, 2nd consists of fits derived from a REST2-based

reference irradiance dataset. The resulting model, and its tabulated data, are expected to be

incorporated in the 2009 edition of the ASHRAE Handbook of Fundamentals.

Reference: Christian A. Gueymard a,*,1, Didier Thevenard b

3) Convection heat loss from cavity receiver in parabolic dish solar thermal power

system:

This paper aims to present a comprehensive review and systematic summarization of the state of

the art in the research and progress in the convection heat loss from cavity receiver in parabolic

dish solar thermal power system can significantly reduce the efficiency and consequently the cost

effectiveness of the system.

Conclusion:

It is believed that this comprehensive review will be beneficial to the design, simulation,

performance assessment and applications of the solar parabolic dish cavity receivers.

Reference: Shuang-Ying Wua,*, Lan Xiao a, Yiding Cao b, You-Rong Li a


39

4) Field-test of a solar low delta-T Stirling engine:

The aim is to develop a simple solar pumping system, using the concept of low delta-T Stirling

engines. This paper describes the

Date post:	14-Sep-2015
Category:	Documents
Upload:	aitazaz-ahsan
View:	46 times
Download:	2 times

Final Thesis, Solar Dish Engine System 1 Uet Taxila

Documents