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LUMINESCENT SOLAR CONCENTRATORS

Marc Baldo Massachusetts Institute of Technology

&Department of Electrical Engineering Computer Science.baldo@mit edu

://http . .softsemi mit edu:// . . /http rle mit edu excitonics

World Bank May 20th , 2010

http://softsemi.mit.edu/








InstallationInverter, charge

controller,breaker, cables,

mountingReal estateLabor

System integrator margins

Permitting, design,shipping

Warranty

Maintenance

65%

:COST BREAKDOWN FOR SOLAR ELECTRICITY

1MW system size

rend: Installation is an increasing fraction of installed costs….

Module costs reduced by lowcost manufacturing & cellefficiency.

Installation costs scale ~90% with area.Installation costs reduced by economies of scale and cell efficiency.



65%

:COST BREAKDOWN FOR SOLAR ELECTRICITY

1MW system size

Three aims

1. High efficiency (helps both module & balance of system)

2. Low cost manufacturing (helps module cost)

3. Building integrated (helps balance of system)



.1 HIGHER EFFICIENCY?

Problem: high efficiency technologies are harder to make and expensive

Obstacles

•Mechanical – adds cost andmaintenance•

•PV needs cooling•

•

Must be widely spaced to avoidshadowing•

•Needs direct sunlight

Solution? Use solar concentrator to get more electricity from small (expensive cells)



. & .2 MANUFACTURING 3 BUILDING INTEGRATED?-LASS BASED SOLAR CONCENTRATORS

( )ed glass manufactured on a float or similar glass process

, & .icient cheap stable product

, ( - /ies on proven low cost $1 4 m2) manufacturing

, - .ss coupled with high performance surface mounted Si solar cells

/ . % .sently US glass capacity is 6M MT yr Running at 85 capacity

% . / .aining 15 US glass capacity equivalent to solar cell production of 13 5GW year



GLASS IS LOCALLY MANUFACTURED

Like other building materials, manufacturing cost often less than shipping cost.



glass

air

air

Use photons to transfer energy

:Simple construction dye in or on waveguide( )glass

solar radiation

dye

photoluminescence

PV PV

W. H. Weber and J. Lambe, Applied Optics 15, 2299 (1976)A. Goetzberger, W. Greubel, Applied Physics 14, 123 (1977)

- -A NON TRACKING GLASS BASED CONCENTRATOR – THE LUMINESCENT SOLAR CONCENTRATOR

wo fundamental parameters :η PL : ( /the photoluminescent efficiency of the dye photons out photons

)inη trap : (the trapping efficiency fraction of emitted photons confined



e examples of luminescent solar concentration

- . .Our lab proto types are 10x10x0 1cm For ,characterization we attach a Sunpower Si PV cell

to one edge

ey m e t r i c s

G = ( )geometric gain area of face divided by area of edges

F = .flux gain Geometric gain corrected for losses in the collector

, , , & . .,Currie Mapel Heidel Goffri M B Science 3 2 1 , ( 226 2



absorption emission

[ Wavelength λ ]

,

a b

s o

r p

t i

o n

e m

i s s

i o

n

Band gap

2

absorption emission

[ Wavelength λ ]

,

a b

s o

r p

t i

o n

e m

i s s

i o

n

Band gap

3

Solar cell 1

Solar cell 2

Solar cell 3

.abs emission

[ Wavelength λ ]

,

a

b s o

r p

t i

o n

e

m i

s s

i o

n

Band gap

1

‘ ’MULTIJUNCTIONS USING LUMINESCENT SOLAR CONCENTRATORS

. & ’Passive system that concentrates diffuse light doesn t need to track the su

. .2 Higher solar cell voltages due to increase in optical concentration

. : ’3 Lower the cost Don t use expensive semiconductors simply to gather light

. ~ = .1 Each solar cell pumped monochromatically at band edge minimal heating

. -5 Smoothes out non uniform optical excitation

.6 Tolerant of fabrication defects

Advantages



: .Bullets 0 17 HMR FMJ( .)2375fps 4 mm diam

&Shot from an H R

~ .rifle at 50 feet

Optical concentrators show loss near bullet,hole

but light collection at.edges remains strong

…MORE ROBUST THAN CONVENTIONAL PV BULLET DAMAGE TESTS



( & )BUILDING INTEGRATED APPLICATIONS WINDOWS SKYLIGHTS

(Luminescent concentrators have better aesthetics color tunability and image).transmission

.No need for metal oxide transparent contacts

: - ‘ ’Existing technology semitransparent a Si or waffle windows

- %a Si typically 6 efficiency% . .10 transmission Very expensive



and Yb +3 is well known solid state laser material, ( >evel system very transparent to own radiation expect concentration factors 10

-RARE EARTH BASED SOLAR CONCENTRATORS FOR SI SOLAR CELLS(with Harry Tuller, MIT DMSE)

100

80

60

40

20

0

( % )

E x

t e

r n

a l

Q u

a n

t u

m

E f f i

c i

e n

c y

400 500 600 700 800 900 1000 1100 1200

( ) Wavelength nm

300

Sunpower EQE

:Nd glassabsorption

:Nd glassemission

.Needs sensitization to complete spectral coverage

. ( -sion compatible with high performance Si solar cells much cheaper than III V c

.Extremely robust and stable



evelopment of Nd laser glass was driven( ) .y National Ignition Facility NIF

. , = ,NIF now contains approx 10 000 pieces 3 000m2

-of Nd based glass

‘ ’Nd is a rare earth but actually Nd is the 27th most abundant material in

’earth s crust(~ & )half as abundant as copper zinc

Nd2O3 ( ) . / % .the relevant form is approx $10 kg at 99 purity

,Annual production 15 000 t

> %.nsitization the expected power efficiency 10.e competitive with First Solar CdTe solar cells

- …NEODYMIUM BASED SOLAR CONCENTRATORS FOR SI SOLAR CELLS cont

…looks practical

Beam lines at the NIF



absorption

totalemission

edgeemission

faceemission

ation spectrum of Nd + % in phosphate glass

O p

t i

c a l

q u

a n

t u m

e f f i

c i e

n c y

.1 0

.0 8

.0 6

.0 4

.0 2

.0 0

( ) Wavelength nm800 900700600500

:DATA Nd +3 phosphate glass

~ %Observed quantum yield 90

~ %Power efficiency only 3 due to poor overlap with solarspectrum



DATA

Projected power efficiency

E x

t e

r n

a l

q u

a n

t u m

e f f i

c i

e n

c y

.0 3

.0 5

.0 4

.0 6

.0 7%15

%13

%11

%9

%7

%5

Geometric Gain0 50 100 150 200500 600 700 800 900

0

5

10

15

20

25

( ) Wavelength nm

(

A b

s o

r p

t i

o n

c o e

f f

i

c i

e n

t

c m

- 1 ) - ,Sensitized Nd glass 4 mm thick

400

PROJECTIONS

Sensitized glass

700 800 900 1000

2000

4000

6000

8000

Wavelength (nm)

Coun

ts(a

.u.)

Sensitizer luminescence



CONCLUSIONS

•Separate solar energy conversion into optical and electrical parts.••Use conventional solar cells for electrical part.

••Pre-process sunlight using excitonic systems & materials

absorption emission

[ Wavelength λ ]

,

a b

s o

r

p t

i o

n

e m

i s s

i o

n

Band gap 2

absorption emission

[ Wavelength λ ]

,

a

b s o

r p

t i

o n

e

m i

s s

i o

n

Band gap

3

Solar cell 1

Solar cell 2

Solar cell 3

.abs emission

[ Wavelength λ ]

,

a b

s o

r p

t i

o n

e m

i s s

i o

n

Band gap

1

ample : ‘ ’Multijunctions using luminescent solar concentrator





Use metric $/W p :

(cost of PV cell divided by power

generated at peak solar illumination)

Best option? Improve efficiency. 1% increase in efficiency = $0.10 / W pIncluding installation costs: 1% increase in efficiency > $0.30 / W p

New semiconductors/fabrication techniques alone will not achieve large cost savings.

PV cost$

p

p

W

Lη

=

WHAT ABOUT CHEAP BUT LOW EFFICIENCY SOLAR CELLS?

η p: power efficiency

L: solar power

Example:The CdTe process at First Solar

(>300 MW/year of 10% modules, throughput = 4µ m thick films every 40s)

* See Zweibel, Solar Energy Materials & Solar Cells, 59, 1-18 (1999)† Latest production data from First Solar

CdTe associated costs < 10% of manufacturing cost.Remainder dominated by substrate (glass) and module costs (labor, wiring etc..).

Capital cost of CdTe evaporation = $0.04/W p* Semiconductor cost = $0.04/W p*

shipping crate = $0.02/W p*

Total manufacturing cost = $1.00/W p†