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Thermophotovoltaic Generation

of Electricity

Joachim Luther

Fraunhofer Institute forSolar Energy Systems ISE, Freiburg

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Principle of TPV generation of electricity

n1

emitter PV cellelectromagneticradiation

heat electricity

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50 Watt TPV system,

Paul Scherrer Institut

Source: Durisch, PSI, 2002

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Selected characteristics of TPV

no moving parts robust and reliable

radiation emitterand PV

at low distance

high power density

spectral shaping and

photon recycling

high PV efficiency

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Competing technologies I,

selected characteristics and efficiencies

+ long term experience today 10 % - 35 %

maintenance

power > 1KW

combustion engines

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Competing technologies II,

selected characteristics and efficiencies

+ simple, robust, reliable today 3 % - 5 %900 K 1200 K future 7 %

thermoelectrics

+ low operation temp. today 20 % - 30 %

special fuel future 50 % - 60 %

fuel cell systems

+ robust, reliable today 2 % - 3 %

1200 K 1700 K future 10 %

TPV (projected)

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Future markets for TPV,

3 examples

autonomous and auxiliaryenergy supply units

domestic cogeneration of heat and electricity,

autonomous systems (with respect toelectricity)

conversion of waste heat radiation inindustrial processes

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Principle of TPV generation of electricity

n1

emitter PV cellelectromagneticradiation

heat electricity

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Technological challenges of TPV

highly efficient fuel to radiation conversion,heat recuperation

photon management and spectral shaping,selective radiation emitters,

filters, reflectors

efficient PV conversion,low-bandgap cells, high power density

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Blackbody spectra and bandgap positions of PV cells

1200 K1500 K1700 K2000 K

0 1 2 3 4 5 6 7 8

10

20

30

40

50

InSbInAsGaSbSi

wavelength [m]

radiant power density [W/cmm]

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Low bandgap cells for TPV,

examples

GaSb wafer cells, Zn diffusion

MOVPE grown cell structures onGaSb and InP,monolithic interconnected modules

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PV efficiency in TPV, blackbody radiation,

GaSb cells

cut-off at = 1800 nm

whole blackbody spectrum1100 1300 1500 1700900

5

10

15

20

25

30

35 efficiency [%]

temperature [K]

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Power density in TPV, emissivity of emitter 0.6,

GaSb cells

900 1100 1300 1500 1700

0.5

1.0

1.5

2.0

2.5 power density [W/cm]

temperature [K]

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Infrared emitters for TPV

durable at high temperatures

optically selective with respectto E

gof PV cell

- suitable metals (with AR coatings)

- rare-earth oxides

- mechanically modified metal surfaces

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Mechanically structured tungsten emitter,

emissivity

structured

unstructured0 2 4 6 8 10 12 14

0,2

0,4

0,6

0,8

1,0

wavelength [m]

emissivity

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Projected TPV system characteristics

fuel to radiation emitted 0.7

radiation emitted to radiationabsorbed in PV cells 0.8

radiation absorbed to electricity 0.25

electronics and peripherals 0.8

system efficiency 0.1

power density 1 W/cm

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This presentation:www.ise-solar.info

Next TPV conference:

June 14 16, Freiburg, Germany