Thermophotovoltaics
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This document discusses thermophotovoltaics, which convert thermal radiation into electricity using photovoltaic diodes. The key components are a thermal emitter, photovoltaic diode, and spectral control filter. Photons above the diode's band gap are converted to electricity, while lower energy photons are partially recycled or lost as heat. Efficiency is limited by the Carnot efficiency but can reach 83% with optimal temperatures. Practical efficiencies are lower due to non-ideal emitters, filters, and diodes. Common emitter and diode materials, as well as advantages over solar cells, are described. Applications include military, space, and off-grid power generation.
Thermophotovoltaics
- 2. What is thermophotovoltaics Working Efficiency Active components and material selection Advantages over photovoltaic cells Applications
- 3. Static energy converters that convert thermal radiation into electricity by means of photo voltaic diode MAIN COMPONENTS ARE: Thermal emitter Photovoltaic diode Spectral control component(filter)
- 4. Work on the same principle of solar cell 1.Emitter converts heat into radiation 2.This is selectively filtered by optical filter. Part of it is transmitted to PV diode and the rest is reflected back to emitter 3.The PV diode converts the transmitted photons with energies in excess of the diode energy band gap into charge carriers
- 5. Thephotons below the band gap are partially absorbed and converted into waste heat and partially recycled back to emitter by the back side contact
- 7. The absolute upper limit for efficiency in TPVs is the Carnot efficiency that of an ideal heat engine The efficiency is given by: Tcell is the temperature of the converter Temit is the temperature of the emitter
- 8. For a practical TPV maximum efficiency is 83% for Tcell = 300 K and Temit =1800 K CAUSES OF INEFFICIENCIES: Emitters : deviations from perfect absorbing and perfect black body behavior Filters : practical filters often reflect a small percentage of light in desired wavelength ranges or transmit light of non- ideal wavelengths Converters : inefficiencies associated with non- radioactive recombination and ohmic losses exist
- 9. EMITTERS : Factors to consider while choosing emitters 1.Efficiency 2.Temperature resistance 3.Cost Existing emitters: Polycrystalline silicon carbide (SiC): 1.thermally stable up to 1700 c 2.radiates in the longer wave lengths 3.cheaper and used in commercial applications Tungsten: 1.temperature same as that of SiC 2.radiates in the visible and near IR range 3.used in burner TPVs
- 10. Other selective materials used for emitters are Rare earth oxides (Yb2 O3 & Er2 O3) and photonic crystals PHOTOVOLTAIC DIODES: Factors to consider are 1. availability 2. low cost 3. ease of manufacture 4. low energy band gap Existing PV diodes are: Gallium antimonide (band gap of 0.72 ) Indium gallium arsenide antimonide (band gap of 0.55 eV) Indium gallium arsenide(band gap of 0.75 eV)
- 11. Requires less maintenance Any fuel may be used to heat the radiant surface High photo voltaic conversion efficiency of radiation to electricity owing to recycling of unabsorbed photons Can generate current densities 300 times that of conventional photo voltaic cells
- 12. Military applications In space Commercial applications Off - grid generators Recreational vehicles