THERMOPHOTOVOLTAICS
What is thermophotovoltaics Working Efficiency Active components and material selection Advantages over photovoltaic cells Applications
CONTENTS
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)
What are thermo photovoltaic cells?
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
Working of TPV
The photons below the band gap are partially absorbed and converted into waste heat and partially recycled back to emitter by the back side contact
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
Efficiency
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
EMITTERS : Factors to consider while choosing emitters1.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
Active components and material selection
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 gapExisting 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)
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
Advantages of TPV over photo voltaic cell
Military applications In space Commercial applications Off - grid generators Recreational vehicles
Applications
Burner TPVs
http://www.mit.edu/~ivanc/Publications/2004_1D%20and%202D%20Photonic%20Crystals%20for%20TPV%20Applications.pdf
http://en.wikipedia.org/wiki/Thermophotovoltaic
Refernces
Thank you