The Azimuth Project
Thermophotovoltaic power




Thermophotovoltaic (TPV) energy conversion is a direct conversion process from heat differentials to electricity via photons. A basic thermophotovoltaic system consists of a thermal emitter and a photovoltaic diode cell. The temperature of the thermal emitter varies between different systems from about 900 °C to about 1300 °C, although in principle TPV devices can extract energy from any emitter with temperature elevated above that of the photovoltaic device (forming an optical heat engine). The emitter can be a piece of solid material or a specially engineered structure. A conventional solar cell is effectively a TPV device in which the Sun functions as the emitter. Thermal emission is the spontaneous emission of photons due to thermal motion of charges in the material. For normal TPV temperatures, this radiation is mostly at near infrared and infrared frequencies. The photovoltaic diodes can absorb some of these radiated photons and convert them into free charge carriers, that is electricity. Thermophotovoltaic systems have few, if any, moving parts and are therefore very quiet and require low maintenance. These properties make thermophotovoltaic systems suitable for remote-site and portable electricity-generating applications. Their efficiency-cost properties, however, are often rather poor compared to other electricity-generating technologies. Current research in the area aims at increasing the system efficiencies while keeping the system cost low.



One research group Global Climate Energy Project - GCEP at Stanford has been doing research and is trying to:

This research is investigating a novel design for thermophotovoltaic devices with the potential to boost their energy conversion efficiency beyond current efficiency records of about 30%. In the proposed design, the absorber and the emitter consist of tungsten photonic crystals whose properties can be tailored to provide broad-band absorption of light over the entire solar spectrum and to adjust the emission spectrum to match the absorption characteristics of a silicon photovoltaic cell. The absorber and the emitter are integrated within the intermediate to optimize thermal transfer. See also their latest progress report in the references.


Abstract: We present theoretical considerations as well as detailed numerical design of absorber and emitter for Solar Thermophotovoltaics (STPV) applications. The absorber, consisting of an array of tungsten pyramids, was designed to provide near-unity absorptivity over all solar wavelengths for a wide angular range, enabling it to absorb light effectively from solar sources regardless of concentration. The emitter, a tungsten slab with Si/SiO 2Si /SiO_2 multilayer stack, provides a sharp emissivity peak at the solar cell band-gap while suppressing emission at lower frequencies. We show that, under a suitable light concentration condition, and with a reasonable area ratio between the emitter and absorber, a STPV system employing such absorber-emitter pair and a single-junction solar cell can attain efficiency that exceeds the Shockley-Queisser limit

category: energy