Thermophotovoltaic

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.

In the design of a TPV system, it is usually desired to match the thermal emission's optical properties (wavelength, polarization, direction) with the most efficient conversion characteristics of the photovoltaic cell, since unconverted thermal emission is a major source of inefficiency. Most groups focus on Gallium Antimonide (GaSb) cells. Germanium (Ge) is also suitable. [cite web
last = Poortmans
first = Jef
title = IMEC website: Photovoltaic Stacks
url=http://www.imec.be/wwwinter/energy/space_main.shtml
accessdate = 2008-02-17 ] Much research and development in TPVs therefore concerns methods for controlling the emitter's properties.

Many attribute the idea of this system to the French scientist Pierre Aigrain (1956).

TPV cells have often been proposed as auxiliary power conversion devices for regeneration of lost heat in other power generation systems, such as steam turbine systems or solar cells.

A protoype TPV hybrid car was even built. The "Viking 29" [cite paper
author = Seal et al
title = Use of a Thermophotovoltaic Generator in a Hybrid Electric Vehicle
date = 1968
url =http://vri.etec.wwu.edu/pdf%20files/v29paper.pdf
publisher = Vehicle Research Institute, Western Washington University, Bellingham, Washington 98225
format = PDF
accessdate = 2008-02-17] was the World’s first thermophotovoltaic (TPV) powered automobile, designed and built by the Vehicle Research Institute (VRI) at Western Washington University.

TPV research is a very active area. Among others, the University of Houston TPV Radioisotope Power Conversion Technology development effort is aiming at combining thermophotovoltaic cell concurrently with thermocouples to provide a 3 to 4-fold improvement in system efficiency over current thermoelectric radioisotope generators.

External links

* [http://vri.etec.wwu.edu/tpv.htm Thermophotovoltaics] at Western Washington University.
* [http://lees.mit.edu/lees/projects/thermophotovoltaics_project.htm Thermophotovoltaics] at Massachusetts Institute of Technology.
* [http://pvlab.ioffe.ru/technology/tpv.html Thermophotovoltaics] at the Ioffe Institute.
* [http://proceedings.aip.org/proceedings/confproceed/738.jsp 6th International Conference on Thermophotovoltaic Generation of Electricity]
* [http://gltrs.grc.nasa.gov/reports/2005/TM-2005-213981.pdf NASA Radioisotope Power Conversion Technology NRA Overview]
* [http://www.technologyreview.com/read_article.aspx?id=16945&ch=nanotech New thermophotovoltaic materials could replace alternators in cars and save fuel]

References