A new approach to converting heat into electricity using solar cells could make a technology called thermal photovoltaics more practical. A Boston company, MTPV Corp, claims it can deliver "an order of magnitude" more power than regular thermal photovoltaics.
Thermal photovoltaics use solar cells to convert the light that radiates from a hot surface into electricity. A conventional solar panel absorbs light from the entire spectrum but it only converts certain colours efficiently. As a result, the maximum theoretical efficiency of a conventional solar cell is 30 percent. If the sunlight is first concentrated using mirrors, 41 percent efficiency is possible. In a thermal photovoltaic system, light is concentrated onto a material to heat it up. The material is selected so that when it gets hot, it emits light at wavelengths that a solar cell can convert efficiently. As a result, the theoretical maximum efficiency of a thermal photovoltaic system is 85 percent.
Although the theory of thermal photovoltaics has been known since the 1960s, only low efficiencies have been achieved because most of the photons generated in the heated material are reflected back into the material when they reach its surface (in the same way that light is trapped in fibre-optic cables). Research by Robert DiMatteo, MTPV’s chief executive, has shown that if the gap between the heated material and the solar cell is less than the wavelength of the light being emitted, the surface no longer reflects light back and the solar cell will generate ten times as much electricity as a conventional thermal photvoltaic system.
So far, MPTV has only achieved 10 to 15% efficiency on prototypes large enough to be practical. But this is already competitive with conventional solar cells and MTPV believes that its thermal photovoltaic technology has much greater potential for further improvement.