Thermophotovoltaic (TPV) energy conversion is a direct conversion process from heat to electricity via photons. A basic thermophotovoltaic system consists of a hot object emitting thermal radiation and a photovoltaic cell similar to a solar cell but tuned to the spectrum being emitted from the hot object. As TPV systems generally work at lower temperatures than solar cells, t. Typical photovoltaics work by creating a near the front surface of a thin material. Conventional (RTGs) used to power spacecraft use a radioactive material whose radiation is used to heat a block of material and then converted to electricity using a. constructed an elementary TPV system at in 1956. However, is widely cited as the inventor based on lectures he gave at MIT between 1960–1961 which, unlike Kolm's system, led to research and. The upper limit for efficiency in TPVs (and all systems that convert heat energy to work) is the, that of an ideal. This efficiency is given by: where Tcell is th.