Thermo-photovoltaic energy: PV heat conversion and its application in energy storage systems


Just as a solar cell converts sunlight into electricity, a thermo-photovoltaic (TPV) cell converts the thermal radiation emitted by incandescent objects into electricity. In other words, it directly converts heat into electricity with no need for moving parts or fluids. The Solar Energy Institute at UPM is working on one of the many applications of this technology: a new concept in thermal energy storage that uses molten silicon at around 1400 °C and TPV cells to transform stored heat into electricity. As such it is possible to achieve energy densities of more than 1 MWh per cubic metre, one of the highest of any other existing storage technology.

Thermo-photovoltaic (TPV) cell works in exactly the same way as a solar cell: the absorption of photons into a semiconductor material produces electrons that are supplied to create an electric current. The difference lies in the absorption spectrum which in a TPV cell is displaced towards the infrared to efficiently convert thermal radiation instead of solar radiation. For this, semiconductor materials are used that are able to absorb low energy photons, such as for example, germanium or gallium antimonide, instead of semiconductors that efficiently absorb sunlight such as silicon or gallium arsenide.

In general terms a TPV cell works with thermal sources that exceed 1000°C and their conversion efficiency to date is in the region of 20%1. In addition they can generate very high electric power densities: in the region of 1 W/cm2 for temperatures of 1100°C and some 10 W/cm2 if the temperature rises to 1900°C. These values are between 50 and 500 times, respectively, the power generated by a conventional solar cell This makes possible to achieve relatively low costs per unit of power (in €/W), even when III-V compound semiconductors are used (that are expensive but more efficient) for their manufacture. Read more…

Alejandro Datas
Research Scientist at Instituto de Energía Solar – Universidad Politécnica de Madrid