A silicon-based energy storage solution is being advanced by researchers from Universidad Politécnica de Madrid (UPM), Spain, for the reliable and efficient use of excess solar and other renewable energy.

In the technology under development, surplus electricity is stored as heat in molten silicon at temperatures as high as 1400 °C, which is the melting point of silicon.

Molten silicon stores excess power as heat, which is converted back to electricity on demand via thermophotovoltaic cells.According to the researchers, the isolated molten silicon can store more than 1 megawatt-hour of energy per cubic meter, over 10 times the capacity of current systems which use molten salts. The system has the potential to achieve output electric energy densities in the range of 200–450 kWh/m³, comparable to the best performing state-of-the-art lithium-ion batteries.

“At such high temperatures, silicon intensely shines in the same way that the sun does, thus photovoltaic cells, thermophotovoltaic cells in this case, can be used to convert this incandescent radiation into electricity,” says research lead Alejandro Datas, from UPM’s Solar Energy Institute. “The use of thermophotovoltaic cells is key in this system, since any other type of generator would hardly work at extreme temperatures.”

These cells can generate 100 times more electric power per unit area than conventional solar cells, and can attain conversion efficiencies that exceed 50%. Initial applications are expected to be in the solar thermal energy sector, thus avoiding the complex systems that use heat transfer fluids, valves, and turbines to produce electricity.