Innovative molten silicon-based energy storage system

The unstoppable progress of renewable energy, especially wind and photovoltaic energy, has given rise to a global challenge in the energy sector: the storage of such dispersed and intermittent energy. In recent years, a large number of devices have been developed for this purpose. Some of these devices have reached the advanced testing phase and even the commercialization phase. And this is the case of the solar thermal energy, in which sunlight is stored as heat molten salt, and then the energy is and converted to electricity upon demand through a thermal generator.

However, there are still problems with the existing solutions due to excessive costs, safety problems or lack of material resources in the future. Therefore, research centres and companies worldwide are seeking alternative solutions by using low cost and abundant materials lacking of great risks to the safety of people.

Researchers from Solar Energy Institute at UPM are developing a new energy storage system in which the entry energy, either from solar energy or surplus electricity from a renewable power generation, is stored in the form of heat in molten silicon at very high temperature, around 1400 °C.

Silicon has unique properties that confer the ability to store more than 1 MWh of energy in a cubic meter, ten times more than using salts. Molten silicon is thermally isolated from its environment until such energy is demanded, when this occurs, the heat stored is converted into electricity. Alejandro Datas, the research promoter of this project said: "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. The use of thermophotovoltaic cells is key in this system, since any other type of generator would hardly work at extreme temperatures.

In addition, these cells can produce 100 times more electric power per unit area than conventional solar cells. These thermophotovoltaic cells are able to reach higher conversion efficiencies, even over 50%.

The final result is extremely compact system with no mobile parts, silent and able to store up to10 times more of energy than existing solutions using abundant and inexpensive materials.

The first application of these devices is expected to be in solar thermal energy sector, thus avoiding the complex systems that use heat transfer fluids, valves and turbines to produce electricity. By simplifying the setting, the energy costs generated could dramatically reduce, and along with a higher storage capacity can turn this solution into a profitable solution system and an appropriate alternative of renewable generation.

These systems could be also used to storage electricity in the housing sector and to manage all energy needs (electricity and heating) in urban areas at medium and long term.

The team of UPM researchers has recently achieved funds through the EXPLORA project from Ministry of Economy and Competitiveness. Now, they are starting to manufacture the first lab-scale prototype.

In parallel, researchers have started the business project SILSTORE that aims to industrialize these results. The project has been recognized as one of the best startups born in 2015 at UPM.