Researchers from the Solar Energy Institute at the Universidad Politécnica de Madrid (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.

The novel system was created allowing the storage of energy in molten silicon which is the most abundant element in Earth’s crust most often though of as sand. The system has patent pending status in the United States, and aims to develop a new generation of low cost solar thermal stations and becoming a innovative storage system of electricity and cogeneration for urban centers.

The research paper about the system has been published in the Energy Journal. The researchers aim to develop a new generation of low cost solar thermal stations and develop an innovative storage system of electricity and cogeneration for urban centers.

Image Credit: Solar Energy Institute at the Universidad Politécnica de Madrid. Click image for the largest view

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 percent.

The final result is an extremely compact system with no mobile parts, silent and able to store up to 10 times more of energy than existing solutions using abundant and inexpensive materials.

The first application of these devices is 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. 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 been granted funds through the EXPLORA project from Ministry of Economy and Competitiveness. Now, they are starting to manufacture the first lab-scale prototype.

Paralleling the research the team has 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.

It is a kind of surprise to think of using what is essentially glass to store heat. But then glass has some interesting qualities readily observed. Its stable and very much non-reactive. Its dense and holds a lot of heat. It also gains heat slowly and releases it slowly. These attributes makes one wonder why its so late to the heat storage game. Might be because such a system will need pretty high temps to get going. But that’s a good thing and solar collection is getting there for supplying the heat quickly.


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