Storage is a major concern for renewable energy systems such as wind and solar. When the air isn't moving or the sun isn't shining, electricity isn't flowing as much from these farms. And when they are, the grid can only handle so much at once.
But MIT researchers are taking a new look at a decades-old idea for thermo-chemical energy storage. Specifically, solar. In a recent study in the journal Angewandte Chemie, they describe chemically storing solar energy within a molecule called fulvalene diruthenium to create a "rechargeable heat battery."
Comprised partly of ruthenium, a rare metal in the platinum family, the molecule absorbs sunlight, switching to a higher energy state as it does so. According to the study, the molecule will stay stable in this state until exposed to a catalyst, which would then release the energy. In the meantime, it would hold the energy as heat, and could even be transportable. Changing structure as it transitions between the two energy states, the fulvalene diruthenium is able to go back and forth repeatedly, and whenever needed. So in a sense, it's rechargeable. When released, the heat energy can reach temperatures of almost 400 degrees Fahrenheit.
The problem? Ruthenium is prohibitively expensive.
Researchers have searched for substitutes but haven't been able to find any. What the MIT researchers have discovered, however, is that between energy states, another step exists in which the molecule forms a semi-stable configuration. By looking at this behavior, learning more about how the molecule works (see video below), and sifting through databases of many other molecular options, the MIT scientists hope they can find another cheaper material that acts like it.
In a statement, MIT's Jeffrey Grossman speaks of the storage method's potential should such a material be found.
It takes many of the advantages of solar-thermal energy, but stores the heat in the form of a fuel. It’s reversible, and it’s stable over a long term. You can use it where you want, on demand. You could put the fuel in the sun, charge it up, then use the heat, and place the same fuel back in the sun to recharge.
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