Energy Storage – a la Fulvalene Diruthenium (say what??)

The intermittency of many renewable energy fuel resources greatly inhibits the ability of these technologies to economically compete with non-renewable technologies like coal, natural gas, and nuclear power. In some ways, this is the opposite of the problem experienced by fossil fuel plants, which ramp their output up and down to meet demand that could jump up or drop down at any moment.

When the sun slips behind a cloud or dips below the horizon for the night, the solar panels you installed become interesting roofing tiles, instead of a valuable generation resource, sending you back to the fossil fuel-based grid for your energy. Because of our inability to economically store the energy that you captured with your panels during the day, their usefulness is limited to the periods of the day when the sun is shining.

The renewable energy panacea  = economic, large-scale energy storage.

Researches throughout the world, including several here at the University of Texas, are working to figure out a way to store large amounts of energy for small amounts of money. One area of focus – material science, or more specifically the study of different materials to figure out how they can be used to economically store energy.

A recent discovery by MIT researchers, in partnership with colleagues at LLNL and UC Berkeley, might be the one we look back on and say “that was the moment that changed everything”… or maybe not… but either way, MIT’s determination of how a molecule called fulvalene diruthenium stores and releases heat on demand is pretty awesome.

According to a paper published on Oct. 20 in the journal Angewandte Chemie, fulvalene diruthenium actually undergoes a structural transformation when it absorbs sunlight, putting it into a higher-energy state where it can remain stable indefinitely. By adding a small amount of heat or a catalyst, the molecule “snaps” back to its original shape, releasing heat. Well… sorta…. According to Dr. Jeffrey Grossman, professor of power engineering in MIT’s Department of Materials Science and Engineering:

“It turns out there’s an intermediate step that plays a major role…that was unexpected.”

What is the importance of this unexpected step?

According to Grossman, this step results in the stability and reversibility that makes it possible to produce a “rechargeable heat battery” with this material. In this battery, we can store and release heat energy, bringing me back to solar energy.

Fulvalene diruthenium has the ability (in theory) to store heat up to 200 degrees C, which could be used directly to heat your home – kind of the opposite of the Ice Bear concept. So, what if we could store excess solar power during the day in portable, rechargeable batteries that we could run our cars with, power our lights, or even combine together until we have a big enough system to generate electricity for our street or town? This might be possible with MIT’s discovery.

But, before folks get too excited, I should note that these ruthenium is very expensive (and rare) and so is not itself a good candidate for cheap, abundant energy storage. But, understanding its behavior could lead to finding less rare materials that exhibit the same behavior. According to Grossman,

“[Ruthenium] is the wrong material, but it shows it can be done…It’s my firm belief that as we understand what makes this material tick, we’ll find that there will be other materials [that work the same way]”

To check out the journal article referenced in this post, check out the following reference:

Yosuke Kanai, Varadharajan Srinivasan, Steven K. Meier, K. Peter C. Vollhardt, Jeffrey C. Grossman. Mechanism of Thermal Reversal of the (Fulvalene)tetracarbonyldiruthenium Photoisomerization: Toward Molecular Solar-Thermal Energy Storage. Angewandte Chemie International Edition, 2010; DOI: 10.1002/anie.201002994

Thanks to Science Daily for bringing this paper to my attention. Very cool.