The newly discovered fulvalene diruthenium changes conformation, acting as a molecular heat battery. Similar, cheaper molecules could offer affordable solar power storage.  (Source: Jeffrey Grossman/MIT)

Current solar thermal energy storage methods, such as molten salt, aren't very efficient.  (Source: SolarReserve)
Technology could answer the need for power storage if affordable production methods are found

Scientists have long debated how best to store solar power.  The best current solutions -- like storing heat in tanks of molten salt -- aren't very efficient and tend to be quite expensive.

That's why it's exciting that that researchers at MIT have described how a recently discovered molecule called fulvalene diruthenium -- which consists of two aromatic carbon rings, plus attached transition metal -- acts as a molecular heat battery. 

The molecule stores heat energy by changing conformation and is remarkably stable.  But when you add a small amount of additional heat or a catalyst, the molecule snaps back to its original conformation releasing its stored load.

While this behavior was previously known to some extent, the MIT team led by Materials Science professor Jeffrey Grossman, determined how exactly it works.  Describes Professor Grossman, "[The compound] can get as hot as 200 degrees C, plenty hot enough to heat your home, or even to run an engine to produce electricity.  It turns out there's an intermediate step that plays a major role."

The discovery on an intermediate step helps to explain why similar molecules with the ruthenium replaced didn't work.

Professor Grossman says the material stacks up favorably compared to past technologies, stating, "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."

Unfortunately Ruthenium, a platinum-like transition metal, is relatively rare and costs as much as $650 for 150 g, making it somewhat impractical for large-scale commercial applications.  However, now that they know how the mechanism works, Professor Grossman and his colleagues are scouring chemical databases looking for cheaper analogues (i.e. without rare earth metal components) that behave in the same way.

The new research is published in the journal Angewandte Chemie and is funded by grants from The National Science Foundation and the MIT Energy Initiative.

"We don't know how to make a $500 computer that's not a piece of junk." -- Apple CEO Steve Jobs

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