Some 40 years ago, while at MIT, I was involved with two energy-related projects.  One involved the development of a conversion from honest-to-goodness-solid waste [HGSW] to methane (natural gas), via microbial means, the one that occupied a major portion of my time.  The other project, working with a different professor, involved screening compounds that would store and release energy reversibly. Why this project? One of the problems we have with energy is that we need it in fits and starts, but that is not an economical method to produce it.  Also, if we want to collect solar energy, it is available during the day- what do we do at night?

Yes, we can use batteries.  However, even now, 40 years later, our batteries are not very efficient.  (Don’t you recall that we gave several grants to battery manufacturers, just in the past two years, to help them develop better systems?).

We can even do what Dominion Power did for its Bath County power plant some 20 years ago. This plant has a conventional power system, along with two water reservoirs connected by a huge tunnel; the difference in height between the two reservoirs is 385 meters.  At night, when the demand is low, the conventional power plant pumps the water from the lower reservoir to the higher reservoir.  During the morning and afternoon peaks, the water is released from the higher reservoir through the turbines, thereby converting the potential energy (the water stored at higher elevations) to kinetic energy (and power).  This means the plant can use conventional fuel at a constant rate (the most efficient design) and  provide additional power when needed.  Obviously, this uses a lot of space.

Which is why folks at MIT are still looking for reversible physicochemical reactions.  And,  Dr. Jeffrey Grossman (in conjunction with Lawrence Livermore Labs and UC Berkeley researchers) just published a study in Angewandte Chemie. A ruthenium based compound  (fulvalene diruthenium), in conjunction with carbon tetrachloride,  is able to absorb sunlight and change its morphology.  (It is stable up to 200 C or about 400 F.)  This shape change is stable and requires a catalyst to be reversed,  thereby releasing the stored energy.  Moreover, the shape change involves a metastable state, so there are two releases of energy.  Not surprisingly, this compound is very expensive.

But, assuming the cost can be reduced or a similar compound be found (that is cheaper), the compound could be placed in a pond, whereby it would change shape and store energy.  It could be pumped to a different location where the energy release could be harnessed.

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