One of the problems facing the distributed renewable power is that sometimes zapping the electricity down wires isn't your best choice, either for reasons of efficiency or of convenience. The Paul Scherrer Institute (PSI) and the Swiss Federal Institute of Technology Zurich have come up with a novel solution, at least for solar power: store it in a metal ore.
Solar heat is used to crack zinc from zinc oxide; the metal can then be readily moved around. The zinc can then be used in zinc-air batteries or to help crack hydrogen from water vapor. In both cases, the reaction with oxygen creates zinc oxide, which can then be used by the solar heater.
The first trials of the solar power-plant have used thirty-percent of available solar energy and produced forty-five kilos of zinc an hour, exceeding projected goals. During further tests this summer a higher efficiency is expected. Industrial size plants, for which this is a prototype, can reach efficiency levels of fifty- to sixty-percent. The success of this solar chemistry pilot project opens the way for an efficient thermo-chemical process whereby the sun's energy can be stored and transported in the form of a chemical fuel. In this process the zinc is combined with coal, coke or carbon biomass which acts as a reactive agent, yet in this reactor only a fifth of the usual amount of agent is used. The sun's rays are concentrated on this mixture by a system of mirrors and the zinc forms as a gas which is then condensed to a powder.
So the question for you engineering types out there: at what point does this become preferable to storing the power in batteries?
Jamais, you ask "at what point does this become preferable to storing the power in batteries?" But remember that earlier you mentioned that it'd be used _in_ batteries. You'd presumably have power plants generating the zinc, then ship that to local places that "recharge" zinc-air batteries with it.
Zinc-air batteries are very cool, but have some downsides, too. According to http://micro.magnet.fsu.edu/electromag/electricity/batteries/zincair.html , "The advantages of a zinc-air battery include flat discharge voltage, safety and environmental benefits, good shelf life, and low cost. In addition, zinc-air batteries have high volumetric energy density compared to most primary batteries. The disadvantages of such batteries are that they rely on ambient conditions, they dry out once exposed to outside air, they have flooding potential, they have limited output, and their active life is short..."
I believe things like zinc become preferable to batteries when one has successfully developed internal combustion engines to burn them. This means dealing with ash in condensed phase, unlike the gaseous ash that IC engines now dump to air. The fuel tank becomes bicameral: part for before, part for after. It is significantly smaller and lighter, even when all the fuel has moved over to the ash bin, than a hydrogen tank, even though the contents are heavier than that tank's contents.
The numbers for the linked story don't quite work out; 45 kg zinc per hour on 300 kW of input power would be 20 percent, not 30, and carbon is also consumed. They don't say how much. Inevitably the efficiency on both input energies is significantly below 20 percent.
Also see my comment from a few years ago.
--- Graham Cowan, former hydrogen fan
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