Hydrogen has been the Holy Grail of the post-fossil energy world: half-decent energy density, incredibly abundant, clean-burning, greenhouse-benign, well understood.

But the problem has been the liberation of hydrogen – it’s the most common element in the universe, but it’s also highly reactive, meaning that there are no practical natural sources of pure hydrogen gas. So far, solar energy (electricity in general, in fact) hasn’t been efficient in liberating hydrogen, and most hydrogen production now actually involves reforming natural gas, which makes the whole exercise near-pointless, from an environmental point of view. In this sense, hydrogen is effectively an energy storage medium, rather than a vast natural resource to be mined.

Now, it seems that there might be a breakthrough. Using a tower more than 50 metres high, sunlight is concentrated to heat zinc oxide and wood charcoal to 1200°C. They react to produce zinc (and carbon monoxide, which is recycled or burnt as fuel). The zinc becomes the energy storage medium: it can be used directly in zinc-air batteries or reacted with water to produce hydrogen and zinc oxide. The zinc oxide can then be recycled back into the start of the process.

Very neat. If this works out to have a reasonable cost, it could turn out to be momentous. Not just the option of producing hydrogen with a reasonably clean process – using zinc as the energy transport medium rather than hydrogen could drastically reduce the (staggering) cost of establishing a hydrogen distribution system. Hydrogen is explosive; it needs a lot of redundant, heavy infrastructure to set up a reliable network. I know nothing about the energy density of zinc powder, but I’m guessing that it would be a lot more benign to deal with.

Even better, the zinc-air battery approach might be a goer in the world of electric cars, which currently are far more advanced, practical, and environmentally positive than hydrogen. It can be convincingly argued that the whole hydrogen thing’s just a scam.

The wood charcoal is an interesting aspect. Burning wood specifically for this process would, of course, generate greenhouse gases; but if it’s making use of already-burnt wood, that’s fine. Now, if we can just get some kind of efficient chimney scrubbers so everyone can have their guilt-free open fire…