Catching the sun’s heat
Broadly speaking, there have been two approaches to capturing the sun’s energy: photovoltaics, which turn the sunlight into electricity, or solar-thermal systems, which concentrate the sun’s heat and use it to boil water to turn a turbine, or use the heat directly for hot water or home heating. But there is another approach whose potential was seen decades ago, but which was sidelined because nobody found a way to harness it in a practical and economical way.This is the thermo-chemical approach, in which solar energy is captured in the configuration of certain molecules which can then release the energy on demand to produce usable heat. And unlike conventional solar-thermal systems, which require very effective insulation and even then gradually let the heat leak away, the heat-storing chemicals can remain stable for years.Researchers explored this type of solar thermal fuel in the 1970s, but there were big challenges: Nobody could find...