Generating electricity is not the only way to turn sunlight
into energy we can use on demand. The sun can also drive reactions to create
chemical fuels, such as hydrogen, that can in turn power cars, trucks and
trains.
The trouble with solar fuel production is the cost of
producing the sun-capturing semiconductors and the catalysts to generate fuel.
The most efficient materials are far too expensive to produce fuel at a price
that can compete with gasoline.