What do you see when you imagine a zero-carbon future? Electric buses zipping by? Rolling hills covered with solar panels? Offshore wind farms towering over the sea? If batteries are part of your vision, good thinking. But there's a promising, if whimsical, piece of the renewable energy puzzle that might be missing from your mental picture: the world of gravity energy storage.

The huge disruption caused by the coronavirus crisis has highlighted how much modern societies rely on electricity. Millions of people are now confined to their homes, resorting to teleworking to do their jobs, e-commerce sites to do their shopping, and streaming video platforms to find entertainmen

German manufacturing giant Thyssenkrupp has completed a successful, first-of-its-kind demonstration of running a steel furnace completely on hydrogen, a development that is likely to further dent the future prospects for the global coal industry.