The Okeechobee Clean Energy Center was designed to use the fossil fuel natural gas when it opened two years ago among the lakes of central Florida. Now the power plant’s owner, NextEra Energy, is preparing it to handle a second fuel: hydrogen. Hydrogen burns like natural gas without carbon dioxide emissions and can be produced by separating water molecules using electricity. This excites engineers pursuing a solution to the variability of solar and wind power as it spreads across electric grids.

They say surplus renewable electricity produced during hours of slack demand can power electrolysis machines to make hydrogen, eventually providing a store of carbon-free energy for dispatch when demand is strongest. The $65m Okeechobee pilot project will “utilise solar energy that would have otherwise been clipped” to create hydrogen to replace some natural gas, Rebecca Kujawa, chief financial officer at NextEra — which last year briefly overtook ExxonMobil as the most valuable US energy company — has said. But producing hydrogen, storing it and then using it to generate electricity, a process known as “power-to-gas-to-power,” is inefficient and expensive.