RheEnergise's HD Hydro 500 kW demonstrator will soon begin construction at mining company Sibelco's facility in Cornwood outside Plymouth in Devon, UK.

Hydroelectric power systems are the world's leading eco-friendly means of electricity production, accounting for 4,300 terawatt hours (TWh) of output or 15 percent of all electricity. Even though hydroelectrics have expanded in recent years, there's not much room for expansion – potential sites in practical locations are largely saturated.

That's because traditional hydro needs a large body of reliable water, with a high enough head for efficient electricity generation. If you live in the Pacific Northwest, you can run the entire region on hydroelectric, but if you're in Florida, you're a bit out of luck.