Utility-scale hydropower facilities do pump water uphill. But their goal is not so much to gain or create more energy as it is to reduce overall losses. The utility grid needs to be able to provide power on demand, but its power plants (coal, natural gas, nuclear, and hydro) are slow to come online or take offline. And solar and wind facilities sometimes make power when it’s not needed. To meet changing customer needs, plants are often running “in wait,” with nowhere to send that power—that energy is potentially wasted. Hydro facilities can divert that unused power to pumping water back to the top of the hydro dam, where the potential energy can be stored for use when loads on the utility grid surge again. The reservoir is used like a giant battery for grid energy. And while efficiencies on that pumping are 70% to 85% (a 15% to 30% net loss), that’s a lot better than wasting all of the excess power of idling power plants.