Energy from a battery

While battery technology has improved by leaps and bounds over the past decade or two, this article about a giant battery sort of inside the earth is interesting to think about. The idea is simple: when there's extra flow coming out of a dam, the flow can be literally recycled back up above the turbines, saving the flow for when more charge is needed. There are some reservations about reusing the flow this way, particularly for those benefiting from downstream flow into nearby lakes, but the environmental savings are significant.