Using an Abandoned Coal Mine for Pumped Water Energy Storage

The most common sort of energy storage in the world's power grids is pumped water. It's pretty simple: when you have excess power you pump water uphill, and when you need extra power you let it flow back down. In Germany they have hit on a scheme to do this in an old, 600-meter (2000-foot) deep coal mine. Not as much water is needed as in a traditional scheme because the vertical distance is so great, and there's no evaporation when it's under ground. This also provides a handful of jobs in a district where the decline of coal mining has hammered the local economy. Pretty clever.