The battery is a key instrument in the renewable energy world. We need to store electricity as the sun and wind don’t always deliver energy. Most batteries are made from lithium and lithium mines are not exactly environmentally friendly activities. There’s another problem with batteries: They can balance minute-to-minute shifts in supply. But they can’t absorb solar power generated in summer, say, and deliver it in winter. Here are five great energy storage technologies that don’t have a negative impact on the environment.