Electrical energy is converted to chemical energy when you charge a battery, and then the process is reversed when you draw power from it. That would equate to about 7% of the world’s energy capacity. Such ancillary services are increasingly important to help match supply and demand as a growing amount of intermittent wind and solar power comes online. Instead of exporting immediately, hybrid farms can store power to sell later at higher prices. The bigger and denser the battery, the more chemical energy it can store and therefore the more electricity it can generate.

Source: The Guardian January 14, 2019 07:01 UTC