In an earlier post, I noted the importance of energy storage. I was also surprised by the fact that more than half of this comes from water that is pumped into a reservoir in order to serve as temporary hydropower. Here is an interesting article on the world's largest "battery" of this kind. This is considered by some to be more environmentally-friendly than conventional hydropower in that it can be used in brown fields (such as abandoned quarries) and can be used to supplement intermittent forms of renewable energy such as solar and wind.