Source phys.org
Air could be the world’s next battery
The least expensive method is to use hydropower reservoirs as ‘batteries’: i.e. generate electricity using the stored water, when power is in short supply, and subsequently pump the water back uphill when surplus renewable energy is available. However, this is a practical solution only in mountainous regions, such as we have in Norway and a few other countries.
From our very good friends over at phys.org