What is the most efficient way to store solar energy? – Mark Diesendorf

Renewable energy systems are important ingredients in the development of a sustain- able economic system, and energy storage is an essential requirement. The following item is a response by Mark Diesendorf to the question “What is the most efficient way (form of energy and method) to store solar energy for the night?” which appeared in Quora on 14th August.

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For an electricity grid with solar farms, pumped hydro is an efficient and often inexpensive form of storage. When there is excess variable renewable energy (e.g. solar and wind) over demand, the excess is used to pump water from a lower to a higher reservoir. When demand is high and/or variable renewable energy output is low, water is released from the upper reservoir to generate electricity on its return journey to the lower reservoir. Pumped hydro is the principal form of electricity storage used around the world.

Off-river pumped hydro is currently just starting to be rolled out in dry regions with little potential on rivers. In this case the bottom reservoir can be the ocean or a disused mine-shaft. For example, the state of South Australia now has over 50% of annual electricity generation from wind and solar, but has no conventional on-river hydro potential.

In order to enable South Australia to continue its transition to 100% renew- able electricity by 2030, four or five off river pumped hydro schemes are under development. It also has the largest battery in the world and more batteries are being installed.

Dr Mark Diesendorf is attached to UNSW.