Energy Storage System

There is large potential for large scale, low-cost, Short-Term, Off-River pumped hydro Energy Storage (STORES) to reduce the effect of variable output from renewable energy generators, and for arbitrage between the daily peaks and troughs in demand. STORES can also help to increase the capacity factor on transmission lines and cope with unexpected outages because of its rapid (1 minute) response time. STORES is a highly competitive storage option. Little is known about the potential scale and location of STORES systems in Australia and in other countries. Research into the potential of STORES in is needed, including finding potential sites and refining costings.

Pumped hydro energy storage (PHES) involves pumping water through a pipe or tunnel to an upper reservoir when there is excess electricity, and later recovering that energy by allowing the water to flow back to a lower reservoir through a turbine. In a closed PHES system the same water circulates indefinitely between upper and lower reservoirs, thus eliminating the need for a river. This is called off-river PHES. The amount of energy stored is proportional to both the elevation difference (“head”) between upper and lower reservoirs (typically 100-1,000 m) and to the volume of water stored in the upper reservoir.


PHES is by far the most widely used from of energy storage. World-wide capacity is 150 GW (three times Australia’s electricity generation capacity) and it forms 99% of all electricity storage. Most existing PHES is integrated with hydroelectric generation systems on rivers. Round-trip energy storage efficiencies of 80% are possible for well-designed systems, accounting for losses in the pumps, pipes and turbines; i.e. 20% of the stored energy is lost, which is similar to batteries.