How pumped hydro could cover for “wet and windless” weeks in the West

The southwest needs large-scale long-duration energy storage (GWh) for overnight storage and “wet windless weeks in winter”. The cheapest option is pumped hydro energy storage (PHES).

Although the Western Australia Energy Market (WEM) does not have premium PHES like in the east, it does have numerous moderate-quality sites up to a size of 50 GWh (equivalent to 110 Victorian Big Batteries).

The WEM will eventually need storage of around 100 GWh when all energy is supplied by solar and wind following full decarbonisation. 

Example sites

The figure shows a 50 GWh site at Yarloop. Visualisation is here. Other examples can be visualised here and here. 

Aqueducts can reduce the effective separation between upper and lower reservoirs to a few hundred metres to further reduce costs. Short pressure pipes can be used instead of tunnels, which greatly reduces geotechnical risk and increases the speed of construction.

Water use is modest because the water cycles between upper and lower reservoirs for 100 years. The reservoirs can be filled gradually over a decade to support slowly growing deployment of solar and wind. 

Sites can be greenfield (two new reservoirs), bluefield (an existing reservoir) and brownfield (a mining precinct). Land use is small. For example, the Yarloop 50 GWh site floods 800 Ha which is equivalent to 6 kWh per m². The Victorian Big Battery doesn’t do much better at 15 kWh per m². 

Pumped hydro and batteries

PHES is much cheaper than batteries for large (5-5000 GWh) long duration (20-200 hours) energy storage. Batteries shine for short-term (1-4 hours) high-power storage.

Hybrid PHES-battery systems offer cheap energy storage ($/GWh) coupled with cheap storage power ($/GW). Trickle recharging of batteries by PHES and vice moderates both negative and high prices.

PHES constitutes 95% of energy storage. The ANU global pumped hydro Atlas contains 820,000 sites in the size range 2-5000 GWh with combined storage equivalent to 2 trillion EV batteries. Low-cost PHES is characterised by large head, large slope, large W/R ratio, large scale and long duration, as described here. 

Snowy 2.0 ($12B, 350 GWh) has a capital cost of $34/kWh for 100-year-lifetime storage which is 10X cheaper than the GenCost estimate for batteries. It is equivalent to only $400 for a fully-installed 12 kWh home battery!

Andrew Blakers is professor of engineering, Australian National University