Pumped water energy storage can be easily scaled to any required storage capacity at known and affordable costs.
But there’s a twist. Almost all good PHES sites are located far from rivers, for the simple reason that most of the Earth’s landscape is not near rivers. Australian National University Global Pumped Hydro Atlas lists 616,000 sites with a combined storage capacity of 23 million GWh, which is about 100 times more than is needed to support a global 100% renewable energy system.
PHES can be easily scaled to any required storage capacity at a known and affordable price. Future technological developments could further reduce the cost of electrochemical electricity storage, such as Li-ion batteries. However, current PHES technology puts a solid upper limit on storage costs, which are already affordable and highly available in almost all countries.
Businesses and governments can confidently move forward with terawatt-scale deployment of cheap, variable solar and wind power, knowing that at least one highly credible, scalable, and affordable energy storage technology already exists. No hand waving required future cost savingsand resource constraints are minimal.
In an off-river PHES, water is pumped uphill from one reservoir to another higher one for storage. When power is needed, the water is released to flow downhill through the turbines, generating electricity on its way to the lower reservoir.
For example, a pair of 100-hectare reservoirs – at an average depth of 20 meters, a few kilometers apart and connected by a tunnel, height difference 600 meters – can store 24 GWh of energy. This means that the system could produce 1 GW of power for 24 hours.
Reservoirs can be built on hilly land, away from all rivers. Alternatively, existing lakes or reservoirs can be used. Since most sites are far from rivers, there is no need for flood control or new dams. Annual operating costs are low and the system’s lifetime is 50-100 years. The working fluid is more water than electrochemical.
One hour at a time analysis over many years Several countries suggest that around 2 GW of storage for one day (50 GWh of storage energy) per million people is sufficient to support a 100% renewable energy system in a prosperous country, depending on local factors.
The the country’s claim is very small: 4 square meters per person. The the need for water is also small, about 4 liters per day per person for initial filling. To compensate for evaporation, water is recycled up and down the hill for 100 years.
For comparison, about 30 square meters of solar panels per person requires 10 MWh of electricity for each person per year, which is typical of the annual electricity demand of wealthy countries.
The Global PHES Atlas lists 616,000 sites that can be panned and zoomed to a resolution of 30 meters. National parks are not included in the atlas. Tunnel routes, dam walls, flooded land and cost categories (A–E) are shown for each site. Clicking on the site produces pop-ups that list 16 different attributes, including location, head, length of tunnel, and amount of enclosed water.
Photo: ISES
There are 35,000 good sites in the US with 1.4 million GWh of combined storage, mostly in the Rockies, but a good number in the East as well. Huge Texas Solar and Wind Potential can be connected to local PHES storage to deliver solar electricity to the east and west coasts in the middle of the night.
Although there are relatively few destinations in northern Europe, there are many good destinations in the south. Strong north-south grid connections enable northern wind energy to be exchanged for southern solar energy and PHES storage.
Professor Andrew Blakers (ANU) and Professor Ricardo Rüther (UFSC)
Andrew.blakers@anu.edu.au and rruther@gmail.com
ISES, International Solar Energy Association is an NGO accredited by the UN. It was founded in 1954.
