Stop hyping batteries, it’s pumped hydro that will save the planet
Here’s how it works
Why wind and solar need long-term storage
To function properly, power grids must be able to match the incoming electricity supply to electricity demand in real time or they risk shortages or overloads.
There are several techniquesthat grid managers can use to keep that balance with variable sources like wind and solar. These include sharing power across large regions via interstate high-voltage transmission lines, managing demand – and using energy storage.
The Kidston pumped hydro project in Australia uses an old gold mine for reservoirs (Credit:Genex Power)
Batteries deployed in homes, power stations and electric vehicles are preferred for energy storage times up to a few hours. They’re adept at managing the rise of solar power midday when the sun is overhead and releasing it when power demand peaks in the evenings.
Pumped hydro, on the other hand, allows for larger and longer storage than batteries, and that is essential in a wind- and solar-dominated electricity system. It is also cheaper for overnight and longer-term storage.
Off-river pumped hydro energy storage
In 2021, the U.S. had43 operating pumped hydro plantswith a total generating capacity ofabout 22 gigawattsand an energy storage capacity of 553 gigawatt-hours. They make up 93% of utility-scale storage in the country. Globally,pumped hydro’s shareof energy storageis even higher– about99% of energy storage volume.
Pump hydro projectscan be controversial,particularly when they involve dams on riversthat flood land to create new reservoirs and can affect ecosystems.
Creating closed-loop systems that use pairs of existing lakes or reservoirs instead of rivers would avoid the need for new dams. A project planned in Bell County, Kentucky, for example, uses anold coal strip mine. Little additional landis needed except for transmission lines.
Examples from the atlas of off-river reservoirs with the potential to be paired for pumped hydro near Castle Rock, Colorado (Credit:Andrew Blakers, CC BY)
An off-river pumped hydro system comprises a pair of reservoirs spaced several miles apart with an altitude difference of 200-800 meters (about 650-2,600 feet) and connected with pipes or tunnels. The reservoirs can be new or useold mining sitesorexisting lakes or reservoirs.
On sunny or windy days, water is pumped to the upper reservoir. At night, the water flows back down through the turbines to recover the stored energy.
A pair of 250-acre reservoirs with an altitude difference of 600 meters (1,969 feet) and 20-meter depth (65 feet) can store 24 gigawatt-hours of energy, meaning the system could supply 1 gigawatt of power for 24 hours,enough for a city of a million people.
The water can cycle between upper and lower reservoirs for a hundred years or more.Evaporation suppressors– small objects floating on the water to trap humid air – can help reduce water evaporation. In all, the amount of water needed to support a 100% renewable electricity system is about3 liters per person per day, equivalent to 20 seconds of a morning shower. This isone-tenthof the water evaporated per person per day in the cooling systems of U.S. fossil fuel power stations.
Storage to support 100% renewables
Little pumped storage has been built in the U.S. in recent years because there hasn’t been much need, but that’s changing.
In 2020, aboutthree-quartersof all new power capacity built was either solar photovoltaics or wind power. Their costs have been falling, making themcheaper to build in many areasthan fossil fuels.
Australia isinstalling solar and windthree times faster per capita than the U.S. and is already facing the need formass storage. It hastwo systemsunder constructionthat are designed to have more energy storage than all the utility batteries in the world put together; another dozen are under serious consideration. None involve new dams on rivers. The annual operating cost is low, and the working fluid is water rather than battery chemicals.
Shifting electricity to renewable energy and then electrifying vehicles and heating can eliminate most human-caused greenhouse gas emissions. The U.S. has vast potential for off-river pumped hydro storage to help this happen, and it will need it as wind and solar power expand.
Story byThe Conversation
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