Gravity power? How to store wind, solar energy without batteries

One of the challenges in the shift to clean energy is that wind and solar power generation produces electricity only when the wind is blowing and the sun is shining, which doesn’t necessarily coincide with when we need the most electricity.

That’s one of the reasons the International Energy Agency considers ramping up energy storage technologies to be a key part of a global energy strategy to keep global warming below 2 C, as the Paris Agreement demands.

Grid-related energy storage was projected to increase 15-fold between 2019 and 2030, to about 160 gigawatt hours worldwide, according to a recent U.S. Department of Energy report.

Lithium-ion batteries have become the technology of choice for new installations, thanks to falling prices and the fact that they can be installed just about anywhere. But batteries aren’t the only option. 

Here’s a look at how the energy industry is turning to water and earth to help wind and the sun power a clean grid.

Pumped hydroelectric storage

While batteries dominate new installations, most existing storage capacity is actually pumped hydro, a technology developed in the 1920s. It uses surplus power to pump water up into a reservoir. When you need the power, you let the water run down through some turbines that generate electricity, just like you do with conventional hydropower. 

Pumped hydro is generally cheaper and higher-capacity than other kinds of storage. It’s also 80 per cent efficient and can make use of existing hydroelectric infrastructure, enabling the expansion of green energy in places like Quebec.

Underground pumped storage hydropower

A downside of pumped hydro is that it can be difficult to find a suitable location and build there. So some projects are now being developed that store water underground.

One strategy is to make use of existing underground infrastructure. For example, the Elmhurst Quarry Pumped Storage Project in Illinois plans to use an abandoned mine near Chicago.

Goleta, Calif.-based Gravity Power is building a one-megawatt demonstration plant in Germany where a piston is suspended in a water-filled shaft. The pumped water pushes the piston up for storage. Later, the piston pushes the water through a turbine to release the energy. The company says it takes up so little space that it could be installed in the middle of cities. Germany-based New Energy Let’s Go is working on a similar technology. 

Houston-based Quidnet Energy has developed a technology called geomechanical pumped storage, which stores the water between layers of shale rock and can be installed, say, underneath farm fields. It has signed a contract to build a two-megawatt demonstration in New York state. Emissions Reductions Alberta also lists a demonstration in Brooks, southeast of Calgary.

Gravity storage

Traditional pumped hydro relies on gravity to store and release energy. Gravity storage is a similar concept — but without the water. Instead, it relies on raising and lowering giant bricks or slabs of rock. Companies developing the technology say that could allow them to be built almost anywhere. 

Two projects are expected to go online soon. Lugano, Switzerland-based Energy Vault completed a 35-megawatt demonstration plant in that country last year that is undergoing final testing (see photo above). Meanwhile, Gravitricity, based in Scotland, uses cables to suspend weights of up to 5,000 tonnes in a deep shaft. A 250-kilowatt demonstration is being built in Edinburgh and is scheduled to be completed this year.

Stay tuned. In one of our upcoming issues, we’ll look at a few other options for storing energy without batteries.

— Emily Chung

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