Green energy is essential for a sustainable future, but it faces a significant challenge: storage. The intermittent nature of wind and solar power means that the energy they produce cannot always be utilized when needed. Sometimes, the sun doesn’t shine, and the wind doesn’t blow, while other times there is an excess of both. This mismatch between renewable energy production and fluctuating demand calls for increased energy storage to balance the grid.
Battery technology is rapidly advancing to improve efficiency and storage capacity. However, it has not progressed quickly enough to keep up with the growing number of renewable energy projects worldwide. To address this issue, scientists and companies are exploring alternative ways to store energy. Many of these options involve retrofitting existing energy storage technologies to meet the demands of the 21st century.
One promising solution lies deep beneath the surface of Texas and Louisiana, where massive salt caverns store hundreds of millions of barrels of petroleum. These caverns could potentially be repurposed to store compressed air or excess wind and solar power converted into green hydrogen. Salt has excellent isolation properties, making it an ideal medium for energy storage, according to Oliver Duffy, a research scientist at the University of Texas at Austin.
Creating these caverns involves drilling into salt deposits and injecting fresh water to dissolve the salt around the drill hole. The resulting brine is pumped out, leaving behind a cavern that can be used as a storage tank. These caverns can be enormous, with some large enough to engulf the Empire State Building.
However, there are environmental challenges associated with building and using these caverns. The process requires a significant amount of water, and disposing of the brine in an environmentally friendly manner is a challenge. Poorly managed projects can contaminate water supplies and cause leaks or ground subsidence. Additionally, these caverns may also store hydrogen produced with non-renewable energy sources.
Despite these challenges, there are ongoing developments in utilizing salt caverns for energy storage. The world’s largest green hydrogen storage facility, partially funded by the U.S. Department of Energy, is under development in Utah and relies on salt caverns. China has also opened its first salt cavern for compressed air energy storage in 2022.
Another technology gaining renewed interest is pumped storage hydropower. Unlike traditional hydropower, which allows water to pass through a dam only once, pumped storage hydropower collects water in a basin at the bottom for reuse. Powerful pumps then move the water back up towards the reservoir in front of the dam when energy needs to be stored, and it can flow through the dam again when energy is needed.
Pumped storage hydropower is a mature technology with known costs and minimal energy loss, according to Professor Sebastian Sterl of the Free University of Brussels. The Bath County Hydro Pumped Storage Facility, often referred to as “the world’s largest battery,” has operated since 1985. The conversion of California’s Hoover Dam into a pumped storage hydropower installation is also underway.
Interest in pumped storage hydropower is growing worldwide, with installations in Switzerland, Spain, Bulgaria, and Finland. This technology is less vulnerable to water supply issues and can function with just two lakes with a height difference. It does not always require a river with a strong flow.
One startup is even exploring the possibility of using pumped storage hydropower on the ocean floor, where water supply and pressure are abundant. The University of Groningen in the Netherlands developed the concept of an “ocean battery” that involves building reservoirs under high pressure on the seabed. When there is excess energy, the reservoirs can be emptied against the water pressure using pumps. When energy is needed, the reservoirs are opened, and pressure pushes water inside, generating electricity through a turbine.
Ocean Grazer, a startup spun out from the University of Groningen, aims to build smaller installations in lakes before moving to the seafloor within five years. These ocean batteries would be located near offshore wind farms, allowing surplus wind energy to be stored close to its source.
The need for energy storage is urgent, as a significant amount of energy is currently lost due to the lack of storage capabilities. The renewable energy sector is expanding rapidly, and there is a pressing need to scale up the development and use of storage technologies to ensure a sustainable energy transition.
