From pumping water uphill to heating thermal batteries, businesses are trying new solutions to keep the power on tap as the world shifts from fossil fuels to renewables.

FREMONT, CA:As the world transitions from fossil fuels to renewables, a solution is to store excess energy during periods of sunlight and wind and discharge it when necessary. Large lithium-ion rechargeable batteries are being used to store energy to some extent, but battery technology only can cover up to four hours. Although that will improve in the coming years, there are likely still be periods when batteries are not sufficient. Therefore, there is a need for an alternate solution to back up the energy system.

Long-term energy storage becomes crucial at this point. Long-duration energy storage (LDES) is any form of technology that can store energy for multiple hours, days, or even weeks or months and then provide that energy when needed. Technology is essential to increasing the proportion of renewable energy, given that it is an inherently intermittent source. Several technologies are being worked on, with different degrees of advancement, but the benchmark is pumped hydro storage because of its high round-trip efficiency, or the proportion of the energy stored in this way that can later be pulled out, which is around 80 per cent.

Technology has been around for more than a century, involving the movement of water between lower and higher reservoirs to store and generate energy. However, it is the most used storage method, with around 160 GW of power capacity installed in the previous year. Although geographical constraints are a limitation on the use of the technology, particularly in the case of overground large-scale facilities, new developments will allow for its deployment on non-mountainous terrain.

Another technology uses excess energy to compress and store air, then release it to turn generator turbines. Alternatively, there are electrochemical technologies like vanadium flow batteries. These use large tanks of separately charged vanadium electrolytes to store energy but have a lower round-trip efficiency compared with other options. Heat for heavy industry is more often generated by burning natural gas.

Investment in LDES has significantly increased over the years. A commercial market for large-scale and long-term storage is yet to be developed. The system's use of renewable energy has not yet increased enough to create a market for long-term storage solutions, and the regulatory environment has not been helpful for market entry. Today, the commercial case for better battery storage is straightforward. LDES may be beneficial in places that seek to decarbonise but lack an interconnected energy grid in poorly interconnected areas where they rely on diesel or gas generation at the moment, as it is not feasible to build the grid to those locations. These locations will take the LDES route, and there will be indications of how the rest of the market will develop.