Decarbonisation Technology - August 2023 Issue

Solutions for long-duration energy storage A renewable grid requires storage that lasts more than a few hours, but as the need increases, technology is evolving at a rapid pace

Jim Berry Just In-Time Energy Company

A s the penetration of renewable energy on the grid increases beyond about 30%, energy storage becomes an essential requirement. While batteries are a good approach for short-term storage, mechanical and fuel-burning systems will be needed when solar and wind cannot meet peak demand – both to supply natural gas for peaking power generation and to provide cost-effective, long- duration storage of excess renewable energy to be reclaimed at peak periods. But there is a problem. The growing presence of renewables on the grid means that natural gas usage is likely to decline steadily. There will be a collision of peak gas demand at the same time as the need for peak backup power ramps affordable long-duration energy storage is driving innovation. Several solutions have been proposed, including a combined gas and electric storage system. These systems store both natural gas and excess electric energy in various forms and repositories, including within the pipeline network, using renewable energy sources. In this way, both natural gas and green energy are available whenever the direct supply of wind or solar energy falters. New approaches to energy storage Despite the enormous expansion of renewable energy over the last two decades, 40% of the electric power in the US continues to be produced from natural gas-fired generation (EIA, 2023). As the penetration of renewable power generation rises even further, the number of operating hours for fossil-fuel units will drop. up. This presents a real challenge. The good news is that the need for

Thus, natural gas consumption will gradually fall along with the average amount of gas in storage reservoirs. There will be no incentive to store gas that will not be used. That said, demand for gas-based generation during peak demand periods is likely to remain. When renewable generation is hindered by cloud cover or lack of wind, reserves of stored energy will be needed to help meet grid demand. In some cases, this can come from the storage of excess renewable energy in battery energy storage facilities. But that will not nearly be enough. A mix of short-, mid-, and long- duration storage options will be required to maintain a stable grid. Traditional approaches to longer-term storage include compressed air energy storage (CAES) and pumped hydro. CAES uses air that is compressed using excess renewable energy and stored at high pressure underground. When needed, electricity is produced by feeding the high-pressure air to a turbine to produce power. Pumped-hydro plants use excess energy to pump water to a higher elevation. When the power is needed, water is released to power a turbine in the same way that hydroelectric power is generated. But there are plenty of advances on the horizon. One concept funded by the Department of Energy (DOE) is based on what is known as Compressed Natural Gas Energy Storage (CNGES) technology. It is currently being studied at the Abbott Power Plant in Illinois. The main difference to CAES is that natural gas is stored rather than air and in a pipeline rather than an underground cavern. How does it work? Gas pressure is raised