Utility-Scale Energy Storage
Utilities have long operated on the model of producing sufficient electricity to meet demand in real time. To supplement large coal, gas, or nuclear plants, they rev up highly polluting “peaker” plants as needed. Energy storage—daily, multiday, and longer-term or seasonal—is vital to reduce peaker emissions and accommodate the shift to variable renewables, namely wind and solar.
How does a utility store large amounts of electricity? One option is pumping water from lower reservoirs into higher ones, ideally 1,500 feet higher. The water is released back down into the lower reservoir as needed and runs through power-generating turbines. There are more than 200 pumped-storage systems in the world at present, accounting for 97 percent of global storage capacity.
Concentrated solar power plants are also at the forefront of energy storage, where molten salt is used to hold heat until it is needed to generate electricity. Then, there are batteries at scale. Dozens of start-ups and established companies are racing to create low-cost, low-toxicity, and safe batteries that will revolutionize energy storage, while some utilities are already installing banks of lithium-ion batteries to help meet peak demand.
Taken on its own, the use of energy storage does not reduce emissions; instead, energy storage enables adoption of high shares of variable renewable energy sources as wind and solar power. No carbon impact numbers are included herein in order to prevent double counting with the renewable energy solutions themselves. As with other forms of grid flexibility, the costs and total growth are not modeled directly.