“Low-cost storage is the key to enabling renewable electricity to compete with fossil fuel generated electricity on a cost basis,” says Yet-Ming Chiang, a materials science and engineering professor at MIT.

But exactly how low? Chiang, professor of energy studies Jessika Trancik, and others have determined that energy storage would have to cost roughly US $20 per kilowatt-hour (kWh) for the grid to be 100 percent powered by a wind-solar mix. Their analysis is published in Joule.

That’s an intimidating stretch for lithium-ion batteries, which dipped to $175/kWh in 2018. But things look up if you loosen the constraints on renewable energy, the researchers say. Then, storage technologies that meet the cost target are within reach.

The team picked four locations—Arizona, Iowa, Massachusetts, and Texas—and gathered 20 years of data on those solar and wind resources there. Such resources can change considerably with the seasons and over the years, and their longer-term analysis—while previous studies had used data from just a year or two—captures the variations that may occur over the lifetime of a power plant, the researchers say. They modeled the costs of wind-solar-plus-storage systems that would reliably meet various grid demands, such as providing baseload energy 24/7 and meeting peak-hour spikes in demand for a few hours.

Energy storage would have to cost $10 to $20/kWh for a wind-solar mix with storage to be competitive with a nuclear power plant providing baseload electricity. And competing with a natural gas peaker plant would require energy storage costs to fall to $5/kWh.

But those figures are only for scenarios in which solar and wind meet power demand 100 percent of the time. If other sources meet demand just 5 percent of the time, storage could work at a price tag of $150/kWh. Which technologies could hit that target?