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 and meeting peak hour spikes in demand.
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?
Lithium-ion batteries are within reach of the $150/kWh target, and their share in the utility-scale energy storage is growing. Yet they face materials scarcity challenges exacerbated by a rising electric car market.
Pumped hydro and compressed air, which use extra power to pump water uphill or to pressurize air, both of which can be used to turn a turbine and generate electricity when needed, already have a low energy cost of $20/kWh, the researchers say. But these systems need a large amount of space and special geological features such as mountains or underground caverns, so cannot be used everywhere.
Another viable technology is flow batteries that would use abundant, low-cost chemicals to store energy in large tanks. But not all flow battery chemistries are inexpensive. One of the main types, vanadium redox flow batteries, have an estimated cost of $100/kWh, the researchers say, but more development could bring down costs. Yet-Ming Chiang, an author on the present study, has recently developed an aqueous sulfur flow battery that could cost as little as $10/kWh.
There are other battery technologies to keep an eye on. High-temperature sodium-sulfur batteries cost $500/kWh, but with more development, their costs could fall by up to 75 percent by 2030, according to the International Renewable Energy Agency. Meanwhile, the cost of sodium nickel chloride batteries could fall from $315 to $490/kWh at present to $130 to $200/kWh by 2030.
There are many other ways to store renewable energy that the researchers didn’t consider, such as with flywheels, supercapacitors, thermal storage in molten salts, and using excess electricity to liquefy air or to make fuels such as hydrogen and methane.
The Eland project and others announced recently show that renewables combined with storage are already starting to make economic sense. Advancing energy storage technologies and economies of scale should help drive down costs further and allow renewables to meet their full potential.
Editor’s note: This story is published in cooperation with more than 250 media organizations and independent journalists that have focused their coverage on climate change ahead of the UN Climate Action Summit. IEEE Spectrum’s participation in the Covering Climate Now partnership builds on our past reporting about this global issue.