Utilities need cheap, long-lasting ways to store the excess energy produced by power plants, especially as intermittent power from solar and wind farms is added to the mix. Unfortunately, the batteries available for grid-level storage are either too expensive or don’t last for the thousands of cycles needed to make them cost-effective.
A new battery developed by Aquion Energy in Pittsburgh uses simple chemistry—a water-based electrolyte and abundant materials such as sodium and manganese—and is expected to cost $300 for a kilowatt-hour of storage capacity, less than a third of what it would cost to use lithium-ion batteries. Third-party tests have shown that Aquion’s battery can last for over 5,000 charge-discharge cycles and has an efficiency of over 85 percent.
The company has now received $30 million in venture capital to step up manufacturing of its sodium-ion batteries. The new technology could be the cheapest way to store large amounts of energy for the power grid using batteries, says Jay Whitacre, the company’s founder and chief technology officer.
Aquion’s battery uses an activated carbon anode and a sodium- and manganese-based cathode. A water-based electrolyte carries sodium ions between the two electrodes while charging and discharging. The principle is similar to lithium-ion, but sodium ions are more abundant and hence cheaper to use. Compared to solvent-based electrolytes, the aqueous electrolyte is also easier to work with and cheaper. Even better, the materials are nontoxic and the battery is 100 percent recyclable, Whitacre says.
Grid-scale trials of the technology are next. Aquion has started shipping pre-production battery prototypes to off-grid solar power companies. Next month, a 1,000-volt module will go to KEMA, a Dutch energy consulting and testing outfit, which has a facility outside Philadelphia.
Utilities use stored energy to meet electrical demand during peak usage periods, a practice called peak shaving, which helps keep the grid reliable and efficient and electricity prices low. Whitacre says Aquion’s battery is designed for these grid applications. “It’s very well-suited for off-grid solar and wind support, and also for peak shaving,” he says. “It’s two very different applications, and our battery has been shown to be effective in both.”
John Miller, an electrochemical capacitor expert and president of consulting firm JME in Shaker Heights, Ohio, says Aquion’s battery could be the cheapest of the various battery technologies vying to provide grid storage. He compares it to today’s most common grid storage technology, pumped hydro, which accounts for 95 percent of utility-scale energy storage. Pumped hydro involves moving water to an elevation when electricity demand is low, and releasing that water through turbines during peak periods. It is, however, limited by geology and space, and pumped hydro systems take many years and millions of dollars to build. Utilities are now starting to look at batteries because they can be delivered in months and, in principle, can be sited anywhere.