Proponents of solar and wind energy are quick to point out that these energy sources are best because, well, they’re free. But for utilities looking to incorporate these energy sources into their grids, they’re not exactly cheap either.
Wind and solar energy storage on the electric grid has always been hampered by the natural fluctuations associated with these sources. Flow batteries can smooth out the highs and the lows for uninterrupted, reliable grid power storage, but this decades-old technology has been too expensive and bulky to implement. In recent years, however, researchers and entrepreneurs have made progress toward making flow batteries more viable for grid storage.
This spring, researchers from the U.S. Department of Energy’s (DOE) Joint Center for Energy Storage Research and Stanford University’s SLAC National Accelerator Laboratory developed a new flow battery design (http://stanford.io/ZOU8pD), published in the May issue of Energy & Environmental Science, made from more economic materials that, according to Stanford associate professor of materials science Yi Cui, “are easy to scale and still efficient.”
Flow batteries pump two different liquids – which contain very rare and expensive materials -- into an “interaction chamber” where their dissolved molecules go through chemical reactions. An ion exchange takes place across a membrane that separates the active ions and permits the inactive ions to pass between the liquids. According to the Stanford/SLAC announcement, the researchers’ new design “uses only one stream of molecules and does not need a membrane at all. Its molecules mostly consist of the relatively inexpensive elements lithium and sulfur, which interact with a piece of lithium metal coated with a barrier that permits electrons to pass...”
Another flow battery design comes from an MIT spinoff, Sun Catalytix. The startup is basing its design on, as reported in MIT Technology Review, “cheap ingredients” sourced from China, which are then combined with ligands to form the active battery materials. “During charging and discharging,” the article describes, “the two liquid electrolytes travel through grooves carved within each plate to trigger the chemical reaction across the membrane.”(http://bit.ly/1ajRMGP)
Both the SLAC/Stanford researchers and Sun Catalytix are working toward a field demonstration unit. For wide adoption in utility installations, cost and long will determine flow batteries’ success. Both flow designs require less expensive materials and the SLAC/Stanford team reports “excellent” storage performance through more than 2000 charges/discharges in its lab test. As solar and wind continue to account for a growing amount of power on the grid, successful demonstrations of these designs could provide optimism for proponents of alternative energy and attract utilities with the reliability and cost benefits they need.