Researchers from the U.S. Department of Energy’s (DOE) SLAC National Accelerator Laboratory and Stanford University have designed a low-cost, long-life battery that might make solar and wind energy major suppliers to the electrical grid.
An electrical grid’s tolerate of large and sudden power fluctuations from wide swings in sunlight and wind power sources is a serious problem. As solar and wind’s combined contributions to an electrical grid approach 20%, energy storage systems need to be available to smooth out the peaks and valleys of the intermittent power supply by storing excess energy and discharging when input drops.
Yi Cui, a Stanford associate professor of materials science and engineering and a member of the Stanford Institute for Materials and Energy Sciences explains, “For solar and wind power to be used in a significant way, we need a battery made of economical materials that is easy to scale and still efficient. We believe our new battery may be the best yet designed to regulate the natural fluctuations of these alternative energies.”
Cui and his colleagues’ research results have been published in the May issue of Energy & Environmental Science. The work is some of the earliest supported by the DOE’s new Joint Center for Energy Storage Research battery hub.
Among the most promising batteries for intermittent grid storage today are called “flow” batteries, because it’s relatively simple to scale their tanks, pumps and pipes to the sizes needed to handle large capacities of energy. The new flow battery developed by Cui’s group has a simplified, less expensive design that presents a potentially viable solution for large-scale production.
Today’s flow batteries pump two different liquids through an interaction chamber where dissolved molecules undergo chemical reactions that store or give up energy. The chamber contains a membrane that only allows ions not involved in reactions to pass between the liquids while keeping the active ions physically separated. This battery design has two major drawbacks: the high cost of liquids containing rare materials such as vanadium – especially in the huge quantities needed for grid storage – and the membrane, which is also very expensive and requires frequent maintenance.
The new Stanford/SLAC battery is a very different take on a sound idea. The design uses only one stream of molecules and does not need a membrane at all. Its molecules consist primarily 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 without degrading the metal. When discharging, the molecules called lithium polysulfides, absorb lithium ions; when charging, they lose them back into the liquid. The entire molecular stream is dissolved in an organic solvent, which doesn’t have the corrosion issues of water-based flow batteries.
Cui notes some impressive early results with, “In initial lab tests, the new battery also retained excellent energy-storage performance through more than 2,000 charges and discharges, equivalent to more than 5.5 years of daily cycles.”
To demonstrate their concept, the researchers created a miniature system using simple glassware. Adding a lithium polysulfide solution to the flask immediately produces electricity that lights an LED.
A utility grid sized version of the new battery would be scaled up to store many megawatt-hours of energy.
For the future Cui’s group plans to make a laboratory-scale system to optimize its energy storage process and identify potential engineering issues, and to start discussions with potential hosts for a full-scale field-demonstration unit.
For wind and solar to make credible progress cheap storage is a “must make” goal. As Europe and Germany in particular are rapidly discovering, high energy costs can devastate economies. A few miss thought through decisions there are forcing an expensive and urgent reassessment of energy’s role in maintaining a successful economy.
Wind and solar could be important additions with attractive growth and pricing to consumers. But without very low cost storage grid systems saddled with wind and solar could very well kill the economic engine of the social system served.