Researchers from the US Department of Energy’s SLAC National Accelerator Laboratory and Stanford University have designed a low-cost, long-life battery that could enable solar and wind energy to become major suppliers to the electrical grid.
Currently the electrical grid cannot tolerate large and sudden power fluctuations caused by wide swings in sunlight and wind. As solar and wind’s combined contributions to an electrical grid approach 20 percent, energy storage systems must be available to smooth out the peaks and valleys of this “intermittent” power – storing excess energy and discharging when input drops.
As a result, for solar and wind power to be used in a significant way, a battery made of economical materials that are easy to scale and still efficient is needed, according to Yi Cui, a Stanford associate professor of materials science and engineering and a member of the Stanford Institute for Materials and Energy Sciences, a SLAC/Stanford joint institute. Cui believes the new SLAC/Stanford battery may be the best yet designed to regulate the natural fluctuations of these alternative energies.
Among the most promising batteries for intermittent grid storage currently available are “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, Stanford says.
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 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 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.
In initial lab tests, the new battery also retained what Stanford calls “excellent” energy-storage performance through more than 2,000 charges and discharges, equivalent to more than 5.5 years of daily cycle.
In February, Samsung SDI and Xtreme Power were selected by the Center for the Commercialization of Electric Technologies to install a 1 MW/1 MWh lithium ion-based battery energy storage system at the Reese Technology Center in Lubbock, Texas, as part of a $27 million smart grid demonstration project. The system will be connected to the electric co-op’s distribution grid at the Reese Technology Center as part of an ongoing wind technology program. The BESS will focus on combing utility scale energy storage with wind generation. Potential uses for the BESS include mitigating intermittent fluctuations of a number of nearby wind turbines.