April 26th, 2013 by James Ayre
A new low-cost, long-life flow battery has been created by researchers at the DOE’s SLAC National Accelerator Laboratory and Stanford University that has the potential to help address some of the perceived issues with intermittent sources of power such as solar and wind energy. The researchers think that this new battery may be the best one yet with regards to regulating these intermittent sources of power.
“For solar and wind power to be used in a significant way, we need a battery made of economical materials that are easy to scale and still efficient,” said 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. “We believe our new battery may be the best yet designed to regulate the natural fluctuations of these alternative energies.”
As more and more renewable energy capacity is added to the grid it becomes more and more important to find ways to “smooth out” the fluctuations that accompany these intermittent sources. Though, it’s important to note that the these “issues” are much less of a problem than critics make them out to be. In fact, recent research has shown that the US could integrate and balance many times the current level of renewables with no additional reliability issues.
Improvements in storage technology are of course of great value though, and will help to reduce costs and overall grid performance.
The new battery is a “flow” battery. Flow batteries are one of the most promising types for intermittent grid storage, mostly because of the relative ease of scaling them up the large capacities. The new battery is an improvement over older designs largely thanks to its greatly simplified, more economical design.
The press release from the DOE/SLAC National Accelerator Laboratory notes:
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.
Initial lab testing has found that the new battery “retained excellent energy-storage performance through more than 2,000 charges and discharges, equivalent to more than 5.5 years of daily cycles.”
As of now, the new battery design has only been demonstrated via a miniature system composed of simple glassware, but it should be easy to scale the technology up to utility scale, capable of storing many megawatt-hours of energy, according to the researchers.
The next step for the researchers is to create a laboratory-scale system in order to further optimize the energy storage process and to help identify any potential engineering problems. which will be followed by the creation of a full-scale field-demonstration unit.
The new research will be detailed in the May issue of the journal Energy & Environmental Science.
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