Renewables like solar or wind power depend on intermittent sources of supply – so what do you do when the demand for energy exceeds the amount of sun or wind available? A new type of flow battery, based on the chemicals plants use to store energy, may provide one answer.
A group of small and inexpensive organic molecules, called quinones, are used to store and transfer energy within plants. Researchers from Harvard University screened the properties of over 10,000 such molecules, and found a good candidate for energy storage in a quinone similar to those found in rhubarbs. The team used this as the basis of a flow battery, which stores energy in the form of chemical fluids.
Unlike solid-state batteries, flow batteries have separate power-conversion hardware and chemical storage components, which determine the peak power capacity and energy storage capacity, respectively. This means that the power-to-energy ratios of flow batteries can be adjusted to suit particular applications, allowing them to store larger amounts of energy than solid-state batteries, and at a lower cost.
However, most flow batteries use valuable metals such as platinum or vanadium in their design, and are therefore expensive to buy. The Harvard team’s research “has the potential to greatly reduce the cost of [flow] batteries,” says Brian Huskinson, author of the paper detailing the breakthrough, adding that this will make them “more appealing for commercial applications, with the ultimate goal of increasing grid reliability and easing the integration of renewables like wind and solar into the grid.”
With such a device, commercial-scale tanks could be used to store energy from solar or wind farms for later use. On a smaller scale, a flow battery the size of a household heater unit could store a day’s worth of energy collected by a solar-panelled roof – potentially enough to power a home from late afternoon to the following morning.
“This is a very exciting development, and it brings much-needed innovation to the flow battery field”, says Yushan Yan, a chemical engineer at the University of Delaware, who notes that the fast kinetics of the quinones leads to a high power density. However, he cautions that the use of bromine in the demonstration battery cell could raise some safety issues.
The Harvard team are now working to improve their battery design, and together with their collaborators, Sustainable Innovations, LLC, hope to develop a horse trailer-sized portable unit capable of storing enough power for a commercial building within the next three years. – Ian Randall
Photo credit: Eliza Grinnell, Harvard School of Engineering and Applied Sciences