A group of Harvard scientists recently hit on a new form of battery that could massively expand the potential for renewable energy use. And the linchpin of the technology is an organic compound nearly identical to one found in — wait for it — rhubarb.
To explain: most of the batteries found in our cars, laptops, smartphones and whatnot rely on chemical solids. And the nature of the technology requires combining the two key parts of the battery — the material that holds the charge and the hardware that converts the charge to electricity — into one complete unit. But there’s another type of battery called a “flow battery,” which uses liquids to store the charge. Those liquids are stored in separate tanks, then pumped into conversion hardware as needed to produce electricity. The upshot is that the charge storage and the electrical conversion are physically decoupled, meaning the only limit to how much charge a flow battery can hold is the size of the tanks.
This comes with several advantages. Flow batteries can be easily scaled up or down for use by large utilities or for individual consumers. They’re rechargeable, the fluids holding the charge can last a very long time, and once they’re used up new tanks can be easily swapped in. The big downside is that the chemical fluids holding the charge use high-cost metals like vanadium or platinum, which can make the batteries uneconomical.
Enter the Harvard team. According to a paper just published in Nature, they successfully built and tested a flow battery using metal-free liquids. Instead, they used an abundant and inexpensive organic (i.e. carbon-based) compound called a quinone. These compounds are often found in green plants, and the specific type of quinone the team settled one is almost identical to one found in rhubarb. The Harvard team’s battery performs just as well as the typical flow batteries that rely on vanadium, and it functions even faster — allowing it to be charged and discharged much more quickly. The quinones are even dissolved in water, reducing fire hazards.
The reason this could such a big deal for renewable energy is that, right now, renewable sources like solar and wind are mostly dependent on when the sun shines and when the wind blows to generate their power. But those times don’t always line up with when most people on the electrical grid are using power. If the excess power can’t be stored and then rereleased when people do need it — and right now, battery technology of that size is hard to come by — the power goes to waste. (Fossil fuel power, by contrast, can be switched on or off in response to demand for electricity.)
But the scalability of the Harvard team’s flow battery means small versions could be built to service either an individual homeowner who has a rooftop solar array, or large versions for a utility’s entire wind farm. And if the rhubarb-based technology pans out, those batteries would be far more cost-effective and marketable.
So far, the Harvard team has successfully run a small version of their battery through about one hundred cycles, while maintaining over 99 percent of the charge capacity. They’ll need to get through thousands of cycles before they know it’s ready for commercial use, and they’ll have to make sure it functions safely and well at much larger sizes.
It’s worth noting the scientists received funding support from the U.S. Department of Energy’s Advanced Research Project Agency–Energy (ARPA-E). That agency was set up in 2007 by Congress and President George W. Bush. But it didn’t receive any funding until 2009, when President Obama’s stimulus bill pumped $400 million into the agency.