A team of Harvard scientists and engineers has demonstrated a new type of battery that it is believed could fundamentally transform the way electricity is stored on the grid, making power from renewable energy sources such as wind and solar more economical and reliable.
The novel technology was reported in a paper published in Nature on January 9. Research was largely funded under the OPEN 2012 programme by the U.S. Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) to develop the battery and plans to work with ARPA-E to catalyse further technological and market breakthroughs over the next few years.
The paper reports a metal-free flow battery that relies on the electrochemistry of small organic (carbon-based) molecules called quinones, which are similar to molecules that store energy in plants and animals. They are naturally abundant and inexpensive, .
The battery was designed, built, and tested in the laboratory of the Harvard School of Engineering and Applied Sciences. Professor Roy G. Gordon led the work on the synthesis and chemical screening of molecules. Professor Alán Aspuru-Guzik used his pioneering high-throughput molecular screening methods to calculate the properties of more than 10 000 quinone molecules in search of the best candidates for the battery.
Flow batteries store energy in chemical fluids contained in external tanks — as with fuel cells — instead of within the battery container itself. The two main components — the electrochemical conversion hardware through which the fluids are flowed (which sets the peak power capacity), and the chemical storage tanks (which set the energy capacity) — may be independently sized. Thus the amount of energy that can be stored is limited only by the size of the tanks. The design permits larger amounts of energy to be stored at lower cost than with traditional batteries.
By contrast, in solid-electrode batteries, such as those commonly found in cars and mobile devices, the power conversion hardware and energy capacity are packaged together in one unit and cannot be decoupled. Consequently they can maintain peak discharge power for less than an hour before being drained, and are therefore ill suited to store intermittent renewables.
"Our studies indicate that one to two days’ worth of storage is required for making solar and wind dispatchable through the electrical grid," said Aziz.
To store 50 MW hours of energy from a 1 MW power capacity wind turbine, for example, a possible solution would be to buy traditional batteries with 50 MWh of storage, but they’d come with 50 MW of power capacity. Paying for 50 megawatts of power capacity when only 1 MW is necessary makes little economic sense.
For this reason, a growing number of engineers have focused their attention on flow battery technology. But until now, flow batteries have relied on chemicals that are expensive or difficult to maintain, driving up the energy storage costs.
The active components of electrolytes in most flow batteries have been metals. Vanadium is used in the most commercially advanced flow battery technology now in development, but it is very expensive, as is the platinum used as an electrocatalyst in fuel cells.
The new flow battery developed by the Harvard team already performs as well as vanadium flow batteries, with chemicals that are significantly less expensive, and with no precious metal electrocatalyst.
"The whole world of electricity storage has been using metal ions in various charge states but there is a limited number that you can put into solution and use to store energy, and none of them can economically store massive amounts of renewable energy," Gordon said. "With organic molecules, we introduce a vast new set of possibilities. Some of them will be terrible and some will be really good. With these quinones we have the first ones that look really good."
