From Harvard, a Cheaper Storage Battery
The findings, which were published on Wednesday in the journal Nature, come as utilities are under pressure to overcome one of the major shortcomings of renewable energy: how to make the electricity available even when the sun is not shining or the wind is not blowing.
California recently became the first state to order utilities to install storage.
The breakthrough came in the type of materials used to store the energy. The Harvard researchers reported using a carbon-based molecule found in crude oil and other substances as the material to hold the electric charge. Most battery chemistry in use today uses metals, including the familiar nickel metal-hydride and lithium-ion, which are more costly.
Each of the carbon-based molecules holds two units of electrical charge, compared with one unit in most batteries in commercial use now, meaning that a battery could store twice as much energy in a given volume.
“These are really cool preliminary results,” said Cheryl Martin, acting director of the Energy Department’s Advanced Research Projects Agency-Energy, which makes grants to develop energy technologies that are novel and risky but offer big rewards.
Officials at that agency said that the carbon-based molecule used at Harvard, called a quinone, was only one of many similar molecules and some of the others might prove even more effective.
“They’re really uncovering the tip of the iceberg,” said John Lemmon, the program manager for the battery project. “That’s the breakthrough.”
Arpa-e gave the Harvard team $590,000 under a one-year contract that is now being completed. The agency is discussing a three-year, $3.75 million contract extension.
The Harvard team’s results so far are at a tiny scale. Team members say that in another three years, they might produce a prototype the size of a trailer that could be towed to a house with a rooftop solar array and store daytime production for nighttime use. But commercial success would require further improvements in the process.
The design is for a “flow battery,” which resembles an ordinary battery but has a material that can accept charged particles when absorbing electricity and give them back later. In this case the material is a liquid pumped into external tanks, so enormous amounts of energy can be stored. Flow batteries are already in commercial use but they are far too expensive for use in anything but specialized applications.
The authors of the Nature paper predict that their battery could be used to store bulk amounts of energy produced from intermittent sources, like wind and sun.
But a challenge is cost. One basic unit of battery storage capacity is the kilowatt-hour, the amount of energy needed to move an electric car about three miles. A kilowatt-hour sells at retail for about 11 cents. Currently, advanced batteries cost about $400 per kilowatt-hour stored; the Energy Department has a goal of cutting that to $100. The battery is supposed to last through 10,000 cycles of charging and discharging.
According to the Nature paper, the quinones needed to store 1 kilowatt-hour cost about $30. Reaching $100 per kilowatt-hour of storage would require cutting the cost of other key components, too, notably the material used to aid the flow of electrons into and out of the quinones.