Greener Storage for Green Energy

Greener Storage for Green Energy

— Renewable energy solutions like wind and solar operate on nature's timetable. When the sun blazes or when the breeze blows, power is plentiful -- but not necessarily at the moments when consumers need it, like on a hot, calm summer night. Storing energy from these intermittent sources has aroused interest, yet practical economics and basic chemistry have limited the wider use of green energy. Storage, to be viable, cannot add much to the price of renewable electricity without making it unacceptably expensive. Fossil fuels remain the world's chief energy source due to their relatively low cost.

To give renewals a fighting chance, a team led by engineers and chemists at Harvard University will use a one-year, $600,000 innovation grant from the U.S. Department of Energy's Advanced Research Projects Agency-Energy (ARPA-E) program to develop a new type of storage battery. The grant may be subject to renewal beyond a year, depending on performance. The award is part of a $130-million funding effort by ARPA-E through its "OPEN 2012" program, designed to support innovative energy technologies.

Called a flow battery, the technology offers the prospect of cost-effective, grid-scale electrical energy storage based on eco-friendly small organic molecules. Because practical implementation is a core driver for the program, the researchers are collaborating with Sustainable Innovations, LLC, a commercial electrochemical system developer.

"Storage of very large amounts of energy is required if we are to generate a major portion of our electricity from intermittent renewable sources such as wind turbines and photovoltaics," says lead investigator Michael Aziz, Gene and Tracy Sykes Professor of Materials and Energy Technologies at the Harvard School of Engineering and Applied Sciences (SEAS). "Currently no cost-effective solution exists to this large-scale storage problem. Flow batteries may make stationary storage viable in the marketplace, and that will enable wind and solar to displace a lot more fossil fuel."

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. Studies indicate that 1 to 2 days (the cycle of day/night) are required for rendering renewables like wind and solar dispatch able through the current electrical grid.

To store 50 hours of energy from a 1-megawatt wind turbine (50 megawatt-hours), for example, a possible solution would be to buy solid-electrode batteries with 50 megawatt-hours of energy storage. The effective result, paying for 50 megawatts of power capacity when only 1 megawatt is necessary, however, makes little economic sense."Not only are existing solid-state batteries impractical for storing intermittent wind and solar energy, but flow batteries currently under development have their own set of limitations," says Aziz. "The chemicals used for storage in flow batteries can be expensive or difficult to maintain."

Aziz believes that using a particular class of small organic molecules may be the key. These molecules, which his team has already been working on, are found in plants and can be synthesized artificially for very low cost. They are also non-toxic and can be stored at room temperature. Furthermore, they cycle very efficiently between the chemical states needed for energy storage.

For further information visit: http://www.sciencedaily.com/releases/2012/11/121129103414.htm