Harvard's flow batteries keep solar and wind power constant

Harvard scientists have developed a rechargeable battery that could help solve the problem of intermittent energy production from solar and wind sources.

These sources are dependent on environmental factors, such as sunlight and air currents, which results in an inconsistent power flow.

The new “flow battery" utilises widely available compounds that are non-toxic, non-flammable and are capable of storing excess electricity which can be used during periods of low energy production.

Solar and wind are currently hindered by their inconsistency and rely on other means of energy generation, such as fossil fuels, as a fall-back option for when they are not producing.

The flow battery solution is touted as both safe and cost-effective for residential and commercial use.

"This is chemistry I'd be happy to put in my basement," says Michael J. Aziz, Harvard professor and principal investigator on the project.

"The non-toxicity and cheap, abundant materials placed in water solution mean that it's safe - it can't catch on fire - and that's huge when you're storing large amounts of electrical energy anywhere near people."

Unlike solid-electrode batteries, flow batteries store energy in liquids contained in external tanks, similar to fuel cells.

The tanks (which set the energy capacity), as well as the electrochemical conversion hardware through which the fluids are pumped (which sets peak power capacity), can be sized independently.

Since the amount of energy that can be stored can be arbitrarily increased by scaling up only the size of the tanks, larger amounts of energy can be stored at lower cost than traditional battery systems.

This new battery chemistry was discovered by post-doctoral fellow Michael Marshak and graduate student Kaixiang Lin working together with co-lead author Roy Gordon, a materials and chemistry professor at Harvard.

"We combined a common organic dye with an inexpensive food additive to increase our battery voltage by about 50 per cent over our previous materials," says Gordon. The findings "deliver the first high-performance, non-flammable, non-toxic, non-corrosive and low-cost chemicals for flow batteries."

The active components of electrolytes in most flow battery designs have been metal ions, such as vanadium dissolved in acid.

The metals can be expensive, corrosive, tricky to handle and kinetically sluggish, leading to inefficiencies. However, the new design uses organic compounds instead which are safer and abundant in nature.

Harvard believes the technology holds the potential to provide scalable grid-level storage solutions to utilities and has licensed it to a European company.

American electric car manufacturer Tesla Motors unveiled a similar battery system in May designed to store energy when rates are cheap for use during expensive peak times.

Although conceptually similar, the flow batteries have a number of advantages over the Tesla system, such as the cost and length of time it can maintain peak discharge power compared to lithium batteries.

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