Redox Batteries Will Be a Boon for Grid-Scale Electricity Storage

Recent breakthroughs in redox flow battery technology could see battery storage systems gaining traction in grid-scale deployments. Researchers at Harvard recently discovered a new class of energy-storing molecules that’s being touted as a “game changer” to large scale energy storage systems.

Battery storage technologies could boost efficiencies in both traditional electricity generation and power generated from renewable sources such as solar and wind by allowing systems to store excess power to be tapped when needed. Renewables often suffer reliability issues when the wind stops blowing or a day is overcast. Battery storage systems can help power facilities store excess energy that’s generated from renewable sources during various periods to use when the weather doesn’t allow for enough electricity to be generated to meet demand. For traditional coal-fired power plants, the amount of coal burned must meet rising demand during peak hours. With battery storage systems in place, however, a coal-fired plant could maintain a consistent burn rate through the day and night, and store excess energy to meet peak demands. But the costs associated with large-scale deployments of batteries have proved a lasting obstacle.

Researchers are now developing ways to bring down the costs of redox flow batteries (RFBs) for large scale deployments. The batteries are named for the reduction and oxidation processes that take place within the system. RFBs store electricity in two large tanks filled with fluid that interact with electrodes. RFBs are better suited for use in grid-scale systems because they’re economically scaleable, have low vulnerability for storing energy, and offer more flexibility for power rating than other electrochemical energy storage systems. RFBs are able to decouple the rate of electricity flow from the amount of energy stored, which makes them well suited for long-term energy store applications — RFBs could potentially hold energy from one season to the next, which would be a huge boon for renewable energy installations. According to the industry body Energy Storage, current RFBs can be used for systems between 10 KW to 10 MW, and for duration periods between 2 to 10 hours.

There are more benefits to RFBs: the liquid electrolyte fluid used in RFBs isn’t harmful to the environment and can be cycled back into storage systems infinitely. Researchers at Harvard are experimenting with adding organic electrolytes to the storage fluid which could help to further reduce costs of the batteries and boost energy storage capacity. These scientists have developed a non-corrosive, non-flammable and non-toxic organic chemical mix that uses quinones and the food additive ferrocyanide that can be produced at a very low cost. The new energy-storing molecules are similar to the vitamin B2, which helps store energy in the body. “We designed these molecules to suit the needs of our battery, but really it was nature that hinted at this way to store energy,” said Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, and co-senior author of the research paper.

The largest con to RFBs is the size of the tanks. While the RFB systems scale cheaply, they do require a lot of physical space. RFBs also discharge electricity at a much slower rate than Lithium-ion batteries, which would prove challenging for grid stabilization applications. Instead, RFBs could be part of a larger energy storage system that also utilizes Lithium-ion batteries.
IHS predicts the global energy storage system market will double in 2016 to reach 2.9 GWh, and grid-connected energy storage systems will reach 21 GWh by 2025. Lithium-ion batteries will make up 80% of the global grid-connected energy storage system capacity. Navigant Research predicts installed capacity of RFBs will reach 5.77 GW by 2025 across commercial, industrial and residential deployments.

Here’s a video explaining redox flow batteries:

Feature image: A new class of high-performing organic molecules, inspired by vitamin B2, that can safely store electricity from intermittent energy sources like solar and wind power in flow batteries, like the one above. (Image courtesy of Kaixiang Lin/Harvard University)

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