Flow battery breakthrough can store renewable energy cheaply

With today's battery technology, the dream of relying on renewable energy sources independent of fossil fuels remains impossible. Storing enough energy to supply needs on calm or cloudy days costs too much using today's batteries. A discovery by a team at the Harvard School of Engineering and Applied Science promises new progress in cutting our umbilical cord to to coal and oil.

There are two major problems with the vision of battery storage sufficient to make an all-renewable grid viable. The use of rare earth and other metals with limited supply or geo-political strings attached raises costs and threatens supply. Even more critically, most existing battery technologies link the storage capacity of the battery with the power conversion capacity.

zemlinki!/CC BY 2.0

Think of it like using water through a garden hose. Existing batteries effectively store the water in the hose. To store more water, you need a larger diameter hose, which would then supply the water at an even faster maximum rate. This creates unnecessary costs for scaling up storage while the demand remains constant. The SEAS press release describes the problem in a nutshell:

To store 50 hours of energy from a 1-megawatt power capacity wind turbine (50 megawatt-hours), for example, a possible solution would be to buy traditional batteries with 50 megawatt-hours of energy storage, but they'd come with 50 megawatts of power capacity. Paying for 50 megawatts of power capacity when only 1 megawatt is necessary makes little economic sense.

Fuel cells provide the ability to store unlimited amounts of fuel decoupled from the power conversion hardware capacity, but these rely on precious metals and other metals with limited supply to catalyze the conversion of fuel to energy.

© Eliza Grinnell, SEAS Communications

The mega flow battery announced by the Harvard team decouples storage from supply. The technology stores electricity in quinones, a metal-free organic (carbon-based) molecule similar to the chemicals used by plants and animals to store energy in biological systems. The quinones remain dissolved in water which reduces the flammability risk.

The mega flow quinone battery also uses a glassy carbon electrode and bromine to generate electricity. Bromine derives mostly from concentrated seawater; comparable to chlorine, it has risks but these are not more serious or less manageable than the risks of other technologies (think about the hazards of lithium ion battery technology).

The quinone tested (9,10-anthraquinone-2,7-disulphonic acid or AQDS, as reported in Nature, in case you are interested) exists naturally in rhubarb but can also be synthesized cost effectively. This particular quinone won the screening of over 10,000 quinones in the best-in-batteries category.

With technology like this, one can envision wind or solar farms with tanks on-site to store large quantities of energy-laden quinones capable of being converted to supply several days of power to bridge the intermittent nature of renewable electricity generation.

That makes "flow battery technology" the newest watchword on the green energy beat.

Tags: Alternative Energy | Batteries | Renewable Energy

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