Iron Reconsidered As Long-term Electricity Storage

Researchers gave up on inexpensive iron and chromium as a means for long-term and high-volume energy storage some 40 years ago. Now they've given it another look, and a new solar energy company called EnerVault says it works.

On May 22 near Modesto, CA, EnerVault demonstrated a huge "flow battery" that can hold a megawatt-hour of electricity -- enough to run 10,000 100-watt light bulbs for an hour -- and is among the least expensive ways to store large amounts of energy.

A "flow battery" stores water in two separate tanks. In one tank is water that contains iron, and in the other it contains chromium. When energy is needed, the liquids are mixed in a device called a stack, where they generate electricity.

And in a flow battery, size matters: The bigger the tanks, the more liquids can be stored, and therefore the cheaper the electricity. Both iron and chromium are abundant and inexpensive.

EnerVault explains that iron and chromium are safe, but when they were tested in the 1970s, they had undesirable chemical reactions, including the release of hydrogen, which quickly degraded their ability to store electricity.

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EnerVault CEO Jim Pape said his company has reversed those problems, allowing the batteries to last for more than 20 years.

EnerVault executives said the company already has successfully tested smaller versions of the battery over the past two years, attracting $30 million in financial backing, including a $5 million grant from the U.S. Department of Energy.

The government of California says energy storage is crucial to the state's effort to generate more renewable power. That includes solar and wind energy, but both of those sources vary with the weather.

So last year, the state's public utilities commission directed utilities in the state to invest in energy storage that can hold more than 1.3 billion gigawatts of electricity by 2020. That's enough electricity for nearly 1 million homes.

By Andy Tully of Oilprice.com