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Steve Graham

Steve Graham photo courtesy of Steve GrahamSteve Graham is an award-winning freelance Web and magazine writer living in a Fort Collins, Colorado, neighborhood that will soon produce all of its own energy. He is a former newspaper reporter, editor and designer. He has worked for an alternative weekly and community newspapers in Colorado, and a large daily newspaper in California. Find links to some of his other writing at his Grahamophone blog.

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Beyond Hot Air: Are Gravel Batteries the Answer to Storing Wind Energy?
Wednesday, 05 May 2010 00:00  |  Written by Steve Graham | Blog Entry

Offshore Wind Power photo by Phault“The Simpsons” TV show recently nailed it on renewable energy. Everyone’s favorite yellow family bought a wind turbine and unplugged from the grid. All was well until the wind stopped blowing and Homer suddenly realized that windmills themselves don’t store energy. Too bad Homer didn’t put Professor Frink, the animated series’ brainy but socially awkward scientist, on the case.

We need some more good minds cracking the energy-storage conundrum. Thankfully, there are already some creative and possibly lucrative ideas in the works for storing wind-generated electricity for when the wind isn't blowing.

About six months ago, I wrote about Panasonic’s plan to sell what amounts to a huge cellphone battery—a 1.5 kWh lithium-ion cell—for this purpose. There have been several exciting advances since then on the large-scale energy-storage front.

First, Japan jumped so hard on the large lithium-ion bandwagon that it's now in the driver’s seat. Sharp invested $5.5 million in Eliiy Power, which recently started mass-producing big lithium-ion batteries. It can make 200,000 batteries per year, each having about 60 times more storage capacity than a cellphone battery.

The company has started selling sets of the batteries to governments and corporations for emergency backup power systems. In two years, it plans to open a larger adjacent factory that can produce one million batteries per year, providing sufficient economies of scale to sell inexpensive batteries for either electric cars or solar storage for homeowners.

Meanwhile, a team of Cambridge engineers has unveiled a fascinating new electric-storage concept based on heating and cooling gravel.

The system has two silos filled with gravel. When the wind is blowing, a portion of the generated electricity is used to pump compressed and heated argon gas into the first silo. In turn, the gas heats gravel to 500°C (932°F).

Once the gravel is all hot and bothered, the argon is pushed into the second silo and allowed to expand to its natural state. This cools the other pile of gravel to -160°C (-256°F). The storage medium is essentially the temperature differential between the two silos. Cycling the gas between them generates electricity when needed.

The system is a distant relative of large-scale compressed-air systems, which have been used in European cities since 1870. In one of their many forms, they use power to compress air or gas in an underground cavern. In the case of a wind power plant, the air is later released to power a turbine when the wind is not blowing.

However, the gravel-battery developers claim the system is cheaper and more efficient than either underground compressed gas or large-scale hydroelectric storage. A good illustration of this assertion involves the biggest electric-storage facility in the world, a pumped-storage dam in Virginia. Two reservoirs there store 30 gigawatts of power while covering 820 square acres. A set of silos could reach the same capacity in about three acres, according to researchers.

The gravel-battery company, which is considered one of England’s top green-energy companies, is apparently talking with a utility and some major investors. If gravel batteries live up to their hype, they may prove to be a very profitable investment, not to mention highly useful in promoting wind energy.

If only Homer Simpson had a couple of gravel silos in his backyard.

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