Tuesday, September 11, 2007

Storing wind power for a calm day

One common critique of wind power is it's only available when the wind is blowing. Often hot days have no wind, hence the power isn't available when it's most needed. And wind is gusty, the strongest winds might be happening at times other than when the power is needed. While this point is thrown out to say that wind power is no good, what it means is to use wind power means finding a way to store electricity generated when the wind is strong and releasing it when its needed later.

A strategy that's used in California, that could be used for electricity from wind power, is to pump water uphill. Since electricity rates are low at night there's an economic argument to make that one can use night-time electricity to pump water to an uphill reservoir, and then release that water through hydroelectric facilities during the day when electricity rates are higher. Indeed this does happen in California and probably elsewhere.

Another strategy might be to use excess electricity to electrolyze water and extract hydrogen. Store the hydrogen in a tank, then release it later to generate electricity. This can be done either with fuel cells or by burning in a turbine.

Utility will use batteries to store wind power covers storing the electricity in batteries. American Electric Power is an electric utility operating in Ohio, Virginia, West Virginia, Kentucky, Tennessee, Indiana, Oklohoma, Arkansas, Louisiana, and Texas.

AEP to deploy additional large-scale batteries on distribution grid is their press release. The battery technology uses a sodium sulfur chemistry and goes under the trademark NAS ®. The press release seems to be saying the batteries will be used similarly to a peaker plant, which is a strategy where a "small" natural gas power plant can be fired up during the day, during peak demand times, to handle peak loads, hence the name "peaker". They are also including wind power in their generating network and due to the gusty effects of wind will also see peak generating times. They describe the size of these installations as "1 megawatt" or "11 megawatts" but that is a nonsensical measure for battery packs. "Megawatt" is a measure of current at a given moment, what's important here is how long can the plant sustain that power delivery. Can it only provide 11 megawatts for 1 second? Or over an hour? Or for a full day? Inquiring minds want to know.

The reasoning in the article goes like so:

They can charge at night, when the wind is strong but prices are low, and give the electricity back the next afternoon, when there is hardly any wind but power prices are many times higher, company officials said. That strategy would reduce the amount of power generated from inefficient peak-demand units.

The batteries can also insert energy into the grid during brief voltage drops, reducing the chance of a blackout and stabilizing the grid for all users. They may also delay or eliminate the need for transmission upgrades in some areas, the company said.

This appears to me to match the reasoning of peaker power plants, not wind power. But as I said earlier wind generation has its own peak times which don't necessarily match peak times of customer demand, so this gives the utility some extra flexibility to adopt wind power.

AEP Commissions First U.S. Demonstration of the NAS Battery describes the battery technology, but again does not describe the actual size of the systems they are installing. The page has a picture looking like a relatively small installation you could see on a concrete pad in a parking lot. The battery technology is said to come from Tokyo Electric Power Company (TEPCO) and NGK Insulators, Ltd., (NGK) and elsewhere it says Ford Motors originally discovered the battery chemistry, which makes this yet another example of an American company skipping over developing some technology only to allow foreign companies to exploit it.

Saving wind power for later is another technique developed by General Compression to use a wind turbine to compress air, and release the compressed air through another turbine when electricity is required. They sell these as combined units.

It seems the critical item in all the different strategies for storing wind power, is the cost of the storage system. We're facing the same issue in electric vehicles where the best batteries to store electricity are also expensive.