Friday, December 29, 2006

The Wayward Wind

The front page of yesterday's New York Times Business section featured an article by Matthew Wald about the fickleness of wind as an energy source (it was also in the International Herald Tribune). Click the title of this post for the whole article. Here are some excerpts.
[B]ecause it is unpredictable and often fails to blow when electricity is most needed, wind is not reliable enough to assure supplies for an electric grid that must be prepared to deliver power to everybody who wants it -- even when it is in greatest demand. ...

[P]ower plants that run on coal or gas must "be built along with every megawatt of wind capacity," said William Bojorquez, director of system planning at the Electric Reliability Council of Texas. The reason is that in Texas, and most of the United States, the hottest days are the least windy. ...

Frank P. Prager, managing director of environmental policy at [Xcel Energy, which serves eight states from North Dakota to Texas and says it is the nation’s largest retailer of wind energy], said that the higher the reliance on wind, the more an electricity transmission grid would need to keep conventional generators on standby -- generally low-efficiency plants that run on natural gas and can be started and stopped quickly. ...

Without major advances in ways to store large quantities of electricity or big changes in the way regional power grids are organized, wind may run up against its practical limits sooner than expected. ...

In May, Xcel and the Energy Department announced a research program to use surplus, off-peak electricity from wind to split water molecules into hydrogen and oxygen. The hydrogen could be burned or run through a fuel cell to make electricity when it was needed most. Xcel plans to invest $1.25 million, and the government $750,000. But storage imposes a high cost: about half the energy put into the system is lost.

The Electric Power Research Institute said that existing hydroelectric dams could be used as storage; they can increase and decrease their generation quickly, and each watt generated in a wind machine means water need not be run through the dam’s turbines; it can be kept in storage, ready for use later, when it is most needed. [If the reservoir is already full, however, then the water is run through the dam without generating electricity. --Ed.]

The institute listed another possibility, still in the exploratory stage: using surplus electricity made from wind to pump air, under pressure, into underground caverns. At peak hours, the compressed air could be withdrawn and injected into generators fired by natural gas. Natural-gas turbines usually compress their own air; compression from wind would cut gas consumption by 40 percent, the institute said.

That would help with an important goal, reducing consumption of natural gas, which is increasingly scarce and costly in North America. But not everyone is so sanguine that wind will do that.

Paul Wilkinson, vice president for policy analysis at the American Gas Association, the trade group for the utilities that deliver natural gas, said that wind, while helpful in making more gas available for home heating and industrial use, would still need a gas generator to back it up. And the units used as backup are generally chosen for low purchase price, not efficient use of fuel.

At the American Wind Energy Association, Robert E. Gramlich, the policy director, said that one solution would be to organize control of the electric grid into bigger geographic areas, so that a drop-off in wind in one place would be balanced by an increase somewhere else, reducing the need for conventional backup. That is among several changes the wind industry would like in the electric system; another is easier construction of new power lines, because many of the best wind sites are in prairies or mountain ranges far from where the electricity is needed.

A problem for new power lines is that they would be fully loaded for only some of the year, since the amount of energy that the average wind turbine produces over 12 months is equal to just 30 to 40 percent [actually, 20-30% --Ed.] of the amount that would result from year-round operation at capacity.
wind power, wind energy