Fact Check: Backup Power

From Eric Garretson of Lake Forest, Calif., comes a letter to the Orange County Register that includes this passage:

Wind power is a viable source to a point, but there is a problem with wind because sometimes it stops blowing. What do you do then? You need a 100 percent source of energy backup with coal, gas or nuclear source to make up the difference when the wind turbines are off-line.

This is true of every power plant. Sometimes it is out of service for repairs or maintenance, and other power plants are used to supply customer demand.

More broadly:

- Wind power is variable, but so is customer demand for electricity. It varies throughout the day, and utility system operators turn power plants on or off as needed to balance supply and demand. Wind power can supply 20% or more of the total electricity on a system without adding significantly to normal variability.

- Wind power is variable, and therefore is not an efficient way to meet peak electricity demand. The following very simplified example cases are designed to illustrate this:

Case 1: You have 1,000 MW of load and 1,000 MW of conventional generation. You add 200 MW of wind. You don’t need any additional conventional generation.

Case 2: You have 1,400 MW of load and 1,000 MW of conventional generation. You add 200 MW of wind. You still need 400 MW (roughly) of conventional generation. Since in Case 1, we know that wind can be added without the need for additional “backup,” the reason you need 400 MW of conventional generation is actually to meet peak loads.

In both cases, adding 200 MW of wind reduces fuel combustion and greenhouse gas emissions—addressing two of the most serious problems with our current electricity supply system (fuel price spikes and global warming). For example, adding 200 MW of wind to the average U.S. utility mix results in a reduction in emissions of 380,000 tons of carbon dioxide annually, equivalent to taking 58,000 vehicles off the road. Looking through the other end of the telescope, we could say: "It's fine to add conventional generators to meet peak load, but you still need wind power to protect against fuel price spikes and reduce global warming pollution."

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Caveats:

Case 1: Depending on the fuel mix of the system, additional conventional generation might be required. A system with heavy reliance on nuclear and, to a lesser extent, coal would not have much “flexibility” and might need more quick-response hydro or gas generators to deal with wind’s variability.

Case 2: Adding 200 MW of wind does make it slightly easier to meet peak load, so a few megawatts less than 400 (perhaps as little as 350) of conventional generation might be needed to balance the system.

Regards,
Tom