Friday, October 06, 2006

Wind Energy and Utility Systems

One of the favorite whipping boys of anti-wind (and pro-nuclear) groups and individuals today is the claim that "wind cannot substitute for a baseload electricity source" or "wind is not reliable."

I've spent some time in dialogue with one of our in-house experts on these issues (a guy who is talking with utilities, regulators, and transmission system operators on a daily basis) and the following brief discussion is the result.

I know it will be boring and overly technical for some, so apologies in advance for that, but it's gotta be done, otherwise the mis- and disinformation will just continue to spread. Anyone with questions, feel free to contact me at tgray [at] awea [dot] org.


The terms "baseload," "intermediate," and "peaking" (often used to describe various types of power plants) are convenient shorthand, but they are not fully accurate, and in some ways, looking at the utility system as made up of only these three types of systems is an obstacle to understanding how wind fits into electricity generation.

For example, a "baseload" plant is one that is designed to run inexpensively as much of the time as possible at full output, and utilities commonly plan on having approximately the same amount of baseload capacity as their minimum daily demand. The theory here is that such plants can then basically operate around the clock. However,

- All power plants, even baseload plants, require scheduled maintenance and sometimes experience unexpected outages due to equipment failure. No plant runs 100% of the time.

- While wind power plants are not baseload, they can and do displace electricity from baseload plants for some hours of the day if there is enough wind generation on a utility system and the wind is blowing. This is because utilities use the cheapest power available during the day, and since wind power plants use no fuel, they are often the cheapest option available. As wind farms start up during the day, they first displace the most expensive power being generated (peaking, if peaking plants are being used), then the next most expensive (intermediate), and finally baseload.

The issue, therefore, is not whether wind fits neatly into one of the traditional utility pigeonholes (it doesn't), but what happens when wind power plants are added to the utility system, in terms of how many kilowatt-hours are generated by wind at what times of the day and year. That in turn varies from utility to utility, depending on the times when the wind typically blows and how fast it blows (the "profile" of wind speeds), and how well those times match up with the profile of customer demand.

The question of overall system reliability is similarly confused. How can adding an "unreliable" generator like a wind power plant to a utility system INCREASE, not decrease, its reliability? (It does.) It increases reliability because it reduces the probability that, at any given time during the day or year, the utility will be unable to supply the amount of electricity that is needed--and that probability (formally called Loss of Load Probability, or LOLP), is how utilities measure reliability.

In a typical utility system, the utility will need to have enough power plants that are ready to run to meet 115% or 120% of peak projected customer electricity demand. This is because, as stated above, no power plant runs 100% of the time, and so by having more power plants than are normally needed (a "reserve requirement") utilities reduce the probability of failing to meet demand to very low levels. Wind is a variable source of electricity, and a wind plant runs far less of the time at full capacity than fueled power plants. Even so, if there is a 10% or 20% chance that a wind farm will be producing electricity during a peak demand period, it improves the likelihood that a utility will be able to meet demand.

So, returning to our original two questions:

Can wind substitute for a baseload electricity source? Yes, but with reservations. It's probably not the most efficient substitute, because it will take a lot of wind capacity to achieve the same reliability benefit as adding a baseload unit.

Is wind reliable? Yes. In spite of the fact that it's variable, adding wind to a utility system increases that system's overall reliability.

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