Fossil Fuels and Nuclear Are Intermittent, Too


The fossil fuel power plant industry likes to spread the myth that fossil fuel plants work 24/7, 365 days a year, while solar and wind are intermittent. This is meant to discount the reliability and cost-effectiveness of renewable energy, relative to polluting generators.

The reality is all electric generating plants are intermittent. Coal-fired power plants break down all the time. For example, one huge coal-fired power plant in the Midwest had an availability factor of around 65 percent for a decade after it started up. That means 35 percent of the time, if the utility company wanted to turn this plant on, it couldn’t.

There have been times when coal plants have reduced power production because they couldn’t get enough coal (because it was frozen), and when nuclear plants have throttled down because there wasn’t enough water for cooling.

As Chuck Kutscher noted in his “Tackling Climate Change” column last issue, the utility industry deals with the intermittent nature of fossil fuel plants fairly well and manages to keep the lights on. Utilities maintain about a 15 percent reserve margin of generating sources. That means, if they have a peak demand of 100 megawatts, the utility will have 115 megawatts of generating capacity. They don’t have to own that 115 megawatts of generating capacity. They can enter into agreements with neighboring utilities or merchant power providers to meet their reserve margins.

Solar and wind power plants break down far less often than do coal-fired power plants. For example, many wind turbines have a 95 percent guaranteed availability rate and actually demonstrate a 97 percent or higher availability factor. There isn’t a single coal-fired power plant builder who would offer a guarantee for a 95 percent availability factor.

They would laugh at you if you asked for one. Solar and wind are intermittent because their fuel sources are intermittent. In one sense, this is an easier problem to deal with because one can predict the wind and sun better than one can predict when a high-pressure, high-temperature machine is going to break. The point is, our electric generation sources have always been intermittent, and utilities know how to meet that challenge. They will continue to do so as we transition to a generation system based more and more upon wind and solar.

Robert Ukeiley ( is a lawyer who represents environmental nonprofits in Clean Air Act litigation affecting energy issues.

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