To supply the extra juice, utilities turn on inefficient single-cycle gas turbines, which turn 25% of the fuel's energy into electricity, as opposed to 45% for combined-cycle plants that use turbine exhaust to make steam to run a second generator.

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Legge notes that newer fossil fuel plants use the heat that was once wasted to turn an extra steam turbine, a process known as combined cycle.

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Combined-cycle gas turbines, which use hot exhaust gases from one turbine to generate steam to turn a second one, can transform 6, 800 Btu of gas into a kilowatt-hour of electricity, enough to light one lightbulb for ten hours.

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