In short, this means that traditional sources of energy are much less economically attractive. In fact, in the United States, it has become cheaper to build and operate an entirely new wind or solar plant than it is to continue operating an existing coal one, according to Gregory Nemet, a University of Wisconsin at Madison professor and author of “How Solar Energy Became Cheap.” Upfront capital-equipment costs have fallen, and once the equipment is installed, wind and sunshine are essentially free; by contrast, coal plants still have to pay for the coal and the people to operate the plants.
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