Answer: evaporating water
A new study published today in Nature Communications examines the potential of open bodies of water in the continental U.S. (excluding the Great Lakes) for generating power through natural evaporation. The results estimate that upward of 325 gigawatts — or 87 percent of the power currently generated worldwide by nuclear power plants — could be produced per year.
Unfortunately the study did not examine any environmental or economic effects of evaporation farming, as the materials and technology required are still in the hypothetical stage of development. Among the primary concerns are potential effects on recreation and weather, since the farms could be eyesores on the water, and would theoretically prevent almost half of the evaporated water from entering the atmosphere. However, all that water returning to the surface could provide more water to areas currently lacking, like Southern California.
“These are very important issues, but we don’t know enough about the technology to make these judgments. The present study is only one piece of the puzzle,” Columbia University’s Ozgur Sahin, lead author of the study, told Gizmodo. “The technology is not sufficiently developed to assess how it might affect the local environment.”