Energy harvested from evaporation

In the first evaluation of evaporation as a renewable energy source, researchers at Columbia University find that U.S. lakes and reservoirs could generate 325 gigawatts of power, nearly 70 percent of what the United States currently produces.

Though still limited to experiments in the lab, evaporation-harvested power could in principle be made on demand, day or night, overcoming the intermittency problems plaguing solar and wind energy. The researchers' calculations are outlined in the Sept. issue of Nature Communications.
"We have the technology to harness energy from wind, water and the sun, but evaporation is just as powerful," says the study's senior author Ozgur Sahin, a biophysicist at Columbia. "We can now put a number on its potential."
Evaporation is nature's way of cycling water between land and air. Sahin has previously shown how this basic process can be exploited to do work. One machine developed in his lab, the so-called Evaporation Engine, controls humidity with a shutter that opens and closes, prompting bacterial spores to expand and contract. The spores' contractions are transferred to a generator that makes electricity. The current study was designed to test how much power this process could theoretically produce.
One benefit of evaporation is that it can be generated only when needed. Solar and wind power, by contrast, require batteries to supply power when the sun isn't shining and wind isn't blowing. Batteries are also expensive and require toxic materials to manufacture.
Read more here: https://www.sciencedaily.com/releases/2017/09/170926125154.htm 
Read the original Nature Comm article here:
Ahmet-Hamdi Cavusoglu, Xi Chen, Pierre Gentine, Ozgur Sahin. Potential for natural evaporation as a reliable renewable energy resource. Nature Communications, 2017; 8 (1)
DOI: 10.1038/s41467-017-00581-w