Is harvesting energy from evaporating water a serious renewable energy prospect?

A recently published study estimates that up to 70 percent of US electricity needs could be met through a newly devised system that harvests power from evaporation. This novel renewable power source uses bacterial spores to generate electricity and can sit on top of lakes and reservoirs.
Back in 2015, Ozgur Sahin and a team of scientists from Columbia University revealed an exciting new potential source of renewable energy. The team had created a way to generate energy from the natural process of evaporation using a certain type of bacterial spore. These spores expand and contract as they absorb evaporating moisture, and this oscillating motion could be harnessed to generate a small amount of power.
The team developed a device that held these spores and to prove the system’s effectiveness created a miniature car that ran on this evaporation energy system. At the time the technology was an interesting concept but one not hugely appropriate for large-scale implementation.
Now Sahin and colleagues have posed an even more expansive thought experiment, publishing a new paper hypothesizing how much energy could be generated if such evaporation power-harvesting technology was implemented across lakes and reservoirs in the United States. The study estimates an enormous 325 gigawatts of power could be generated using the method.
"We have the technology to harness energy from wind, water and the sun, but evaporation is just as powerful," says Sahin. "We can now put a number on its potential."
This massive number, nearly 70 percent of what the US currently produces, is not exactly a realistic proposition. After all, this hypothetical level of power generation requires nearly every large body of water in the country to be covered with the energy-harvesting system. Notwithstanding the general public’s loss of access to these large bodies of water for recreational activities, the effects of this kind of system on weather patterns needs to be seriously considered.
But the paper suggests such an expansive interruption to localized evaporation patterns would have negligible effects on major weather patterns, which are primarily dominated by ocean evaporation.
"Locally, feedback effects will also be small if the dimensions covered by an engine are below 500 km (311 mi)," write the authors. "This is due to the important role of horizontal heat and moisture transport in the atmosphere that couples neighboring regions."
A more practical outcome for the technology comes when the study focuses on hypothetically converting specific locations into evaporation power plants. The E.V. Spence Reservoir in Texas, for example, could generate 178 megawatts annually if its 38-sq km (14.7-sq mi) surface area was completely covered by the system. This power output is more than 50 percent greater than a nearby wind farm.
Of course, if you’ve read this far you are probably wondering how much this all would cost? The study neglects to consider how much rolling out this technology on such a massive scale would cost. While the proof-of-concept paper is more interested in theoretically testing how much power could be generated, this is a reasonably irrelevant figure without a cost attached.
Other environmental implications are also neglected in the paper. Does the process affect the quality of the water, for example?
The search for new, safe, renewable forms of energy is undoubtedly important as we move away from fossil fuels, and the idea of using evaporation as an energy source is certainly an interesting one, but this study shows it is still very much in the theoretical category of renewable power sources for now.