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Evaporation as a renewable energy source is more sustainable than most sources. A new study shows that, if it can be scaled up at a practical cost, it could provide two-thirds of the electricity used in the United States.
Obviously changing liquids to gasses involves the absorption of energy. Water has an unusually high specific latent heat, meaning a high amount of energy required to cause a particular amount to change state. Consequently, it normally represents an energy sink, not a source.
Usually, it would take a long time for the environment to change sufficiently for anything useful to come of this, but the Columbian biophysicist Dr Ozgur Sahin placed his tapes inside a container part filled with water. Some were attached to a shutter. When sunlight evaporated some of the water ina container, the air became humid, stretching the tape and opening the shutter. Outside air caused the humidity to fall, which in turn contracted the tapes, closing the shutter. Even after some of the energy produced was used to control the shutters, enough was left to drive miniature cars or power a small light.
If the engines were placed on water bodies like lakes and reservoirs across America, they could produce 15 Watts per square meter in the right circumstances, and 325 gigawatts nationally, even without tapping the Great Lakes. This equals 69 percent of the electricity America now consumes.
Unfortunately these machines would be expensive, but there would be benefits as well. Somewhat ironically, the machines reduce the rate of evaporation, preserving fresh water in dry areas – exactly the places where the evaporation is fastest, and possibly help paying for the system.
Most importantly, because evaporation is powered by sunlight and wind, so there will be a continuous flow of energy even on still nights, although it will slow down. Consequently, a grid powered by evaporation would need less battery storage than one depending on solar or wind.
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