Energy harvested from evaporation could power much of US, says study

Energy harvested from evaporation could power much of US, says study
The southern and western United States have the greatest capacity to produce evaporation-generated power from lakes and reservoirs, a new study in Nature Communications finds. Credit: Columbia University

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 could in principle be made on demand, day or night, overcoming the intermittency problems plaguing solar and . 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.

Energy harvested from evaporation could power much of US, says study
Evaporation-harvested energy can cut by half the water lost to natural evaporation, researchers say. Water-strapped cities with growing populations and energy needs could benefit most, including greater Phoenix, served by the above reservoir and irrigation system fed by the Colorado River. Credit: Central Arizona Project
"Evaporation comes with a natural battery," said study lead author, Ahmet-Hamdi Cavusoglu, a graduate student at Columbia. "You can make it your main source of power and draw on solar and wind when they're available." Evaporation technology can also save water. In the study, researchers estimate that half of the water that evaporates naturally from lakes and reservoirs into the atmosphere could be saved during the energy-harvesting process. In their model, that came to 25 trillion gallons a year, or about a fifth of the water Americans consume.

States with growing populations and sunnier weather can best capitalize on evaporation's capacity to generate power and reduce water waste, in part because evaporation packs more energy in warm and dry conditions, the researchers say. Drought-prone California, Nevada and Arizona could benefit most.

The researchers simplified their model in several ways to test evaporation's potential. They limited their calculations to the United States, where weather station data are readily accessible, and excluded prime locations such as farmland, rivers, the Great Lakes, and coastlines, to limit errors associated with modeling more complex interactions. They also made the assumption that technology to harvest energy from evaporation efficiently is fully developed.

Klaus Lackner, a physicist at Arizona State University who was not involved in the study, expressed support for the team's findings. Lackner is developing artificial trees that draw carbon dioxide from the air, in part, by harnessing the power of .

"Evaporation has the potential to do a lot of work," he said. "It's nice to see that drying and wetting cycles can also be used to collect mechanical energy."

The researchers are working to improve the efficiency of their spore-studded materials and hope to eventually test their concept on a lake, reservoir, or even a greenhouse, where the technology could be used to simultaneously make power and limit loss.


Explore further

Renewable energy from evaporating water (w/ Video)

More information: Ahmet-Hamdi Cavusoglu et al, Potential for natural evaporation as a reliable renewable energy resource, Nature Communications (2017). DOI: 10.1038/s41467-017-00581-w
Provided by Columbia University
Citation: Energy harvested from evaporation could power much of US, says study (2017, September 26) retrieved 20 November 2018 from https://techxplore.com/news/2017-09-energy-harvested-evaporation-power.html
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Sep 26, 2017
I would think that condensation would be a good source of energy. It takes a huge amount of energy to evaporate water. When it condenses back into liquid form that energy must be released. If energy from clouds could be captured it would be a great resource.

Sep 26, 2017
If this is about thermal energy, there is a big problem to be solved. If a machine works with some close extreme temperatures, then the efficiency is small. So one would have to evaporate / condense water in such a way as to greatly decrease / increase one temperature with respect to that of the environment.

Practical thermal machines are well approximated by the endoreversible cycle, with thermal efficiency = 1 - sqrt(Low temp. / Hight temp.), with temps in Kelvin.

At a difference of 6 K efficiency is 1%, at 32 K is 5%, at 70 K is 10% for low temp. = 300 K.

Sep 26, 2017
At a difference of 6 K efficiency is 1%, at 32 K is 5%, at 70 K is 10% for low temp. = 300 K.

Where difference = High temp. - Low temp.

Sep 26, 2017
The water that evaporates naturally becomes rain, spreading the water to parts of the earth that are not near lakes. If that water becomes tied up in an evaporation energy generation scheme, then those parts of the earth that are rained on will become drier, perhaps even deserts.

Sep 26, 2017
Crap article, no details about any engineering.
As for Carnot efficiencies, I'll take a 5% efficiency when the Delta T is ubiquitous and abundant over a 70% efficiency that needs infrastructure and a fuel industry. I have worked on low temperature heat engines in the past, the lesson learned is that lower yielding energy generators make you more energy conscious and using the energy needs more efficient applications.
Evaporation pans to create salt which can be used with forward osmosis as a generator have been considered before. But solar ponds are much better at creating a high temperature gradient and heat storage system than evaporation alone.

Sep 26, 2017
Offhand, isn't evaporation "nature' way" of cycling between liquid and vapor? I'm not convinced "land" or "air" are states of matter, though they are each certainly dominated by specific phases.

Sep 26, 2017
I think the nursery fable of the Chinese brother drinking all the water up from the ocean is more practicable than this nonsense.

Sep 26, 2017
This article - https://www.techn...-caveat/ gives some more details on the project. Seems there is a lot to be skeptical about. Wonder if they will ever build a pilot - then could really get some numbers.

Sep 26, 2017
"If energy from clouds could be captured it would be a great resource."

If you can see the cloud, the water content has condensed...

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