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Water evaporation could be a promising source of renewable energy

Water evaporation could be a promising source of renewable energy

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There’s a lot of water to work with

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This device sits on the surface of water and uses evaporation to harness energy. The shutters control how much energy is stored.
This device sits on the surface of water and uses evaporation to harness energy. The shutters control how much energy is stored.
Photo by Ozgur Sahin

Solar and wind power get all the attention, but harvesting energy from evaporation could go a long way toward solving our power problems — at least in theory.

This method of harvesting energy is in very early stages. Unlike solar and wind power, evaporation technology is not commercialized yet and won’t be for a while. So is it worth pursuing further? Scientists wrote a model to figure this out, and predicted that the energy potentially available from evaporation is comparable to that of wind and solar power. The research was published today in the journal Nature Communications.

If we were able to harvest evaporation energy from the existing lakes and reservoirs in the US — excluding the Great Lakes in the Midwest — we could generate 325 gigawatts (2.85 million megawatt hours per year). That’s about 70 percent of the total US electrical energy generation in 2015. Energy from evaporation, unlike solar or wind, is less dependent on the weather. Of course, it’s not likely that we’d be able to use the water from every lake, and the authors do note that this could affect freshwater resources. But the paper suggests that evaporation-based energy could have a big impact.

How do you harvest energy from evaporation? Study author and Columbia University biophysicist Ozgur Sahin first developed the “evaporation engine” in a 2015 paper. Imagine you have a material that changes size when there’s a lot of water inside it. (In Sahin’s case, the material were tiny spores.) The spores absorb water and get bigger. When it’s hot, the water evaporates and the spores shrink.

Now, if you think of the spores as a muscle that contracts and elongates, says Sahin, you can connect it to a generator that produces electricity from motion, and then harvest energy from that process.

The spores are attached to tiny plastic strips, and expand and contract depending on whether it’s humid or dry.
The spores are attached to tiny plastic strips, and expand and contract depending on whether it’s humid or dry.
Photo by Ozgur Sahin

Sahin’s tiny “evaporation engine” sits on the surface of water. As water from the surface enters the device, it changes the shape of the spores, which create electricity. The spores are also connected to shutters that control how much water evaporates. This means that you can control how much energy is generated, and even store and release it over time to create continuous power. Other forms of renewable energy are more dependent on the amount of sun or wind. (Remember the solar eclipse? It disrupted power generated from solar panels.)

The same team also created a mill with spores on it, half in a humid environment and half in a dry environment. When attached to a tiny wheels, the device powered the wheels using evaporation.

This “moisture mill” was attached to a tiny platform with wheels, like a toy car. It powered the tiny car.
This “moisture mill” was attached to a tiny platform with wheels, like a toy car. It powered the tiny car.
Image by Ozgur Sahin

There are a lot of steps before this method can be put to use. The team is working to develop materials that can be manufactured on a large scale, and want to test their engine on a larger body of water, like a pool. But they could one day have a lot of impact — after all, the Earth is 70 percent water.

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