The innovators: US scientists harness the power of evaporating water

A team at Columbia University hope to use the energy produced by bacteria when they expand and contract

A small Lego device on the shelf of professor Ozgur Sahin’s office at Columbia University could open up the possibility of another form of renewable energy, and one that is much cheaper than solar and wind.

Sahin has used the simple gadget to prove that evaporating water can be used to generate power, which could eventually lead to energy being generated from still reservoirs. At the centre of the research by Sahin and his team in New York are spores of common soil bacteria that expand, much like a muscle, when there is moisture in the atmosphere, and contract in drier conditions.

In 2009, Sahin started to investigate whether there was a practical application to this expansion and contraction. By putting thin layers of the spores on plastic tapes and controlling the amount of moisture in the air, they expand and contract very quickly, creating movement on the tapes. By putting a large number of tapes together, they produce an energy force that can be captured.

In the case of the device which now sits on his office shelf, Sahin coated a rubber sheet with spores. By putting a glass of water beside it, the sheet changes its curvature with the moisture in the air, and pushes and pulls on a seesaw mechanism. This motion was then converted into electricity using a coil and magnet.

To the naked eye, there is nothing happening to the water, but molecules leave the surface in a constant process of evaporation. With open bodies of water, such as reservoirs or lakes, they are eventually replenished with rain.

“A device can sit at the interface where water is evaporating. It can pick moisture from the water surface and give it to the dry air and take some energy,” he says.

With that proof that the system could work, Sahib and his team then developed other devices using the same principles. An “evaporation engine” sits on the surface of the water and as moisture enters the device, the spores on plastic tapes curve and open shutters, allowing moisture to escape from the unit. When the shutters close again, the moisture fills the device and the system starts again.

Another device called a “moisture mill” has spore tapes placed around a wheel. As the spores start to flex, the device starts moving.

One of the possible uses for the technique is on reservoirs where there is a substantial amount of evaporation, particularly in drought-affected areas. In Los Angeles, millions of black plastic “shade balls” were placed on the surface of a reservoir to reduce water loss.

Sahin says long sheets of plastic painted with the spores could be stretched across parts of the water and generate power while at the same time reducing the amount of water lost through evaporation.

“What we are envisioning is flexible spore-based materials that float on the surfaces of reservoirs that stretch from one end of the reservoir to the other. Then there is a generator on one end that produces electricity as it expands and contracts over the surface,” he says.

The set-up costs of the evaporation method would be cheaper than other renewable energy sources such as wind and solar, he says. Enough spores to cover a 10m by 10m area would cost less than $1.

With more funding to expand the research into other areas, possibly by using swimming pools, he says the system could be useable on a large scale in between 10 and 15 years.

“We have shown that all of the parts work together in the lab. There could be problems if you go from lab to the real environment, but for that you just need to test it and identify it and you cannot do that until there is more research funding on this,” Sahin says.

At present, there are just three people working on the project, he adds, a number that would need to increase tenfold to develop it further.

In theory, the volume of energy that can be produced is similar to solar power, he says.

Source: The Guardian