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Utilising evaporating water to generate power

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

Prof. 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 Prof. Sahin and his team in New York are spores of common soil bacteria; these spores expand, much like a muscle, when there is moisture in the atmosphere, and contract in drier conditions.

In 2009, Prof. 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 which can be captured.

Rubber coated with spores

In the case of the device which now sits on his office shelf, Prof. Sahin coated a rubber sheet with spores. By putting a glass of water beside it, the rubber 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 an attached coil and magnet.

To the naked eye, there is nothing happening to the water. But molecules are leaving the surface in the constant process of evaporation. With open bodies of water, such as reservoirs or lakes, these 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, Prof. Sahin and his team then developed other devices using the same principles. An ‘evaporation engine’ sat on the surface of the water and as moisture entered 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 is the ‘moisture mill’ where spores on tapes were placed around a wheel . As the spores start to flex like a muscle, the device starts moving.

Useful in reservoirs

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. Prof. 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 which is 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 compared with other renewable energy sources such as wind and solar, he said. With more funding to expand the research into bigger areas, possibly by using swimming pools, he said that the system could be useable on a large scale in between 10 and 15 years.

More funding needed

“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,” Prof. Sahin said. At present, there are just three people working on the project, he said, a number which needs to increase tenfold to develop it further.

In theory, the volumes of energy which can be produced are similar to solar power, he says. — © Guardian Newspapers Limited, 2015





New device can use energy made by bacteria when it expands and contracts