Professors David Kwok and Larry Kostiuk squeezed a syringe of water through a two-centimetre wide glass disc cut by 480,000 holes, or "microchannels". When electrodes were attached at each end they were delighted to find they had generated just enough power to light a small bulb.
By itself this is not a new energy source. Some source of energy must be used to make the water flow.
Thanks to a phenomenon called the electric double layer, when water flows through these 10-micron-diameter-wide channels, a positive charge is created at one end of the block and a negative charge at the other - just like a conventional battery.
They held a reservoir of water 30 centimetres above the array and allowed it to flow through the disc under hydrostatic pressure, generating a current of 1500 nanoamps in the process.
The research team led by Professor Daniel Kwok and Professor Larry Kostiuk, of the University of Alberta, Edmonton, Canada, claim they have created a new source of clean non-polluting electric power with a variety of possible uses, ranging from powering small electronic devices to contributing to a national power grid.
"The applications in electronics and microelectronic devices are very exciting," says Kostiuk. "This technology could provide a new power source for devices such as mobile phones or calculators which could be charged up by pumping water to high pressure."
Their proposal to use their device as a battery really amounts to using highly pressurized water as the medium for storing energy. But that sounds impractical. The casing that holds the water would have to be strong enough to hold it under fairly high pressure. The water and the case would both add mass. Plus, the case has to have an incredibly strong valve that can open and close to let the highly pressurized water out as necessary. Fuel cells powered by a liquid hydrocarbon fuel seem like they'd have a better energy to mass ratio. Both compressed air and compressed fluids are being explored as energy storage methods in cars. But for something as lightweight as a cellphone compression of water has to compete against fuel cells and, perhaps further into the future, lithium polymer batteries.
And might it one day power everything? "You'd need a really big area, like a coastal region," said Dr Kostiuk. "But then again, I guess, those are available, aren't they?" For a clean, free form of electricity, the answer must surely be yes.
One problem with using ocean water to generate electricity is that the water would have to be filtered before passing into the microchannels. But large scale manufacture of nanodevices might eventually provide the ability to use this approach to make devices that could generate electricity from waves or tide flow.
There is also the prediction of 1964 CMU professor Fletcher Osterle that this method of generating electricity will turn out to be very inefficient.
"Probably the reason no one carried on Osterle's work is that he concludes the efficiency can never be better than .04 percent. We haven't done much better than that so far, but we do think that we can do much better — we have much better technologies today, like [microelectromechanical systems] than they did in the 1960s," said Kostiuk.
Water can already flow thru turbines at dams in order to generate electricity. Though turbines today are big things it will probably eventually be possible to make microelectromechanical systems (MEMS) turbines. Therefore MEMS microchannels are not the only imaginable approach for the use of MEMS devices to generate electricity from flowing water. MEMS turbines might turn out to be a more efficient than MEMS microchannels as a way to harness very small water flows.
|Share |||Randall Parker, 2003 October 24 11:31 AM Energy Electric Generators|