WHAT'S NEXT: Drip, Drip, Zap: Electrical Current From Flowing Water
January 1, 2004 By IAN AUSTEN
N.Y. Times
MOST people are familiar with how water can be used to make electricity. Allow it to flow downhill past the blades of a turbine, turning them as it rushes by. Attach the turbine to a generator, and power is generated - hydroelectric power, the kind produced by the megawatt at dams around the world.
But there is another, far less familiar way of generating electricity from the movement of water. Dripping it through microscopic channels - the kind found by the hundreds of thousands in a standard ceramic laboratory filter, say - creates a buildup of positive and negative charges. Tap into these charges with electrodes, and current will flow.
Researchers at the University of Alberta in Canada have made such an electrical generator, inserting a filter into the bottom of a beaker, attaching two coils of wire to the filter to serve as electrodes, and filling the beaker with water.
Unfortunately, the amount of electricity produced by this "electrokinetic" method is extremely small - it won't do much more than nudge the needle of an extremely sensitive voltage meter. But the researchers say the method holds promise and may someday be used to power small electronic devices. If the materials can be successfully scaled up to giant proportions, they say, it might even be used to build power plants free of both pollution and moving parts.
Larry W. Kostiuk, a professor of mechanical engineering at the university and the co-author of a recent paper on the water generator, said the process would never overtake conventional ways of making electricity, including electrochemical batteries. But he added, "We find it exciting that we have revived an area of science that's been forgotten."
Edmonton, site of the University of Alberta campus, is better known for its links to the oil and gas industry than for research on alternative sources of energy. Until recently Dr. Kostiuk's research in his department was devoted to studying flares used at oil wells to burn surplus gases.
But after Dr. Kostiuk agreed during a sabbatical to become the chairman of the mechanical engineering department, he realized that he had one shortcoming for his new post. "I was a bit of a lab rat," he said. "I wasn't the most social of people. So when I came back I thought I had to find out what everybody was doing in the department."
Dr. Kostiuk began stopping by the offices of other faculty members, asking them to explain their work. A particularly long session unfolded with Daniel Y. Kwok, an assistant professor who studies the interaction between materials at the molecular level as part of his research into nanotechnology. Like other researchers in that field, he measures voltage changes caused by the interaction of liquids with solids.
To Dr. Kwok, such measurements were mostly a way to study the interactions, not experiments in generating electricity. But Dr. Kostiuk was interested in the electrical characteristics of the interaction.
"If you draw current, does it kill the whole system? Does it start strong but drop off rapidly?" Dr. Kostiuk recalled asking. "The more I asked Daniel these and other questions, the more uncertain he was about what the voltage characteristics would be."
In an effort to address those questions, Dr. Kwok had a graduate student search through scientific papers. When the student came up empty-handed, the filter-in-the-beaker experiment was born. "It was a really, really bad experiment," Dr. Kostiuk said. "I'm not sure the best way to build electrodes is by just coiling up a few inches of wire."
But the experiment did show that the water passing through the pores generated a current. As has long been known, the movement of water past a solid like the filter causes ions on the filter's surface to become negatively charged, while adjacent ions in the water are positively charged. The experiment revealed that the tiny channels of the ceramic filter - it had about 450,000 - align the ions to create a negative end and a positive end, allowing a current to flow.
Despite the crudeness of their materials (Dr. Kostiuk said the filter used in the experiment was chosen only because it was at hand), the researchers found that several factors affected the electricity that emerged from their no-moving-parts generator. In particular, the type of water used made a significant difference.
Distilled water, which has relatively few ions, created higher voltages but very little current in comparison with Edmonton's tap water. Salt water made lower voltages but higher current. Perhaps more important, the experiment suggested that the easiest way to create more power is simply to run more water through more microchannels like the openings in the filter.
After their paper - whose authors also included two graduate students, Jun Yang and Fuzhi Lu - appeared in the November issue of The Journal of Micromechanics and Microengineering, Dr. Kostiuk became aware that the concept of using water and tiny channels to create electricity had been proposed in 1964 by J. Fletcher Osterle, a professor of mechanical engineering at Carnegie Mellon University.
Dr. Osterle raised the idea in a paper that dealt mostly with an effect that is the opposite of the one proposed by the Alberta team: how, by applying electricity, the electrokinetic effect could be used to make water flow.
While electrokinetic pumps that move liquids without any moving parts are now in common use for testing drugs, the study of electrokinetic generation seems to have all but vanished.
Although Dr. Kostiuk cautions that much research remains to be done, he suggested that electrokinetic generation on a small scale might someday be used to power micro-electro-mechanical systems, or MEMS, microscopic machines that are fabricated by using silicon chip technologies.
At the other extreme, he said it might be possible to dribble huge quantities of water - perhaps at a treatment plant - through an enormous porous surface to create significant amounts of power. The low efficiency of the current beaker generator, however, would have to be vastly improved to make either use possible.
Ernest F. Hasselbrink Jr., an assistant professor of mechanical engineering at the University of Michigan who has long studied electrokinetic pumping, recently turned his attention to using the effect for power generation. While he thinks it has potential for powering small objects, he said the extremely high efficiency of dynamos will probably doom any efforts to create electrokinetic power plants.
"I can't think of any situation where you have a large amount of water and you can't install a turbine," Dr. Hasselbrink said.
But Dr. Kostiuk said there was a good precedent for novel forms of power generation that ultimately overcome initial skepticism and shortcomings: solar panels. "Photovoltaics were a curiosity with amazingly poor efficiency until the U.S. space program needed them," he said.