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Communications and External Relations
Fishing for answers
OAK RIDGE, Tenn.,
July 26, 2012
Harnessing the power of water currents has never been easy, but predicting how hydrokinetic energy conversion will affect fish is an even tougher task. Scientists at Oak Ridge National Laboratory are trying to do just that.
Underwater turbines are structurally and functionally similar to wind turbines, but they rely on the movement of water instead of air for the generation of electricity. These spinning electric generators could extract enough energy to support small cities, presenting a clean and renewable energy source.
With hydrokinetic turbine projects being planned in the Mississippi River Basin and along the East Coast, Glenn Cada and colleagues in the Environmental Sciences Division have their hands full trying to foresee the potential threats of these turbines to aquatic life.
"Our goal is to make sure that there are no serious environmental issues waiting for this technology," Cada said. "We hope to anticipate any problems so that we can correct them before the turbines get built."
The Department of Energy is concerned with three main issues that might endanger fish: electromagnetic fields that surround the submerged generators and transmission wires, noise from the turbines and the potential of the blades to strike fish.
For the last two years, Cada and his research team have studied the effects of electromagnetic fields on the behavior of freshwater fish. Researchers at DOE's Pacific Northwest National Laboratory are conducting similar studies on saltwater organisms.
"We try to use freshwater animals that may be representative of endangered species because those are rare and need to be protected," Cada said. "We also use fish that we believe may be particularly sensitive to the stress."
When individual turbines transmit electrical currents through wires to the shore, they produce an electromagnetic field that extends along the wire's length. Some researchers fear that this man-made electromagnetic field will interfere with the naturally occurring electromagnetic fields used by fish for both navigation and catching prey.
Through a series of behavioral studies, however, Cada has concluded that most freshwater fish they have studied do not react to the electromagnetic fields.
"We've been testing as many freshwater organisms as we can," Cada said. "But for the most part, there has been very little effect. So it looks like this may not be a problem for the industry, at least in freshwater applications, which is good news."
In the next couple of months, Mark Bevelhimer, one of Cada's colleagues, will tackle the second concern that deals with noise. Using a similar type of behavioral study, Bevelhimer and his team will introduce sounds from the turbines to the fish, tracking their movements using radio-transmitting tags. This will allow the researchers to determine whether the whirring of the blades and the clanking of the generator's metal components alter the natural behavior of fish.
The most challenging potential problem is "strike," which involves the likelihood that fish will be injured by the spinning blades. Cada says that in an ideal situation, the best test is to drop one of these turbines into the Mississippi River and note how many fish get struck. But ORNL does not have that luxury, so it will be difficult to determine how fish will respond.
"These turbine blades rotate relatively slowly, not nearly as fast as a fan blade," Cada said. Many people think that fish can easily avoid the blades that spin at up to 40 revolutions per minute. Others believe that the blades are moving so slowly that even if fish are struck, they won't be seriously injured.
"I doubt that these devices are going to be a serious issue when we are talking about only a few turbines in the rivers or oceans," Cada said. "But if we ever get to the stage where there are 200 or 300 of them in a fairly short stretch of the Mississippi River, then the probability of fish being struck by one of the turbine rotors will increase, and more field monitoring will be necessary."
Because of the size of each turbine, the only way to get significant amounts of power is to install hundreds of individual turbines in the water. Each turbine has a generating capacity of about 35 kilowatts, which is a small amount of power compared to a large nuclear power plant rated at 1,000 megawatts.
While hydrokinetic technologies cannot provide all the energy needed to support heavily populated areas like New York City, they can contribute to the electrical power mix. "If you have a particular area where the environmental conditions are right and you have a need for small amounts of electricity — these are perfect," Cada said. These generators would have no problem supplying the power for small, isolated communities, such as a fishing village in Alaska that requires 5 megawatts of power for operation.
"Our hope is to find out that all three of these concerns will not be an issue," Cada said. "And based on our research so far, it looks like this might be a pretty environmentally safe way to generate electricity."
If that is the case, these machines will be placed in rivers and oceans sooner, providing a renewable source of energy that can begin to harness the estimated 255 million megawatt hours of untapped energy in U.S. water currents every year.