Calculating tidal energy turbines' effects on sediments and fish

Dec 13, 2010
Model results of the water speed around a turbine blade. Currents are slower (blue) behind the blade, and faster (red) at the blade's tip. Credit: University of Washington

The emerging tidal-energy industry is spawning another in its shadow: tidal-energy monitoring. Little is known about tidal turbines' environmental effects and environmentalists, regulators and turbine manufacturers all need more data to allow the industry to grow.

Engineers at the University of Washington have developed a set of numerical models, solved by computers, to study how changing water pressure and speed around turbines affects sediment accumulation and fish health. They will present their findings this week at the American Geophysical Union's meeting in San Francisco.

The current numerical models look at windmill-style turbines that operate in fast-moving tidal channels. The turbine blade design creates a low-pressure region on one side of the blade, similar to an airplane wing. A small fish swimming past the turbine will be pulled along with the current and so will avoid hitting the blade, but might experience a sudden change in pressure.

This video is not supported by your browser at this time.
This is a computer simulation of how sediment particles suspended in the water would change as they pass through a tidal turbine. Some particles speed up (turn red) as they pass the turbine, while others slow down (turn yellow) and eventually fall to rest on the ocean floor. Credit: University of Washington

Teymour Javaherchi, a UW mechanical engineering doctoral student, says his model shows these pressure changes would occur in less than 0.2 seconds, which could be too fast for the fish to adapt.

If the pressure change happens too quickly the fish would be unable to control their and, like an inexperienced scuba diver, would either sink to the bottom or float to the surface. During this time the fish would become disoriented and risk being caught by predators. In a worst-case scenario, severe pressure changes could cause internal hemorrhaging and death.

It's too early to say whether tidal turbines could harm fish in this way, Javaherchi said. The existing model uses the blade geometry from a wind turbine.

"The competition between the companies is very tight and they are hesitant to share the designs," Javaherchi said.

The researchers are open to working with any company that wants to use the technique to assess a particular turbine design.

Another set of numerical modeling looked at whether changes in speed of water flow could affect the settling of suspended particles in a tidal channel. Slower water speeds behind the turbine would allow more particles to sink to the bottom rather than being carried along by the current.

Javaherchi's modeling work suggests this is the case, especially for mid-sized particles of about a half-centimeter in diameter, about two-tenths of an inch. This would mean that a rocky bottom near a tidal turbine might become sandier, which could affect marine life.

The UW research differs from most renewable energy calculations that seek to maximize the amount of energy generated.

"We are [also] interested in the amount of energy that can be extracted by the turbines, but we are aware that the limiting factor for the development of these technologies is the perception by the public that they might have a big environmental impact," said Alberto Aliseda, a UW assistant professor of mechanical engineering and Javaherchi's thesis adviser.

As to whether any negative effects discovered for tidal turbines would be preventable, Aliseda said, "Absolutely."

"We need to establish what is the lowest pressure that the animals can sustain and the period of time that they need to adjust," Aliseda said. "The blade can be shaped to minimize this effect."

Aliseda says engineers in the wind-turbine industry are already adapting the UW work to look at interactions between wind turbines and bats, since high-frequency pressure changes are now thought to be responsible for the mysterious deaths of bats caused by .

"Maybe the best turbine is not the one that extracts the most energy, but the one that extracts a reasonable amount of energy and at the same time minimizes the environmental effects," he said.

Explore further: And now, the volcano forecast

Related Stories

Oxford turbines to harvest energy from tides

Sep 10, 2008

Oxford researchers have developed a new tidal turbine which has the potential to harness tidal energy more efficiently and cheaply, using a device which is simpler and more robust and scaleable than current ...

Harnessing tidal energy

Oct 26, 2010

A new company, Kepler Energy Limited, has been formed to develop a tidal turbine which has the potential to harness tidal energy more efficiently and cheaply, using a device which is simpler, more robust and ...

Whale-inspired ocean turbine blades

Nov 28, 2010

Interest in developing alternative energy sources is driving the consideration of a promising technology that uses underwater turbines to convert ocean tidal flow energy into electricity.

Smart wind turbines can predict the wind

Jan 05, 2010

Risø DTU researchers have recently completed the world’s first successful test on a wind turbine with a laser-based anemometer built into the spinner in order to increase electricity generation.

Recommended for you

Tropical Depression 9 forms in Gulf of Mexico

2 hours ago

Tropical Depression Nine formed over the western Bay of Campeche, Gulf of Mexico and is forecast to make a quick landfall on Mexico's Yucatan Peninsula. NOAA's GOES-East Satellite captured the birth of the ...

$58 million effort to study potential new energy source

7 hours ago

A research team led by The University of Texas at Austin has been awarded approximately $58 million to analyze deposits of frozen methane under the Gulf of Mexico that hold enormous potential to increase ...

And now, the volcano forecast

8 hours ago

Scientists are using volcanic gases to understand how volcanoes work, and as the basis of a hazard-warning forecast system.

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

SiBorg
3.7 / 5 (3) Dec 13, 2010
Interesting work, an environmental assessment of the impact of a tidal farm will be an important part of the development process.
Modernmystic
not rated yet Dec 13, 2010
LOL. Even "green" power generation isn't immune to the ecofreakos.