Schooling Fish Offer New Ideas for Wind Farming

The quest to derive energy from wind may soon be getting some help from California Institute of Technology (Caltech) fluid-dynamics expert John Dabiri -- and a school of fish.

As head of Caltech's Biological Propulsion Laboratory, Dabiri studies water- and wind-energy concepts that share the theme of bioinspiration: that is, identifying energy-related processes in biological systems that may provide insight into new approaches to -- in this case -- wind energy.

"I became inspired by observations of schooling fish, and the suggestion that there is constructive hydrodynamic interference between the wakes of neighboring fish," says Dabiri, associate professor of aeronautics and bioengineering at Caltech. "It turns out that many of the same physical principles can be applied to the interaction of vertical-axis wind turbines."

The biggest challenge with current wind farms is lack of space. The horizontal-axis wind turbines most commonly seen -- those with large propellers -- require a substantial amount of land to perform properly. "Propeller-style wind turbines suffer in performance as they come in proximity to one another," says Dabiri.

In the Los Angeles basin, the challenge of finding suitable space for such large wind farms has prevented further progress in the use of wind energy. But with help from the principles supplied by schooling fish, and the use of vertical-axis turbines, that may change.

Vertical turbines -- which are relatively new additions to the wind-energy landscape -- have no propellers; instead, they use a vertical rotor. Because of this, the devices can be placed on smaller plots of land in a denser pattern. Caltech graduate students Robert Whittlesey and Sebastian Liska researched the use of vertical-axis turbines on small plots during a class research project supervised by Dabiri. Their results suggest that there may be substantial benefits to placing vertical-axis turbines in a strategic array, and that some configurations may allow the turbines to work more efficiently as a result of their relationship to others around them -- a concept first triggered by examining schools of fish.

In current wind farms, all of the turbines rotate in the same direction. But while studying the vortices left behind by fish swimming in a school, Dabiri noticed that some vortices rotated clockwise, while others rotated counter-clockwise. Dabiri therefore wants to examine whether alternating the rotation of vertical-axis turbines in close proximity will help improve efficiency. The second observation he made studying fish -- and seen in Whittlesey and Liska's simulation -- was that the vortices formed a "staircase" pattern, which contrasts with current wind farms that place turbines neatly in rows.

Whittlesey and Liska's computer models predicted that the wind energy extracted from a parcel of land using this staggered placement approach would be several times that of conventional wind farms using horizontal-axis turbines. Once they've identified the optimal placement, Dabiri believes it may be possible to produce more than 10 times the amount of energy currently provided by a farm of horizontal turbines. The results are sufficiently compelling that the Caltech group is pursuing a field demonstration of the idea.

Dabiri has purchased two acres of land north of Los Angeles, where he is establishing the Caltech Field Laboratory for Optimized Wind Energy (FLOWE). The pilot program at the site will feature six vertical turbines on mobile platforms.

Dabiri and his team will systematically move the turbines around, testing various configurations to find the most efficient patterns.

"Our goal is to demonstrate a new technology that enables us to extract significantly more wind energy from a given parcel of land than is currently possible using existing methods," says Dabiri. "We want to take advantage of constructive aerodynamic interference between closely spaced vertical-axis wind turbines. Our results can potentially make better use of existing wind farms, allow for wind farms to be located closer to urban centers -- reducing power transmission costs -- and reduce the size of offshore installations."

Three of Dabiri's turbines are being provided in partnership with Windspire Energy. In exchange for the use of the turbines, Dabiri will share his research results with the company. Each Windspire turbine stands approximately 30 feet tall and 4 feet wide, and can generate up to 1.2 kW of power.

"This leading-edge project is a great example of how thinking differently can drive meaningful innovation," says Windspire Energy President and CEO Walt Borland. "We are very excited to be able to work with Dr. Dabiri and Caltech to better leverage the unique attributes of vertical-axis technology in harvesting wind energy."

Three turbines from another manufacturer have been purchased; the six turbines give the pilot facility a total power capacity of 15 kW, enough to power several homes.

"This project is unique in that we are conducting these experiments in real-world conditions, as opposed to on the computer or in a laboratory wind tunnel," says Dabiri. "We have intentionally focused on a field demonstration because this can more easily facilitate a future expansion of the project from basic science research into a power-generating facility. Our ability to make that transition will depend on the results of the pilot program."

The initial phase of the study will attempt to demonstrate which configuration of units will improve power output and performance relative to a horizontal-axis wind turbine farm with a similar sized plot of land.

"In the future, we hope to transition to power-generation experiments in which the generated power can be put to use either locally or via a grid connection," Dabiri says.

The American Recovery and Reinvestment Act provided partial funding for this project.

California Institute of Technology (2010, May 23). Schooling fish offer new ideas for wind farming. ScienceDaily. Retrieved May 24, 2010, from http://www.sciencedaily.com­ /releases/2010/05/100517152532.htm

From Oil Sector to Wind Power

Eying the vast potential for establishing wind farms at sea, companies along Norway's west coast are making the leap from offshore oil to offshore wind power.

Developing offshore wind power could prove just as profitable as petroleum industry projects, and the potential for value creation is enormous.
Statoil and Statkraft, Norway's heavyweight energy companies, recognise this potential and have already secured a key position in Great Britain, where the development of wind power is highly subsidised. The two Norwegian companies, together with the energy companies Scottish and Southern Energy and RWE npower, will develop Dogger Bank, by far the largest British wind power project to date.
West Coast firms at the starting line Other Norwegian companies are also getting in line to compete for contracts for large development projects for offshore wind farms.
More than 40 companies primarily from Hordaland and Rogaland counties have joined the Arena NOW (Norwegian Offshore Wind) network. Every member company has experience in the oil and gas industry; some have already landed their first wind power contracts and completed their first installations.
"This surge toward wind power will bring some profound changes to this region's industrial makeup," says Yngve Aabø, Chairman of Arena NOW.
German wind farm draws on Norwegian expertise The German wind farm Alpha Ventus, located off Germany's northwest coast, has drawn upon Norwegian technology and expertise for the production and installation of wind turbine foundations.
Bergen-based OWEC Tower and Trøndelag-based Aker Solutions Verdal have supplied steel structures for six foundations each. Another Bergen company, NorWind, installed the OWEC foundations.
From powering platforms to power systems for wind farms Troll Power, another Bergen company, currently supplies power to the petroleum industry. Its new company Troll WindPower, together with wind power supplier NorWind, is now gearing up to supply power systems for offshore wind farms. At the Bergen Group Rosenberg shipyard in Stavanger, the first modules for a power station designed exclusively for wind farms will soon be completed.
Troll Power has developed a tool to detect risks in the power grid when various energy producers and users are connected to the grid. This new tool will be very valuable to grid operators and energy companies as more and more wind farms go online.
"It would not have been possible to establish Troll Power and Troll WindPower without funding from the Research Council and Innovation Norway," says Mr Aabø, CEO of both companies as well as chairman of the Arena NOW network board.
Leader in floating wind turbines Sway AS, located south of Bergen, is a worldwide leader in floating wind turbines. The company has developed a floating wind turbine that can be placed anywhere the sea is deeper than 30 metres.
Most of Sway's 20 employees were recruited from the petroleum sector. Indeed, many others from this sector are intrigued by the prospect of applying their offshore expertise to the dynamic field of renewable energy and helping to drive its progress at Sway and similar companies.
Sway is owned by its employees and Statoil, Inocean, Lyse, Statkraft and NorWind. Sway's floating wind turbine project has been receiving funding under the Research Council's RENERGI programme for many years.
New wind turbine technology soon full-scale The engineers at Sway are confident in their windmill design, which unconventionally places the rotor behind the nacelle. As the floating tower leans some 6-8 degrees away from the wind, this downwind design allows the unit to tilt forward -- keeping the blades aligned with the wind's force to capture its maximal energy. Sway collaborates with German wind turbine manufacturer Multibrid, which has specially developed this innovative turbine. The first full-scale Sway windmill is planned for launch in 2011, most likely in Spain.
"Our goal is to harness offshore wind energy without public subsidies some day," says Michael Forland, CFO of Sway. He estimates that this could be the case within a decade.

The Research Council of Norway (2010, April 7). From oil sector to wind power. ScienceDaily. Retrieved April 16, 2010, from http://www.sciencedaily.com­ /releases/2010/03/100329082013.htm

Deep-sea Oil Rigs Inspire Designs For Giant Wind Turbines

An MIT researcher has a vision: Four hundred huge offshore wind turbines are providing onshore customers with enough electricity to power several hundred thousand homes, and nobody standing onshore can see them. The trick? The wind turbines are floating on platforms a hundred miles out to sea, where the winds are strong and steady.

Today's offshore wind turbines usually stand on towers driven deep into the ocean floor. But that arrangement works only in water depths of about 15 meters or less. Proposed installations are therefore typically close enough to shore to arouse strong public opposition.
Paul D. Sclavounos, a professor of mechanical engineering and naval architecture, has spent decades designing and analyzing large floating structures for deep-sea oil and gas exploration. Observing the wind-farm controversies, he thought, "Wait a minute. Why can't we simply take those windmills and put them on floaters and move them farther offshore, where there's plenty of space and lots of wind?"
In 2004, he and his MIT colleagues teamed up with wind-turbine experts from the National Renewable Energy Laboratory (NREL) to integrate a wind turbine with a floater. Their design calls for a tension leg platform (TLP), a system in which long steel cables, or "tethers," connect the corners of the platform to a concrete-block or other mooring system on the ocean floor. The platform and turbine are thus supported not by an expensive tower but by buoyancy. "And you don't pay anything to be buoyant," said Sclavounos.
According to their analyses, the floater-mounted turbines could work in water depths ranging from 30 to 200 meters. In the Northeast, for example, they could be 50 to 150 kilometers from shore. And the turbine atop each platform could be big--an economic advantage in the wind-farm business. The MIT-NREL design assumes a 5.0 megawatt (MW) experimental turbine now being developed by industry. (Onshore units are 1.5 MW, conventional offshore units, 3.6 MW.)
Stable enough for towing
Ocean assembly of the floating turbines would be prohibitively expensive because of their size: the wind tower is fully 90 meters tall, the rotors about 140 meters in diameter. So the researchers designed them to be assembled onshore--probably at a shipyard--and towed out to sea by a tugboat. To keep each platform stable, cylinders inside it are ballasted with concrete and water. Once on site, the platform is hooked to previously installed tethers. Water is pumped out of the cylinders until the entire assembly lifts up in the water, pulling the tethers taut.
The tethers allow the floating platforms to move from side to side but not up and down--a remarkably stable arrangement. According to computer simulations, in hurricane conditions the floating platforms--each about 30 meters in diameter--would shift by one to two meters, and the bottom of the turbine blades would remain well above the peak of even the highest wave. The researchers are hoping to reduce the sideways motion still further by installing specially designed dampers similar to those used to steady the sway of skyscrapers during high winds and earthquakes.
Sclavounos estimates that building and installing his floating support system should cost a third as much as constructing the type of truss tower now planned for deep-water installations. Installing the tethers, the electrical system, and the cable to the shore is standard procedure. Because of the strong offshore winds, the floating turbines should produce up to twice as much electricity per year (per installed megawatt) as wind turbines now in operation. And because the wind turbines are not permanently attached to the ocean floor, they are a movable asset. If a company with 400 wind turbines serving the Boston area needs more power for New York City, it can unhook some of the floating turbines and tow them south.
Encouraged by positive responses from wind, electric power, and oil companies, Sclavounos hopes to install a half-scale prototype south of Cape Cod. "We'd have a little unit sitting out there and...could show that this thing can float and behave the way we're saying it will," he said. "That's clearly the way to get going."
This research was supported by the National Renewable Energy Laboratory.
Adapted from materials provided by Massachusetts Institute Of Technology.

Thermal Conductivity Of Seafloor

The first German offshore wind facility is expected be put into operation sometime in 2009. A total of 12 giant wind turbines out at the North Sea will turn near the isle of Borkum, each one generating 5 megawatts of power, the largest worldwide. The electrical current they will produce will be conveyed over a distance of 45 km past Norderney to the mainland, at a depth of two to three meters buried in the seafloor.

In addition to many other technical challenges making the whole project controversial, a measurement problem regarding the cable needed to be resolved: How could the thermal conductivity of the seafloor be determined accurately enough to be able to predict the later influences of temperature on the buried cable?
The seafloor contains great quantities of pebble gravels which create many inhomogeneities and, naturally water which additionally interferes with any measurement due to convection. After several renowned test institutes had given up in the face of these obstacles , the commissioned engineering company turned to the measurement experts of the Physikalisch-Technische Bundesanstalt (PTB). And they were able to help.
Using a method they had recently developed themselves, they successfully measured the thermal conductivity of several seafloor samples at the required accuracy. The instrument had already proven its worth in in-situ measurements of river sediments of the Spreewald situated near the German town of Lübben. The measuring instrument is all-purpose. A manufacturer will soon be bringing it on the market under licence. First it will be presented from 26 to 28 May 2009 at the Sensor&Test trade fair in Nuremberg at the PTB booth.
Adapted from materials provided by Physikalisch-Technische Bundesanstalt (PTB)