Image: vattenfall via flickr CC

From Joined-up thinking smooths wind power:

When it comes to incorporating more wind power into electricity supply systems, a key worry is the renewable-energy source’s variability with time as wind speeds fluctuate. Now a US team has found that linking up offshore wind turbines spread over a distance of roughly 2,500 km down the eastern seaboard of the US could help smooth out this variability.  “When location of wind farms and transmission are picked to make best use of large-scale meteorological patterns, there is a dramatic improvement in how steady we found the produced electric power to be,” Willett Kempton of the University of Delaware told environmentalresearchweb. “In five years of data, there was never an hour with no power production.”  Not only would such wind farm interconnection reduce variability and remove periods of zero power production, it would also mean that any remaining variations in power output happened more slowly. This would give electricity suppliers more time to ramp up or down alternative sources or transmission links to meet consumer demand.  Together with colleagues at Stony Brook University, US, the Delaware team analysed wind-speed data from eleven meteorological stations off the east coast, stretching from the tip of Florida in the south to Maine in the north. The researchers used this data to estimate power output from turbine arrays for the period 1998 to 2002.

Currently power supply operators use existing systems such as reserve generators and redundant power-line routes to manage the variability in wind-power output; as well as combining remote wind farms via electrical transmission, as discussed here, it’s also possible to employ energy storage, either at a central location or at distributed sites, for example through home heaters or plug-in cars, to smooth supply.  There are plans for wind-turbine arrays with a total power capacity of about 2,500 MW off the eastern coast of the US. This amount, which is roughly equivalent to the output of a large coal or nuclear power plant, is only 0.1% of the available wind resource in the region.  The researchers say that to connect these turbines would require 350 miles of submarine cable, which would add around $1.4 bn, less than 15%, to the estimated $10.5 bn installation costs. This supplement is roughly equivalent to levelling wind output via existing generation, which as a rule of thumb adds 10% of the wind-power cost for an electricity mix containing up to 20% wind power, and more for higher levels of wind power. And it’s much cheaper than smoothing output via energy storage schemes, such as pumping water into higher-level reservoirs – these have capital costs roughly equal to those of generation.

Read the full article on Environmental Research Web.

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Image via physicsworld

From “Fish inspire wind farm configuration”, Edwin Cartlidge

Conventional wind turbines work best when located as far as possible from the destructive vortices of neighbouring turbines. However, a pair of scientists in the US have worked out that the performance of other kinds of turbine actually improves when they are placed close to one another, concluding that wind farms could therefore be made much smaller than they are today.  The familiar propeller-like turbine with a horizontal axis of rotation can convert 50% or more of the energy from the wind that it is exposed to. In a wind farm, however, the wake from one turbine will disturb the air reaching the blades of its neighbours meaning that turbines must be placed far apart.

A less familiar family of turbines have a vertical axis of rotation.  Individually, these vertical-axis turbines are less efficient than the horizontal-axis devices because only part of the turbine can be pushed by the wind at any one time, and they have therefore proven far less popular. However, these turbines have a significant advantage over the horizontal-axis variety – their power output can be increased when they are placed very close to one another.  Now, Robert Whittlesey and John Dabiri of the California Institute of Technology have worked out how best to arrange such closely spaced turbines by drawing on the work of aeronautical engineer Daniel Weihs, who showed in the 1970s how fish save on energy by swimming within schools. Such fish form a series of offset rows, and Weihs found that fish get carried forward by the vortices created by the swimming motion of their two closest companions in the row immediately in front of them. Whittlesey and Dabiri wondered whether the relative spacing of vortices produced by an individual fish might serve as a good template for the arrangement of vertical-axis turbines within a wind farm and set up a computer model to test this idea.

Read the full article by Edwin Cartlidge.

Harvesting the wind
From the window of a TGV hurtling through France, the countryside flattens to a smudge—electrical towers rise and recede in clusters, and tall, lanky wind turbines seem to whip off pirouettes like a young Moira Shearer. Most passengers turn their heads, nodding off on a neighbor or burying their noses in Le Monde, but for a tri­umvirate of young designers, the sight is a view of the future. The passing turbines and pylons augur a new way to harness renewable energy in a country that relies almost entirely on nuclear power. “When we’re riding on the train, we al-ways see pylons, and some turbines too,” Nic­ola Delon says. “We say, ‘Both are here. Can’t we mix them together?’”

Delon, who is 31 and an architect, is the recip­ient of Metropolis’s 2009 Next Generation prize, along with Julien Choppin, also a 31-year-old architect, and Raphaël Ménard, a 34-year-old engineer. Their project, Wind-it, addresses this year’s theme—which beseeched entrants to “Fix Our Energy Addiction”—with the effortless simpli­city of a Pythagorean proof. The team proposes inserting wind turbines into existing electrical towers or, where infrastructure is broken or spare, building new towers that double as wind-power generators, thus introducing a fount of renewable energy into an aspect of civilization that’s as certain as taxes. With three potential sizes, the turbine towers could be integrated nearly anywhere: Lille, France, China’s Sichuan Province, or the streets of New York City.

The full article can be found here.