A wind turbine for commercial buildings

A windsail or vertical axis wind turbine is said to generate power on-site. It is also quiet, bird-friendly, likes turbulent winds, and catches the eye, says the developer. A few features some obvious and some less so include:

• It generates electricity on site and safely connects to the building’s electric power system.
• It is quiet. The slow rotation of the sail generates electricity. Rotational speed does not exceed 80 rpm.
• It is bird-friendly. Birds can see its shape and easily avoid collision. It is also friendly to bats and butterflies.
• It likes turbulence. It harvests winds from any direction and can be installed near or on the building it serves.
• It is an eye-catching and customizable with logos, graphics, and color. It projects leadership, sustainability, and a hopeful future.

  Windenergy Corp.
  www.windenergycorp.com

The right turbine and placement produces 10x power increase

The power output of a wind farm of vertical-axis designs can be increased about tenfold simply by placing the turbines so they react with each other, say researchers at the California Institute of Technology led by John Dabiri, Caltech professor of aeronautics and bioengineering, and colleagues during the summer of 2010. They have been conducting a field study at an experimental two-acre wind farm in northern Los Angeles County.

VAWTs are ideal for this experiment, Dabiri says, because they can be positioned close to one another letting them capture nearly all of the energy of the blowing wind and even wind energy above the farm. Having each turbine turn in the opposite direction of its neighbors increases their efficiency, the researchers found, possibly because the opposing spins decrease the drag on each turbine, allowing it to spin faster (Dabiri got the idea for using this type of constructive interference from his studies of schooling fish). A paper describing the results of field tests appears in the July issue of the Journal of Renewable and Sustainable Energy.

Conventional wind farms use horizontal-axis turbines. But despite their improvements, says Dabiri, they are rather inefficient. Individual turbines in them are spaced far apart so the wake generated by one turbine does not interfere with those downwind. The result: “Much of the wind energy that enters a wind farm is never tapped,” says Dabiri.

Turbine designs have trended to larger units on taller towers to capture more of the available wind at heights where it is stronger and steadier. But this brings other challenges, such as higher costs and more complex engineering problems.

The solution, says Dabiri, is to focus on the design of the wind farm, to maximize its energy-collecting efficiency at heights closer to the ground. Winds may blow less energetically at 30 ft. rather than 100 ft., “But the global wind power available at 30 ft is greater than the world’s electricity usage, several times over,” he says. That suggests smaller, less expensive vertical axis turbines arranged in the right way can capture sufficient energy in a less environmentally intrusive manner.

During the summer 2010 field tests, Dabiri and colleagues measured rotational speed and power generated by each of six turbines when placed in a number of different configurations. Tests showed one arrangement in which spacing the turbines four rotor diameters apart nearly eliminated aerodynamic interference between neighboring units. The six VAWTs generated from 21 to 47 W/m² of land. A comparably sized conventional farm generates just 2 to 3 W/m².

In comparison, removing the aerodynamic interference between horizontal axis wind turbines required a spacing of about 20 diameters, more than a mile between the largest wind turbines now in use.

“The next steps are to scale up the field demonstration and to improve on the off-the-shelf wind-turbine designs used for the pilot study,” says Dabiri. During the past summer, Dabiri and colleagues studied a larger array of 18 VAWTs to follow up last year’s field study.

No Shortage of Amusing Wind Turbine Ideas

Arizona State architectural student, identified only as Joe, says his idea is to retrofit horizontal steel structures that currently hold freeway signs with two horizontal-axis wind turbines powered by the turbulence from passing cars. (Joe admits borrowing the turbine design from U.K. based quietrevolution). He figures (without showing figures) that with an average vehicle speed of about 70 mph and an average wind speed of 10 mph, each turbine could annually produce 9,600kWh.

Inventor and consultant Larry Dobson has built a working model of his vertical axis involute spiral drag propulsion wind turbine. He posts a video of it at http://tinyurl.com/larrydobson. He says he has experimented with several designs to find a best one. Dobson says the vertical axis wind turbine is a drag propulsion device with strong lift components that let the rim exceed wind speed, which continually diverts wind mass to work on the sail.  Results from two tests indicate he can increase the low-speed power significantly over a horizontal axis wind turbine, largely because it uses drag from large surface-area vanes instead of just lift propulsion from a thin airfoil-shaped blade.

The Wind Tunnel Footbridge is part modern sculpture, part green technology, and part weird admits Designer Michael Jantzen. He surrounds the bridge with five bladed wheels that spin… like windmills. Each wheel spins in an opposite direction and at varying speeds to make best use of wind direction. Best of all, he says, this entertaining concept bridge could harness the wind that propels it to produce and store energy. Jantzen suggests constructing these at public attractions such as museums and parks, but would like to see them replace skywalks over highways.

::Windpower Engineering::

Vertical-axis turbines starts generating at less than 3 m/s

There are two basic types of wind turbines: vertical and horizontal axis. Each has pros and cons. Horizontal-axis turbines tend to capture more power per square meter of wind, but are noisier, vibrate more, present hazards to birds, require more empty space around them, and must be elevated away from people. Vertical-axis turbines, on the other hand, are quiet and do not need to turn towards the wind to maximize their power output.

Turbines can also be classified as lift turbines and drag designs. Drag turbines simply rotate from the push of the wind. They start easily, but cannot move faster than the push from the wind. Lift turbines use aerodynamic blades to rotate faster than the mere push of the wind would allow, but this class has more difficulty starting.

The Wind Lotus from Leviathan Energy, Los Angeles, is said to have advantages of both. The patent-pending aerodynamic shape is one reason for its good performance. In addition the design uses five blades, whereas almost all lift turbines, whether horizontal or vertical, have three. This translates to more starting power, better balance, and minimal noise.

The aerodynamic design increases wind velocity where it hits the blades letting the turbine produce more power than larger units. The Wind Lotus is said to have a lower cut-in speed than other turbines which increases its cost effectiveness. Cut-in speed is the wind speed at which the turbine starts to produce electricity. The aerodynamic design improves its performance over other turbines so it produces more power. The table presents a few specs.

Vertical axis turbine works well atop office building

One forecast for small scale wind generators (sometimes called microgeneration) has them providing 30 to 40% of all the UK’s electricity needs by 2050. The British Wind Energy Association hints that with price trends for crude oil continuing up, the cost of small scale wind could be competitive with fossil fuels by as early as 2010.
Although the UK has excellent wind resources, where the turbine is located is still crucial to the output expected from it. Ideally, a wind turbine would have no obstructions between it and the prevailing wind direction.
In an urban or built-up environment, some wind turbulence is inevitable unless the turbine is sited well above any surrounding buildings. Most of the time, turbulence from surrounding buildings will affect a wind turbine to some extent. This is the primary reason for opting for a vertical-axis wind turbine, because the design doesn’t require wind from a consistent direction to produce power. A horizontal axis wind turbine, on the other hand, has to physically rotate into the wind every time the direction changes.
U.K.-based quietrevolution says its 5-kW helical design ensures good performance even in turbulent winds. It is also responsible for almost eliminating noise and vibration. At five meters high and three meters diameter, it is compact and easy to integrate. And with just one moving part, maintenance can be limited to an annual inspection. The table includes a few specs: