March 2016

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Blowing In The Wind

Wind speed is a critical feature of wind resources, because the energy in wind is proportional to wind speed.
Jim Sinopoli
Jim Sinopoli PE,

Managing Principal,
Smart Buildings LLC

Contributing Editor

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WindmillThe earliest use of wind power, probably about 10 centuries ago, was the sail boat. Ancient sailors came to understand the power of wind. Around 500 AD windmills were created to convert wind power into mechanical energy.  The windmills liberated people from some manual labor and allowed them to pump and store water and mill grain from their crops by turning stones.

Today’s wind power is generated by modern wind turbines, a somewhat updated version of a windmill. Wind power is considered very clean and a major renewable energy source. Wind power does not generate carbon emissions, pollutants or consume water. The wind turbines convert the wind into electricity; the blades are connected to an electro-magnetic generator that produces electricity when the blades spin. A typical small wind turbine may have several blades that are assembled atop a steel tube-shaped tower. Larger wind turbines may be over 300 feet and service a large development or campus. Multiple wind turbines in a location is called a wind farm.

There are some downsides for wind power. The largest issue is that wind speeds can vary throughout the day and year. However wind power may be used in conjunction with other electric power sources to provide a reliable supply; this could include a connection to a utility grid, the use of other renewable sources such as solar and power storage.

Can wind power be used in buildings? Yes, but there are many questions and serious concerns. Tall buildings are the best candidates because wind speed increases with height, but the wind flow is very turbulent on a tall building; wind turbines work better with laminar (smoothly or in regular paths) wind flow.

If a turbine is installed on a building it’s likely to be small, resulting in minimal energy production.  In addition, noise, stresses and vibration are all serious concerns which are created by the turbine which can be transmitted to the building structure. There are other issues with land use, noise produced by the rotor blades, aesthetic impacts, and birds and bats having been killed (avian/bat mortality) by flying into the rotors and obtaining insurance.

Some manufacturers are using wind velocities from the building parapet but the wind flow is very narrow thus minimizing energy production. One could install a wind turbine on a rooftop, although experts suggest that a wind turbine be elevated at least 30 feet within anything within 500 feet. In addition, rooftops with turbines would have to be quite sizable in order to be cost effective. Overall, the idea of a significant turbine on a building generally would have a very long ROI, and provide numerous risks and challenges.

A commercial wind project requires about 60 to 70 acres of land per megawatt (MW), primarily to facilitate and protect wind flow. A small amount of the land is for equipment, access roads and infrastructure such as conduit, cable, connectivity and  substations. The rest is a buffer zone to preserve wind flow.

Some farmers lease their farmland to a “wind farm” to provide another source of income. They can continue to farm the land although wind agreements can create complex legal and financial issues related to the land use. Wind-power leases often last 25-50 years. A frequent fear of landowners is that the developer or contractor of the wind farm will default or dissolve and the landowner will be left with large inoperable equipment on the property.

Wind Turbines

In order for a wind turbine to work efficiently, wind speeds usually must be above 12 to 14 miles per hour to generate electricity. The turbines usually produce about 50 to 300 kilowatts of electricity each. Once electricity is produced made by the turbine the electricity from the entire wind farm is collected and sent through a transformer. There the voltage is increased to send it long distances over high transmission power lines.

Most modern wind turbines are the horizontal-axis variety, like the traditional farm windmills used for pumping water. The vertical-axis design, is like an eggbeater-style called the Darrieus model, named after its French inventor.

Wind turbines are available in a variety of sizes. The largest machine has blades that span more than the length of a football field, stands 20 building stories, and produces enough electricity to power 1,400 homes. A small home-sized wind machine has rotors between 8 and 25 feet in diameter and stands upwards of 30 feet and can supply the power needs of an all-electric home. Utility-scale turbines range in size from 50 to 750 kilowatts. Single small turbines are used for homes, telecommunication equipment or water pumping.

 Wind turbine

Wind energy is very plentiful in many parts of the United States. Good wind resources have an average annual wind speed of at least 13 miles per hour. Wind speed is a critical feature of wind resources, because the energy in wind is proportional to wind speed.

Cost and Economic Issues

Over the last five years, the cost of solar panels has been lower as the solar panels become more efficient. Solar power can now produce 60% more power for the same money spent on wind turbines obviously effecting the wind power market. The result is that the value of wind turbines has contracted. This market change has ended the U.S. Department of Energy “Residential Small Wind Turbines”. The cost of wind power has also been higher than conventional electricity generation cost, with a much slower return on investment. Although once the wind turbines are constructed, the cost for ongoing operations and maintenance is fairly low.

Reliable ControlsUSA wind power topped 4 percent of the U.S. power grid in 2014 for the first time. In two states, Iowa and South Dakota, wind power now exceeds 25 percent of total electricity production. The United States is recognized as a world leader for wind energy production, primarily thanks to a massive capital infusion of more than $120 billion in the last 15 years via federal and state subsides, tax incentives and grants, that distort the real cost of wind power, with many foreign companies being eligible for the subsides. The tax credit for wind is $0.023/kWh.

It is interesting that a few years back, Warren Buffett a famous investment guru, and one of the richest and most respected businessmen in the world, once told an audience in Omaha, Nebraska. "For example, on wind energy, we get a tax credit if we build a lot of wind farms. That's the only reason to build them. They don't make sense without the tax credit."

Wind Energy Worldwide

The worldwide market for wind energy is robust. Now the global wind energy market has seen 44 percent year-on-year growth, with a total of 369,553 MW of operating wind capacity. 45% of new wind power installations in 2014 were in China, which had 110,000,000 homes powered by wind energy by the end of 2014 (total capacity 114,609 MW) (source: The Economist, 1 August 2015). In 2014, the United States represented 17.8% of the world's installed wind.  Twenty four countries have more than 1,000 MW of wind power installed across the world; 11 countries have installed more than 5,000 MW.


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