From coast to coast, wind towers, technically horizontal axis wind turbines (HAWTs), dot the landscape. They represent a fusion of the windmills first pioneered in Europe in the 13th century and airplane propeller technology.
They have grown into giants that dwarf human scale. After seven centuries of development, HAWT technology may be reaching the end of its usefulness.
This situation developed swiftly. Until the 1990s, the US had no wind farms. Now they produce about 6% of our electricity.
How HAWTs work
Modern wind turbines generate electricity when the wind causes a rotor to spin. The overwhelming majority are HAWTs with three blades.
HAWTs consist of three major parts, the tower, the rotor, and the nacelle. “Horizontal axis” means that the rotor spins around an axis that is parallel to the ground and therefore perpendicular to its tower. Nacelle is the name for the generator, related machinery, and their protective cover. “Related machinery” covers an array of complicated equipment.
- In most HAWTs, the rotor must face into the wind. So the nacelle needs a wind vane to determine wind direction, an anemometer to determine its speed and a yaw drive, pitch drive, and their motors to adjust the position of the rotor.
- The rotor spins too slowly to generate electricity. It must attach to a gear box that increases the rotational speed from about 30-60 revolutions per minute (rpm) to about 1,000-1,800 rpm.
- Wind turbines work effectively and safely within a range of wind speeds. The anemometer transmits wind speed data to a controller within the nacelle that starts the machine when wind speed passes the minimum threshold and applies the brake to stop it when wind speed exceeds about 55 miles per hour.
- All these components require a multitude of computer hardware and software to make them work together.
Why and how HAWTs have become so big
The higher the rotor sits, the stronger and steadier the wind it encounters. Turbines in the earliest wind farms were mounted on lattice towers, much like the windmills frequently seen in the rural landscape since the middle of the nineteenth century.
Once the height of towers reached 60 meters, the lattice construction could no longer bear the weight of the turbine. Manufacturers turned to a tubular steel construction which can grow almost an additional 40 meters before they reach their limit.
HAWT towers taller than 100 meters are desirable because the winds that high are stronger and steadier. A 100-meter tower produces about 12% more electricity than an 80-meter, but some technological and economic obstacles had to be overcome to build any.
Because the force of the wind is higher at that elevation, taller towers must be stiffer. Conventionally, designers simply use more steel. The top 20 meters would be so much more expensive than the bottom 20 meters that a 100-meter steel tower costs way too much to be economically practical. Hybrid towers, with steel on a 40-meter concrete base, provide one solution.
Steel towers are often built in four sections. The heaviest weigh more than 50 tons. The trailers needed to transport each section cost half a million dollars each. It can cost as much at $180 per mile to move them from the factory to the site.
The size of the tower sections requires huge cranes and 32-foot-wide access roads to move them into place.
Rotors, too, have stretched to enormous size. The amount of energy produced increases exponentially with longer turbine blades, and thus the surface area the rotor covers.
Building fewer and larger turbines is more cost-efficient for a wind farm than building more numerous and smaller ones.
In 2012, Siemens built what was billed as the longest wind turbine blade in the world for Denmark’s Østerild test station. According to an article I saw four years ago that has since been taken down, that turbine had already been replaced by an even larger one. A single blade was almost the length of the world’s largest airliner, the Airbus A380.
The rotor, mounted on a 75-meter tower, covered 18,600 square meters, or the size of two and a half soccer fields. The tips of the blades reached speeds of 80 meters per second, or 290 kilometers per hour. Siemens developed special lightweight materials to make the blade weigh 20% less than it would have with conventional construction.
Making HAWT rotors larger and towers higher has had a huge impact on bringing down the cost of wind-generated electricity. But large turbines have a significant disadvantage, as wind conditions at the top and bottom of the rotor’s sweep can be very different. The control algorithms and input from many sensors makes them practical.
Why giant HAWTs are not sustainable
Despite claims of critics with ties to fossil fuel industries, modern wind turbines are dependable and efficient. Competently installed and maintained, they can survive really bad weather.
One wind farm on the Texas coast continued to operate throughout Hurricane Harvey. The ones that shut down during the storm resumed operation three or four days after landfall.
Using current technology, HAWTs cannot withstand the winds of a Category 4 hurricane. Most onshore windfarms are far enough inland not to encounter such strong winds. Offshore windfarms could not survive.
The sheer size of the newest towers and rotors causes environmental problems. Besides the high cost of transporting them, it is often necessary to cut down trees to build wide enough access roads. The loss of trees cancels out some of the environmental benefits of wind-generated electricity.
In addition, the larger the turbines, the farther apart they must be to avoid interfering with each other. HAWT wind farms require large tracts of land, which means they must be far away from the population centers that will use the electricity. That, in turn, requires very long transmission lines—expensive to build, and difficult to operate and maintain.
Gigantic turbines create such an eyesore that the very idea often arouses vociferous opposition to new wind farms.
Faced with a choice between natural scenery and a crowd of gigantic towers and spinning blades, most of the population probably prefers scenery. Relatively few people oppose wind energy in principle. The questions being raised concern the direction of the wind industry. Large wind farms will make a good profit for their owners, but are they really the way to achieve environmental sustainability?
The United States declined to participate in the rush to build a supersonic passenger plane. The French and British had to deal with the fallout from the environmentally destructive and nearly useless Concorde. The competition to build the world’s most gigantic HAWT seems headed in the same direction, with the United States heavily involved.
How gigantic HAWTs can destroy ways of life.
Texas leads all US states in its development of wind power. Wind farms make the most environmental and economic sense in the sparsely populated western part of the state. The closer to population centers, the more controversial they become.
The Horse Hollow Wind Farm, near Abilene, comprises 47,000 acres with 421 HAWTs. Some of them have blades 120 feet long. They destroy the natural beauty of the area. The wind farm operators lease the land, but the land owners often don’t live in the area. The company rolled over residents’ opposition and made no attempt to mitigate the destruction of scenery.
Opponents of a large wind farm off Cape Cod were more successful. Cape Wind was proposed in 2001 and Energy Management, Inc. received a lease from the federal government in 2010. It planned to build as many as 130 turbines offshore in an area surrounded by Cape Cod, Nantucket, and Martha’s Vineyard.
Senator Edward Kennedy, in general a proponent of renewable energy, promptly joined those who tried to block construction of the project. In November 2017, the company finally announced that it had decided to abandon it and terminate the lease.
Cape Wind would have been visibly offensive from popular beaches and hampered the tourism industry. It would also have disrupted the fishing industry.
Environmentalists oppose offshore drilling for oil or natural gas partly because of the damage it does to other industries and the local way of life. Why should offshore wind farms be held to any lower standard?
Therefore, offshore wind farms will have to be built far enough from shore that no one can see them. That means building in deeper water than the technology proposed for Cape Wind can handle.
Will HAWTs that dwarf their surroundings eventually go the way of the supersonic transport?
The inside of a wind turbine / US Department of Energy Office of Energy Efficiency & Renewable Energy Office
What’s holding up tower technology? / Nic Sharpley, Windpower. April 15, 2013
What was once hailed as first U.S. offshore wind farm is no more / Brian Eckhouse and Joe Ryan, Bloomberg. December 2, 2017
Windfall: Wind Energy in America Today / Robert W. Righter. Norman, Oklahoma: University of Oklahoma Press, 2011-Kindle edition
East Somerton wind farm. © Copyright Stephen Craven and licensed for reuse under this Creative Commons Licence
Wind turbine diagram. Public domain from Wikimedia Commons
Wind turbine tower delivery. Photo by Paul Anderson. Public domain from Geograph
Huge wind turbine blade. Photo by Chris English from Wikimedia Commons
Some rights reserved by Dennis Jarvis
Great Yarmouth. © Copyright Chris Downer and licensed for reuse under this Creative Commons Licence