Wind turbines are large objects, and have been around now for several decades, reaching high into the sky to take advantage of the steady winds. But how tall are they exactly? Most wind turbines are out in the middle of nowhere – out to sea or high atop mountains – so it’s hard to gauge just how tall they actually are. At the same time as they work to make turbine materials greener, by making them recyclable, engineers are also pushing to make turbines even taller. But how tall is too tall? In this article, we’re going to break down how tall turbine towers can get, as well as the factors that dictate their size.
The average height for the tower of a wind turbine is between 60 and 120 meters. In the US, the typical 1.5 MW turbine has a tower height of about 80 meters. The Haliade-X by GE, the world’s largest wind turbine to date, has a tower height of 138 meters.
Why Build Taller Turbines?
Taller wind turbines have access to higher quality winds. At higher altitudes, the wind faces fewer obstacles like trees, hills, and man-made objects like buildings. This makes for a steady wind, allowing the turbines to generate more power. While there isn’t any solid guidance for the ratio between hub height and blade radius, one study found that the ratio fluctuated between 0.5 and 0.7, with larger turbines having larger ratios.
There’s also the concept of aerodynamic drag. Low altitude winds are directly affected by the surface. Moving air creates friction with the ground, significantly slowing down its speed. In addition to obstacles, the heat radiation from the ground also has an effect on air density. Wind speed, air viscosity, and density change dramatically with an increase in altitude. As tall as they are, most wind turbines still don’t escape the surface layer. The turbines would need to be between 200 to 300 meters in height to reach winds that are relatively undisturbed by the surface.
Taller turbines can significantly raise the capacity of a given area. An NREL study found that raising the hub height for 3 MW and 5 MW turbines increased capacity by 10%. In regions with relatively low wind speeds, taller turbines can raise the value of an area with low wind potential.
The height of a tower isn’t chosen solely based on altitude and wind speed. Costs and stability are also taken into account. Although while the upfront costs may be higher for taller turbines, it actually costs less overall. Taller turbines generate more electricity, so fewer are needed to produce a set amount of power. Smaller wind farms with larger turbines cost less to build, install, and maintain. They also take up less space.
Taller wind turbines can also support larger blade spans. More area covered equals more energy captured, which leads to more power. The largest blades made so far are just over 107 meters long and belong to the gargantuan Haliade-X. They have a rotor diameter of 220 meters mounted on a 138 meter tower, and a total height of 248 meters. The blades come within 28 meters of the ground at the bottom of their rotation.
Offshore Wind Turbines
You may have noticed the larger size of offshore wind turbines. They tend to be taller and have larger blades. This is to take advantage of the higher wind energy available at sea. There’s significantly less drag over the ocean as compared to land since the water moves with the wind. That translates into stronger winds and higher energy potential.
Towers for offshore turbines must be built to withstand the rough environment of the ocean. They must weather strong waves, constant salt sprays, and stronger wind speeds than those on land. This is in addition to having to support larger blades and a heavier gearbox. The towers for offshore turbines are still made of steel but are usually treated with an anti-corrosive coating, all to ensure that they last for as long as possible, before requiring replacement.
While offshore turbines tend to be taller than their onshore counterparts, they’re actually even larger than they seem. The turbine must be anchored to the seafloor, making them significantly taller than land-based turbines as a portion of their height is under the waves. The tower is usually anchored to a concrete mast when installed in shallow water. Deepwater turbines have yet to be widely implemented, but engineers are testing underwater lattice-type tripods to give the turbine a wider base to better withstand the strong deepwater currents.
Wind turbines are limited in how tall they can be. The tower is made of steel and can only support so much weight. To double the height of the turbine, the diameter must also be doubled, and four times the amount of material is necessary to ensure stability. After a while, larger turbines are simply unfeasible. The tower must resist the constant forces from the rotation of the blades while supporting the rotor and nacelle. Eventually, the problems of safety, costs, and the laws of physics become a hindrance to building bigger turbines. Turbines like the Haliade-X may be the upper limit of turbine height, at least until stronger materials and sturdier designs are conceived.
Even without the physical constraints, the logistics of building large turbines are difficult. Bigger wind turbines need larger warehouses for manufacturing. Then there’s the transportation. Wind turbines are already difficult to transport. They’re considered an oversized load and require entire ships to get them to their destination. Constructing taller turbines necessitates massive cranes that can lift heavier blades onto taller towers. Once built, maintaining these turbines will require that workers climb higher to reach the equipment, an already dangerous job made even more hazardous. Even if the higher costs are worth the investment, the initial payload may simply be too big of a task.
Aviation regulations can put a limit on how tall a wind turbine can be. In the US, turbines that exceed 500 feet, or about 152 meters, must file a notice with the FAA. This is considered the lowest safe altitude that a pilot is allowed to fly. As turbines get taller, aviation standards are going to come into conflict with the wind industry. Some areas are already off-limits to wind farms, and other areas may see restrictions on tower height.
Engineers are finding ways to build taller wind turbines. The higher altitudes could pay off with higher power capacities and smaller wind farms. But building taller turbines comes with its own set of challenges. The GE Haliade-X, the largest wind turbine to date, may just be pushing the upper limits of turbine size. With a tower height of 138 meters, simply finding cranes able to hoist the blades that high is difficult. But the logistical challenges might be worth it, as the increased power capacity can significantly lower costs in an industry that thrives in economies of scale.
Frequently Asked Questions
The height of a wind turbine tower ranges between 60 and 120 meters. The typical 1.5 MW turbine found in the US is about 80 meters tall.
Taller wind turbines are better equipped to take advantage of the higher wind speeds at high altitudes. They can generate more power and can support larger blades.
The tallest wind turbine built so far is the Haliade-X by GE. It has a tower height of 138 meters. The total height of the turbine is 248 meters, with the rotor included.
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