Onshore
with 118m-long blades and a rotor diameter of 242m will also debut in 2022, and the Global Wind Energy Council (GWEC) says there’s still a long way to go. By 2030, the GWEC’s latest report predicts, the industry could be looking at 20MW offshore wind turbines with a rotor diameter of more than 245m. While wind energy’s story started on land, offshore turbines have been able to grow much larger than their onshore counterparts in recent years. At sea, there are fewer transportation, logistical and regulatory issues and no nearby residents worried about visual or sound pollution in their backyards. Yet, as wind energy has become more cost competitive – with feed-in tariffs switching to auctions and wind power increasingly having to vie for customers with the likes of solar PV – onshore turbines are increasing in size faster than ever before. As Daniel Laird, director of the National Wind
Technology Center (NWTC) at the US government’s National Renewable Energy Laboratory (NREL), explains, this trend is not just out of a love for larger turbines. “The higher you go, the better the wind resource. Larger turbines, especially on taller towers, allow you to access higher wind speeds. They can also be more cost-effective because you have fewer turbine foundations, fewer roads within the wind plant, fewer crane lifts and so on. This means the resulting wind plant has fewer moving parts. And while these fewer moving parts are larger and more difficult to handle, thus far larger turbines have resulted in lower cost per megawatt hour.” Feng Zhao, head of strategy and market intelligence at the Global Wind Energy Council, (GWEC), says this increasing cost pressure has led turbine OEMs to release new products at a startling rate. “If you look at the Q1 and Q2 auction results in China, for example, the majority of the models are in the 4.X class, but at the same time many OEMs are in the process of launching 6.X onshore turbines,” he notes.
Transportation challenges Zhao and Laird are keen to stress that it’s not technological constraints that have prevented onshore turbines reaching the size of offshore machines; the physical challenges are mainly transport related. Larger turbines require extensive road surveys, road improvements and land acquisitions or blade lifters. Sometimes, motorways must be blocked entirely to transport blades. There’s even a limit to transporting them by rail because of standards governing the curvature of the tracks. Aviation is another factor that needs to be considered; a wind farm can’t be too close to a civilian or military air base or airport. For example, the turbines at RWE Renewable’s Alcamo II wind farm in Italy required a custom- designed bottom section for their towers, simply so they could pass under a bridge. The company says it
World Wind Technology /
www.worldwind-technology.com
is continuously working with its suppliers on new tower and foundation concepts and on solutions to simplify transport and assembly, as well as operation and maintenance to overcome these challenges – and it’s not alone.
“As well as modular or segmented approaches, operators are looking at on-site manufacturing. Is there any way to bring in raw materials and make these very large structures right at the site where they’re going to be deployed?” Laird says. Manufacturers are also looking at lighter materials and new installation approaches that reduce the need for the largest cranes.
Social acceptance However, it won’t be technological limitations or even logistical challenges that decide how tall turbines can go. In developed countries, social acceptance is one of the biggest barriers the onshore wind energy faces, with court cases frequently hitting the headlines. One of the most recent, in Australia, could become a landmark legal battle. While the operator says it’s taken measures to mitigate noise, the plaintiffs are claiming damages and aggravated damages, saying they suffered sleep deprivation, loss of income and decreased property values. They are also seeking an injunction to have the turbines turned off under certain conditions, particularly at night. “In [more] developed countries, people living in rural areas are generally well educated, they know how to use the law to protect themselves,” Zhao says, adding that it’s important to remember it’s a very different story in the developing world, including China. “In China, the majority of turbines have been installed in the north-east or north-west, where the population density is much lower than Europe,” he says. “In poorer developing countries, people tend to think these ‘monsters’ can help with local jobs and bring electricity. Normally, the utility companies who create the projects help them build libraries, schools and so on, so they see them in a different way.”
Due to fewer
transportation, logistical and regulatory barriers, offshore turbines have grown at a pace that has far outstripped their onshore counterparts.
14MW Total power capacity of GE’s Haliade-X offshore turbine prototype, based in Rotterdam, the Netherlands, which began production in 2021. GE
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