Finding a site with good wind resources is perhaps the least of the problems developers face as they seek new locations for future wind-power projects. A great deal is now known about wind speeds, directions and patterns across the globe, and although that data is insufficient for detailed planning of wind farms, it does at least provide developers with places on the map that can be stabbed with speculative drawing pins.
Received wisdom is that the best sites have already been snapped up but, as Michael Brower, chief technology officer of renewables consultancy AWS Truepower, points out, talking purely in terms of wind speed this is not strictly true. "There are plenty of good high-wind sites around the world that are just being opened up, or not yet even on the horizon of the wind industry," he says. "Think about the steppes of central Asia, for example. That's virtually undeveloped, as are large parts of South America, such as Patagonia."
Whether it makes financial sense to launch big wind projects on the Patagonian plateau is another matter. Good wind resources have to be balanced against a huge range of geo-economic factors - from site accessibility and the ease with which it can be connected to the grid, to the skills and equipment available locally for construction and maintenance. Overriding all other concerns, of course, is whether the wind power generated at the site can be priced at a level to give developers an acceptable return on their investment. This will vary according to the costs of other forms of energy generation in the region, and the policy mechanisms and support systems (if any) that the host country has in place for wind power. Developers also have to have sufficient confidence in the country's political stability to assume a working life of 20 to 30 years for their projects. That factor alone can extract a number of drawing pins from the maps, whatever the wind charts indicate.
Wind power's need for political and pricing stability, together with the importance of access to sophisticated grids that can make the best use of its variable generation, have meant that wind is an energy-generation source largely for developed countries. That trend has become more pronounced since 2009-10 with the rapid progress in turbine technology designed to optimise energy generation from low wind speeds. Turbines on taller towers with longer blades have enabled developers to build wind projects reasonably close to high-demand centres on sites that were considered unsuitable just a few years earlier. The ability to reach high above the tree tops opened up forested areas in particular.
This has not necessarily made wind planners' work any easier. Predicting the energy production of large turbines on complex sites remains a challenging task, beyond the capability of meteorological masts to deliver, argues Brower. "It's becoming much more important to understand the wind-resource characteristics across the whole plane of the rotor," he says. "That means, with very tall towers and rotors getting to be upwards of 100 metres across, you have to measure winds to heights of at least 150 metres. And that means remote sensing is clearly becoming more and more important."
The new generation of low-wind turbines are colossal machines. Take the Nordex N117/2400, judged the best in the 2.1-3.5MW power range in Windpower Monthly's 2013 Turbine of the Year awards. The standard tower provides a hub height of 91 metres, but that can be extended to 141 metres with the use of a taller, concrete-steel hybrid tower. Its rotor blades are 57 metres in length for a rotor diameter of 117 metres and, despite the use of lightweight composite materials in their construction, weigh nearly 11 tonnes apiece. Performance is impressive: Nordex claims a 40% capacity factor for inland sites with average wind speeds at hub height of 6-6.5m/s.
But that performance comes at a cost. According to the US National Renewable Energy Laboratory (NREL), extending the rotor diameter of a multi-megawatt turbine from 90 metres to 100 metres adds $300,000 (EUR 220,000) to its overall capital costs. Taller towers also add to the upfront bills. NREL calculates this at $100,000 for a 20-metre extension.
Developers also have to look beyond the costs of the hardware to the installation, transport and logistical challenges posed by such large pieces of equipment. Few forested sites come with the roads and clearings to accommodate the turning radius of a truck carrying 60-metre blades, or the cranes required to mount a rotor 140 metres above the ground.
Hard-headed economics may lead the considerations of wind planners, but other factors quickly come into play that influence the design — and the viability — of potential projects. Conflict over airspace with the aviation sector, especially in countries that have very densely populated airspaces, such as the UK, are a particular source of contention.
According to industry body RenewableUK, more than half of UK wind farm applications are subject to objections from the aviation sector, mainly over issues relating to radar interference. RenewableUK is still analysing the latest research for 2013 applications, but preliminary results suggest that 4-5GW of onshore wind and 7-8GW of offshore could be freed from the pipeline if all aviation issues could be immediately resolved.
This is not a new problem. Mindful of the effect the delays were having on investor confidence, the UK's Department of Energy and Climate Change (Decc) started working on research with the country's military and civil aviation authorities and wind developers in 2008, with the aim of applying the findings to real-world solutions.
The fixes vary according to the specific problem, but they include the wind industry and government agreeing to fund a new £20 million (EUR 24.5 million) radar system from Lockheed Martin for Ministry of Defence operations on England's east coast. This led to five offshore projects totalling more than 3GW of capacity getting the green light in 2010. The use of in-fill radar systems, such as C Speed's Lightwave, to enhance smaller airport's radar capabilities, has also helped push projects through the pipeline. Work continues on a full set of technical answers to all affected radars in a long-term programme that RenewableUK estimates will have cost up to £100 million by 2020.
Conflicts with the aviation sector are by no means unique to the UK. Pioneer Green Energy's 150MW Great Bay project in Maryland on the eastern US seaboard was under threat following the state government's decision to delay construction until completion of a study into the possible effects of the turbines on the radar system at the nearby Patuxent River naval base, not expected until July next year. In the meantime, turbine installation was prohibited within a 90-kilometre radius of the base. Pioneer, which had already spent $4 million and four years on the development, threatened to walk away if the delay was enforced. State governor Martin O'Malley vetoed the moratorium bill to allow the project to go ahead. US Navy demands have also forced E.on to relocate the planned position of 29 turbines at its Brush Canyon project in Oregon, and to restrict the height of transmission lines to under 37 metres.
Birds and bats are more likely than aeroplanes to upset the plans of American wind developers. The $1 million fine handed out last November to Duke Energy Renewables over the deaths of 14 golden eagles at two of its wind farms in Wyoming serves as a stark reminder of the consequences of getting it wrong. Wind turbines' reputation as a serial bird killer was established by the world's first wind project cluster at the Altamont Pass in California in the late 1970s and 1980s.
Research since then has shown that fewer, larger turbines sited in accordance with birds' migratory paths reduces the fatality count immensely. The Vasco repowering project in the cluster, which in 2012 replaced 438 old turbines for a total capacity of 80.5MW with 34 2.3MW Siemens units, recorded a 97% decrease in eagle deaths in its first year of operation.
The turbine has yet to shake off its bird-slaughtering image, despite extensive research showing that it is far from the worst offender. According to the American Wind Energy Association (AWEA), wind farms account for fewer than 2% of golden eagle fatalities caused by humans in the US annually — far less than are killed by power lines, vehicle strikes, lead poisoning and illegal shooting. But, as AWEA points out: "The wind industry is doing more than any other known mortality source to find ways to reduce its impact."
American developers also have to be aware of the Indiana bat, listed as an endangered species by the US Fish and Wildlife Service (USFWS). Their numbers have crashed in recent years, largely due to a disease called White-Nose Syndrome. Only a handful are known to have been killed by wind turbines, but their discovery has caused one or two wind farm operators to slow or even cease production at nights. AWEA, together with USFWS and NREL, formed the Bats and Wind Energy Cooperative (BWEC) to research bat interactions with turbines and find ways to reduce their fatality rate.
The wildlife conflicts don't get any easier by moving wind offshore. The discovery of a colony of a rare bird species, the red-throated diver, prompted the Dong Energy-led consortium to scrap its 240MW extension to the London Array project in the UK. Finding larger than anticipated numbers of basking sharks - protected under the UK's Wildlife and Countryside Act - was among the reasons Iberdrola called a halt on its 1.8GW Argyll Array project in the Irish Sea.
Another rare species that has run (albeit slowly) into conflict with the wind industry is the Blanding's turtle. The turtles' presence has delayed the development of Gilead Power's 22.5MW project in the Canadian province of Ontario. In February the Ontario divisional court ruled in favour of the project, but in April allowed a further appeal from a local naturalist group on the grounds that building turbine foundations and access roads would destroy the turtle's natural habitat.
But it seems that the biggest obstacle to successful wind power development comes in human form. Planners have to think beyond the official channels as they steer their projects through the permitting process. They have to be ready to counter the protests and claims of local people opposed to the development.
Research in many countries, including the UK, the US and Australia, invariably shows that the majority of people are broadly in favour of wind power. But that doesn't mean they want it on their own doorsteps. If their visual impact provokes the main opposition, a host of other factors can be wheeled in for support, including the infamous "wind turbine syndrome", the less-than-scientific assertion that living close to a wind farm is bad for your health. The setback areas that are now being enforced on projects in some states of Australia for that reason, for example, have effectively halted wind development.
Some argue that developers largely have themselves to blame for losing ground to anti-wind groups. "More often than not, developers do not go the extra mile to truly engage the local community," Ben Kelahan and Jan Christian Andersen of US consultancy Five Corners Strategies, wrote in a recent article, "Smart Community Engagement: Twelve tips every wind developer should know". "They take a successful outcome for granted based on the additional tax dollars they provide, or assume they can quietly escape the wrath of the opposition by trying to avoid it. Failure to engage consistently costs developers several hundreds of thousands of dollars in construction delays, if not millions in sunk costs because the project never gets off the ground."
AWEA says only one in ten projects as originally conceived by a developer will actually get constructed. Perhaps it's more surprising that any get built at all.