Technology

How to design a wind farm

 By Nicholas Newman

For investors, developers and operators of wind farms, considerable effort and costs are expended in finding a suitable site, gaining planning approval, purchasing its components and supervising its construction and commissioning…

This feature looks at some of the issues involved in getting a commercial onshore wind farm fully commissioned and serving the grid.

Getting started

The essential ingredients for a successful project include capital, a favorable site, expert assessment and planning approval. To get any such project off the ground, major wind farm developers usually employ specialist engineering designers and consultants to deal with the regulatory, environmental, operational and legal issues. Wind developers can also buy off-the-shelf schemes that have already completed all the regulatory, planning and design stages from specialist companies.

Wind speed is everything

The best locations for strong, reliable winds lie in coastal areas, the tops of rounded hills, open plains or gaps in mountains. As this wind speed map indicates, the best locations for wind turbines are concentrated in the Alps, the Apennines, and Scandinavian Mountain Ranges and in coastal areas.

In selecting a potential area or site, the wind developer’s engineering consultants will initially view wind maps produced by government agencies, such as the Met Office in the UK, the Department of Energy in the US and the European Centre for Medium-Range Weather Forecasts. Having narrowed the field down to one area, a feasibility study using software tools such as Windnavigator and GNV DL’s WindFarmer to analyze topography, weather conditions and aerodynamics can help to optimize the very best location within the chosen area.
Next, developers can begin a series of wind power feasibility studies, testing the project as well as support installations for estimated cost and financial returns according to scale and local feed-in-tariff rates (if available). If the project proves viable on a risk and return basis, the developers can move forward and prepare a planning application that will include specifications of the site, wind speeds, proposed physical infrastructure, access, communications and grid access. In addition, any application will incorporate a decommissioning plan, detailing financial provision and how the installations will be dismantled, refurbished or replaced.

Commercial viability

In essence, developers will calculate how much energy their proposed site can produce at a given price at a given range of turbine numbers and sizes. For example, a typical grid-scale wind turbine costs between £1 million to £2 million per megawatt (MW) of nameplate capacity installed. However, most turbines installed today are bigger and produce 2 MW and cost roughly £3-£4 million each installed. The larger and the more turbines a site has, the greater the benefit from economies of scale.
Typically, turbines account for 75% of the cost of a typical onshore wind farm; grid connection for 12%, civil works 8% and the remaining 5% for miscellaneous expenses. Another critical consideration is the investment’s internal rate of return, which depends on the size and number of wind turbines as well as forecast wind speed. This can range from a low of 2% to a high of 15%.

Wind farm design

In the 1990s, a typical wind tower stood 20 meters high, its blades spanned about 17 meters and it produced around 75 kilowatts of electricity. Today’s towers are more than 100 meters tall, their blades span 126 meters and they can produce 7.5 MW of electricity, enough to power 2,330 homes.
Current wind towers manufactured by Denmark’s Vestas, America’s General Electric and Spain’s Siemens Gamesa are soon to be surpassed by 11 MW colossi with hubs 125 meters above ground level and blades spanning 190 meter. Calculations of returns will take into account that wind turbines rarely run at full capacity since their energy generation is weather-dependent.

Wind farm construction

Large and heavy wind turbines require bigger foundations and cost more to install. But no matter what size of turbine or their numbers, all must be connected to transformers, a communication network and substations. Performance is monitored by a supervisory control and data acquisition (SCADA) information system. Choice of turbines, placement and associated infrastructure are best overseen by specialist engineers in relation to available finance and energy goals.
It can take just a few months to over a year to assemble a wind farm depending on location, number and size of turbines and distance from the grid. For instance, the Den Brook Wind Farm in Devon, England needed 7.5km of site roads, crane hardstanding and reinforced concrete foundations for nine 2 MW Vestas wind turbines. That was in addition to high voltage power and a SCADA system, cabling and offsite highway improvement works that included a 150-meter section of new road.

wind-farm-planning-research-commissioning
Today's towers are more than 100 meters tall, their blades span 126 meters (Dennis Schroeder, Wikimedia)

The logistics of transporting the components of a wind farm can be daunting. A typical wind turbine is comprised of 8,000 weighty components. For example, General Electrics’ 1.5 MW turbine model has a nacelle that weighs more than 56 tons, a blade assembly that weighs more than 36 tons and a tower itself that ranges from 71 to 164 tons in total. The corresponding weight for the Vestas V90 is 267 tons in total; the Gamesa G87 comes in at 334 tons.
In addition to the increasing weight is the height. The blade tips of these models can scythe the air at a height of two-thirds that of New York City’s Empire State Building. As a result, specialist transporting and construction equipment have been developed.

Commissioning

The construction and installation phase of a wind farm is typically followed by a six-month commissioning period that involves connecting the power cables to the transformer, which, in turn transmits power to the main grid. A series of electrical and structural tests are performed to ensure the site is ready for commercial operation.
The ultimate arrival of a wind farm is the product of multiple actors and numerous stages that must satisfy an abundance of public, environmental and regulatory requirements while at the same time ensuring commercial viability for investors and operators.

READ MORE: The technology behind the turbines by Peter Ward

about the author
Nicholas Newman
Freelance energy journalist and copywriter who regularly writes for AFRELEC, Economist, Energy World, EER, Petroleum Review, PGJ, E&P, Oil Review Africa, Oil Review Middle East. Shale Gas Guide. https://nicholasnewman.contently.com/