What is a Wind Farm?

By Thomas HornigoldApr 3 2018

Image Credit: Shutterstock/Angela Rohde

Introduction

Wind power is arguably one of the oldest human technologies. Today, wind power is symbolized in most people’s minds by a big, white, monolithic wind turbine. As we try to move into the post-carbon era, it’s worth remembering that only wind, nuclear, and solar have the same technical potential to provide energy as fossil fuels do today. Perhaps the face of future power generation won’t be huge smokestacks, but fields of wind turbines.

A wind farm is any group of wind turbines that, together, generate a sizeable amount of electricity and act as a power plant. Individual wind turbines were used to generate electricity as far back as 1887. Professor James Blyth of Glasgow constructed a 10m windmill that charged an early battery, which he used to power the lights in his home – although those living in the local town of Marykirk turned him down when he offered to light the main street from this windmill, saying that “electrical power was the work of the devil.” Devil’s work or not, we all rely on it to an increasing extent in the modern world.

Wind Turbines

It took nearly a century from Professor Blyth’s windmill for the modern, industrial-scale harvesting of wind energy to take root. The first modern wind farm was constructed in 1980, in New England. Like so much renewable energy research and development, it was sparked by the oil/energy crisis of 1973, which led the Carter administration to invest in solar and wind power as alternatives to dependence on foreign oil. This wind farm used 20 small wind turbines to generate 0.7 MW of power; they’ve grown in size since then.

Large wind farms can consist of hundreds of turbines spread over a large area of land; the largest wind farm in the world is the Gansu wind farm in China. The aim was to have 20 GW of power capacity installed by 2020; currently, 6.5 GW has been installed – over 7,000 wind turbines. The winds that sweep in over the Gobi desert have proved fertile ground for this new kind of farm.

Various estimates have been made for the global potential for wind power, with the most optimistic suggesting that we could generate many times more electricity than the world currently consumes using a combination of onshore and offshore wind farms. Lu et al, for example, suggested that wind turbines could provide more than 40x current global electricity consumption – and several times our global energy consumption in all forms. However finding the appropriate location for wind farms has proved a difficult challenge.

Naturally, you need wide-open space, although the area between turbines can be used for certain kind of agriculture (typically grazing land.) At the same time, you need an average wind-speed of greater than around 4.5 m/s to be economical – the faster the windspeed, the quicker the project will pay for itself and begin realising profit, so this is an important factor.

Image Credit: Shutterstock/carloscastilla

Consistent windspeeds throughout the year are ideal for the stability of the grid, and it’s usually considered advantageous to build the windfarms at height or in flat regions where the windspeed isn’t disrupted by orography or man-made structures. Some regions can provide particularly good windspeeds – an example is ‘micrositing’, where wind turbines are placed on ridgelines to take advantage of the acceleration of the wind due to the sudden change in topography.

These requirements must be balanced with the need to build the wind farm reasonably close to places that need a power supply, such as cities. If the electricity has to be carried a great distance, even with high-voltage DC cables, the losses can render the power plant less economical than it would be otherwise.

However this consideration has to be balanced with the prospect that some people find the wind turbines unsightly in the countryside – a phenomenon called NIMBYism (Not In My Back Yard.) Typically site selection for wind farms requires consideration of all of these factors, followed by a measurement campaign to narrow down between sites that meteorological data suggests will be useful.

Off-Shore Wind Farms

A more recent phenomenon has been the creation of off-shore wind farms. The first of these was installed in Denmark in 1991, and they have grown in stature since. Opening up the ocean wind resource to exploitation increases the area that wind turbines can cover. It’s also the case that wind can be substantially stronger offshore; driven by the heating of the oceans during the day, that sea breeze can be strongest in the afternoon, when power demand is increased.

Image Credit: Shutterstock/Max Topchii

Typically it’s considered best to locate them just offshore from major coastal settlements, reducing the length of electrical cable and associated losses. Until 2017, most wind farms were fixed-foundation – this required them to be built in shallow waters less than around 30 m in depth, allowing bases for the wind columns to extend down to the sea floor. Renewable energy fans will be interested to watch the progress of the world’s first floating wind farm, which could potentially allow wind potential from the deep ocean to be harnessed.

The floating wind farm, consisting of five 175 m turbines, started supplying power to Scotland in October 2017. Early indications are that it is operating at high capacity, and, with further development, it may prove to be a major player in the coming energy transition.

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