Wind farm

A wind farm is a collection of wind turbines within a region used to generate electricity. Wind farms may be very large, covering areas of hundreds of square miles. They can also be offshore, located in a body of water.

Asia and Europe lead the world's electricity generation by means of wind, with an installed capacity of 141 000 MW and 134 000 MW, respectively. China makes up over 80% of the installed capacity of Asia and contains some of the world's largest wind farms, the largest being the Gansu Wind Farm, with a small portion of it seen in Figure 1.

The capacity factor of wind farms is relatively low however, for many it is around 20% over a full year. This means that only 20% of the installed capacity is used on average, due to the intermittency of wind. This can be compared to the capacity factor of a coal-fired power plant or a nuclear power plant, both of which typically achieve 90% of their capacity year-round.

Figure 1. A small portion of the Gansu Wind Farm in northwestern China, which has a total capacity of over 6000 MW.

Location

Wind farms require a fairly consistent wind flow, travelling at just the right speed (not too slow, yet not too fast). Therefore it is important to analyze the prevailing winds in a given region, in order to determine the ideal spots to place a wind farm. Other factors taken into consideration include relative proximity to structures like buildings and houses, along with possible environmental impacts of building the farm. There are many guidelines in place to accommodate the building of a wind farm.

Once a location is selected, the placing of wind turbines is important in order to maximize the amount of power received from the wind. Turbines must be spaced about 3-10 rotor diameters apart (about 180-600 metres for a wind farm using 60 meter diameter turbines). This spacing is made as compromise - compactness of a wind farm would reduce the land costs, however put them too close and the wind received by turbines in the back will be moving too slow to spin them, known as shadowing.

Power Output and Costs

The power a turbine is capable of producing has increased drastically since the 1990s, from 100 kW to over 20 000 kW. The cost of turbines has also decreased by about a factor of 3, meaning the building of turbines is much more practical today - it currently costs around $1000 per kW of rated capacity. Because of these reasons, there has been a vast boom in wind farm construction globally in the past decade: from 40 000 MW in 2004 to 370 000 MW in 2014, nearly a tenfold increase.

A wind farm is connected to the electrical grid just like any other power plant, where a transformer is used to step-up voltages of the electricity in order to reduce energy losses. These transformers are often housed within a turbine tower, and the electricity from each turbine is connected to a single point via underground power lines.