From a single machine to a group
A single wind turbine can power a house or a farm. A wind farm is a group of turbines, usually from a few to hundreds, placed together and connected to the electricity grid so that their output goes to many customers. The idea matters because it changed wind from a private solution into part of the public power supply. Grouping turbines also reduces costs, since they share roads, cables, a substation and maintenance crews.
The first wind farms
Utility-scale wind turbines were tried earlier, in Vermont in the 1940s and in Denmark in the 1950s, but these were single machines. Groups of turbines appeared in the late 1970s and early 1980s, after the oil price shocks. The first wind farm is often given as one in New Hampshire in 1980, with 20 small turbines, though such “firsts” depend on how a wind farm is defined and the claim should be read with caution.
California soon became the center of activity. Federal and state policies in the late 1970s and early 1980s, including tax incentives and rules requiring utilities to buy power from small producers, encouraged developers to install thousands of turbines in windy passes such as Altamont, Tehachapi and San Gorgonio. Many early machines were small by today’s standards, rated at tens of kilowatts, and quality was uneven. Some failed, and when the incentives were cut back in the mid-1980s, the market slowed.
Denmark and the cooperative model
Denmark followed a different path. Turbines there were often owned by cooperatives of local residents, and manufacturers refined a sturdy, three-bladed design that suited conditions in the country. A number of Danish machines were exported to California, and the experience from those wind farms helped Danish makers improve. Over time, wind farms spread across Germany, Spain, the United States, India, China and elsewhere, supported by various national policies. Policies differed and changed, and wind development often rose and fell with them.
How a wind farm works
The turbines in a wind farm are spaced apart because each one disturbs the air behind it, leaving a slower, more turbulent wake. Placing them too close reduces the output of those downwind, so developers study wind records and use computer models to choose positions. Cables collect the electricity at a substation, where the voltage is raised for transmission over longer distances. Operators monitor the turbines remotely and use short-term forecasting of wind to predict how much power will be available in the coming hours and days, so that grid managers can plan for the other power plants they need.
Going offshore
The sea offers stronger and steadier winds and more space than crowded land. The first offshore wind farm is generally cited as Vindeby in Denmark, completed in 1991 with 11 turbines of 450 kilowatts each, about 4.95 megawatts in total. Other small projects followed in the Netherlands, Sweden and the United Kingdom, and from the 2000s much larger projects, especially in the North Sea, became common.
Offshore work is harder. Foundations must be driven into the seabed or built as large structures, turbines and blades are installed from specialized ships, and submarine cables carry the power back to shore. Maintenance requires boats or helicopters, and storms can delay repairs. These costs were high at first, but they fell as projects grew in size and experience built up. In deeper water where fixed foundations are impractical, floating designs have been developed. The Hywind Scotland project, which started operating in 2017 with five 6-megawatt turbines, is often described as the first floating wind farm, though similar pilot projects exist.
Challenges and criticism
Wind farms have costs as well as benefits. Their output changes with the weather, so the grid needs other sources, long-distance transmission and, increasingly, energy storage to balance supply and demand. When wind farms generate more than the grid can take, operators may have to curtail them. Good wind sites are often far from cities, so new power lines are needed, which can be slow and controversial.
There are local concerns as well, including views, noise, effects on birds and bats, and impacts on marine life and fishing grounds offshore. Studies and mitigation efforts continue, and views about the balance of benefits and costs vary between communities. In debates about electricity, wind farms are often compared with solar farms, which have different strengths: solar produces in daytime, and wind often produces at night or in winter, so the two can complement each other.
Scale and reliability
Wind farms reached large scale because of repeated small improvements: taller towers, longer blades, better controls and cheaper batteries on the grid, such as lithium-ion batteries used to smooth short-term swings. A large wind farm may have a peak capacity similar to a conventional power plant or even a nuclear reactor, but it produces that peak only part of the time, and its average output is lower than its rated capacity. Comparing the two requires looking at annual energy produced and not just the size on paper.