Wind power has been used by humans for thousands of years. Wind mills were introduced at about the same time as water mills in the 13th century. The world's first power producing wind mill was build in 1891 by Paul la Cour, who was a weatherman and aerodynamicist. Today, Danmark is one of the leading countries when it comes to wind power and as early as 1918 they had already installed 3 MW of wind power for the production of electrical power. In Sweden, the interest grew dramatically in connection with the referendum on nuclear power and the oil crisis. Two pilot projects were created with the heelp of government aid in the form of three mills of 3 MW which were placed at Näsudden on Gotland as well as outside Trelleborg in the south of Sweden. However, the latter was dismantled after a few years.
The way today's wind turbines work is basically the same as their predecessors - the wind mill. The wind makes the rotorblades rotate. The blades are directly connected to a generator which then converts the rotation to electricity. Since the wind cannot be stored in the same way as water for water power, wind power can only be exploited when it is windy. The wind turbines produce energy in wind forces between 3 and 25 m/s. Maximum output is given in wind forces between 12 and 15 m/s. Wind turbines can have one, two or three rotorblades. Three-bladed designs are the most common designs today. The blades are attached to a hub which transfers the power to a generator via a shaft and a gear box component. The gearbox component makes sure the generator operates at a suitable rotation speed. There are however wind mills which lack the gearbox component and only use a direct generator. The tower, which carries the machine house and the rotor blades, is firmly attached on a concrete foundation in the ground. Modern wind mills are equipped with two independent braking systems for security. At the top of the tower is an engine that turns the machine house towards the direction of the wind. There are two types of rotorblade designs; Pitch-regulated, which means that the blades rotate around the vertical axis, and Stall-regulated which means that the mounting of the blades is fixed. The set angle of the blades cause them to successively lose their lifting capacity at higher wind speeds which in turn controls the power output so that maximum output is not exceeded.
Wind mills erected today have far reaching automation and need little continuous supervision. With a number of sensors, data is collected regarding wind speed, wind direction, temperature, rotation speed, output etc. Based on this information the mill is controlled automatically.
Wind power today produces 0.6% of the total energy demand of 160 TWh in Sweden which correponds to the average in the world. However, Europe has a slightly higher average of 2.6%. In Denmark the amount of electricity produced by wind power amounts to approximately 20% of the total demand. In northern Germany, this percentage is very high, more than 5%.