Page - 112 - in Clean Water Using Solar and Wind - Outside the Power Grid

112 Clean Water Using Solar and Wind: Outside the Power Grid China, India, North America and Europe. Unquestionably there is a huge wind power capacity waiting to be utilised. The fundamental properties of a wind turbine power are explained in 9.1. Like solar PV, the wind turbine produces power intermittently. Therefore, the wind capacity factor is important to know, as explained in 9.2. Intermittent production and the need for energy storage is the topic of Chapter 10, while economic and financing aspects for renewable energy are described in Chapter 12. 9.1 BASIC PROPERTIES OF WIND TURBINE POWER The kinetic energy from the wind creates the rotational energy of the wind turbine. Then a generator converts the rotational energy into electric energy. Obviously, the generated power of wind turbines depends on the wind speed. Theoretically, it is proportional to the cube of the wind speed. This means than when the wind speed is doubled, the wind power increases by a factor of eight. If the wind speed is too low, then the turbine does not produce any power and it may also stop producing power if the wind speed is too high. It is also a well-known fact that the wind speed can change within minutes, so the generated power from a single turbine is apparently quite variable. If several turbines are combined in a wind farm, then the variability can be reduced. Today it is common that turbines generate electric power at varying speeds, so the rotor is continuously matched to the wind speed. This will of course utilise the wind power more than if the turbine generated electric power only at a given rated speed. The kinetic energy stored in a flow per unit volume is E v= ⋅ ⋅ 1 2 2ρ where ρ is the density of the air. For a stream flowing through a transversal area S (here it is the area that is swept by the wind turbine) the flow rate is S ⋅ v. The generated mechanical power P is determined When the wind speed doubles the wind power increases eight times. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user