Urban wind turbines: a case study for the city of London

Energy captured by a wind turbine is limited by the maximum theoretical energy capture from the wind. This is known commonly as the Betz efficiency. This is well documented and limits the maximum power that a turbine can extract from the wind to 59% of the available power in the wind. There are losses to each system from other components, reducing the ability to convert energy. Generators on small wind turbines could convert more than 90% of the energy delivered to them, while in the case of generators installed on bigger turbines, the efficiency get closer to 100%. Some turbines also adjust for wind speed and direction, increasing the energy capture. As with all machines, the number of operating hours is likely to be less than the maximum possible because of maintenance, planned or otherwise. A study of a small turbine over 5 years found that it was available for operation for 93% of the time. It estimates that typically a small turbine will capture 20% or less of the energy in the wind. Also of importance is that small turbines are typically designed to perform best in low wind speeds. At higher speeds, designers can afford to capture less wind energy. Likewise all industrial application, safety is the primary concern: an automatic control system provides to regulate the machine, make it operate at optimal functioning conditions; in the meanwhile, the system looks after safe functioning, stopping the aero generator if wind blows too strong or in case of malfunctioning.