Modern wind turbines use the wind's lift forces to turn aerodynamic blades that turn a rotor which creates electricity.
Wind energy
In the UK we have 40% of Europe's total wind energy. But it's still largely untapped and only 0.5% of our electricity requirements are currently generated by wind power.
Wind power is proportional to the cube of the wind's speed, so relatively minor increases in speed result in large changes in potential output. Individual turbines vary in size and power output from a few hundred watts to two or three megawatts (as a guide, a typical domestic system would be 2.5 - 6 kilowatts, depending on the location and size of the home).
Uses range from very small turbines supplying energy for battery charging systems (e.g. on boats or in homes), to turbines grouped on wind farms supplying electricity to the grid.
Small scale wind and your home
Wind speed increases with height so it's best to have the turbine high on a mast or tower. Generally speaking the ideal siting is a smooth-top hill with a flat, clear exposure, free from excessive turbulence and obstructions such as large trees, houses or other buildings.
Wind speed is one of the most important factors influencing the output of a wind turbine. Wind speed is affected by many factors including height above the ground, presence of obstructions such as trees, houses or other buildings that might disrupt the wind speed and cause turbulence. We recommend that, if you are considering a domestic building mounted installation and electricity generation is your main motivation, then you only consider a wind turbine under the following circumstances:
- The local annual average windspeed is no less than 5 m/s. To check the approximate figure for your location click here.
- There are no significant nearby obstacles such as buildings, trees or hills that are likely to reduce the windspeed or increase turbulence
It is recommended that you ask an experienced installer (or the product manufacturer) what reassurances they can provide you in support of any performance claims they make. This is especially important for small wind turbines, due to the variability in local wind conditions. For some newer wind turbines, particularly those designed for mounting on buildings, there may not be (or only limited) independent long-term performance data verifying performance claims.
Planning issues such as visual impact, noise and conservation issues also have to be considered. System installation normally requires permission from the local authority.
Stand-alone or grid-connected system?
Small-scale wind power is particularly suitable for remote off-grid locations where conventional methods of supply are expensive or impractical. Most small wind turbines generate direct current (DC) electricity. Off-grid systems require battery storage and an inverter to convert DC electricity to AC (alternating current - mains electricity).
You also need a controller to divert power to another useful source (e.g. space and/or water heaters) when the battery is fully charged.
It's common to combine this system with a diesel generator for use during periods of low wind speeds. A combined wind and diesel system gives greater efficiency and flexibility than a diesel only system. It allows the generator to be used at optimum load for short periods of time to charge batteries when there is little wind, rather than by constant use at varying loads.
Wind systems can also be installed where there is a grid connection. A special inverter and controller converts DC electricity to AC at a quality and standard acceptable to the grid. No battery storage is required. Any unused or excess electricity can be exported to the grid and sold to the local electricity supply company.
Cost and maintenance
Systems up to 1kW will cost around £2,000 - £6,000 whereas larger systems in the region of 2.5kW to 6kW would cost between £12,000 - £20,000 installed. These costs are inclusive of the turbine, mast, inverters, battery storage (if required) and installation, however it's important to remember that costs always vary depending on location and the size and type of system.
NB: figures are extracted from the UK Government’s ‘Low Carbon Buildings Programme’ guidance
Turbines can have a life of up to 25 years but require service checks every few years to ensure they work efficiently. For battery storage systems, typical battery life is around 6-10 years, depending on the type, so batteries may have to be replaced at some point in the system's life.