Wind turbines use wind energy to rotate turbines and generate electricity. Turbines can be free-standing or roof-mounted and have horizontal or vertical axes.

Requires: Regular at least moderate winds, planning permission.

Works well with: Battery Storage, Heat Pumps (particularly those with a Thermal Store).

Wind turbines convert wind energy into an electrical current when the wind is strong enough. As they rely on wind, turbines generate variable amounts of electricity over the course of the day and night. They can be installed on a roof (under 2kW generation capacity) or free-standing on the ground (typically 5-6kW).

The location of wind turbines is of critical importance because site has a major impact on wind speed. Ideally these should be around 5ms^-1 (11mph). It is advisable to install an anemometer (wind gauge) at a prospective site for several months prior to installation to assess a location’s wind speed profile so the most appropriate turbine can be selected. Various combinations of cut-in speeds, below which the turbine will not rotate, rated speeds, above which electricity output will not increase, and cut-out speeds, above which the turbine will not rotate, are available so data from the anemometer should be used to choose the most suitable technology.

Free-standing turbines are the most efficient, but placement can be problematic. A large area without tall trees and buildings is needed for this type of model. Planning permission can be a problem, particularly in urban areas. Several-kilowatt turbines should typically be mounted with their turbine centre 10-15m above the next highest object in a 150m radius. Higher output turbines can be centred 30m or more above ground, which is often significantly more expensive and planning permission can be more difficult to obtain. However, at such heights, wind speeds are consistently faster and less turbulent so more electricity can be generated, and carbon dioxide (CO₂) emissions abated.

Roof mounted turbines are a smaller-scale option and less expensive to install. They are smaller because the weight, torque, vibrations, and noise of bigger turbines can pose practical challenges. Turbines are most effective when high above nearby buildings and trees, which is not possible with some building locations.

Horizontal axis turbines are the most common design. These face one direction, with the main rotor shaft and generator in a box at the apex of a high column. The advantage of such a design is that it is robust enough to withstand strong forces. This design is common in areas where the wind is high. The drawbacks of horizontal axis turbines are that, due to their size and strength, they require heavy construction work, costing more and emitting more CO₂, and they are more visually obtrusive. Notably, because they are on a fixed axis, this type of turbine only face one direction so when the wind blows in a less common direction the turbines will not generate electricity.

Vertical axis turbines are becoming a more common alternative. These are ideal for urban environments and rooftop arrays. They can be positioned closer to the ground, and not necessarily directly into the wind. Planning permission for this arrangement is usually less problematic because they are shorter and installation costs are generally cheaper because they are lighter. Vertical axis turbines are less efficient in higher winds.

Wind turbines generate direct current, unlike the grid-supplied electricity appliances use, which is alternating current. An inverter will require installation to convert direct current into alternating current.

Turbines should last over 20 years. They should be inspected every few years. The inverter may not last as long as the turbines.