About Wind Turbines

Wind turbines have been installed throughout the UK for over 20 years.  Up until recently it has been dominated by the large turbines which stand some 125m to the top of the hub, some larger particulary the offshore turbines.  With the introduction of the Feed in Tariff and the push for small scale renewable energy generation, there are many options available for medium (~ 50m turbines) and small scale (10-15m turbines) turbines. 

How does a wind turbine make electricity?
Most wind turbines have three blades which face into the wind; the wind turns the blades round, this spins the shaft, which connects to a generator. A generator produces electrical energy from mechanical energy.

1. The wind blows on the blades and makes them turn.
2. The blades turns a shaft inside the nacelle (the box at the top of the turbine)
3. The shaft goes into a gearbox which increases the rotation speed enough for...
4. The generator, which uses magnetic fields to convert the rotational energy into electrical energy. These are similar to those found in normal power stations

Making a decision as to which type of turbine is best for you can be difficult.  We can help you with the decision making process and steer you in the right direction. Some key points are set out below.

• Small-wind turbines on farms and estates can be used to power ventilation (livestock or grain storage, potato storage), lighting, light machinery, or domestic use. They are most likely to be viable where the electricity generated substitutes for imported electricity throughout the year although the newly proposed export tariff will reduce the difference.
• In order to maintain continuous power either a battery system or connection to the grid is necessary. The introduction of the export tariff makes battery storage less cost effective.
• Viability is improved where the installation costs are reduced such as through the use of farm labour to erect and install the wind turbine or suitable steel framed buildings are available to gain height.
• Planning permission is required.
• A number of different power measurements are used making comparison of turbines difficult. Particular care needs to be taken to distinguish between; the power curve for a turbine (the power for a given wind speed) from the annual energy production for a given average wind speed.
• While height generally increases wind speed, and therefore efficacy, care must be taken to ensure that building structures can withstand the additional stress.
• Medium sized turbines (<70m to tip) are a good alternative capturing the benefit of greater wind speeds and potentially generate excellent returns.

To maintain continuous power, either the turbine recharges a battery during periods of excess power generation or the shortfall is made up from the grid.  Larger installations producing an electricity surplus of over 500 kWh may be able to sell power back to the grid during periods of excess generation. 

In order to use the electricity stored in the battery, an inverter is used to convert the direct current (DC) into alternating current (AC) so that it can be used with standard electrical appliances.  The charged battery typically lasts for 2-3 days, so an alternative source of power may be needed for periods of insufficient wind to recharge the battery.  Excess electricity produced by a wind turbine can be used to heat water which would be stored until needed and could displace other fuels.  In practice the use of battery storage is becoming less worthwhile now that the export tariff is likely and connection to the grid is becoming easier.

A third option is to use surplus electricity to heat water, for example, for central heating systems or swimming pools.

Turbine information

Turbines typically have a life span of 20-25 years and are available in a variety of sizes, both in terms of electrical output and physical size.  Wind speeds increase with height above ground level so the higher a turbine is, the more power it can generate both through its greater blade size and access to higher wind speeds.  This in turn determines the ground area required for the site, as the higher the turbine, the larger the foundations required. 

Table 1: Small wind turbine dimensions

Source: Various manufacture/installer sources

Wind Speed

At the most basic level, the power output of a turbine depends on wind availability and the size of the blade. 

However, the minimum wind speed required to operate a turbine (the cut in speed) varies from about 2m/s to 4/ms (generally, but not always, smaller turbines operate at lower wind speeds).  As wind speed increases the power increases up to a maximum after which power generation tends to fall.  Several of the more sophisticated turbines are designed to move in line with the wind in severe weather conditions in order to avoid damage. 

Chart 1 showing the wind power against the likelihood of each wind speed (at an average of 7m/s)