Strangely enough wind power all starts with the sun. When the sun heats an area of land the hot air absorbs the heat and rises (as hot air is lighter than cool air), and cooler air is sucked into the gap left by the hot air, thereby creating wind! Placing a rotor blade in front of that wind will cause some of the energy of the wind to be transferred to the rotor creating motion. This is a transfer of kinetic energy from wind to the rotor.
When the rotor blades start moving they spin a shaft that leads from the hub of the rotor to a generator, which is then used to create electricity. Therefore, simple wind turbines consist of 3 main components:
- Rotor blades
- Shaft
- Generator
Not surprisingly the efficiency of wind generators depends solely on the amount of wind available and for this reason this technology is not suited for everyone. Next we will look at the requirements for placing a small scale turbine so that you can determine if you are suitable. Wind speeds vary throughout the year and therefore the industry standard for determining a sites wind energy potential is to determine an Annual Mean Wind Speed (AMWS). This is the average wind speed at a specific site over the course of a year. The UK Government has a database that gives the AMWS in meters per second (m/s) for each 1km square all over the British Isles for a height of 10m called the NOABL (can be found at www.bwea.com/noabl/index.html). For wind turbines to be effective you need a minimum AMWS of 5m/s and preferably more. However, it should be noted that as the AMWS increases, the energy efficiency of the turbine increases exponentially. That is, a small increase in AMWS can generate a much larger incremental increase in energy generation.
The AMWS is not the only factor you need to consider, there is also the local geography of the area under consideration:
- Wind direction: The best wind source in the UK comes from the South-West and the turbine should be facing in this direction.
- Buildings: There should not be any buildings blocking the wind in the immediate vicinity. It has been proven that wind speed in urban areas can be significantly lower than in rural locations and this is one of the main reasons that domestic roof based turbines are not advisable.
- Trees: Trees are another source of wind block that need to be avoided. It is not just in the immediate vicinity of the wind turbine, but within a larger area that could block the flow of the wind or create turbulence of the wind flow, as this significantly reduces the efficiency of the turbine.
- Hills and Valleys: Wind speeds up as it approaches a hill and slows down on the other side as the land acts as a wind barrier. Therefore you would want to place a turbine on the top of a hill to get maximum exposure to the wind source and avoid placing the turbine in a valley or on the descending slope of a hill (remembering that the turbine should be South West facing in the UK).
In summary, there are many factors that determine if your site is suitable for a wind turbine. The first consideration should be in a non-residential area with maximum exposure to wind from the South West. You should then check your postcode in the NOABL to see if you have a sufficient AMWS in your area. Following this you will still need a site survey from the turbine supplier (normally a service offered free of charge, although you need to be aware they have a vested interest in the results of the survey).
Once you have determined that your site is suitable (assuming you have continued reading this!), the next step is to decide the optimal tower height (which, of course, is also dependant on your budget and your energy needs/ambitions). Standard towers range from 6, 9, 13, 15, 18 and 23 meters for small scale projects (offshore wind farms can use significantly higher towers with longer rotor blades). Wind speed increases the further away it is from sea level, and therefore the higher the tower the greater the potential for wind energy. Thus, despite increased costs for larger turbines, the increased energy generation can greatly exceed the incremental cost. Also, for sites that have obstacles in the way, such as trees etc, a higher tower may overcome these wind blocks and make an unsuitable site more suitable. That said, taller towers require more space around them for safety reasons, increased installation costs, stronger foundations and are more difficult to get planning permission for. All this would be considered on a site survey when one is conducted and you should get a range of options for different tower heights, that states the amount of energy generation for each height. From there you can use our payback calculator to determine which height is best for you.
Planning permission: You need planning permission from your local authority to erect any kind of wind turbine system. Whilst planning authorities have become more receptive to renewable energy projects, there are a number of factors they will consider:
- Noise: wind turbines do generate noise and therefore they need to be far enough away from your house and any neighbours.
- Safety: wind turbines have large foundations and rotating blades and these need to far enough away from human activity.
- Environment: wind farms have been accused of harming local wildlife such as birds and they can be seen as an eyesore in areas of natural beauty.
That said, the UK Government is encouraging local planning authorities to be more receptive to wind turbines and this is likely to be helpful in your application.
One final point about the turbines: whilst the amount of energy generated is dependent on there being sufficient wind in the area, there can be too much wind. The turbines need a constant flow of wind and are susceptible to strong gusts. This means that they will have to be switched off during times of very strong winds and won’t produce any energy in such times. Also, smaller turbines may be liable to damage in heavy wind if they are not properly maintained. That said, most turbines have automatic safety valves that will lock the system if the wind gets too strong (the strong wind will turn the rotor at an increasing rate causing larger vibrations in the shaft).
Visit the Wind Home page
Other pages of interest in this section:
- What is Domestic Wind Power?
- How does it work?
- How much energy does it produce?
- How much does it cost?
- Are there Grants and Funding available?
- What is the Payback Period?
- Future Technology
- Overall Assessment
