It may sound obvious, but one of the first things to determine is exactly how windy your site is. The best sites are usually in coastal areas, at the top of rounded hills, on open plains or in gaps in mountains. When a wind project fails to deliver it is more often a fault of the site selection than the technology.
To work effectively, wind turbines need an average wind speed of no less than five metres per second (5m/s). Wind maps can be used to give an initial indication of the wind speed at your site. Visit, for an example, the Action Renewables website.
However, wind maps do not take account of the landscape on a small scale; factors which may have a considerable effect on the wind speed. The wind speeds reported could also be recorded at heights that are greater than most small wind turbines. In short, wind maps will not replace the need to record accurate wind measurements at your site.
Once you have established that you have a good windy site, selecting just the right spot to place your turbine will often be a compromise between a number of factors. Ideally, you are aiming to locate the turbine as close as possible to the point of electricity use but at least 40m from any buildings. Consideration should also be given to the ease of access to the site. If, for example, a road needs to be built to transport the turbine from a main road, this will have a significant impact on final costs.
Grid connection can also have big cost implications. If the electricity grid is not close to the site and needs extending, or if it needs upgrading to take the amount of electricity generated, then these costs can sometimes make the project prohibitively expensive. It is advisable to establish the situation for grid connection in your locality before investing too much time or money in the project.
As wind speeds increase with height, it makes sense to put your wind turbine on as tall a tower as you can, within your budget and local planning constraints. It also helps to limit the effects of turbulence, created by the wind passing over obstacles on the ground such as trees or buildings. Turbulence has a significant detrimental effect on the amount of electricity generated, and increases wear and tear on a turbine.
Once you have selected a suitable site, you now need to select the right turbine. In Northern Ireland we experience a wide variation in wind speeds and it is essential that the turbine can cope with this. Every turbine has is own power curve graph, which provides information on its performance at different wind speeds. This graph will be a useful part of the process for choosing a turbine that is suited to the wind conditions experienced by your site.
Turbines are given a power rating by the manufacturer. Generally, the larger the turbine’s power rating the more electricity it can generate. The size selected will be determined by the demand for energy, project budget, grid strength and planning constraints.
Developing a sound business case for the project is essential. The financial returns come from combining the savings made from using your own electricity and not buying it all at the tariff price; the income generated from any electricity sold back to the grid; and the Renewable Obligation Certificates (ROCs), which are issued in relation to the amount of renewable electricity generated and have a market value. However the ROCs incentives will not normally be available for new wind projects after March 2017.
If the maths adds up, your next harvest could be blowing in the wind.
For further information, please contact Cathal Ellis, Senior Renewable Energy Technologist, CAFRE, at firstname.lastname@example.org.