It has never been so easy or economical to own your own wind turbine. We hope to answer the most frequently rasied questions regarding small wind turbines below.
Why buy a wind turbine ?
There are many reasons for owning a wind turbine:
- to reduce or eliminate electricity bills.
- to provide an income from the Feed in Tarriff.
- to increase security of electricity supply.
- to protect against electricity price rises.
- to provide electricity to a remote location which does not have grid connection.
- to reduce or offset carbon emissions.
- to provide an investment and home improvement that pays for itself.
- for educational purposes.
What size wind turbine will I need ?
Before looking at sizes and specific requirements of turbines you will need to compare turbines in order to make an informed choice.
Power ratings (maximum kW ouput) of turbines are determined at a certain wind speed, which is often above that at which the turbine usually operates. Size is not always the best.
Size of the area 'swept' by the blades as they turn is one of the best ways to compare wind turbines. This is known as the 'swept area' and is clearly related to the size of the rotors. The Gaia 133 has a large swept area of 133m2. This is very significant for a small wind turbine of this class. It enables the Gaia to out perform some 20 kW wind turbines at typical wind speeds.
The Evance R9000 whilst the swept area remains important, it manages to out perform its nearest compeptitors (including a 6 kW wind turbine) because of its unique blade design and exceptional efficiency. The Evance R9000 is the most efficient 5 kW wind turbine currently available on the market.
Rated power is a factor when considering wind turbines, but the real issue is how much energy will be generated by the turbine annually. Dorrell Renewables Ltd. will advise and guide on which is the most suitable turbine for your individual needs, be it an Evance R9000, Gaia or Endurance. We will take into account your budget and assess your site, current use of electricity, potential generation capacity and future usage of electricity and give you our recommendations for the most suitable wind turbine for your needs.
How much electricity will the turbine generate ?
This is site specific, dependent on turbine type and the annual mean wind speed at site. Please contact Dorrell Renewables Limited for an estimate.
Average households use approximately 4MWh of electricity annually. This does not include electricity used for heating. Larger premises such as community centres, school, farms and commercial outlets can use up to 20 MWh and more.
What wind speed do I need ?
Strength of the wind over time will affect the output of the wind turbine. The power available increases by the cube of the wind velocity multiplied by the swept area of the blades. For example an increase of wind speed of 1 m/s from 4.5m/s to 5.5m/s will nearly double the output from our 5 kW turbine, from 6,900 kWh annually to 11,200 kWh. Wind speed capture is paramount for maximum generation.
A steady wind flow is ideally required to produce a constant generation. Turbulent air flows can be caused by topography, trees and buildings.
Annual Mean Wind Speed (AMWS) is the measurement used to provide the wind speed records. Please contact Dorrell Renewables Limited and we will produce an estimated wind speed for your site. Please have your postcode at hand in order for us to carry out the estimate.
For optimum results and acceptable payback times an Evance R9000 requires an AMWS of at least 4.7m/s (10.5mph), the Gaia 133 requires an AMWS greaterthan 4.2 m/s (9.6 mph) and the Endurance an AMWS greater than 5.0 m/s (11.2 mph)
In some locations an estimate of the AMWS can be made from the effect of the wind on trees and bushes. Vegetation can be 'thrown' in a particular direction due to the strength of the wind over long periods of time. Griggs Putmen Index of Deformity calibrates 'flagging and 'throwing'. This index should be used with caution, but can give reasonable estimates of wind speeds. The AMWS can vary over small distances and vegetation on the coast can be affected in a similar way by salt in the air.
What impact will site have on wind speed ?
Siting is paramount for optimum generation. Dorrell Renewables Limited will endeavour to find the best location for maximum generation. The higher and steadier the wind speed is the more electricity will be produced by the wind turbine.
Dorrell Renewables Limited will carry out a desk top survey using a national database to estimate your AMWS at the proposed location of wind turbine. This is to ascertain whether the site meets minimum wind speed requirements. We will apply an adjustment to the figure obtained from the database to take into consideration the surroundings of your site.
The required distance from neighbours and turbine location differs between types of turbines. An Evance R9000 and Gaia require a minimum of 100m distance and an Endurance turbine requires between 250 - 400m distance between properties. This is to prevent objections of view, noise and shadow flicker. Dorrell Renewables Limited would also advise that you position your turbine at least 75m from your own property for an Evance R9000 or Gaia. However if you are considering an Endurance turbine we would recommend you siting the turbine 250m from your own property to prevent issues of view, noise, shadow flicker and turbulence.
What is shadow flicker ?
When sunlight passes through the blades of a wind turbine, especially when the sun is low in the sky, a light flickering effect can be caused. The turbine blades are coated in a way to minimise reflection of the sun from them and our surveyors would take this into account when selecting a site.
What affect does turbulence have on wind turbines ?
Wind turbulence is caused by obstructions between prevailing winds and turbine. Obstructions can be hedges, trees, buildings, etc. Turbulence effects can be increased if the obstructions are downwind of the prevailing wind direction (usually south westerly).
Some manufacturers claim that vertical axis wind turbines overcome the problem of turbulence by having blades designed to capture the wind from any direction. Dorrell renewables Limited is not convinced of this. For any given size of wind turbine a Horizontal-axis turbine will produce more energy that a Vertical-axis turbine. Additional maintenance is likely to be required over a shorter period with vertical-axis turbines as the air flow close to the ground produces turbulent flow introducing issues of noise vibration and bearing wear.
Dorrell Renewables Limiteds advise would be to install turbines with the tallest towers possible to enable capture of stronger, less turbulent winds for maximum electrical production. However we would also take into consideration other factors such as visiblity, impact on neighbouring properties and surrounding area.