Wind Turbines Tipperary - wind energy - evance wind turbines Ireland

This is probably the most asked question of any, and the one to which there is the least agreement in the entire worldwide small wind industry, as to the correct answer. Evance does not currently supply a wind turbine that can be mounted onto a roof and does not generally recommend a small wind generator in an urban environment.
Mike Bergey, head of the world’s largest small turbine manufacturer has been quoted as saying he:
“wishes people would stop asking us about mounting turbines on buildings”
Paul Gipe, one of America’s most respected small wind experts says;
“Mounting wind turbines--of any kind--on a building is a very bad idea. I've yet to see an application where this has worked or will likely work.”
What is however clear, and accepted by (nearly) everyone is that, if you are going to mount a turbine on a roof then you have to consider some issues, which are more prevalent than with a mast mounted rural one;

There will be increased turbulence and this will result in higher stresses on the turbine and lower energy capture for any given wind speed.
There will be more people living and working near the turbine so increased margins of safety need to be applied, and lower noise generated.
Extra measures may need to be taken to limit the transmission of vibrations into the structure of the building.
The average wind speed in a town or city environment will be a lot less than in a similar rural location, and this will significantly reduce the annual energy capture.

Ideally, the turbine should be sited as far away as possible from buildings or trees, which may block the wind and cause turbulence. As a guide, the wind generator should be about twice the height of obstructions in front of it (for at least the prevailing wind direction). This test should be applied for all obstructions that are within a distance from the wind turbine of 20 times the height of each obstruction. See the diagram below.
As an example, if there is a 7m high building then the turbine should be sited 7 X 20m away, i.e. 140m, or on a 15m tower (being more than 2X the height of the building). This is especially important where the obstruction is between the turbine and the prevailing wind.

Our standard towers are 9, 12 and 15m metres high. In general, the higher the tower, the higher the average wind speed that the turbine will experience, and it is normally the case that a taller tower will generate sufficient extra energy to justify it's additional cost, especially if there are local obstacles to be avoided.
Compared to a 12m tower, a 15m tower may increase the annual energy by 15% and a 9m tower may reduce it by 15%. If however there are local obstructions, then the impact of changes in the tower height could be larger.
For sites where there are obstructions near the turbine, a tall tower may be needed to get the turbine above the turbulence created by nearby trees or buildings, as illustrated by the diagram to the left.
The taller the tower, the more the cost of the tower, the foundations and the installation, so you should not simply ask for the tallest tower that is available, but if the turbine is to be located near (< 200m) to surrounding obstacles, then a taller tower may be the best option.
Other factors, such as planning, may dictate the maximum height of tower you are able to install and some areas of the world.

Tower Type
Depending upon the type of the turbine, Iskra can offer either a free-standing tower, or a guyed tower.

Guyed towers will tend to be used in rural locations, and have four guy wires going from the middle of the tower to concrete ground pads. They use slightly less steel than a free standing tower, but would not be considered suitable where people would be around the turbine a lot, as you don't want to risk damage to the guy wires
A free-standing tower or "monopole" has no guy wires, but stands on a single concrete foundation with no other supporting structure. In many cases the choice is really down to personal preference, as to which one you prefer to look at.

Wind speed varies with time, from nothing on calm days to occasional violent gusts. If the wind speed at a site is recorded over a year, it will be seen to vary about a mean wind speed value. This is the annual mean wind speed (AMWS) and is an indication of how much wind energy is available. In Europe, the AMWS could be as low as 4 m/s (9.0 mph) for an inland site to around 8 m/s (13 mph) or higher on the most exposed sites.
In general, you need an AMWS of at least 5 m/s to be able to generate a reasonable amount of energy, and ideally more than 5.5 m/s. The Evance Iskra R9000 works well at low wind speeds, but because the energy available in the wind is a function of the cube of its speed, there is very little energy available to be harvested at wind speeds less than 4 m/s.
The height of the tower can also have a significant impact as described in our 'What is the best tower type and height for me?' answer.
Seasonal Variations
Another thing to bear in mind is that there is normally more wind in the winter months than the summer ones. A wind turbine is therefore a very good match for heating and lighting requirements which are of course needed more in winter, but maybe not so well matched to air conditioning needs.
Wind Direction
In order for the turbine to be effective, it must have access to a good wind resource. This is one of the most difficult things to asses but in general the further away from buildings and trees, the better the average wind speed will be. This is especially true for any obstacles which are in the direction of the prevailing wind.
Hills and Valleys
An important consideration is that of valleys and hills. Wind speeds up as it nears the top of a slope and slows down considerably on the other side of hill as it descends into the valley. The exact impact of this effect is very dependant upon the exact local conditions but the diagram to the right gives a good indication of the impact of this. This can have a dramatic effect on the energy that the wind turbine will generate.
Urban Environments
Evance does not generally recommend a small wind generator in an urban environment as the AMWS in a town or city is likely to be substantially lower than in a rural environment and this will significantly reduce the annual energy output. This is due to the cumulative impact of the buildings that may surround the wind generator causing increased drag on the available wind and possibly severe turbulence.
Wind Speed Measurement
One thing you can do is actually measure your wind speed with an anemometer, which simply measures the wind speed. When this is connected however to a data logger, you can collect and analyse your average wind speed over a period of time. You would need to measure the wind speed for a period of at least 3 years to get a truly accurate average, as the wind speed not only varies during a year, but you can get “windy” and “calm” years, which can make a significant difference. You can however measure for a much shorter period and correlate your reading with a local weather station.

Do wind turbines frighten livestock and wildlife?
Evance and the relevant planning authority aim to ensure that all turbines are appropriately sited.
The Evance Iskra R9000 is a small wind turbine and therefore is unlikely to have a significant impact on surrounding livestock and wildlife. There is considerable evidence to suggest that sheep, cows and horses are not disturbed by wind turbines.
Livestock are able to graze in the same field as a turbine undisturbed by its presence. Similarly there is no evidence to suggest damage to other wildlife.

Danish Wind Industry Association: Birds and Wind Turbines
American Wind Energy Association: Putting Wind Power's Effect on Birds in Perspective, an article by Mick Sagrillo with a special section on 'Home-sized wind systems'
Royal Society for the Protection of Birds: Policy - Wind farms

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