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.

Is bird-strike likely to be a problem?

Bird-strike is not likely to be a problem. More information about this can be found on the following pages:

• 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

The wind turbines generate power by rotating a permanent magnet generator which generates three phase AC at the frequency of the turbine's rotation. The AC power from the generator is not only the wrong voltage to be connected to the local power grid, but also, as the wind speed changes so does the rotational speed of the turbine, and therefore the frequency of the power generated. The power from the generator therefore needs to be converted to DC and then fed into a special electronic device called an inverter, to ensure that it is always at the correct frequency and voltage for the local grid.

Any power you generate will be first used by your own property, thereby saving you the maximum amount possible on your electricity bill. Any excess energy your wind turbine generates, e.g. on windy days or at night, is "spilled" to the power grid and your electricity supplier pays you for it.

In order to charge your electricity supplier for any energy that you export to the grid, you need to have a new bi-directional electricity meter installed which will work both when you buy (import) and sell (export) electricity. Depending upon your local requirements, there may be additional meters needed to record energy generation to enable a claim for a Government subsidy.

Shown below is a simplified block diagram of how all the system components are connected in the UK.



The inverter also provides essential safety features to control the power output from the turbine, and to automatically switch off the current if the grid connection should fail. This means that should the grid connection fail, the inverters will switch off their output and there is therefore no danger to any maintenance engineers fixing the fault. This does however mean that the wind turbine will produce no power to the property if the mains connection fails.

Iskra however shortly hopes to offer an off-grid package which when combined with a battery pack, and optionally solar PV panels and/or a diesel generator will enable the generation of “mains” power where there is no grid connection.
 

Will the turbine have an impact on TV and radio reception? 

The Evance Iskra R9000 wind turbine is unlikely to disrupt TV and radio signals as it is a refined design specifically meeting the requirements of a small scale renewable energy source. The materials used to make the R9000 turbine are unlikely to create electromagnetic interference (EMI) by "chopping up" a signal.

Any problems should be identified in the planning process and Evance will ensure that appropriate advice is given as to the best possible location for your turbine.

How noisy is the R9000 wind turbine?

The R9000 has been designed to be very quiet indeed. The rotor design and in particular, the low rotor tip speed, coupled with the direct drive system (no gearbox), all ensure quiet operation. As a general rule, the nearest neighbouring residents to the wind turbine should be more than 100m away from the wind turbine base The sound from the wind turbine is however gentle in tone, and it would be quite reasonable to locate the wind turbine less than 75m from your home .

Will I have a problem with ‘flicker’ from the turbine blades?

Potentially, reflection from the blades, or the shadow from the blades in the rising and setting sun, causes a flickering effect. The design and coatings used on the turbine have been selected to minimise the reflection problem. The possibility of the shadow from the wind turbine causing flickering should be considered at the site selection stage. It is normally possible to avoid this problem.
 

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;

1. There will be increased turbulence and this will result in higher stresses on the turbine and lower energy capture for any given wind speed.
    

2. There will be more people living and working near the turbine so increased margins of safety need to be applied, and lower noise generated.
    

3. Extra measures may need to be taken to limit the transmission of vibrations into the structure of the building.
    

4. 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.

Further Reading

If you would like to learn more about the issues with roof mounting or urban installations of small wind generators, then the links below may be of interest to you.

• Times article on urban turbines - 17th February 2007.

• REUK article on Consumers Disappointed With Micro Turbines - 15th January 2007.

• BBC Newsnight "Ethical Man" video clip on roof top turbines - 22nd December 2006.

• Guardian article on roof top mounted small wind turbines - 21st December 2006.

• Warwick Wind Trials - A real life study of small rooftop mounted wind turbines.

• Council for the Central Laboratory of the Research Councils (CCLRC) report on building mounted turbines.

• European Union "WINEUR" project on urban wind.

• Paul Gipe's article on roof mounting small wind turbines.

• Paul Gipe's article on UK roof mounted turbine manufacturers.

• Ocean Solar's experiments in roof mounting.

• Hugh Piggot's "Windspeed Measurements in the City".

• Observer article of roof top mounting small wind turbines - 15th June 2006.

• Building for the future article on roof mounting (Page 17).

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.

The diagrams illustrate some impacts of obstacles and ground features on the wind resource available to a wind turbine.

The ideal location for a wind turbine is at the top of a gentle slope and the worst location is just to the downwind side of a large building.

The Danish Wind Energy Association provides an excellent and detailed on-line guide to these issues which is well worth reading before deciding where to site your own turbine.

Many people will say that one of the answers to the height question is to mount the turbine on a roof to gain extra height, but this is not a simple solution, as our Building Mounted FAQ explains.

In general, if you have a number of obstacles, e.g. buildings or trees, within 200m of the proposed turbine location, then you should seriously consider a taller tower, e.g. 15m rather than 12m. The benefit that you will get from a taller tower will be greater, the more obstacles that are around your proposed location.

Space is also needed to set out the anchorage points for a guyed tower and to lower the tower for maintenance. The ground area required depends on the type and height of the tower.

Noise Issues

The wind generator will also create a small amount of noise, so planning authorities will not let you site one too close to your neighbours. The actual distance however will depend upon a number of factors, including the local terrain, trees and the background noise in the area. As a guideline however, the Iskra R9000 should be sited at least 100m from your nearest neighbour and at least 50m from your own house. Planning authorities vary in their requirements and it is therefore important that you talk to your local planning authorities about their own interpretation of the rules.

In general you should aim to site the turbine where it will not impact your neighbours either visually or with noise. This may however involve a compromise with the best location for energy generation and you may need to enter into negotiations with your neighbours and planning authorities.
 

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.

Further Reading

A more detailed guide to the energy generation from wind generators can be found on the Danish Wind Energy Association's excellent web site, and this is well worth a read when considering your turbine.

There is a good guide to Wind Resource Assessment for Small Wind Turbines on the web site of the Small Wind Industry Implementation Strategy's (SWIIS) web site.

The EU funded project WINEUR has its own web site containing many documents on urban wind for those considering such an installation.