DESCRIPTION

Wind energy is one of the most cost effective methods of renewable power generation. Wind turbines can produce electricity without carbon dioxide emissions ranging from watts to megawatt outputs. The most common design is for three blades mounted on a horizontal axis, which is free to rotate into the wind on a tall tower. Developments in the vertical axis turbine are making them increasingly viable alternatives with a number of benefits over the traditional horizontal axis variety. The blades drive a generator either directly or via a gearbox (generally for larger machines) to produce electricity. The electricity can either link to the grid or charge batteries. An inverter is required to convert the electricity from direct current (DC) to alternating current (AC) for feeding into the grid.

WHERE CAN WIND TURBINES BE USED?

Modern quiet wind turbines are becoming viable in low density areas, where ease of maintenance and immediate connection to the grid or directly for use of the electricity in a building, may make them cost effective, despite lower wind speeds than in open areas. Wind turbines are generally less suited to dense urban areas as their output will be affected by potentially lower and more disrupted wind speeds, and the use of larger more cost effective machines may be prohibited by their proximity to some building types. However, small turbines can be used in inner city areas. Small turbines can also be mounted on buildings. There are currently few practical installations of roof mounted wind turbines in the UK but it is anticipated that this will be a growing market and a number of companies are marketing small roof mounted turbines. Potential public resistance has restricted the use of large-scale wind turbines (above 50kW) although studies show that in general the local perceptions of wind farms/turbines improve once it has been erected. Less resistance has been noted for small-scale systems where the key consideration is likely to be noise, rather than visual. However, all sites should be assessed in the first instance for their suitability, as with early community involvement, a wind turbine could provide a landmarkshowing the  commitment of a development and a particular community to sustainable development. Community consultation and buy-in would be essential for the success of larger turbines. Small-scale turbines are likely to have less of an impact. There are examples of community groups funding their own wind turbines in the UK.

COST RANGES

The Clear Skies Programme gives a cost range of £2,500 - £5,000 per kWe installed. Suppliers should be contacted for up to date costs and any bulk discounts that may be applicable.

OUTPUT RANGES

Wind turbines are available with outputs ranging from 600W to 3.6MW.
The main factor affecting the output of wind turbines is the average wind
speed. This varies for different areas of the UK but increases with the
height of the turbine above ground level. Local topography can
significantly impact upon local wind speeds. A small difference in wind
speed will make a large difference to output.
A database on www.bwea.org.uk can be used to predict the approximate
wind speed at a particular set of co-ordinates at different heights.
Using Proven wind turbines as an example (data taken from Proven data
sheets www.provenenergy.com), Table 5 shows yearly output in kWh for
different sizes of turbine:

Table 5 Yearly output for different rated turbines

A gas heated, 2 bed/4 person flat (built to 2002 Building Regulations)
uses approximately 1,500kWh/yr in electricity (for lights and appliances).
From the table above, it can be seen that a 600W turbine would provide
all of the flat’s electricity needs over a year, providing a saving of
approximately £140 (based on 9p/kW for electricity).
A gas heated 4 bed/ 7 person 3 storey terraced house (built to 2002
Building Regulations) uses approximately 2,500kWh/yr (for lights and
appliances). From the table above, it can be seen that a 600W turbine
would provide all the electricity needs over a year, if there was an average
wind speed of 6m/s, providing a saving of approximately £225 (based on
9p/kW for electricity).

TECHNICAL FEASIBILITY ISSUES OR CONSTRAINTS

Issues to be taken into consideration include:

• The average wind speed at the site. Currently the BWEA suggests a
large wind turbine to be viable where wind speed is 7m/s or above.
However turbines will operate from a wind speed of 4m/s and produce
useful amounts of energy.

• The uneven and turbulent wind patterns that occur near buildings and
other obstacles.

• The need for planning consent. The best practice for a developer is to
speak to the local planning authority at the earliest possible
opportunity to see if there are objections to the proposal which
cannot be negotiated. However, the planning office may also indicate
key issues of concern from which a judgement can be made on how to
deal with the proposal in terms of the design, location, size and scale
of the project.

• The potential visual impact on important public viewpoints and on
local ecology.

• Any landscape designates (such as AONB or SSSI) and Conservation
Areas. See the British Wind Association’s Best Practice Guidelines for
Wind Energy Development for further guidance.

• The need to maintain adequate access for maintenance and
initial installation.

• Possible noise from the turbines (although modern turbines without
gearboxes are quiet and are said to be drowned out by a passing car).
Many areas have 24-hour background noise which can mask
any noise from a wind turbine. For more information see
the BWEA web page www.bwea.com/ref/noise.html.

• The available space for a turbine, as they must be placed a
minimum distance from residential and school buildings due to
noise, reflected light and shadow flicker, which varies according to
their height.

• Some turbine blades come in different colours. The colour could be
chosen to enhance the appearance of the turbine or make it as
inconspicuous as possible (if this was the desired outcome).

MAINTENANCE REQUIREMENTS

There are very few maintenance requirements - a service check every
couple of years would be advisable. A wind turbine typically lasts
20-25 years.

ADDITIONAL BENEFITS OF TECHNOLOGY

• This is one of the more cost effective of the available renewable technologies.

• There could be significant green marketing opportunities for businesses using this technology.

PLANNING AND LEGISLATIVE ISSUES

Planning permission will be required for each location. If the proposed
site for larger wind turbines (above 50kW) is in Greenbelt or Metropolitan
Open Land, demonstration of ‘very special circumstances’ will be required
to obtain planning permission.
The potential impact of noise from turbine blades, mechanical
components and any linked structures should be considered. This includes
structure-borne vibration if turbines are building-mounted. Modern
turbines can be much quieter than earlier models, and variation in size,
design and performance means that specifying universally applicable
distances from housing, schools or other noise-sensitive receptors has
become inappropriate. Variations in local background noise also mean
that proposals need to be assessed in relation to local circumstances.
Particular attention should be paid to how turbine noise compares with
background noise during quieter periods, particularly night (2300-0700)
and to situations where receptors and turbines may sometimes be in
contrasting wind-noise conditions.

LINKS TO SOURCES OF MORE DETAILED TECHNICAL INFORMATION

• Companion Guide to PPS 22: The technical annexes. Available at
www.odpm.gov.uk/planning

• Best Practice Guidelines for Wind Energy Developments, available for
download from www.bwea.com/ref/bpg.html

• The Assessment and Rating of Noise from Windfarms, ETSU report for
DTI. www.dti.gov.uk/renewable/wind_environment.html and
www.dti.gov.uk/renewable/publications.html (also has guidance
on aviation).

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