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Wind Turbines
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FOR MORE INFORMATION ON OUR PRODUCTS AND SERVICES
PLEASE RING 01502 515532 or e-mail:- info@solarenergyalliance.com.
Having your own wind turbine to generate electricity will not only reduce energy bills, it could also provide an income, reduce your dependance on fossil fuels and help to give you energy security. Revenue from your wind turbine comes in two ways.
Selling power back to the grid. The majority of wind turbines are "grid connected", meaning that they are connected to the same mains electrical network, that already supplies you with your power. This system allows you to export your power when your wind turbine is producing more than you are using, and to import it in the usual way when you need more than your wind turbine is producing. Many electricity suppliers will pay you for each unit of electricty you export. The rates and conditions vary from company to company. more information about selling power back to grid
ROCs. The government's Renewable Obligation Certificate Schemes, means every energy company has to provide an annually increasing proportion of their energy from renewable sources. As an owner of a wind turbine and a generator of renewable energy, you will be entitled to Renewable Obligation Certificates for all the energy your wind turbine produces- whether you use it on site or export it to the national grid. Energy companies will buy these certificates from you. more information on ROCs.
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Wind Turbines
In the UK we have 40% of Europe's total wind energy. But it's still largely untapped and only 0.5% of our electricity requirements are currently generated by wind power. Small-scale wind power is particularly suitable for remote off-grid locations where conventional methods of supply are expensive or impractical; power is stored in batteries or can be used for direct heating.
Wind systems can also be installed where there is a grid connection. An inverter converts DC electricity to AC at a quality and standard acceptable to the grid. No battery storage is required. Any unused or excess electricity can be exported to the grid and sold to the local electricity supply company It's common to combine this system with another e.g. solar PV for use during periods of low wind speeds. A combined wind and PV system gives greater efficiency and flexibility.
Planning permission will usually be required, it generally does not cause any great problems but it is always wise to consult your neighbours first, it will take around four weeks and requires a small fee.
As a general rule we would require twice the length of the chosen mast to install the wind turbine and suitable access for delivery, a wind speed of at least 4.6m/s and the turbine should be situated towards south west for the strongest winds. Foundations will be required and can be installed by a local builder or by us, a foundation pack can be sent out several weeks prior to the mast installation.
Micro Wind
Micro wind turbines convert the kinetic energy from wind power to useful energy (either electricity or heat). The rated capacity of micro wind designs varies from 0.1 to 15 kW. They are available in two basic configurations: rooftop-mounted and pole-mounted.
The main components of a micro wind turbine are:
- An aerodynamic rotor – converts the kinetic energy in the wind to rotational motion
- A generator – generates electricity from the rotational motion of the rotor
- Electronic control – controls the electrical output from the rotor and the safe operation of the turbine
- Mechanical furl – typically fins which keep the turbine pointed into the wind in low wind speeds and move the rotor out of the wind in high wind speeds
- Inverter – safely converts the power to a compatible format to the national grid
Rooftop-mounted wind turbines. These require a solid section of building at the roof line to directly attach the turbine; generally they are bolted to an exposed side of a building or mounted on a stand on a flat roof. Sufficient clearance above the apex of the building should be provided to enable the wind turbine to take advantage of the wind resource around the building. The electricity generated by the wind turbine is fed to an inverter installed within the building which is typically connected to the grid via a distribution board. Alternatively, in applications where grid connection is not preferred or not possible, the electricity generated from wind power can be fed directly to immersion heaters in the hot water storage tank in the building.
Pole-mounted wind turbines. These require a small area of land for up to 5m2 of foundations and sufficient space to winch up the turbine. As a general rule of thumb, the tower for the turbine should be sized to ensure the rotor is sited 10m above the nearest obstacle within 100m of the turbine. The electricity generated by the turbines is fed down the tower, through the foundations and buried underground back to a building where it is connected to the grid via a distribution board.
Applications
Micro wind power turbines are applicable in locations where:
- The mean wind speed is greater than 5 m/s at hub height
- There is good exposure to the prevailing wind directions
- There are no planning constraints to development (designated areas and listed buildings can be an issue)
Rooftop or pole-mounted micro wind turbines can be used in low density domestic applications and could supply a good proportion of the total energy demand. Rooftop or pole-mounted micro wind turbines can also be used in commercial applications to reduce energy consumption and CO2 emissions.
Micro wind turbines can be used effectively in hybrid applications with solar PV, hydropower, solar thermal, heat pumps and biomass heating. With solar PV and hydro they are simply connected together through an inverter to supply a greater proportion of renewable electricity to a building. When used in conjunction with solar thermal, heat pumps or biomass, they can be used to supply (indirectly) the electricity required to run the pumps in the systems; thus supplying a significant proportion of renewable energy to a building.
Financial and Environmental Benefit
The current capital cost of a micro wind turbine is roughly £3,000 per rated kW installed. The annual energy yield is typically 1,000 kWh per rated kW installed at a location with a good resource and exposure to the prevailing wind directions. This gives a current payback period of between 12 and 15 years. Annual saving in CO2 emissions are 0.4 tonnes per rated kW in a grid connection application and 0.2 tonnes in a heating application
Wind Power - Larger machines
A wind turbine is a machine which converts the kinetic energy from wind power into mechanical energy and, ultimately, useful electrical energy for the national grid. The kinetic energy is extracted from the wind by means of an aerodynamic rotor, which is connected to a generator to produce electricity. This generator is then connected to the grid to provide electricity for homes, offices and industry.
There are a wide range of wind power turbine technologies available, from micro through to large commercial wind turbines. Wind turbines can also be classed by the orientation of the axis of rotation to the direction of the wind – horizontal axis machines and vertical axis machines. This page concentrates on the larger horizontal axis wind turbines, which are by far the most common.
Since the 1980’s wind turbine manufacturers have been producing wind turbines with a capacity in excess of 100 kW. The scale of commercially available wind turbines increased to over 1 MW by the late 1990’s, and to 5 MW by 2006. The reason for the increasing capacity is the greater efficiency of the system and the improved economies of scale. The picture below shows how the scale of available wind turbines has increased over the past 2 decades.
Figure 1 – Wind Turbine Power output scale Large wind turbines are now available from 100 kW to over 5,000 kW. Those belonging to the lower end of this scale are typically installed individually on small farms or businesses, whilst the top end of this scale are used in off-shore wind farms. Turbines ranging from 1 to 3 MW are typically used on industrial sites or in modern on-shore wind farms.
The amount of power a wind turbine can generate depends on the rating of the wind turbine and the wind regime in which it is to operate. The ‘rating’ is the maximum amount of power the turbine can generate after a certain wind speed (typically 25mph). The power that a wind turbine can generate varies according to the cube of the wind speed, so that doubling the wind speed will produce eight times as much power. It is therefore important to ensure that wind farms are installed on tall towers on windy sites with exposure to the prevailing wind directions.
Wind farm developers must choose sites carefully in order to ensure that whilst there is enough wind to make the project commercially viable, there will also be the least possible adverse impact on the local environment. Factors that need to be considered in the early stages of a wind farm project are the visual impact, noise pollution and shadowflicker impact on local residents, the impact of construction and operation on protected areas and important or protected flora and fauna, and the impact of the development on aviation, television signals and other communications. These negative impacts must be weighed up against the positive impacts, such as reduced levels of carbon dioxide emissions and the creation of local jobs. The results are compiled in an Environmental Impact Assessment (EIA) which is submitted to the local council along with a planning application.
A suitable wind farm site will therefore:
- Have a good wind power resource of at least 7m/s (15mph) at the hub height of the wind turbines
- Not be too close to residential buildings (400m – 800m clearance is typical);
- Not be sited on or near areas of outstanding natural beauty, special protected areas, special areas of conservation, and sites of special scientific interest etc.
- Not be too near military or civil flight paths, tactical training areas, radars or airports (15km is a typical minimum radius).
These are only guidelines and much investment and research will be needed to quantify the impact of a wind farm. If a site has been carefully chosen and planning consent is granted for the wind farm, it can then be constructed and will operate for up to 20 years. After this period, the owner of the wind farm may decommission the project and return the land to its original state or re-power the project with new turbines for a further 20 years. Wind farms therefore offer a sustainable source of energy which will last for as long as the wind blows.
The Power of the Wind: Cube of Wind Speed
The wind speed is extremely important for the amount of energy a wind turbine can convert to electricity: The energy content of the wind varies with the cube (the third power) of the average wind speed, e.g. if the wind speed is twice as high it contains 2 3 = 2 x 2 x 2 = eight times as much energy.
Now, why does the energy in the wind vary with the third power of wind speed? Well, from everyday knowledge you may be aware that if you double the speed of a car, it takes four times as much energy to brake it down to a standstill. (Essentially this is Newton's second law of motion).
In the case of the wind turbine we use the energy from braking the wind, and if we double the wind speed, we get twice as many slices of wind moving through the rotor every second, and each of those slices contains four times as much energy, as we learned from the example of braking a car.
The graph shows that at a wind speed of 8 metres per second we get a power (amount of energy per second) of 314 Watts per square metre exposed to the wind (the wind is coming from a direction perpendicular to the swept rotor area).
At 16 m/s we get eight times as much power, i.e. 2509 W/m 2 .
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