|Technologies - Wind|
Wind turbines convert the kinetic energy from the wind into mechanical energy which is then used to drive a generator that converts this energy into electricity. Due to its location on the Western edge of Europe, the UK has more usable wind power than any other European country. There is therefore considerable potential for large scale wind turbine farms on and offshore will become a major supplier of electricity to the national grid in the next twenty years.
By the year 2008 there are already 175 UK grid-connected wind farms containing 2,032 wind turbines with the capacity to generate 2545 MW (source BWEA)
Horizontal and Vertical Axis Turbines (HAWT and VAWT)
There are two types of wind turbines; horizontal axis and vertical axis.
Horizontal axis turbines are the more familiar ˜windmill' type where the blades rotate in a vertical plane about a horizontal axis and the turbine is head is then rotated on its tower to face the wind.
Vertical axis turbines do not need orientation into the wind, although some versions require a power source to start rotating because of their high torque. However, more recent innovations have helical blade designs that have low torque and can operate without external power. Vertical axis turbines are particularly suited to small wind power applications because they have a small environmental impact and no noise, although these have not yet been scaled up to the larger 5MW + turbine size of horizontal axis designs.
Commercial Onshore Wind Farm Projects
There are a number of commercial on shore wind farms. These can contain large scale wind turbines which have rotor diameters in excess of 100 metres, tower heights in excess of 300 feet and are substantial structures weighing hundreds of tonnes. However, the development of these tpes of schemes has not been as rapid as originally anticipated in the UK, due to the large capital investments, lengthy periods of planning approval (including local consultation and impact assessment on the environment, aviation, aesthetics and wildlife), as well as uncertainty over the future of ROCS.
ROCS (renewable obligation certificates) revenues arise from the electricity generators financial incentive to invest in large-scale wind generation as the government has set a requirement that all UK power suppliers must source a rising proportion of their energy from renewables, currently 7.9% rising to 20% in 2020.
Commercial Offshore Wind Farm Projects
As the UK has a large shallow continental shelf, the sea around the UK coastline is particularly suitable for offshore wind farm projects. Up to 12 nautical miles from the shore the seabed is owned by the Crown Estate who can grant leases for developments. Outside this territorial limit, similar considerations will apply in the Renewable Energy Zone, created under the Energy Act 2004, where the Crown Estate will issue a licence to develop a wind farm rather than a lease.
Developing offshore wind farms has a number of benefits including:
1. Many more available sites
2. Lessens the environmental impact, shortening the planning process
3. Improves turbine efficiency as there is less turbulence in the wind flow over the sea's surface
However these are balanced by the following costs issues:
1. Overall increase in the construction cost compared to a land based project
2. Increases the cost of grid connection via undersea cabling
3. Requires specially treated components to offset the corrosive effect of salt water
4. Increases the maintenance cost which has to be undertaken with access by boat
Despite these negative costs issues, the benefits have still been driving forward the development of offshore wind farms.
Estimates show that within the next 12 years, the seas of Britain could have enough wind farms to power every one of the country's 25 million homes.
Harnessing the vast potential of the UK's island status has entered a new phase with Energy Secretary John Hutton announcing in December 2007 proposals to open up its seas to up to 33 GW (gigawatts) of offshore wind energy.
Small Scale Wind Turbines
Small scale wind turbines for individual dwellings or communities/buildings are particularly suited to off grid, mobile and combined wind & PV applications. The PV/wind power combination is effective because wind power availability is highest in winter when available solar power is at its minimum and vice versa.
Small scale wind turbines vary in size with a range of models available, from less than 100 watts (W) up to 50 kilowatts (kW).
Turbines ranging from 0.6kW to 50kW can be used to provide electricity generation for individual houses and businesses, with rooftop models varying from 0.5kW to 2.5kW in size.
Siting your Wind Turbine
Before committing to a project you need to determine the available wind resource on your site. This will determine the available power. BERR have a database of Mean Annual Wind Speeds at 10, 25 and 45 metres above ground level for the whole of the UK.
This can be located via the following web link:
For maximum efficiency, turbines require a smooth flow of air over the rotor blades at a constant speed. Ideally a turbine should be sited on the top of a hill with a gentle south-westerly slope (the direction of the UK's prevailing wind). Obstructions such as trees or buildings will cause turbulence in the wind flow. The efficiency of a turbine increases dramatically with small increases in wind speed and turbulence increases the wear and tear and thus the maintenance requirements. It is therefore very important to look at the wind speed in your area as the financial viability can vary considerably from location to location even when these are quote close together.
Commercial turbines are sited on tall towers to avoid turbulence that occurs lower down (wind shear) and take advantage of the higher wind speeds higher up, therefore for a small scale winder turbine it is sensible to locate your wind turbine as high as you can within your budget and local planning constraints.
Wind turbines need explicit planning permission. It is important to discuss your plans with your local authority before committing to the project, especially if the proposed site is on a listed building or in a conservation area, National Park or AONB.
However, in July 2006 the Housing Minister, Yvette Cooper announced that from 2007 changes to planning laws will allow householders to install small scale wind turbines without planning permission - as long as they do not impact on neighbours. The government's Planning Portal website gives guidance on planning for domestic renewable projects.
To install any piece of equipment which generates electricity and is connected into the national grid (a grid-connected system), you will need permission from the local Distribution Network Operator (DNO). This is the company who operates the distribution network in your area (this may not be your electricity supplier). DNOs have different policies when it comes connecting small scale renewable generation systems to their networks and it is important to check with your DNO before proceeding..
You will need install an inverter to transform the low-voltage DC power produced by a wind turbine into high-voltage AC power that meets the quality requirements of the electricity network.
It is important to install an inverter that meets the Engineering Recommendations G83/1 - 'connection of small-scale embedded generators in parallel with public low-voltage distribution networks'. This sets out the technical requirements that small-scale generators need to meet in order to connect to the mains network. Although these are only recommendations, as they have been agreed by the DNOs, applications that conform are usually processed more quickly.
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