Wind turbine technology is well-established and due to its flexibility, it can be utilised practically anywhere. There are two basic systems available for using wind turbines to generate electricity - stand-alone or grid-connected. Wind turbine design can be either the more common horizontal axis type or vertical axis design. The turbine design and size to suit your site best is very dependent on your individual circumstances.

Stand-alone systems

Small wind turbines have traditionally been used to generate renewable electricity for charging batteries to run small electrical applications, often in remote locations where it is expensive or not physically possible to connect to a mains power supply. Such examples include rural farms, island communities, boats and caravans. Typical applications are electric livestock fencing, small electric pumps, lighting or any kind of small electronic system needed to control or monitor remote equipment, including security systems.

Grid-connected systems

Here the output of the wind turbine is directly connected to the existing mains electricity supply. This type of system can be used both for individual wind turbines and for wind farms exporting electricity to the electricity network. A grid-connected wind turbine can be a good proposition if your consumption of electricity is high. The energy produced by the turbine can be used to reduce the energy taken from the grid, and for claiming Renewables Obligation Certificates (ROCs). The value of avoided electricity purchases is generally significantly higher than the value that can be obtained from exporting power to the grid.

When a wind turbine connection to the mains supply is made, it has to be approved by your local electricity company. They will insist on the connection being to a high technical standard and therefore the cost of incorporating power import and export metering and approved electrical protection equipment can be high. They may also limit the size of the wind turbine that may be connected in a particular area depending on the loading of the electrical distribution system in the vicinity. For small wind turbines, the cost of grid connection can be a substantial part of the total project cost.

Turbine sizes

Small scale wind turbines vary in size with a range of models available. Turbines ranging from 0.6 kW to 50 kW are used to provide electricity generation for individual houses and businesses, with rooftop models varying from 0.5 kW to 2.5 kW in size.

Siting a Small Wind Turbine

Wind speed

The first stage of any wind energy project is the available resource base. Feasibility assessment determines the average wind speed available on the site and accordingly the amount of energy that can be generated. Electricity produced by a wind turbine over a year depends critically on the annual mean wind speed at the site - higher wind speeds produce more energy. Sites located only a hundred metres apart can be significantly different. The ideal site is on a smooth and exposed hill top or rise and clear of any obstructions within a few hundred metres - such as trees or buildings. If connecting to the grid, the site should not be so far from the property or electricity connection that the cost of connection becomes excessive.

To assess the average wind speed at a particular site, a general indication can be established by using the UK wind speed database, available at www.bwea.com/noabl. This returns an estimated annual mean speed for a given Ordnance Survey grid reference.  In general, small scale wind turbines start to generate electricity in wind speeds of approximately 2.5-4 metres per second (m/s) and their rated optimum wind speed is 10-12 m/s. For instance, a 6 kW turbine at a wind speed of 5 m/s will generate an average of 11,000 units of electricity a year.

Planning

Small wind energy installations require planning permission and local consultation with relevant stakeholders, such as neighbours. Deciding factors include environmental considerations, access to the site, noise and visual effect. Overall, national planning policies support the development of small scale wind energy, as noted below.

Planning Policy Statement 22 (PPS22) sets out a clear national policy framework on renewable energy for planning authorities in England to ensure that the Government’s renewable energy targets are met. Under PPS22 regional and Local Planning Authorities should recognise the full range of renewable energy sources, their differing characteristics, locational requirements and the potential for exploiting them subject to appropriate environmental safeguards. Small scale developments can also be permitted within areas such as National Parks, Areas of Outstanding Natural Beauty and Heritage Coasts provided that there is no serious environmental detriment to the area concerned. PPS22 introduces a new policy area for small systems by encouraging Local Planning Authorities to require that new developments should supply a percentage of their energy needs from onsite renewable energy sources.



Costs of Small Scale Wind Energy

After the initial outlay of the wind turbine itself - and time spent obtaining planning permission, grid connection and power purchase agreement with your local electricity company - running costs are comparatively low and the fuel, the wind itself, is free. Wind energy technology is robust, requiring little in the way of maintenance; in fact most installations only require an annual check up. Turbines typically have a working life of 20-25 years.

Renewables Obligation

In addition to low maintenence costs, wind energy also has the benefit of counting towards the  Renewables Obligation targets, introduced in April 2002. This is a legal requirement placed on electricity supply companies to source an increasing proportion of their supply from renewable resources up to 10% by 2010, and increasing to 15%
by 2015. If your generation capacity is sufficiently large and is ‘supplied’ onwards, i.e. distributed through a network, you may be able to claim ROCs. The minimum required power output is 0.5 megawatt hours per annum.