Small & Medium Wind - Site Selection

This page is suitable for assessing sites for smaller turbines between 50 kW to say 500 kW. It is aimed at domestic up to smaller community turbines It can be used to do a first assessment of a site for its wind energy potential.

To find yourself the proud owner of a successful wind energy generator requires consideration of a few main items:

• The selection of a site which is a suitable distance from obstacles


• Knowing the wind characteristics of that site


• Finding a wind turbine that will provide the amount of energy you require

Small Household

The figure below shows some simple restraint criteria for siting a wind turbine. What you need is an unobstructed steady flow of wind into which you can face the turbine blades. Obstacles such as buildings and trees tend to cause turbulence which disrupts this flow. The turbine needs to be sited around 20x the height of the obstruction from the obstruction itself measured in the direction of the prevailing wind. Alternatively, it needs to be raised well above the turbulence zone by around 10m.

The full wind characteristics include the speed and direction at a particular height and how the wind speed varies vertically over the height of the sweep of the blades. It is possible to erect relatively cheap monitoring equipment for heights up to around 10m or 2x the obstruction height. Armed with this you could make a fair prediction of the expected output from a turbine. Without this, it is possible instead to use the NOABL database of average annual wind speeds to estimate a yearly output. We have reproduced the values and mapped them for you here. But how much is a good wind speed?

Assume you want to offset the energy use of a single family home (3 bed detached, for instance) with electricity needs of around 18,000 kWh/year. You’ve looked at the wind map and you’ve read that your wind speed is 5.0 m/s at a height of 10m. The swept area required would be approximately 86 m² or 5.2 m radius. This is a simple approximate calculation:

Area, A = Energy Required in kWh/yr x 1000 / (0.5 x 1.225 x V³ x 8760 x 1.9 x 20%)

Where V is the wind speed from the maps. An efficiency of 20% of these smaller turbine models is assumed.

Let’s take a look at some manufacturers models and what they might supply under these theoretical conditions:

Turbine Type	Hub Height (m)	Rotor Diameter (m)	Estimated Yearly Output kWh
Evoco 10 kW *	12	9.7	21700
Proven 35-2 *	15	8.5	23200
C&F CF11	15	9.0	24000
*Available on the MCS scheme

Financially, the installation of such a system would be in the order of £45,000 (+VAT). The actual energy cost which is being offset would be around £2000 per annum for this example.

Small Industrial

Let’s look at some larger examples. Say you are a small school or factory or farmer with an annual electricity use of 100,000 kwh/yr. Assuming a single turbine solution again then you would need to look at something at a higher height than 10m say around 25m. Again, the appropriate wind speed map would give you a wind speed for your area. Let’s assume 5.5 m/s for our illustration. Your site would once again need to be around 20x the height of obstructions away from the obstruction itself (including your neighbour) and the swept area you would require would now be 295 m2. Some manufacturers who can provide this type of turbine are:

Turbine Type	Hub Height (m)	Rotor Diameter (m)	Estimated Yearly Output kWh
Endurance E-3129 50 kW	24	19	140,000
ReDriven 50 kW	24	14.3	120,000

Cost of installation around £250,000 for these models. Savings on the energy bill would be around £20,000 per annum.

Small Community

For the next example, let’s take a small village of say 50 homes. Total electricity usage maybe around 900,000 kwh/yr or 900 MWh/yr. The FITs tariff would be returned to the  community company that would need to be formed, say a co-operative. They would own and operate the turbines and then distribute the profits for community use. The appropriate map (45m above ground level) tells you that the average annual wind speed is 6.5 m/s. You would be aiming at a group of turbines at a height of 45m with a total required area of 3200 m2. We would recommend a minimum distance at 400m from properties for first discussions.

Turbine Type	Hub Height (m)	Rotor Diameter (m)	Estimated Yearly Output MWh
Enercon E-33 330 kW (1 no.)	44	33.4	900

Cost of installation for turbine can be estimated at £0.7m with returns for generation tariff at £170,000 per annum (18.8p/kWh) and for export tariff at £27,000 per annum. Origin would propose a JV with the community co-operative in which a profit share could be arranged, with 90% going to the community.

What we can do for you

We would be happy to discuss all aspects of design, turbine selection, financing and management for you. We specialise in community renewables and the benefits that they can bring.

You will also need to obtain planning permission in order to erect any turbines. Zephyr would be pleased to arrange this for you and include this in the overall project cost. Note also that schemes of less than 50 kW need to use the Microgeneration Certification Scheme and anything above this is accredited through the ROO-FIT process.