Wind Site Self Assessment (WSSA)

4 Is your wind speed sufficient?

A good site for a wind turbine needs exposure to wind. The amount of energy and therefore income generated by a wind turbine, increases disproportionately with increasing wind speed, so more wind is always better. It is good practice to position a wind turbine in the most exposed location, though sometimes exposure to wind is sacrificed a little to make a wind turbine less visible, which can help with obtaining planning permission.

How does your windspeed compare?

Wind speed (m/s)		Comment
Less than 5 m/s		Too low for a commercially viable project.
5 – 6 m/s		A bit low for a commercially viable wind turbine, unless you can consume all of the energy on-site to maximise the benefits of offsetting imported electricity.
6 – 7 m/s		A reasonable site with a reasonable return-on-investment, particularly if the electricity can be used on-site.
7 – 8 m/s		A good 'commercial grade' wind site that third-party wind investors would be interested in, so would make a very good private investment once planning consent was obtained.
8+ m/s		Exceptionally high wind speed – if you could get planning consent this would be a valuable wind site with a high return-on-investment.

How accurate is the wind speed estimate?

The wind speed estimation software is based on the old UK Government NOABL database. Although good for initial estimates, we generally find the average estimation error is +/- 0.5 metres per second (m/s) - but unfortunately it can go either way! Despite this, it is as good a tool as any for having an initial free check.

A more accurate check is possible using the Met Office’s basic VMM service, though this would normally only be done at a later stage because it costs money. The NOABL tool is based on the average wind speed over a 1 km² grid square at 45 metre 'hub height'.

We normally supply turbines with hub heights from 25 metres to 125 metres. For higher hub heights the wind speed will be higher than the estimation tool indicates because wind speed increases with height. If the likely turbine is higher than 45m hub height we will apply a correction factor to the wind speed.

5 Mark desired and existing wind turbines on the map

Desired turbine location

If, after consulting the tables above, you consider the wind speed at your site viable for a wind turbine, use the 'Desired turbine location' object to mark the most desirable turbine within your property boundary, i.e. at the best location based on the highest wind speed. If there are multiple locations at high wind speed then choose a location you consider to be suitable.

Existing turbine location

6 Mark and measure proximity of nearest properties

Financially Involved Property

Modern wind turbines are incredibly quiet, but even so they are large machines so will produce some noise. The minimum separation distance between a wind turbine and nearby properties depends on whether the properties are 'financially involved' in the wind project or not.

Non Financially Involved Property

• Using the relevant markers, mark all financially involved properties on the map.
• Next repeat the same process for the three nearest non financially involved properties
• 

  Ruler tool

  Using the ruler tool measure the distance between the desired turbine location and financially involved properties. The distance will appear next to the ruler tool.
• Enter the distances of the first 3 properties of each type in the following fields. (Just type 'n/a' in the relevant box if there are none.)

Distance in meters from Financially Involved Properties

Distance in meters from Non Financially Involved Properties

7 Select appropriate turbine

The turbine rating is effectively the maximum power it can output. This output is related to the size and dynamics of the turbine rotor which in turn affect the noise properties of the turbine. The quieter the turbine, the closer it can be to a residential property.

Using the minimum distance you have measured for Non Financially Involved Properties only , look at the table below to select the turbine with the most appropriate rated output for your location.

8 Statutory Designations

If your land is located nearby statutory designations then a further detailed assessment will be required in order to assess planning sensitivities.

There are several designations that are likely to cause significant issues if your land lies within them

Select any of the following designations that your land lies within:

9 Access

Next it is important to check that it would be possible to access your site with the heavy cranes and large abnormal loads during the installation stage. The longest items are the blades, the widest either the generator or the base of the lower tower section. The latter two items are also very heavy so cannot pass over weak bridges. A summary of typical sizes and weights is provided below:

Delivery vehicle dimensions and weight

Generally speaking, if the wind turbine delivery vehicles can access the site then the installation cranes will also be able to access the site without any problems.

It isn't possible to complete a full access assessment at this stage, but the following checklist will give you a good indication of whether access would be possible at a reasonable cost.

Please answer the following questions in relation to transport to your site:

10 Mark the access route from the nearest 'A' road

Access Route tool

If you have answered positively to the questions above, it may be possible to access your site with a wind turbine. If you can't answer them all positively, it may still be possible but is likely to require more expensive access upgrades. It may also need the agreement of other landowners. We can provide an Initial Access Assessment (IAA) which will give you a clearer idea of what is possible.

If you think access to your site is feasible, use the "Access Route" tool on the map to indicate the route you would consider most appropriate to the site from the nearest A-road.

11 Grid Connection

Three-phase 11 kV power lines look like this

The final check is to ensure there is a suitable grid connection. Single-turbine wind sites generally only need a three-phase 11,000 volt (11 kV) grid power line nearby. Larger developments (typically 5 MW+) may need 33 kV power lines. Higher-voltage lines which are carried on steel pylons have much too high voltage for all but the very largest wind farms – so for smaller projects having pylons nearby is no benefit.

If you consume a large amount of electricity on-site already you will probably have an 11 kV substation nearby, so it may be possible to grid-connect the wind turbine through your existing on-site distribution system. If this isn't possible it would be desirable to have a three-phase 11 kV power line as close as possible to the proposed wind turbine site.

33 kW power lines look like this

Note that three-phase power lines have three wires, and power lines with two wires only have two-phases present and are normally used for single-phase supplies to properties. If you only have two 11 kV wires on your nearest poles, there may be the option to add a third 11 kV conductor to the same poles for a reasonable cost, depending on the length of the upgrade.

If you have large metal pylons on or near your land, they are 132kV or above and are not suitable for connection of this scale of development.

Mark grid infrastructure on the map

Substation

Transformer

3 phase power line

1 phase power line

Once you have worked out which power lines, ground-mounted substations or pole-mounted transformers you have nearby, mark them on the map. Mark substations using the 'Sub Station' tool, Transformers using the 'Transformer' tool and power lines using the appropriate power line tool - 3 Phase (3 cables) or Single Phase (2 or fewer cables). Just double click when you want to stop drawing the power line.

Once complete, use the "measure" tool and fill in the answers to the questions below:

Even if you have suitable grid infrastructure nearby you will still need to obtain permission to grid-connect the wind turbine from the local Distribution Network Operator (DNO) (note we would handle this later in the feasibility process). The DNO will only grant permission if the grid is suitable.

The distribution network is getting increasingly congested and occasionally it's not possible to grid-connect a wind turbine, unless you have large on-site loads to consume the energy.

If you have a strong 11 kV power line close to the site you will have a reasonable chance to connect.

If you cannot consume the energy on-site or have strong 11 kV power lines nearby you may still be able to obtain permission by paying for a grid upgrade, although this can cost anything from a few tens-of-thousands of pounds to millions. How much you can afford to pay for a grid upgrade will depend on the scale of development and how good the wind turbine site is.