Size of turbines, visibility and distance from the coast

Strategic Environmental Assessment (SEA) is the process of assessing the environmental impacts of national plans for offshore energy, oil and gas licensing etc.

For offshore wind farms, the relevant assessments are called the  “Offshore Energy Strategic Environmental Assessments” (OESEAs).

One of the recommendations in OESEA2 relating to the visual impact of wind farms states:

“.. it is recommended that the bulk of new offshore wind farm generation capacity should be sited away from the coast, generally outside 12 nautical miles (some 14 miles).”

In order to site anything closer, special conditions should pertain and proven local acceptability shown.

The larger the turbines, the more visible they are and the further from the coast they need to be sited. In fact, Rampion is already well inside the 14 mile guideline, but the smaller 3.45MW turbines of the current wind farm are likely to be augmented by even larger 16MW turbines (i.e. more than four times as powerful and taller then the Eiffel Tower! – see below for more details). The OESEA3 recommendations indicate that the larger turbines proposed for the Rampion extension should be more than 25 miles offshore (in the dark blue area of the map below) to have relatively low impact. If this is not felt to be possible, then the Sussex bay is simply not appropriate for such a wind farm extension.

The inshore region (as defined in the Marine and Coastal Access Act 2009 and Territorial Sea Act 1987) extends out to 14 miles (12 nautical miles) from the shoreline. Consequently, whatever the size of the turbines, the current Rampion Wind Farm and practically all of the proposed new wind farm will be inshore. No special conditions, other than an greater profit for the developers, warrant this.

It seems important to appreciate the size of what is being proposed. The current wind farm turbines have a blade tip height of 140 metres. The turbines proposed for the new wind farm could have a maximum blade tip height of 325 metres (making them 2.35 times taller) and will be located 13km to 25km (8 miles to 15.5 miles) from the shore. This is according to the Rampion 2 Scoping report published in July 2020 (page 399). However, since more distant objects appear smaller, and the observable height is reduced by the curvature of the earth, the height of the new turbines when viewed from the western part of the Sussex bay will appear significantly greater. From Bognor Regis, for example, the height of the closest new turbine would appear 4.2 times taller than the closest wind turbine of the current wind farm. Most of the turbines in the visible front row of the current wind farm are, on average, further away than the closest one – but when looking directly out to sea at the new wind farm, ALL the turbines in your central view will be at a similar distance to the nearest. The import of this is that the observable height ratio of the new array will actually feel 5.2 times greater.

Figure 1: Relative sizes of the nearest turbine

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