The UN Convention on the Law of the Sea defines an Exclusive Economic Zone of 200nm from the shore of each country.

The UK has invested in offshore wind farms.

One of the contentious issues of these installations is the visual impact from the shore. Tourist destinations oftentimes take pride in their sea view, and interruptions to this can be politically difficult.

If we assume a cliff top elevation of 35 meters, the horizon is ~11.5nm away.

Offshore turbines are ~80 meters high.

In order to completely hide these turbines from view, therefore, they would need to be located ~21nm away from the shoreline.

If the EEZ is 200nm, why are wind farms not typically located out of sight of the shoreline?

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    For what it's worth, the sites being auctioned for round 3 are significantly further out than existing sites. It's fairly likely that the turbines installed will be significantly taller than 80m though. fes.nationalgrid.com/media/1324/davidfloodround3windfarms.pdf – origimbo Dec 26 '19 at 22:35
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    I feel awkward for stating such an evident thing, but height is not the only factor deciding on visual impact. A thin and tall structure will be practically indetectable even if it is not below the horizont. And of course even big structures become way less noticeable even if they can be seen (law of squares applies, doubling distance means that the apparent height-width are both the squared root). Most people who would object to a wind tower 10 meters away would not even notice one that is two kilometers away... – SJuan76 Dec 27 '19 at 1:32
  • And movement emphasises visibility... – 52d6c6af Dec 27 '19 at 9:54
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    I can't imagine a political answer to this question, only technical answers. The answers so far have all been technical (cost of building, maintanance, transmission) Why would you suppose that a political answer exists to this question? – James K Dec 28 '19 at 19:35
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    fwiw – I was watching a documentary on the history and development of electricity distribution in the UK. It was noted that in the early days, there was much criticism that the large transmission towers and ubiquitous distribution lines were "a blight on the landscape". Now we barely even notice them. – spring Dec 29 '19 at 16:05

The cost of servicing them will go up as they move further and further away from land.

Even more importantly, the depth of the water will have a huge impact on the initial construction cost or indeed make construction infeasible. To move 21nm offshore will in many cases move you near or past the limit of the continental shelf. Only certain locations will have conveniently located shallows that far offshore.

Additionally, and this is certainly a personal preference, I don't really mind wind turbines. They're kind of peaceful, much like their windmill kindred. The ones in Hawaii for example are quite beautiful. I understand issues with onland siting and low frequency vibrations for immediate neighbors, but I most certainly would not want my local utility to charge me 50% more for offshore electricity just to make some people happy.

edit: I realize that the UK's situation wrt its continental shelf may be more favorable to remote siting than other countries', but I suspect that depth still increases fairly significantly with distance from shore. And in places like the Channel, locations far from shore could make them more hazardous to ships.

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    You forgot to add - Shortened life because of the depth of the ocean. - Expensive cable management - Rough seas could cause havoc to those wind farms (undersea Base). – user29025 Dec 26 '19 at 23:01
  • The North Sea where most of Northern Europe's wind farms are located is a very shallow sea. The average depth in the south is only 25 to 35 m. For comparison, the average depth of the Atlantic ocean is over 3 000 m. – Björn Lindqvist Dec 29 '19 at 0:08
  • @BjörnLindqvist which is why I edited the bit about UKs suitability for remote siting. theres still a massive cost diff between 25 and 35 m sites though. and in general, though the question was about the UK, it has also surfaced elsewhere, notably amongst Marthas Vineyard NIMBYs. my liking of wind turbine is a preference, but so is that of folk's insistence of not seeing any bits of them. – Italian Philosophers 4 Monica Dec 29 '19 at 6:20

Wind turbines are also rather tall, which means that they can be seen from far away.

Per Wikipedia, the distance to the horizon in km for a 100m turbine is about 36 km.

Add in the distance to any observer's horizon, and a 100m tall turbine is likely to be visible for almost 50 km.

So a 100m turbine would have to be really far out at sea to be invisible.

And the power from the turbine then needs to be delivered to land - by an underwater power cable. The longer the cable, the greater the transmission losses, the more expensive cable maintenance is, and the more likely something will happen to it (ship's anchor, etc). That's another reason distances are limited.

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    And even your distance is predicated on the best case scenario of a low shoreline (or is that what you meant by observer's horizon?). Given for example the Dover cliffs at 110m that distance probably needs to get bumped up some more. – Italian Philosophers 4 Monica Dec 26 '19 at 23:07
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    @ItalianPhilosophers4Monica That's exactly what I meant. So from the Dover cliffs, something 100m tall would be visible over 70 km away, assuming that the appoximation from Wikipedia holds. But I suspect dust/haze/fog in the atmosphere would limit actual visibility to 20 or 30 km on all but the absolutely clearest days. – Just Me Dec 27 '19 at 1:01

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