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A Rough Guide to Offshore Wind Energy and Geography [VIDEO]

Robert Wilson's picture
University of Strathclyde

Robert Wilson is a PhD Student in Mathematical Ecology at the University of Strathclyde.

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  • Mar 28, 2013

It has become a cliche to call the seas around the UK the “Saudi Arabia of offshore wind.” The reasons for this are relatively straightforward. The ideal conditions for an offshore wind farm is a lot of wind and a not particularly deep stretch of water. The North Sea has both, so much so that more or less all of the planet’s offshore wind farms are located there. To demonstrate why the UK is rightly called the Saudia Arabia of offshore wind let’s first consider some simple geometry and then take a quick tour around the world and consider how the UK compares to other regions.

Roughly speaking offshore wind farms are currently restricted to regions where sea bed depth is no greater than 60 metres. And for obvious reasons you don’t want to build one too far from land. On a lot, though not all, of the planet coastal regions gradually get deeper until you get to the continental slope when the ocean gets deep quickly, which goes like this:


If we assumed for simplicity all coastlines on the planet are the same then the distance from shore at which offshore wind is viable will be the same. A simple consequence of this is that, all things being equal, the larger the land mass the lower the relative potential for offshore wind becomes. To show this consider two circular land masses, one much large than the other, with the blue region signifying the fixed distance from shore that offshore wind can be developed.


So, essentially a small island, e.g. the United Kingdom, should, all things being equal, have a significantly higher offshore wind resource than most other countries, which are almost all significantly larger, or have much smaller coastlines.

Of course all things are not equal. Two other factors are very important, average wind speed and sea bed depth. I will only consider sea bed depth, because it is this that gives the United Kingdom an added advantage.

At this point I should perhaps digress to explain how much sea would need to be covered in wind turbines to provide X% of a country’s electricity or energy supply. If you interested in subject this Ted Talk by David MacKay is a good primer. However the gist is this: the UK consumes about 1.25 watts of energy of per square metre, whereas wind farms produce about 2.5 watts per square metre. So, to get all of the UK’s energy needs from wind power you would need wind farms to cover roughly half the area of the UK.

Let’s begin with at the European scale and consider how the UK fares against the rest of Europe.

As I mentioned at the start, most offshore wind farms are restricted to regions where sea bed depths are less than about 60 metres. Below are the regions (coloured black) in the waters around Europe that are shallower than 60 metres.


European waters shallower than 50 metres

So, a huge swathe of the North Sea is available, along with the English Channel and parts of the Baltic Sea. The Atlantic Coast does not have a great deal of potential at this depth, and the Mediterranean is even worse. The North part of the Adriatic has some potential. The UK and Denmark are clearly the most favourable regions, and Holland is not too bad either.

Let’s say we could develop in waters 500 metres deep, which is pretty unlikely any time soon, but is a good indication of the absolute limits of fixed foundation wind farms. What then?


European waters shallower than 500 metres

This expands the range of offshore in the North of Europe greatly, but does very little to the potential in the south of Europe. Mostly it just confirms the advantage the UK and Denmark have over the rest of Europe in terms of their offshore wind resources.

The advantageous geography has already resulted in a proposal to build a wind farm, the Dogger Bank, in the middle of the North Sea. And at a distance from shore close to impossible in southern Europe:


Area of the proposed Dogger Bank wind farm in the North Sea

Let’s shift to America. Here are the regions deeper than 60 metres.


American seas shallower than 500 metres

What leaps out is how much more favourable the Atlantic Coast and the Gulf of Mexico are compared to the Pacific regions. As before, let’s consider regions where sea bed depths are greater than 500 metres.

This improves things a lot in the Atlantic regions, but the Pacific still has little relative potential. This map shows that onshore wind should continue to dominate the US wind industry for some time.


American seas shallower than 500 metres

A quick comparison of US east coast waters shallower than 60 metres with the UK shows that the UK has significantly higher relative offshore wind than the US. (note however that energy use per square kilometre in the UK is about 3 times higher than in the US, so in a less rough guide to offshore wind you wind to adjust for that properly.) Essentially wind farms can be built further from the coast in the UK than almost the entire US eastern seaboard.


European and US eastern seaboard seas shallower than 60 metres

Moving to China, and its western neighbours. First consider Japan and Korea. The regions shallower than 60 metres are:


Japanese and Korean waters shallower than 60 metres

At this depth Japan has some, but limited offshore wind potential. Certainly not comparable with the North Sea. The western coast of Korea is reasonable.  Quite clearly Japan’s potential seems to be much lower than the UK’s. (another digression: Japan has a higher energy use per square kilometre than the UK. It also has close to the highest level of forest coverage in the world, 68%. So, you can easily see that a nuclear-free Japan may have some problems going nuclear free. A subject I will cover in an upcoming post.)

Let’s push it up to 500 metres.

An improvement, but this indicates that offshore wind has some limits in Japan, and will probably need the development of floating turbines to give it a UK level of offshore wind potential.


Japanese and Korean waters shallower than 500 metres

China’s coast runs from Vietnam to Korea. Let’s have a look at that. The regions shallower than 60 metres are shown below.


China’s waters shallower than 60 metres

Sea bed depth then appears to be quite favourable for offshore wind in China. It’s also worth noting that the regions near the major population centres, such as Beijing and Shanghai appear to be even better than the rest of the Chinese coast. However, given the size of China, and its relatively small coastline it is clear its relative offshore wind potential is likely smaller than the UK’s.

For brevity I will skip the other major regions of the world, as I fear that while they back up the point that the UK has a much better offshore wind resource than most of the planet, the reader is likely to be getting slightly bored by the repetition.

A more detailed view of the UK’s offshore potential can be found in the Crown Estate’s Offshore Valuation.

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Lund's picture
Lund on Mar 29, 2013

Hi Robert,

Thank you for another very good input to the debate, with relevant and interesting points.

May I correct a couple of things:

You say:

"the UK consumes about 1.25 watts of energy of per square metre, whereas wind farms produce about 2.5 watts per square metre. So, to get all of the UK’s energy needs from wind power you would need wind farms to cover roughly half the area of the UK."

Well, according to Wikipedia, the average power consumption* in the UK is around 41 GW, and UK's land area is 243.610 square kilometers, so the average consumption is only = 0,17 Watts per square meter.

(* I know you count the primary energy consumption)

So, if the offshore wind farms can produce 2,5 Watts per square meter, you only need 1/15 the area of UK.

Dogger Bank covers and area of 17,600 square meters, with water depths between 15 to 36 meters - so here it should be relatively straight foreward to raise wind turbines.

The wind resources are among the same as on Horns Reef, where the relatively small 2,3 MW turbines now produce 3 Watts per square meter.

I guess we can easily aggree that using 8 GW turbines with 164 m rotor diameter, or 6 MW turbines with 120 m rotor diameter, you can install more capacity on the same area than using 2,3 MW turbines with 93 m rotor diameter, even if you keep the optimal spacing of 5 times the rotor diameter.

- and the mean wind speeds will be higher, simply because the higher towers and larger rotors reach into air streams with higher mean wind speeds.

This is why I have told you before that on locations like Dogger Bank, we can expect capacity factors up to 60%, with the larger and more efficient turbines, and as also the capacity per square meter is higher, it is fair to expect that Dogger Bank can produce at least 3,5 Watts per square meter.

But we don't even have to discuss this for now, because even with your very pessimistic 2,5 Watts per square meter, the Dogger Bank area is plenty to produce an average power equal to the actual UK consumption, because 15 times the Dogger Bank area is clearly larger than UK's land area.

Including the many good locations around the british islands, shown on your map with less than 60 meters depth - especially the areas with much higher wind speeds, north west of Scotland - you can produce several times the power consumption of UK.

And, as you count the whole consumption of primary energy in the UK, wich is now roughly 6,5 times the power consumption, you have to remember that thermal power plants, especially the nuclear ones, typically spent primary energy equal to 2-3 times their electricity output, so when you replace these with windpower, you automatically cut a huge part of the primary energy consumption - and another huge part when you supply electric cars and heat pumps with wind power, in stead of using fossil fuels.

Saudi Arabias oil production, which for the moment is 500.000 barrels per hour, equal to 340 
GW when converted to electricity, can barely keep up with the UK's potential offshore windpower!


Best Regards,

Søren Lund






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