Offshore Wind
Frequently Asked Questions
BWEA has collected the most common questions we get asked about offshore wind energy. Scroll through the questions and click on one to see the answers.
Why?
Why do we need offshore wind farms?
Will they replace onshore turbines?
How big is the offshore wind resource?
Where?
Where will offshore wind farms be built?
How deep will the water be?
How far out to sea will they be?
Is there a limit to how far out to sea these can be built?
How?
How do you build an offshore wind farm?
How realistic are floating platforms?
Won't all the metal bits rust away?
How will the electricity get into our homes?
How much power will the turbines produce?
How many will there be?
Isn't it more expensive to build offshore?
What are the development and planning processes that have to be done?
Can offshore wind power be combined with wave power?
What will they look like?
What would the turbines look like?
How big will they be?
What colour will they be?
How big will they look from the shore?
Will they have flashing lights on them like lighthouses?
Will they show up on ships' radar?
What effects will they have?
What are the environmental effects of offshore wind farms?
Will they disturb the seabed and cause coastal erosion?
Will offshore wind farms affect shipping paths?
Will they affect fishing?
Will they affect marine life?
What about sea birds?
Will any wind come to shore if it's being used by all these turbines at sea?
What if there's a storm at sea?
Are there any environmental benefits?
Finally ...
When will they be built?
How will they be funded?
What other countries have wind farms at sea?
How long will they be up for?
Will offshore wind farms generate jobs in the UK?
How can I get involved?
Where can I find out more?
Why do we need offshore wind farms?
There are several factors which suggest the development of an offshore wind energy industry. The resource is extremely large, the energy costs, although initially higher than for onshore, are cheaper than other renewable technologies and the risks are low, as early projects have shown.
Many people, while agreeing that wind turbines are a useful strategy, are not happy to see them in their area. This is the NIMBY principle - not in my back yard. Siting wind turbines at sea will reduce the constraints that can be found on land, such as the visual impact and planning challenges.
The UK is currently in a position, given the right incentive and initiative, to create a significant new offshore industry. As the field is relatively new, we could take the lead in offshore installation by utilising our existing highly skilled offshore workforce. Conventional energy generation companies are already diversifying their operations into renewable energy sectors and the offshore oil industry is in a unique position to exploit its highly skilled offshore workforce.
Will they replace onshore turbines?
Although the expansion of the wind energy industry offshore will help to meet government targets on renewable generation, they will not replace development onshore. The DTI has indicated that they anticipate wind power to play a major role in achieving the 2010 target of 10% or the total UK electricity supply from renewables technologies. 4% will come from new onshore developments while a further 4% will be met from the emerging large scale offshore sector.
How big is the wind resource offshore?
The wind energy resource at sea is extremely large, and the UK has one of the highest in the world with over 33% of the total European potential. In fact, the UK's offshore resource is equivalent to three times the UK's annual electricity consumption. Conservative calculations show that offshore wind alone could meet the 10% target by 2010.
Offshore wind speeds are generally higher than coastal wind speeds. Ten kilometres from the shore, speeds are typically around one metre per second higher. Given that the power output is a function of the cube of the wind speed, this is very good prognosis! There are large areas of North Sea with wind speeds above 8 m/s and turbulence is lower offshore. This reduces the fatigue loads, but wind/wave interactions will have to be taken into account during design.
Where will they be built?
There are currently four offshore project operating in the UK, making a total of 213.80 MW. You can see a map of these projects, along with other projects with planning consent, on our 'Round 1' map. In the future projects will be larger and futher out at sea, the 'Round Two' projects. A map of 'Round 2' can be found here.
How deep will they be?
The turbines will generally be built in relatively shallow water - less than about 30 metres in depth.
How far out to sea will they be?
BWEA Best Practice Guidelines were revised in 2005 to include offshore considerations. Amongst these is the recommendation that all offshore projects should be sited at least 5 km offshore, although some sites built already are closer to shore than this. All of the 'Round 2' projects are at least 8 km offshore, hard to see on anything but a very clear day.
Is there a limit to how far out to sea these can be built?
Although it is possible to build structures in water deeper than 30 m (for example the oil platforms in the North Sea), it is very expensive and is not economically viable at present for offshore wind turbines.
Wind speeds tend to increase as you move offshore. This means that turbines built further offshore should capture more wind energy. Unfortunately, as the distance to land increases, the cost of building and maintaining the turbines and transmitting the power back to shore also increase sharply, limiting the distance out to sea at which offshore wind projects will be built.
How do you build an offshore wind farm?
There are no technical barriers to installing offshore turbines but the construction, delivery to site and assembly of such large machines needs specialist equipment and vessels, facilities at ports and careful timetabling to make sure that the possibilities of using calm weather windows are maximised.
Most UK developments have been installed using steel monopiles, but projects in other countries have used gravity foundations. Gravity foundations are concrete structures which settle and are stabilised by sand or water and the turbine tower fits into them. Monopiles are long, steel tubes which are hammered, drilled or vibrated into the sea bed until secure and then platforms and towers are installed on top.
How realistic are floating platforms?
Although it would be technically feasible to mount wind turbines on floating structures, studies have shown that it would be very expensive to do this. However, technical developments may make floating offshore wind farms economically feasible in the future.
Won't all the metal bits rust away?
The metal parts of the turbine structures will be specially coated to protect them from corrosion, which is already a common procedure in the offshore oil and gas industry.
How will the electricity get into our homes?
Underwater cables will transport the electricity from the turbines to a transformer located onshore. This will convert the voltage for transmission through the national grid through the local grid connection. You can see this in a diagram here.
How much power will the turbines produce?
Most modern offshore projects have been built with 2 - 3 megawatt machines, but in future this will rise to 3 - 5 MW. Higher wind speeds at sea mean an increased energy production, as energy output is a function of the cube of the wind speed. Each turbine would typically generate enough electricity each year to meet the needs of 2500 households while displacing in the region of 50,000 tonnes of carbon dioxide as it does so.
Should all the sites announced by the Crown Estate go-ahead, they will produce sufficient electricity to power over 4 million households.
How many will there be?
Only a fraction of the UK seabed would be needed to house offshore turbines. Given that the offshore resource is so large, conservative estimates suggest that aside from economic constraints offshore wind alone could meet the Government target of 10% of all electricity generation from renewables by 2010. This would require 10 GW of turbines. Assuming a typical offshore turbine to be 3 MW, this translates to 3,300 turbines in an area of seabed 1,200 km2 - an area roughly the size of a city like London.
If the UK were to match the more ambitious Danish plan and generate 40% of the country's electricity needs by 2030 offshore, then this equates to 48 GW from 16,000 turbines in an area roughly 4,800 km2 - less than 1% of the UK's seabed.
Click on the image to use a simulation game, where you can drag and drop offshore wind farms around the UK coast and see the power they produce. Alternatively click here to see the size and location of the 'Round 2' projects.
Isn't it more expensive to build offshore?
So far offshore energy prices are around 40% higher than onshore costs. Capital costs are around 30-50% higher than onshore, mainly due to foundations and the costs of transporting and installing at sea. This is partially offset by higher energy yields - as much as 30%. However, as happened onshore, these prices are expected to drop as technology improves and more experience is gained.
What are the development and planning processes that have to be done?
Developing a new technology in a previously undeveloped area involves a range of stakeholders, including shipping, fishing, environment, MOD, cabling and many others. 'Round 1' consenting has involved The Crown Estate for the lease of the seabed, DTI for statutory consent along with gaining the permsion of a range of other Government bodies. For 'Round 2' the DTI has created an Offshore Renewable Consents Unit to simplify the process by co-ordinating with all the disperate parts of government, guidelines for which will be released shortly.
Can offshore wind power be combined with wave power?
There are calls to combine tidal and wind power and install tidal stream turbines on the bases of offshore wind turbines. Marine renewables, however, are at an earlier stage of development than offshore wind so it will be many years yet before these developments occur. Find out more about BWEA's marine renewables work.
What do the turbines look like?
Offshore turbines look similar to those onshore with several design modifications. These include strengthening the tower to cope with wind-wave interactions, protecting the nacelle components from sea air (marinisation) and adding brightly coloured access platforms for navigation and maintenence.
How big will they be?
When developing many km offshore, constriants on turbine size due to visual impact and transport are reduced. Foundation costs also remain similar for larger turbines, so offshore the trend is definately larger. Typical onshore turbines are in the 2 MW range, where as future offshore developments will be in the 3 - 5 MW range, with a hub height of around 70m and 50m blades.
What colour will they be?
As with onshore turbines, offshore machines can be almost any colour, but most are very light blue or grey to help them blend into the sky. The lower section of the support towers may be painted bright colours (e.g. yellow) in order to provide navigational aids and highlight the structures for passing vessels.
How big will they look from the shore?
Obviously the closer to shore the turbine are, the bigger they will look. However, BWEA guidelines for offshore development suggest that turbines be installed no closer than 5 kms to shore.
This is a picture taken from the shore of North Hoyle offshore wind farm. There are 30 turbines, 100 m to blade tip, with the closest 5 km away. It's clear that the visual impact is quite low. Click on the image to see a larger version.
Will they have flashing lights on them like lighthouses?
Although the turbines will need to be marked with lights to help navigation, these lights will not be nearly as bright as the beam from lighthouses. They are more likely to resemble the lights currently found on buoys and cardinals.
Will they show up on ships' radar?
The turbine structures will show up clearly on ship radars because not only will the structures themselves reflect the radar signal, but they will also be fitted with radar reflectors.
What are the environmental effects of offshore wind farms?
The environmental impact of offshore wind farms is considerably reduced compared with those onshore; both noise and visual impact are unlikely to be issues, but there are still some considerations. For example, there could be an environmental impact from carrying out work offshore, such as localised disturbance of the seabed.
Will they disturb the seabed and cause coastal erosion?
Any proposed scheme will fully investigate the wave and coastal processes prior to construction. However, the turbine structures are such that it is unlikely they would significantly affect the sea bed or wave patterns.
Will they affect shipping paths?
The turbines would be spaced such that small vessels, assuming the depth of water is adequate, would be able to sail through the array and any developer wishing to build a wind farm offshore would identify whether their proposed site would interfere with shipping routes or pleasure craft. As a part of the consultation process, local sailing organisations and the RYA should be contacted.
Will they affect fishing?
Wind farms are unlikely to be situated in recognised fishing areas. Sensitive site selection would usually ensure that no interference could occur which would disturb fishermen or the underground cabling!
Will they affect marine life?
Studies on existing projects have shown that some foundations can act as artificial reefs with a resultant increase in fish populations from the new food supply.
It has been suggested that the noise from the turbine travel underwater and disturb sea life. This is not apparently the case according to a Sea Mammal Research Unit report which says that as long as there has been some previous exposure to boats, engines etc. it doesn't bother seals at all.
What about sea birds?
The issue of the effect of wind turbines on avian populations holds no more water at sea than it does onshore. Wind energy projects are unlikely to be sited in designated or species rich areas and studies carried out the existing offshore projects and the near offshore project at Blyth harbour show no significant affects on bird populations in those areas which can be attributed to the turbines.
Indeed, the increases in fish populations noted above has a stimulating effect on bird populations in the area, so overall a beneficial rather than detrimental effect!
Will any wind come to shore if it's being used by all these turbines at sea?
While wind turbines are remarkably efficient at converting the energy of the wind, according to a recent report from the Royal Committee on Environmental Pollution, there will still be enough left over for some cooling sea breezes!
What if there's a storm at sea?
As with onshore, turbines are warranted and tested to withstand extreme wind conditions and in the event of severe weather, the blades turn out of the wind and are fixed in position for safety when wind speeds become storm force i.e. 56 miles per hour and above.
Are there any environmental benefits of offshore turbines?
Every unit of electricity generated from the wind, whether on land or at sea, saves a unit generated from coal, oil or gas - depending on what type of power plant it replaces. Therefore each unit of electricity generated by wind energy saves emissions of greenhouses gases, pollutants and waste products.
When will they be built?
The UK first offshore wind farm was built in 2000. There are currently 3 further large scale offshore wind farms generating, with one more 'Round 1' project due for construction next year. The 'Round 2' projects will be built between 2008 and 2010.
How will they be funded?
The Government has indicated that its intention is that renewable energy technologies are to be supported by the market. The Renewables Obligation (RO) together with the Climate Change Levy make renewably-generated electricity an increasingly attractive option for energy companies. An additional £118 million was allocated for offshore wind energy in 'Round 1' in the form of capital grants the help the industry get started. 'Round 2' will only be supported by the RO, and its sucess is partly dependent on the RO review in 2005/6.
What other countries have wind farms at sea?
A total of 14 offshore projects are currently operational worldwide in 5 countries. Click here to see a list of offshore wind projects around the world.
How long will they be up for?
Anticipated plant life of wind turbines tends to be 20-25 years and offshore turbines should be no different.
Will offshore wind farms generate jobs in the UK?
Yes! Just one 75 MW installation would create an estimated 245 jobs. The offshore wind energy industry in the UK represents a total potential market of £48 billion, and the creation of an entirely new industry will have significant effects beyond the employment figures.
How can I get involved?
If you are a company that is interested in benefiting from the development of one of the greatest untapped natural resources in the UK and beyond, then you should consider becoming a member of BWEA. We have a good relationship with the DTI, the Crown Estate and other relevant parties, and are constantly lobbying and research to make UK offshore wind a sucess. Find out about Membership information.
 Alternatively, send an SAE to BWEA, 1 Aztec Row, Berners Road, London, N1 0PW and we'll send you an offshore wind badge.
Where can I find out more?
The Offshore Wind Energy Network (OWEN) is the industry and research establishments' focus on R&D in offshore wind, supported by BWEA.
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