Tag Archives: Offshore wind

Offshore turbines get approval of seals

Researchers tracking the movements of seals in the North Sea reveal that “artificial reefs” created by wind farms and pipelines are becoming attractive as foraging grounds on fishing expeditions. LONDON, 25 July, 2014 − Environmental campaigners and countryside conservators aren’t the only fans of those great arrays of turbines, generating renewable energy from the winds at sea. Grey and harbour seals in the North Sea are beginning to show a preference for offshore wind farms as well. Deborah Russell, research fellow at the University of St Andrews, Scotland, and colleagues tracked the movements of both the harbour seal (Phoca vitulina) and the grey seal (Halichoerus grypus). There are an estimated 56,000 harbour seals in the North Sea and around 65,000 of the greys haul out on the British coast on the North Sea alone. Tagged specimens, with their movements tracked by GPS satellite systems as they surface to breathe, reveal a lot about the ecology of each species and their response to environmental change.

Distinct preference

The researchers report in the journal Current Biology that some of their tagged animals seemed to show a distinct preference for offshore wind farms and associated pipelines. Eleven harbour seals headed for two wind farms: one was Alpha Ventus, off northern Germany, and the other was Sheringham Shoal, off the North Norfolk coast, England. Some individuals regularly cruised the sites, and some even revealed a pattern of grid-like movements as they appeared to forage at individual turbines. Two seals in the Netherlands were tracked along sections of submarine pipeline, on fishing expeditions that lasted 10 days at a time.

A harbour seal with a GPS phone tag used to track movements Image: Current Biology, Russell et al
A harbour seal with a GPS phone tag Image: Current Biology, Russell et al

The guess is that the seals regarded the offshore structures as artificial reefs where crustaceans settle and fish congregate. Turbine blades can swirl at speeds of up to 280 kilometres an hour, and represent a danger to  birds and bats − one estimate is that such structures in the US account for 600,000 bat deaths a year. But marine creatures far below the circling blades seem to value a touch of freshly-planted, three-dimensional shelter in the muddy basin of a shallow sea. “I was shocked when I first saw the stunning grid pattern of a seal track around Sheringham Shoal,” Dr Russell said. “You could see that the individual appeared to travel in straight lines between turbines, as if he was checking them out for potential prey, and then stopping to forage at certain ones.”

Open questions

Only a small proportion of the tracked animals showed a preference for wind farms, and such structures still cover only a trifling area of the available coast. But the research leaves open a number of questions. One is whether, as wind farms add to the available habitat in the North Sea, they will increase the available fish and crustacean populations, or whether they simply attract the prey and make life easier for innovative predators. As offshore investment grows, such studies may help engineers to design farms that help both the consumer and the wild things in the offshore waters. The researchers say: “In this period of unprecedented development of the marine renewables industry, the number of apex predators encountering such structures is likely to increase. The ecological consequences may be dependent on whether such reefs constitute an increase or just a concentration of prey.” – Climate News Network

Researchers tracking the movements of seals in the North Sea reveal that “artificial reefs” created by wind farms and pipelines are becoming attractive as foraging grounds on fishing expeditions. LONDON, 25 July, 2014 − Environmental campaigners and countryside conservators aren’t the only fans of those great arrays of turbines, generating renewable energy from the winds at sea. Grey and harbour seals in the North Sea are beginning to show a preference for offshore wind farms as well. Deborah Russell, research fellow at the University of St Andrews, Scotland, and colleagues tracked the movements of both the harbour seal (Phoca vitulina) and the grey seal (Halichoerus grypus). There are an estimated 56,000 harbour seals in the North Sea and around 65,000 of the greys haul out on the British coast on the North Sea alone. Tagged specimens, with their movements tracked by GPS satellite systems as they surface to breathe, reveal a lot about the ecology of each species and their response to environmental change.

Distinct preference

The researchers report in the journal Current Biology that some of their tagged animals seemed to show a distinct preference for offshore wind farms and associated pipelines. Eleven harbour seals headed for two wind farms: one was Alpha Ventus, off northern Germany, and the other was Sheringham Shoal, off the North Norfolk coast, England. Some individuals regularly cruised the sites, and some even revealed a pattern of grid-like movements as they appeared to forage at individual turbines. Two seals in the Netherlands were tracked along sections of submarine pipeline, on fishing expeditions that lasted 10 days at a time.

A harbour seal with a GPS phone tag used to track movements Image: Current Biology, Russell et al
A harbour seal with a GPS phone tag Image: Current Biology, Russell et al

The guess is that the seals regarded the offshore structures as artificial reefs where crustaceans settle and fish congregate. Turbine blades can swirl at speeds of up to 280 kilometres an hour, and represent a danger to  birds and bats − one estimate is that such structures in the US account for 600,000 bat deaths a year. But marine creatures far below the circling blades seem to value a touch of freshly-planted, three-dimensional shelter in the muddy basin of a shallow sea. “I was shocked when I first saw the stunning grid pattern of a seal track around Sheringham Shoal,” Dr Russell said. “You could see that the individual appeared to travel in straight lines between turbines, as if he was checking them out for potential prey, and then stopping to forage at certain ones.”

Open questions

Only a small proportion of the tracked animals showed a preference for wind farms, and such structures still cover only a trifling area of the available coast. But the research leaves open a number of questions. One is whether, as wind farms add to the available habitat in the North Sea, they will increase the available fish and crustacean populations, or whether they simply attract the prey and make life easier for innovative predators. As offshore investment grows, such studies may help engineers to design farms that help both the consumer and the wild things in the offshore waters. The researchers say: “In this period of unprecedented development of the marine renewables industry, the number of apex predators encountering such structures is likely to increase. The ecological consequences may be dependent on whether such reefs constitute an increase or just a concentration of prey.” – Climate News Network

Staggered turbines 'make most of wind'

FOR IMMEDIATE RELEASE
Wind farms, along with solar energy,  could soon provide enough energy to provide for half the world’s needs, researchers say. The only problem is working out how best to build them.

LONDON, November 6 – US scientists have worked out how to get 33% more power from an offshore wind farm – stagger the turbines rather than line them up in neat, orderly rows.

Cristina Archer of the University of Delaware and colleagues report in Geophysical Research Letters that they started with a real, working offshore wind farm – Lillgrund in Sweden – and then, using computer simulations and real weather data, hypothetically arranged the turbines to achieve the optimum results.

The problem is a real one. In April two US scientists calculated that spacing set practical limits to wind power: the impact of air on turbine blades set them turning but also set up eddies that took the wind out of the sails of the turbine downstream.

Land costs are huge, so there is a limit to the possibilities of spacing for onshore wind farmers. But offshore farms can spread themselves a little more comfortably. Dr Archer and her colleagues tried six simulated configurations, sometimes keeping the turbines at the same distance, sometimes further apart, and sometimes staggering them according to the prevailing wind, in the way theatre seats are staggered to give everyone a better view of the stage.

Hopes of huge potential

It was a combination of the two approaches – more generous spacing, and a staggered alignment – that gave the best results. In general, they argue, the right placement and arrangement could improve energy yields by 13% to 33%.

It all boils down to having the right attitude. Last year, in a display of the power of positive thinking, Dr Archer and a colleague from California calculated that wind turbines could deliver half the world’s energy demands by 2030 with minimal environmental impact. This would require four million turbines at 100 metres above ground level in all the windiest places.

Not everybody agrees: others argue that wind energy in particular cannot match coal, oil or nuclear, because the ratio of power to unit area is so much lower. A few days ago, commentators warned in Nature Geoscience that a world driven by renewable energy would create an enormous demand for metals and minerals – and energy to extract them.

But Dr Archer isn’t the only researcher at the University of Delaware to take a distinctly optimistic view of renewable resources. In January a different team from the same institution reported that a combination of wind power and solar energy could keep the US grid supplied around 99.9% of the time. – Climate News Network

FOR IMMEDIATE RELEASE
Wind farms, along with solar energy,  could soon provide enough energy to provide for half the world’s needs, researchers say. The only problem is working out how best to build them.

LONDON, November 6 – US scientists have worked out how to get 33% more power from an offshore wind farm – stagger the turbines rather than line them up in neat, orderly rows.

Cristina Archer of the University of Delaware and colleagues report in Geophysical Research Letters that they started with a real, working offshore wind farm – Lillgrund in Sweden – and then, using computer simulations and real weather data, hypothetically arranged the turbines to achieve the optimum results.

The problem is a real one. In April two US scientists calculated that spacing set practical limits to wind power: the impact of air on turbine blades set them turning but also set up eddies that took the wind out of the sails of the turbine downstream.

Land costs are huge, so there is a limit to the possibilities of spacing for onshore wind farmers. But offshore farms can spread themselves a little more comfortably. Dr Archer and her colleagues tried six simulated configurations, sometimes keeping the turbines at the same distance, sometimes further apart, and sometimes staggering them according to the prevailing wind, in the way theatre seats are staggered to give everyone a better view of the stage.

Hopes of huge potential

It was a combination of the two approaches – more generous spacing, and a staggered alignment – that gave the best results. In general, they argue, the right placement and arrangement could improve energy yields by 13% to 33%.

It all boils down to having the right attitude. Last year, in a display of the power of positive thinking, Dr Archer and a colleague from California calculated that wind turbines could deliver half the world’s energy demands by 2030 with minimal environmental impact. This would require four million turbines at 100 metres above ground level in all the windiest places.

Not everybody agrees: others argue that wind energy in particular cannot match coal, oil or nuclear, because the ratio of power to unit area is so much lower. A few days ago, commentators warned in Nature Geoscience that a world driven by renewable energy would create an enormous demand for metals and minerals – and energy to extract them.

But Dr Archer isn’t the only researcher at the University of Delaware to take a distinctly optimistic view of renewable resources. In January a different team from the same institution reported that a combination of wind power and solar energy could keep the US grid supplied around 99.9% of the time. – Climate News Network

Staggered turbines ‘make most of wind’

FOR IMMEDIATE RELEASE Wind farms, along with solar energy,  could soon provide enough energy to provide for half the world’s needs, researchers say. The only problem is working out how best to build them. LONDON, November 6 – US scientists have worked out how to get 33% more power from an offshore wind farm – stagger the turbines rather than line them up in neat, orderly rows. Cristina Archer of the University of Delaware and colleagues report in Geophysical Research Letters that they started with a real, working offshore wind farm – Lillgrund in Sweden – and then, using computer simulations and real weather data, hypothetically arranged the turbines to achieve the optimum results. The problem is a real one. In April two US scientists calculated that spacing set practical limits to wind power: the impact of air on turbine blades set them turning but also set up eddies that took the wind out of the sails of the turbine downstream. Land costs are huge, so there is a limit to the possibilities of spacing for onshore wind farmers. But offshore farms can spread themselves a little more comfortably. Dr Archer and her colleagues tried six simulated configurations, sometimes keeping the turbines at the same distance, sometimes further apart, and sometimes staggering them according to the prevailing wind, in the way theatre seats are staggered to give everyone a better view of the stage.

Hopes of huge potential

It was a combination of the two approaches – more generous spacing, and a staggered alignment – that gave the best results. In general, they argue, the right placement and arrangement could improve energy yields by 13% to 33%. It all boils down to having the right attitude. Last year, in a display of the power of positive thinking, Dr Archer and a colleague from California calculated that wind turbines could deliver half the world’s energy demands by 2030 with minimal environmental impact. This would require four million turbines at 100 metres above ground level in all the windiest places. Not everybody agrees: others argue that wind energy in particular cannot match coal, oil or nuclear, because the ratio of power to unit area is so much lower. A few days ago, commentators warned in Nature Geoscience that a world driven by renewable energy would create an enormous demand for metals and minerals – and energy to extract them. But Dr Archer isn’t the only researcher at the University of Delaware to take a distinctly optimistic view of renewable resources. In January a different team from the same institution reported that a combination of wind power and solar energy could keep the US grid supplied around 99.9% of the time. – Climate News Network

FOR IMMEDIATE RELEASE Wind farms, along with solar energy,  could soon provide enough energy to provide for half the world’s needs, researchers say. The only problem is working out how best to build them. LONDON, November 6 – US scientists have worked out how to get 33% more power from an offshore wind farm – stagger the turbines rather than line them up in neat, orderly rows. Cristina Archer of the University of Delaware and colleagues report in Geophysical Research Letters that they started with a real, working offshore wind farm – Lillgrund in Sweden – and then, using computer simulations and real weather data, hypothetically arranged the turbines to achieve the optimum results. The problem is a real one. In April two US scientists calculated that spacing set practical limits to wind power: the impact of air on turbine blades set them turning but also set up eddies that took the wind out of the sails of the turbine downstream. Land costs are huge, so there is a limit to the possibilities of spacing for onshore wind farmers. But offshore farms can spread themselves a little more comfortably. Dr Archer and her colleagues tried six simulated configurations, sometimes keeping the turbines at the same distance, sometimes further apart, and sometimes staggering them according to the prevailing wind, in the way theatre seats are staggered to give everyone a better view of the stage.

Hopes of huge potential

It was a combination of the two approaches – more generous spacing, and a staggered alignment – that gave the best results. In general, they argue, the right placement and arrangement could improve energy yields by 13% to 33%. It all boils down to having the right attitude. Last year, in a display of the power of positive thinking, Dr Archer and a colleague from California calculated that wind turbines could deliver half the world’s energy demands by 2030 with minimal environmental impact. This would require four million turbines at 100 metres above ground level in all the windiest places. Not everybody agrees: others argue that wind energy in particular cannot match coal, oil or nuclear, because the ratio of power to unit area is so much lower. A few days ago, commentators warned in Nature Geoscience that a world driven by renewable energy would create an enormous demand for metals and minerals – and energy to extract them. But Dr Archer isn’t the only researcher at the University of Delaware to take a distinctly optimistic view of renewable resources. In January a different team from the same institution reported that a combination of wind power and solar energy could keep the US grid supplied around 99.9% of the time. – Climate News Network

Delays for the dawn of UK’s new nuclear age

FOR IMMEDIATE RELEASE As the months slip by, the optimism drains away that the UK government will make good on its pledge to build eight new nuclear stations. LONDON, 15 June – The British government’s promise not to subsidise new nuclear power stations in the UK looks set to torpedo its own stated energy policy which is to build a range of new reactors to keep the lights on. Ministers have been in negotiations with the French state-owned giant EDF for more than a year, trying to strike a deal that does not look like a subsidy but guarantees a price for electricity for 40 years – big enough to give investors a return on capital to make building the first two new nuclear stations a worthwhile venture. The government’s pre-election promise was to encourage low carbon energy production, to reach ambitious carbon dioxide emission reduction targets and so become “the greenest government” the UK has known. New generation capacity is needed to keep the lights on in Britain as several “dirty” coal fired stations are being closed because of European Union regulations and some old nuclear stations are nearing the end of their lives. Nuclear tax The problem is that nuclear power continues to get more expensive while renewable costs fall. The price that EDF is reported to be insisting on would provide a bigger subsidy than is paid to wind and solar power. This would make nuclear the most expensive energy in the UK and tie the British consumer to high bills for generations to come. Consumers would in effect be paying a nuclear energy tax. A formal announcement to start work on the first new nuclear build in Britain in more than 25 years has been repeatedly delayed – and the proposed finishing date of the first reactor has already unofficially slipped from 2017 to 2022 before the first concrete has been poured. With the delays new nuclear stations already under construction are experiencing in Finland and France, even this looks optimistic. While negotiations drag on between the government and EDF, the European Union and members of parliament in the House of Commons are investigating the proposed subsidies to be paid to nuclear power. The reason is that “mature” industries like nuclear are banned under European competition rules from being given subsidies because it is classed as “unfair competition.” Cannot go bankrupt The Environmental Audit Committee, made up of MPs of all the UK’s political parties, has been taking evidence on “Energy Subsidies in the UK” to try and work out which form of generation is best value for money for consumers. There is evidence before the committee that the lights can be kept on using renewables, wind, solar, biomass and half a dozen other technologies without resorting to nuclear power. But the inquiry is also an opportunity for the gas industry and others to have a go at the subsidies for renewables like wind and biomass. Some witnesses concentrate only on both the existing and proposed subsidies to nuclear power. Dr Gerry Wolff, representing a think tank called Energy Fair, said nuclear energy already had seven kinds of subsidy. If they were withdrawn, the price of nuclear electricity would rise to at least £200 a megawatt hour. This is compared with the next most expensive form of low carbon energy, offshore wind at about £140 a megawatt hour. The UK has more offshore wind turbines than any other country and plans more with the cost expected to continue to fall as time passes. Nuclear subsidies include the state underwriting the cost of a nuclear accident so the industry does not pay the full cost of insurance or pay for protection against terrorism, Dr Wolff says. He also points out that, as happened 10 years ago when the price of electricity fell below the cost of production, nuclear power is insulated from going bankrupt. The industry is too important in preventing politically unacceptable power cuts to be allowed to fail and would always be bailed out by the government. This is a commercial security no other power company has. The biggest subsidy, according to the Energy Fair evidence, is the cost of dealing with nuclear waste and dismantling nuclear stations. This is a vast and although ultimately spread over centuries, and therefore cannot be quantified, mostly falls on the consumer and taxpayer, not on the company. Dr Wolff says: “Renewables have a clear advantage on cost, speed of construction, security of energy supplies, and effectiveness in cutting emissions of carbon dioxide. Subsidies for nuclear power have the effect of diverting resources away from techniques and technologies which are cheaper than nuclear power and altogether more effective as a means of meeting our energy needs.” The European Union Commission inquiry is politically complex. The British government’s point is that nuclear is a low carbon form of electricity production and should be treated as a renewable. This has never been the case in Europe and there is powerful opposition to this idea in Germany and other EU states that have decided that nuclear power is not for them. As each week passes and no decisions are reached on this variety of issues, delays and therefore nuclear costs continue to mount making the dawn a new nuclear age in the UK seem as far away as ever. – Climate News Network

FOR IMMEDIATE RELEASE As the months slip by, the optimism drains away that the UK government will make good on its pledge to build eight new nuclear stations. LONDON, 15 June – The British government’s promise not to subsidise new nuclear power stations in the UK looks set to torpedo its own stated energy policy which is to build a range of new reactors to keep the lights on. Ministers have been in negotiations with the French state-owned giant EDF for more than a year, trying to strike a deal that does not look like a subsidy but guarantees a price for electricity for 40 years – big enough to give investors a return on capital to make building the first two new nuclear stations a worthwhile venture. The government’s pre-election promise was to encourage low carbon energy production, to reach ambitious carbon dioxide emission reduction targets and so become “the greenest government” the UK has known. New generation capacity is needed to keep the lights on in Britain as several “dirty” coal fired stations are being closed because of European Union regulations and some old nuclear stations are nearing the end of their lives. Nuclear tax The problem is that nuclear power continues to get more expensive while renewable costs fall. The price that EDF is reported to be insisting on would provide a bigger subsidy than is paid to wind and solar power. This would make nuclear the most expensive energy in the UK and tie the British consumer to high bills for generations to come. Consumers would in effect be paying a nuclear energy tax. A formal announcement to start work on the first new nuclear build in Britain in more than 25 years has been repeatedly delayed – and the proposed finishing date of the first reactor has already unofficially slipped from 2017 to 2022 before the first concrete has been poured. With the delays new nuclear stations already under construction are experiencing in Finland and France, even this looks optimistic. While negotiations drag on between the government and EDF, the European Union and members of parliament in the House of Commons are investigating the proposed subsidies to be paid to nuclear power. The reason is that “mature” industries like nuclear are banned under European competition rules from being given subsidies because it is classed as “unfair competition.” Cannot go bankrupt The Environmental Audit Committee, made up of MPs of all the UK’s political parties, has been taking evidence on “Energy Subsidies in the UK” to try and work out which form of generation is best value for money for consumers. There is evidence before the committee that the lights can be kept on using renewables, wind, solar, biomass and half a dozen other technologies without resorting to nuclear power. But the inquiry is also an opportunity for the gas industry and others to have a go at the subsidies for renewables like wind and biomass. Some witnesses concentrate only on both the existing and proposed subsidies to nuclear power. Dr Gerry Wolff, representing a think tank called Energy Fair, said nuclear energy already had seven kinds of subsidy. If they were withdrawn, the price of nuclear electricity would rise to at least £200 a megawatt hour. This is compared with the next most expensive form of low carbon energy, offshore wind at about £140 a megawatt hour. The UK has more offshore wind turbines than any other country and plans more with the cost expected to continue to fall as time passes. Nuclear subsidies include the state underwriting the cost of a nuclear accident so the industry does not pay the full cost of insurance or pay for protection against terrorism, Dr Wolff says. He also points out that, as happened 10 years ago when the price of electricity fell below the cost of production, nuclear power is insulated from going bankrupt. The industry is too important in preventing politically unacceptable power cuts to be allowed to fail and would always be bailed out by the government. This is a commercial security no other power company has. The biggest subsidy, according to the Energy Fair evidence, is the cost of dealing with nuclear waste and dismantling nuclear stations. This is a vast and although ultimately spread over centuries, and therefore cannot be quantified, mostly falls on the consumer and taxpayer, not on the company. Dr Wolff says: “Renewables have a clear advantage on cost, speed of construction, security of energy supplies, and effectiveness in cutting emissions of carbon dioxide. Subsidies for nuclear power have the effect of diverting resources away from techniques and technologies which are cheaper than nuclear power and altogether more effective as a means of meeting our energy needs.” The European Union Commission inquiry is politically complex. The British government’s point is that nuclear is a low carbon form of electricity production and should be treated as a renewable. This has never been the case in Europe and there is powerful opposition to this idea in Germany and other EU states that have decided that nuclear power is not for them. As each week passes and no decisions are reached on this variety of issues, delays and therefore nuclear costs continue to mount making the dawn a new nuclear age in the UK seem as far away as ever. – Climate News Network

Offshore wind at risk from wave power

EMBARGOED until 0001 GMT on Saturday 2 March Offshore wind turbines are vulnerable to sudden and catastrophic destruction in moderately stormy seas, according to new research. LONDON, 2 March – Wind turbines are at constant but unpredictable risk of being snapped in pieces like matchsticks by medium-sized waves, a researcher has found. “The problem is, we still do not know exactly when the turbines may break”, says Professor John Grue from the Department of Mathematics at the University of Oslo, Norway. In 1989 Grue, a leading wave researcher, discovered a phenomenon called ringing, which is a type of vibration that occurs when choppy waves strike marine installations. So far scientists have studied ringing only in small and large waves, but it now appears to be more common in medium-sized waves. For marine turbines with a cylinder diameter of eight metres, the worst waves are those that are more than 13 metres high and have an 11-second interval between them. These waves occur in even small storms, which are fairly common off the Norwegian coast. The ringing problem may increase significantly, because there are plans to build tens of thousands of offshore turbines. “If we do not take ringing into consideration offshore wind farms could lead to financial ruin”, Grue told Apollon, Oslo University’s research magazine. The largest offshore wind farms are off the Danish and British coasts, though these are small scale compared with installations planned in the area of the Dogger Bank, out in the North Sea.

Oil industry also at risk

So far it has not been possible to use an actual turbine to measure the force exerted by ringing. But Grue says laboratory measurements show the biggest vibrations occur just after the wave has passed, not when it strikes the turbine. Immediately after the crest of the wave has passed, a second force hits the structure and it’s this which creates the ringing. “If that resonates with the structural frequency of the turbine, the vibration will be strong… This increases the danger of fatigue”, says Grue. Estimates of the damage caused by ringing are not yet reliable enough to allow an accurate calculation of the material fatigue that it produces, says Grue. “Ringing is very difficult to measure –  there is great uncertainty.” Scientists also need to consider whether the turbines are in deep or shallow water. “The structural frequency also depends on conditions on the seabed. You can compare it with a flagpole in a storm, which vibrates differently depending on whether it is fixed in concrete or in soft ground.” Ringing does not harm wind turbines alone. It is already a big problem for the oil industry. The designers of one oil platform did not take ringing into account, and lost NOK 12 billion (US$ 2.1 bn), says Grue. “It’s possible to build your way out of the ringing problem by strengthening the oil rigs. But it doesn’t make financial sense to do that with turbines.” Many advocates of wind power argue in favour of siting turbines offshore, where they tend to attract less opposition and there’s space to place wind farms far apart (see our story of 27 February, Wind power ‘may be less than thought’. Professor Grue’s research suggests that siting farms at sea could give rise to serious problems. – Climate News Network

EMBARGOED until 0001 GMT on Saturday 2 March Offshore wind turbines are vulnerable to sudden and catastrophic destruction in moderately stormy seas, according to new research. LONDON, 2 March – Wind turbines are at constant but unpredictable risk of being snapped in pieces like matchsticks by medium-sized waves, a researcher has found. “The problem is, we still do not know exactly when the turbines may break”, says Professor John Grue from the Department of Mathematics at the University of Oslo, Norway. In 1989 Grue, a leading wave researcher, discovered a phenomenon called ringing, which is a type of vibration that occurs when choppy waves strike marine installations. So far scientists have studied ringing only in small and large waves, but it now appears to be more common in medium-sized waves. For marine turbines with a cylinder diameter of eight metres, the worst waves are those that are more than 13 metres high and have an 11-second interval between them. These waves occur in even small storms, which are fairly common off the Norwegian coast. The ringing problem may increase significantly, because there are plans to build tens of thousands of offshore turbines. “If we do not take ringing into consideration offshore wind farms could lead to financial ruin”, Grue told Apollon, Oslo University’s research magazine. The largest offshore wind farms are off the Danish and British coasts, though these are small scale compared with installations planned in the area of the Dogger Bank, out in the North Sea.

Oil industry also at risk

So far it has not been possible to use an actual turbine to measure the force exerted by ringing. But Grue says laboratory measurements show the biggest vibrations occur just after the wave has passed, not when it strikes the turbine. Immediately after the crest of the wave has passed, a second force hits the structure and it’s this which creates the ringing. “If that resonates with the structural frequency of the turbine, the vibration will be strong… This increases the danger of fatigue”, says Grue. Estimates of the damage caused by ringing are not yet reliable enough to allow an accurate calculation of the material fatigue that it produces, says Grue. “Ringing is very difficult to measure –  there is great uncertainty.” Scientists also need to consider whether the turbines are in deep or shallow water. “The structural frequency also depends on conditions on the seabed. You can compare it with a flagpole in a storm, which vibrates differently depending on whether it is fixed in concrete or in soft ground.” Ringing does not harm wind turbines alone. It is already a big problem for the oil industry. The designers of one oil platform did not take ringing into account, and lost NOK 12 billion (US$ 2.1 bn), says Grue. “It’s possible to build your way out of the ringing problem by strengthening the oil rigs. But it doesn’t make financial sense to do that with turbines.” Many advocates of wind power argue in favour of siting turbines offshore, where they tend to attract less opposition and there’s space to place wind farms far apart (see our story of 27 February, Wind power ‘may be less than thought’. Professor Grue’s research suggests that siting farms at sea could give rise to serious problems. – Climate News Network