Major offshore wind plant project development is getting closer and closer to reality. The first of five 150 MW demonstration projects in Denmark goes to tender this month and a 40 MW plant is under construction three kilometres off Copenhagen on the submerged Middelgrunden sand bank. But technical, economic and environmental uncertainties have turned past optimism into serious realism: experience is limited so far, and the more the offshore wind resource and infrastructure issues are studied, the more the wind sector is finding it needs to know.
Costs of installation and operation and maintenance (O&M) are going to be higher than first expected, but power output will probably be higher as well. Will the difference be worth it? Nobody yet knows. Siting issues, too, are becoming a can of worms, led by environmental concerns and a looming lack of legal framework. To put it bluntly, offshore wind energy is still a high risk investment, and the wind sector, financiers and government officials alike are anxious for some solid figures.
These were the main conclusions at Offshore Wind Energy in the Mediterranean and Other European Seas (OWEMES), a two day conference on the Italian island of Sicily last month. Held in a grand old hotel perched on the edge of an ancient Greek limestone quarry in Syracuse, the event attracted nearly 150 delegates, mostly from northern Europe. Despite several minor organisational gaffes, the charming hosts -- from Italian energy agency ENEA -- kept the mood relaxed and focused through the long, intense days. From the first presentation, the conference brought to light the meaning of the expression "uncharted waters." Everything -- it was said many times in many ways -- is different at sea: the wind, forecasting, foundations, corrosion, power, stability, access, installation, cost breakdown, O&M -- not to mention real experience for the wind sector. Terms were thrown out alluding to the new field, like "aerodynamic damping," "geostrophic wind measurements" and "suction buckets."
As an appropriate frame to the conference, the first, middle and last presentations dealt with the large Danish demonstration projects, being developed by Danish utilities Elsam and Elkraft (Windpower Monthly, July 1999). The main focus was on the first project, Horn's Rev, off the coast of west Jutland (page 34). Because the 150 MW plant is expected to be the first of many large scale offshore projects -- and because it is so advanced in its planning -- it was referred to in a number of papers. One pressing issue has revolved around access by boat, where rough water has posed a number of challenges for wind and wave monitoring. The measuring mast has been blasted by the elements, with a damaging lightning strike and a hurricane that demolished some instruments. The photo of the hurricane's signature on the mast was talked about outside the conference hall throughout the day.
"There's a large insecurity surrounding offshore development -- like how to get the project built out on the sea," said Elsam's Hans Buus. "At Horns Rev, there's a weather window [of time] to work out there. It's not possible to sail out to Horn's Rev every time we want to go. We need to plan a block of five possible days for a trip." This leads to the cost issue. "If you're building and the weather is unexpectedly poor, you lose time. The cost can be a half million kroner a day to wait. Then if winter comes and you must stop prematurely, you lose more money -- you've bought the wind turbines, you have to pay for them somehow," Buus said.
ElsamProjekt, an Elsam affiliate in charge of technical consulting for the wind projects, has found that helicopter access might be the most practical solution and provide the best access once the wind turbines are built. "We've found it will be cost competitive -- it takes two hours to reach the site by boat, but a quarter of an hour by helicopter," said the company's Jens Bonefeld.
Other speakers added that O&M for offshore is going to be more demanding than first expected -- just to replace one small part requires an enormous amount of planning, one delegate noted. "The most important message so far is that the demand for turbine safety is considerably higher than for onshore," said Buus. "It can be four weeks before you can get out to a turbine. The best way is to make them more reliable -- maybe in ways that have not been cost effective with land-based machines. It will be worth spending more on higher quality components for offshore."
One delegate from a turbine manufacturer said confidentially, "Don't underestimate this point. You can't design an onshore turbine for offshore use. Forget it. You've seen how many problems they had with just measuring equipment. And we're talking bigger and bigger turbines?"
Larger and larger wind turbines have brought with them other new problems, like power control and stability, pointed out Peter Christiansen of ElsamProjekt. "Special attention is needed in this area -- whether onshore or offshore," he said. He also touched on some ideas for monitoring wind turbines at Horn's Rev, such as via a communication fibre optic cable. "Think of the possibilities for a service technician," he said. "He could take a digital picture and transmit it onshore while he's out at the turbine. Or audio -- he could record a digital noise picture as well."
Matters of installing large turbines were also discussed by other speakers, including Ben Hendriks of Dutch energy research foundation ECN. "For equipment offshore, lifting capacity in terms of weight is no problem. It's height that is the problem," he said. "Specially designed tools will be the way to go." Particularly when dealing with installation of large machines, where the top mass -- which needs to be lifted high over the water level in possible windy or wavy conditions -- can weigh 170 tonnes or more.
At Middelgrunden in Denmark, construction of a 40 MW project with 2 MW Bonus turbines owned by a private co-operative and local utility (Windpower Monthly, July 1999), is now underway. Discussion revolved around the choice of foundations that could withstand the heavy ice loads at the site. The result was a 1.5 metre thick concrete plate -- the same type used for megawatt size turbines onshore in Denmark -- resting on the sea bed, with a type of cone jutting outward at surface level to help break up ice. The foundation costs, the cheapest of three offers, were six times greater than on land.
Meanwhile, another small project using two 2 MW Vestas turbines is soon on its way up in the UK at Blyth (Windpower Monthly, March 2000). David Still of Border Wind, the project's English developer, focused on the intricate aspects of permitting for the site. "I want to stress how easy it is to get consents in the UK, but we're obviously trying to change that to make it more difficult," Still quipped, referring to new planning legislation. Nine consents were needed, including those for permission to work on the sea bed and in the harbour, choose the cable route, connect to the grid, get approval from fishermen, and more. A jack-up barge will be used to install the machines, yet just exactly how it will do it is still undecided, said Still.
In the Netherlands
When Dutch energy and environment agency Novem decided to build a 100 MW offshore demonstration project (Windpower Monthly, January 2000), explained Novem's Ruud de Bruijne, it used a process of elimination to find the best location closer than 19 kilometres from shore. The north was ruled out for environmental reasons and for being a military zone. The south had poor winds. The only spot left was sandwiched between the two, with the chosen site eight kilometres from shore in water of 15-20 metres. De Bruijne said Novem will request bids for turbine supply this year. Since there are government plans for 1250 MW offshore by 2020, some major issues need to be tackled, including the lack of any legal framework for sites more than 19 kilometres offshore, he said.
Some of the most interesting technical presentations were given from an EU-funded Joule project, Predicting Offshore Wind Energy Resources (POWER). "It's very difficult to gather data offshore," said Gillian Watson of Rutherford Appleton Laboratory of the UK, adding that the measured resource is scarce and existing data of variable quality. Due to the high cost of traditional wind measuring offshore, the POWER group has worked on -- among others -- measuring based on atmospheric pressure. Though not enough data has been gathered for accurate interpretation, Risø's Rebecca Barthelmie pointed out that two years of measuring at Middelgrunden at 50 metres has allowed an accuracy of plus or minus 5%. These results can only be applied to a wind turbine with a hub height of 50 metres, however, she stressed.
"Eighty to 90 percent of the people here have a background in everything above ground level," noted Jos Beurskens of ECN. "Very few know what happens under the sea."
Some information, however, is available from a study of the Swedish Bockstigen project, four kilometres from Nåsudden off the Gotland coast (Windpower Monthly, March 1999), where loads have been measured under the sea bed. In addition, an onshore reference turbine has been used to see if it was worth the extra cost of installing at sea, comparing loads, power quality, grid interaction and power performance. Significantly, the onshore turbine has shown higher production in winds of up to 10 m/s, said Göran Ronsten of the Aeronautical Research Institute of Sweden, FFA; with higher winds, the offshore units performed better. But is the extra cost worth it? "We don't know yet," Ronsten said.
Several speakers, however, noted that with experience, the expenses of offshore should fall. Said Jørgen Lemming of the Danish Energy agency: "Will costs go down? I think they will. Is it worth it? I think so."