In Europe last year 418 new offshore wind turbines were connected to the grid, 35% more than in 2012. Europe leads the world with offshore wind - it now has more than 2,000 turbines installed in coastal waters.
Whether this is a monumental folly, or a step in the right direction is a moot point. Offshore wind farms are being built.
Outside of Europe, Asia is the fastest developing offshore wind market, both with the installation of offshore wind and the development of the industry to produce and install turbines. The exact drivers vary on a country-by-country basis. China’s insatiable thirst for power to support its industrial expansion is well-documented and includes both onshore and offshore wind turbines. Japan’s political move towards non-nuclear sources of power Post-Fukushima is also a clear motivator.
Steve Sawyer, secretary general of the Global Wind Energy Council says: "Once places like China, Japan and Korea decide to do something, they do it comprehensively and quickly.
"It's not hard to see a situation where Europe cedes its leadership in this area to the Asians. The big heavy engineering companies, Samsung, Hyundai, Doosan, see it as a big opportunity. The Japanese Government is also piling money into the sector. Floating turbines is where they will make their mark."
Development of offshore wind outside of Europe and Asia is not as impressive or ambitious. There is no offshore wind farms in the US or Russia. Pragmatically, a lack of shallow coastal water restricts the opportunities for offshore wind in the US, but there is also political reluctance, says Sawyer. "There's been a lot of talk and announcements in the US, but not much happening," he says. “They started much later [than Europe] and they have no energy policy, because the fossil fuel, and to a certain extent, the nuclear industries, control enough Congress members to ensure that any legislation that constrains the use of fossil fuels doesn’t get through.”
Despite this, construction of the US’s first major offshore wind project, the 454MW capacity Cape Wind project, off Cape Cod, Massachusetts, is planned to begin this year. Sawyer says there is a 50/50 chance it will actually start this year.
Meanwhile in Russia, politics has also stymied the development of the offshore wind sector. Several years ago the Russian Government launched a target of 4.5% for non-hydroelectric renewables,including offshore wind, by 2020. Initial enthusiasm for this policy has cooled however, primarily because the current administration favours the exploitation of arctic oil.
However, the European market is beginning to show signs of slowing down. Almost half of the new offshore wind turbine installations in Europe during 2013 were in the UK, followed by Denmark and Germany. But, there has been a number of high profile project cancellations in the UK recently, notably the 240 turbine “Atlantic Array” wind farm, which was to be built by German energy firm RWE. Most people in the European wind sector predict fewer, more difficult, offshore wind farm projects in the coming years.
One reason for the slowdown is that most remaining British and German projects are more than 80km from the coast. The construction of wind farms further out at sea increases the technical difficulty and costs in several ways.
The political climate regarding offshore wind is also ambiguous in both countries, making it difficult to find backers for the heavy level of investment offshore wind farms require.
Sawyer says that a lack of sufficient grid connections onshore is holding back progress in Northern Germany. A lot of the best wind sites in Germany and Denmark are also already “taken up by vintage equipment from the 1990s,” he adds. "They are paying the price for being early movers in the market.”
Paradoxically, the growth in the size of wind turbines themselves also provides another potential source of delay for projects. The size of wind turbines has increased from the kilowatt range in the 1990s to the 5-8MW giants range being installed this decade. Engineers still have to "iron out the bugs" of the current generation, says Sawyer. “All these factors mitigate the installation of larger and larger turbines. To get the economics to work you have to upscale considerably. But for Northern Europe to meet stringent climate targets there is a role for offshore wind. How big that role is depends on the engineering scale."
Fundamental to the technical issues with offshore wind farms is the lack of development they have received compared to onshore. According to Sawyer, around 70% of a wind farm's cost is the turbines onshore. Offshore, up to 60% of the cost is the balance of plant. Energy firms have favoured the easier option of building turbines onshore and in shallow waters close to shore. Engineers have therefore focussed on improving the turbines themselves,resulting in some great progress and innovations. For example, says Sawyer, the use of lidar on top of nacelles to maximise output and minimise wind stress on wind turbines. However, the amount of attention on grid connection and the cost of running turbines at sea hasn’t been as great.
Sawyer says: "The hope is that the cost of offshore technology goes down while the cost of everything else goes up.The challenge is to get it done cheaply and reliably. That’s something the whole industry is acutely aware of."
Surprisingly, there are few suppliers throughout the world capable of developing the “balance of plant” for an offshore wind farm, equipment such as transformers, substations, High Voltage Direct Current (HVDC) connections and Voltage Source Conversion (VSC) plants. These electrical infrastructure suppliers, like Alstom Grid, ABB and Siemens are working hard to solve the challenge of how to transmit power generated far out at sea onshore. A task which shares the same challenges as installing and operating wind turbines at sea.
As wind farms get larger and further out from shore, its fairly obvious that the amount of cabling required to connect them to the onshore grid will increase. What’s not so obvious is that the size and complexity of the electrical equipment required also substantially increases, as does the means used to contain the equipment and the complexity of the on-site maintenance provision. Offshore construction technology has therefore evolved from flat top deck designs to multi-tier designs, with the latest substations as big and complex as small oil rigs. This evolution has happened fast, within businesses that a decade ago only produced and maintained equipment on dry land only.
“An electrical substation in the middle of the North Sea is not where you want to put one. It’s probably the worst environment - salty water and a whole host of different logistics appraisals for construction and maintenance,” says Dave Walker, country sales director at Alstom Grid. “The general rule of thumb is that every ton onshore costs ten times as much offshore.”
Alstom Grid is developing the grid connection for Dolwin 3, a 900MW wind farm off the coast of Northern Germany. Some 1400 people work at the Alstom Grid and Alstom Power sites from 38 different countries in Stafford, UK. The company’s first offshore substation was a 90MW substation on a monopile structure off the coast at Barrow in the UK built 8 years ago. Dolwin 3 is ten times the size of that station, and will weigh 10,000 tonnes. AC collector stations will be built to bring in the AC power from the turbines, which is then transmitted onto one a single platform to be converted to HVDC and then transmitted through the cable onshore.
Dolwin 3, says Walker is a “completely different animal” compared to smaller substations. For a monopole installation, the substation is constructed on the harbour side, then taken out and dropped onto the pole using a heavy crane. Jacket-type structures for the foundations have to be used for stations that weigh more than 1000 tonnes. But, as the size and weight approaches the lifting capacities of the cranes, less installation equipment is available. “As we get bigger and bigger, other methodologies are coming into play, such as self-floating and jacket type platforms,“ says Walker.
“Within 8 years we’ve used half a dozen different construction methods. It’s down to client’s preferences. There’s no such thing as standard.”
Equally, Walker says that there is no such thing as a standard platform design for offshore wind farms, but there are a number of factors that influence design. These include wave size and water depth and the type of sea bed. In addition, substations are now getting far enough out and big enough to justify being manned and perhaps even used as maintenance staging posts for the turbines. “Now they are going further offshore, they want accommodation for people to stay there for two to three weeks,” says Walker. “That’s a completely different ball game. There are different regulations and rules, people need entertainment and washrooms, canteens, the lot. We’re also seeing people with a big offshore platform with a helideck using them as a staging post for maintenance teams for the actual wind turbines.”
How offshore wind farms connect to the onshore grid also changes the further out they get. It makes financial sense to be AC up to about 80km. Beyond that, HVDC transmission is the most effective. This requires extra equipment, such as Voltage Source Conversion plants. Mike Boden, HVDC technical director at Alstom Grid, says: “900MW is a big number, but it’s done at 320kv. You need huge voltage clearances. So the size of the platform isn’t just defined by how you get the equipment out there and installed, you have to leave air clearance for the voltage as well.”
Redundancy is key for reliability in substations. A transformer could take 12 months to replace, so some clients have two transformers. Both transformers and switchgear are normally enclosed with positive pressure, so when a door is opened a rush of air stops salt spray from getting in the room.
All the substations are remotely monitored, so everything can be done from the shoreline with comms. If the communications go down a maintenance team has to physically visit the sites.
Boden says that calculations and analysis are done for reliability and availability for offshore installations. Boden says: “When you look around the world, Europe is leading the world with HVDC offshore wind. There is a huge push in Germany because of the decision about nuclear power.
“There are wind maps around the world. Oil and gas is looking at power from shore as well. But, offshore is a big investment.You have to make the numbers stack up. It’s a rapidly developing industry, people took the projects, five or six a time and work to manage the risks. It’s a learning curve and it puts hesitation in the market.”