SIEMENS

It’s incredibly stuffy in the dim interior. In fact, without a guide, you could easily get lost in the huge structure — a converter platform that is being built at the Nordic Yards shipyard in Wismar, Germany, on the coast of the Baltic Sea. A tour of the facility is like a visit to the Egyptian pyramids. Indeed, the building’s dimensions are comparable to those of the pharaonic tombs. Thirty-five meters high, 70 meters long, and 50 meters wide, the structure weighs up to 15,000 metric tons. To put it another way, the facility is as tall as a ten-story building and weighs as much as 25 fully fueled and fully loaded Airbus A380 jets.
Workers are visible between the scaffolding in the interior. They wear white uniforms as well and protective goggles. They are welding components and installing sophisticated technology, bringing electrical engineering together with the maritime world to assemble the foundations of a transition to a renewable energy economy. What’s taking shape is the first of three offshore converter platforms that Siemens is building in the coastal cities of Wismar and Warnemünde. The platforms will make high-voltage direct-current transmission (HVDCT) possible. Specifically, they will concentrate the alternating current produced by North Sea wind farms and convert it into direct current, which will be transmitted through submarine cables to the coast.

The platforms are being built because offshore wind power plays a key role in Germany’s efforts to bring about what the country calls an “energy transition.” As it strives to increase wind energy’s share of the total electricity mix to 15 percent by 2025, Germany plans to increase the electrical output of offshore facilities to around 10 gigawatts (GW) by 2020 and 25 GW by 2030. By comparison, Germany currently has only two wind farms in operation (alpha ventus and EnBW Baltic 1), with a combined output of 200 megawatts (MW) or 0.2 GW. Offshore wind facilities have obvious advantages. For example, a 6 MW wind turbine typically generates 23 gigawatt-hours (GWh) of electricity per year when located on land in coastal regions, but 31 GWh if it is used at sea. Thanks to the stronger winds at sea, offshore facilities can operate flat out for more than 4,000 hours, compared to 2,000 hours at peak capacity on land. In other words, much more powerful turbines can be used offshore, and they operate at full capacity almost half of the day. By contrast, high-performance 6 MW turbines generate much less electricity on land, where they generally operate only six hours per day at full load.

Long Distance Efficiency. Until now, offshore wind farms located near the coast have been connected to the grid using conventional alternating current transmission systems. After all, this approach is not only technically feasible but also more economical for distances under 80 kilometers. Over longer distances, however, alternating current lines act like capacitors that charge and discharge 50 times per second. Energy is lost due to reactive power losses at the submarine cable’s insulation layer. HVDCT technology, on the other hand, does not suffer from such losses, and can thus outperform AC systems at distances over 60 kilometers. At voltages of 250 to 320 kilovolts, large amounts of direct current can be transmitted over hundreds of kilometers with almost no losses. “Because offshore projects located far from coasts need HVDCT, this technology is a key element of the energy transition,” says Tim Dawidowsky, CEO of Power Transmission Solutions, which is part of Siemens’ Energy Sector.

At the heart of the new platform is HVDC Plus — a space-saving version of Siemens’ high-voltage direct-current converter. At sea, the system, which Siemens refers to as a Wind Power Offshore Switchgear (WIPOS), can convert up to 1 GW of electricity into direct current. The system is installed on a floating platform that can be pulled to its destination by tug boats. The substructure is placed on the seafloor, generally 20 to 40 meters below the surface. The entire structure is anchored by steel piles driven 40 to 60 meters into the seafloor. Later, the substructure lies below the surface of the water, and the platform’s supports are set on top of it and fixed in place.

Soccer Fields in the Sky. “Once installed, the platforms look like soccer fields suspended a good 20 meters in the air, which is enough height to protect them against the sort of very large waves that occur only about every 100 years,” says Christian Schmitt, who has overall responsibility for the platform construction project, which he manages from his office in Hamburg. “The helicopter pad at the very top is about 60 meters above sea level,” adds Schmitt’s colleague Michael Suhr, who has been a shipbuilder and marine engineer for more than 20 years and now supervises the platforms’ construction. “You could call it a pioneering achievement. After all, we’re basically building a ship without a rudder or a main engine.”
Not only do the huge platforms weigh five times as much as their predecessors; they can also be located five times further from the coast. In addition, the platforms can be erected in water that is twice as deep (40 meters) and they can generate twice as much output (730 MW) on average.

One of the new platforms will be installed more than 100 nautical miles from Heligoland. Out here the weather is extremely rough, the water is deep, the air is salty, and the waves are high. But the ability to meet these challenges pays off, given that wind speeds are much higher on the open seas, resulting in higher wind farm output.
Siemens is currently working on four HVDCT platforms: BorWin beta, HelWin alpha, HelWin beta, and SylWin alpha. The platforms’ names are derived from the names of Borkum, Heligoland, and Sylt — the nearby North Sea islands. SylWin alpha will transmit 864 MW and connect the DanTysk wind farm to the grid from a site 70 kilometers west of Sylt. That’s enough power to cover the needs of 1.5 million German households. “It’s comparable to the output of a large power plant,” says Suhr.
The 160 kilometer-long line connecting SylWin alpha to the grid will be the world’s longest submarine cable for an offshore network connection. A further 45 kilometers of cable will transmit the electricity overland to a connection point in Büttel, where the direct current will be converted back into alternating current for the German power grid. Siemens is building the platforms in cooperation with Nordic Yards; it was commissioned to establish the network connection by the Dutch-German company TenneTTSO.

Offshore wind farms known as Veja Mate and Global Tech 1 are located about 125 kilometers northwest of the island of Borkum and will one day generate up to 800 MW of power. The BorWin beta platform transforms the alternating current supplied by wind turbines from 155 kilovolts to 300 kilovolts before converting it to the same voltage of direct current. The platform houses all of the equipment for the HVDCT converter: the converter itself as well as two transformers, four compensating reactors for the alternating current cables and gas-insulated high voltage switchgear technology.
HelWin alpha and HelWin beta will be used in a similar manner 35 kilometers north of Heligoland, where they will handle capacities of 576 MW and 690 MW, respectively. HelWin beta will serve as a smaller sub-platform, which means it will only have a few emergency shelters instead of comfortable crew quarters like the ones on HelWin alpha. “Staying there would be a bit adventurous, as the platform has no running water and is merely equipped with a chemical toilet,” says Suhr with a grin. The platforms are generally unmanned and can be remotely monitored by the grid operator. The crew quarters are occupied only when the platforms are being installed or undergoing maintenance.

Forests of Offshore Platforms for the UK. The offshore switchgear project is an example of the fact that pioneering achievements are rarely accomplished without a hitch. Aside from technical obstacles, the new facilities had to be certified by the customer.
In addition, the approval processes have been more time-consuming than expected. These processes are very protracted for two reasons. Not only do many components have to be approved separately; the standards aren’t actually defined until participating organizations begin processing the order. Due to these hurdles, the first platform will be delivered over a year later than planned. Costs will increase considerably as a result.
However, the sector has substantial business potential — and not just as far as Germany is concerned. In fact, the UK’s plans for offshore power generation are even more ambitious. The country wants to increase offshore wind energy’s share of its total electricity mix to 25 percent by 2020. In a three-stage process, the UK plans to increase its offshore wind power capacity to 48.6 GW. “England is planning so many platforms and wind farms at the moment that in a few years we’ll be able to walk there!” quips Suhr.
“We are moving in the right direction and are determined to implement and complete the projects needed to create a truly sustainable energy supply,” says Schmitt in recognition of the pioneering work being performed in the North Sea. The first platforms are scheduled to begin feeding electricity into the grid in 2014. The “pyramids” of the North Sea can then be expected to make a big contribution to generating zero-carbon electricity for the future.