By producing gigantic amounts of green energy, offshore wind turbines make a major contribution to the energy transition. Germany alone is planning for the generation of 20 GW by 2030 and is aiming to use some of it in Power-to-X plants for manufacturing hydrogen. To meet that goal, numerous new wind farms are either planned or under construction. One of them is off the island of Borkum in the North Sea and is to include two IMO3-compliant mtu electrical generator sets.
Borkum, the largest and most westerly of the East Frisian islands, offers mile upon mile of sandy beaches interspersed with dunes and stretches of forest. Its vast natural landscape and oceanic climate make it the perfect place in which to relax and breathe deeply.
Although the weather here is changeable, with the changes frequent and unexpected, one element can always be relied upon: the wind. The island of Borkum is never wind-still. However, the breezes blowing over it offer just a foretaste of what happens out at sea. There the wind is, on average, twice as strong. That makes offshore Borkum the ideal location for large-scale wind farms such as “Borkum Riffgrund 3” which is due to enter service in 2024. Danish operator Ørsted has the ambitious plan of erecting 83 wind turbines here to deliver a total of 900 MW – enough for a major city such as Frankfurt am Main.
First wind farm without transformer platform
The special feature of the new wind farm is its innovative grid connection concept. As opposed to other wind farms, the wind turbines off Borkum are to be connected to the offshore convertor platform directly. To do so, transmission system operator Tennet is planning to use a 66-kV three-phase power cable. That means the transformer stations, hitherto a fixed feature of all wind farms, are no longer needed.
The convertor platform – named 'DolWin epsilon' – was planned and will be built by Aibel, a Norwegian service company for the oil, gas and offshore wind industry. This is where the AC power generated by the wind turbines is converted into DC power and the voltage raised from high to extra-high – 320 kV – to minimize power losses during transmission. The cable – 130 km long – leads from the platform onto the sea bed and towards the coast and transports the electric current to the onshore convertor station. Here it is re-converted to AC power, brought to the correct voltage level to be fed into the energy provider's grid.
mtu emergency gensets supplied as turnkey solution with IMO-3 certification
The two mtu generator sets ensure that the lights on the convertor platform never go out, even when its main power supply fails. Furthermore, the generator sets provide emergency power to all the consumers on the platform needed to keep it operational – for example the seawater pumps, platform crane, and heating and ventilation systems.
The gensets meet special maritime requirements and are thus armed with IMO-3 emissions certificates: “The customer wanted his green energy project to include green emergency power too,” explained Detlev Köster from marine sales at Rolls-Royce Power Systems. The engines powering the gensets have been on the market since 2018. Following turbocharging, combustion and fuel injection enhancements, and the addition of an mtu SCR system, their nitrogen oxide and particulate emissions are now substantially lower than those of their predecessors. And without the need for an additional diesel particulate filter.
The electrical generator sets, along with the SCR system, generator, base frame, sensors, fire-extinguishing system, fuel and Ad-blue tank and control systems are housed in a fireproof A60 container. “We're getting a tailormade, turnkey solution complete from Rolls-Royce. The mtu products performed very satisfactorily in the forerunner project 'DolWin beta', so we could be confident about choosing them for this one,” said Martin Lundgren, Senior Buyer for Njord B & Dolwin5 projects at Aibel. The generator sets are scheduled for shipment next spring. By 2024 they should be ready to provide green emergency power on the green wind farm whenever needed.