October 15, 2009
A Vancouver company is proposing to build an offshore windfarm in northwestern B.C., using unique marine construction techniques and equipment developed in Europe. NaiKun Wind Energy Group is developing plans for the construction of the NaiKun Offshore Wind Energy Project. The project would be located in the shallow waters northeast of Hecate Strait, between Haida Gwaii (the Queen Charlotte Islands) and Prince Rupert on the B.C, mainland. "On this wind energy project the work is independent and there is a lot of repetition" said Mike O'Connor, president of Naikun. "The turbines are all identical pieces of construction that are interconnected and link to an offshore platform, which is the most sophisticated component on the project."The project involves the construction of 110 wind turbine generators with a plant capacity of 396 MWs (MW). "The foundation for the turbine, which is very common in Europe, is a giant open-ended steel tube about 4.5 to 5 metres in diameter," said O'Connor. "They are 55-85 mm in thickness, with the thickest section at the seabed, where there are the greatest forces on the piles." Construction of each foundation requires an enormous jack-up vessel, designed to handle high winds and waves. The foundations are transported to the site by barge and received by the vessel, which uses a 440-ton crane and a pile guiding frame to lift them into place.
A 200 to 250 ton pile driver places the piles into the seabed, where the water is a depth of 12 to 20 metres at low tide. "A transition piece, which is 20 metres long, is then slipped on top of the steel pile," said O'Connor. "This piece is the transition form the steel pile foundation to the bottom of the turbine tower. It is in the tidal power portion, so it is specially treated with anti-corrosive paint. Ladders and bumpers are installed through the tidal power zone, so staff can do maintenance." There is a five-metre overlap between the two sections, which is sealed with a special quick-setting high-strength grout.
Once the grout sets, the foundation become one piece. There is a giant flange on the transition piece that meets up with a flange for the installation of the wind turbine tower. The jack-up barge has storage for tower sections, which are lifted into place and secured. The nacelle or hub of the wind turbine generator is lifted about 80 metres above the water to the top of the tower. The blades are lifted vertically attached to the rotor Once this is completed, the jack-up moves to the next location and continues the same operation. This construction process is estimated to take about 1.8 days per foundation including an allowance for weather delays.
Actual working time at each site is expected to last less than one day; with the pile driving itself, taking two to four hours. Foundation installation takes place 24 hours a day, seven days a week. The platform that forms the deck of the offshore converter station will be constructed and installed in the same way. The platform will accommodate the transformers, equipment, maintenance supplies, fuel, waste storage, boat access facilities, and a helicopter pad. It will be built on four or six steel foundations and will be supported by a self-elevating platform.
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