Project construction is expected to take about eighteen months to complete. There will be four distinct phases of construction:turbine manufacturing, upland (land) cable, offshore electric cabling and park construction.
Rotor blades are made using a matrix of fiberglass mats impregnated with polyester or epoxy. Each rotor blade is subjected to extensive static and dynamic testing to ensure its safety and reliability.
The towers are made of steel plate rolled into a conical subsection. Towers are assembled from these smaller, conical subsections which are then cut and rolled into the right shape, and then welded together. Towers are usually manufactured in 65 to 100 ft. sections, transportation to the site being the limiting factor. Tower welds are inspected using ultrasound or x-ray devices.
The nacelles—which contain the key components of the wind turbine—including the gearbox and generator, are manufactured from standard and highly specialized components. For example, the gears used in the transmission are cut from special steel designed to withstand the forces put upon them.
The components—monopile foundations, towers, rotors and nacelles —will be transported to the construction site by ship, avoiding the necessity (and complexity) of moving these components overland.
In this phase, Cape Wind will build all land-based facilities and lay all required upland cabling. As it is currently proposed, the electric grid interconnection point will be at an NSTAR right-of-way in Yarmouth. To bring power from the actual landfall point to Yarmouth, Cape Wind will lay cable under public roads using traditional construction techniques, and then bury the cables and repave the roads.
During this phase, the undersea cables will be deployed. Using an environmentally sensitive process called “hydro-plowing” engineers will bury the cables six feet under the ocean floor. This process uses high-powered jets to fluidize a pathway in the sea floor. The cables are then laid in the pathway and are buried as the sediment settles around them. This technique is minimally invasive and quickly returns the sea bed to its original form.
The cables from the individual turbines connect to the electrical service platform (ESP), which serves as the main connection point and the offshore maintenance facility. From here, the park will connect to the Northeast grid via two undersea cables. For maximum safety, the cables will be buried for the entire distance to land.
The park’s 130 turbines will be installed using specially developed offshore equipment and construction techniques. The turbines will be supported by towers that have been installed on monopile foundations. Each foundation will be between five and six and a half meters across and will weigh between 250 and 350 tons. Depending on the specific seabed conditions, the foundations will be driven approximately 85 feet into the sea bed. With the foundations securely in place, the support towers can be installed, followed by the turbines (nacelles and rotors). When all the turbines are in place, each one is connected to the local cable grid and is then ready to begin producing energy.
Construction will be started only after rigorous studies have been performed and the appropriate permits received to ensure minimal environmental impact and the utmost in safety.