Andy Filak / Principal / AMF Concepts
European companies have developed their offshore wind construction methods to a point where they see it as something to export. They have already succeeded by biding and winning the only offshore wind leases on the U.S. East Coast.
For the follow-on developments (in Massachusetts and New York) Siemens (Germany) and Vestas (Denmark) will be supplying the ‘Topside’ or wind turbine generators (WTGs) in these leases.
The ‘foundations’ for the WTGs will be supplied by Statoil (Norway) a company that favors a deep water, floating foundation with their-spar buoy technology. (www.ingenia.org.uk/Ingenia/Articles/901)
Dong Energy (Denmark) will propose its fixed bottom know-how. Over the last 25 years, Statoil and Dong have done an excellent job transferring their offshore oil-and-gas technology to offshore wind farm development.
Dong Energy’s first project, sited on the continental shelf off the U.S. East Coast, will require them to use jack-up vessels for placing their fixed-bottom turbines. Statoil’s project, however, will require the use of an Ocean Going Deck Barges (OGDB) for upending the spar buoy and ballast placement, as well as a crane vessel for placing the turbine on the spar buoy.
Both Dong Energy and Statoil will have to confront and abide by the 1920 Jones Act. This was enacted to protect and assure that all vessels used in marine transport and construction in U.S. waters are domestically built and crewed by U.S. citizens. Once they have contracted to build these vessels here, it will be almost impossible for a domestic developer to bid new leases on either coast.
America’s entry into the wind export industry
According to the National Renewable Energy Laboratory areas off the west coast of the U.S. and Hawaii have the best renewable energy potential. In addition, the California Renewable Task Force is developing leaseholds on federal submerged lands on the Outer Continental Shelf.
The high population centers on the West Coast and Hawaii all have good harbors that will facilitate construction and deployment for wind farms far (30 miles) offshore. These deep water wind farms, sited with consideration for fishing and sea traffic, will be candidates for the new direct drive, 10 to 20-MW turbines on top of spar buoy foundations. The economics of such facilities suggest they could go on line in four to five years.
Out of sight
One of the main problems with the proposed turbines is their size. They will make a strong visual impact with hub heights 400-ft above sea level and rotors 620-ft diameter. For this reason, people will unwillingly accept or firmly oppose visible wind farms off their shores and beaches. However, siting the wind farm 30 miles offshore reduces the visual impact to almost nothing. The turbines will blend into the sky because their blades and towers are typically painted light gray or off white.
Understanding the component makeup, construction, and deployment of the Statoil and U.S. spar buoy
The definition of a few terms is in order. For instance, the “turbine” is the complete deployment. “Top side” is the wind turbine generator consisting of the tower, nacelle, hub, and blades as a total assembly. The top side is bolted to the top of a “transition piece” which is the mating component that supports, locks, and unlocks the foundation “sub structure” or spar. The spar or spar buoy is a steel or concrete cylinder with a low water plane area. The spar holds its center of gravity below the center of buoyancy. Stone and sea water can be used for ballast. Because the spar and its ballast are extremely heavy (11,000 tons) and will be 385-ft long or tall (depending on construction method) deployment from a standard depth harbor calls for a creative economical solution.
Two construction and deployment methods
Statoil’s method of construction and deployment is to build the spar in steel or concrete in a harbor close to the proposed site. Due to the spar’s large draft (360 ft) it will require horizontal placement in the water of the quay. It will then be towed out to deeper water and then up ended and secured to a ballast-placement barge. Once that spar is stabilized with stone ballast, the wind turbine generator is installed from a crane vessel. The turbine is then towed out to the station keeping hook up in the farm. Statoil’s installation requires a long residency time at sea due to difficult assembly requirements before final tow-out in known sea states.
This extremely slow tow out from port to site can be accelerated by a specialized vessel. The construction and deployment of the innovative U.S. spar concept, made with all proven components, captures the deep water, offshore-wind foundation’s sub structure market for under half of Statoil’s export cost.
This is achieved by constructing the spar foundation’s sub structure standing vertically on one end of an OGDB. The WTG is then assembled and commissioned on the other end of the barge. After a tow out on the OGDB (from port to a site), the spar is lowered into the sea and positioned under the transition piece, then lifted up, by reducing sea water ballast, into the transition piece supporting the WTG. After the turbine is floated away from the OGDB it is handed off to the station keeping crew.
Standardizing on a U.S. spar buoy for an export industry
The sub structure of the spar buoy foundation will allow access to lease sites with deeper water and offer developers larger areas with stronger wind resources in close proximity to the load centers of large populations. This will also reduce grid congestion.
Because the wind industry is technology based, its costs always go down with experience and further development. Therefore, standardizing on a spar buoy, its construction and deployment components, such as the OGDB, will bring costs comparable to land-based wind. And equally important, this product can eventually become a successful U.S. export industry.
About Andy Filak
He is the Principal of AMF Concepts and has previously owned two companies, Formwork Engineering and Formwork Systems with offices in England, Seattle, and Los Angles. The companies provided formwork subcontractor services on high-rises and multi-level airport parking structures of over 10,000 cars. He has also worked in offshore wind projects for the last eight years. Reach him at AMFconcepts@gmail.com
Filed Under: Construction, Offshore wind