U OF MAINE LAUNCHES FIRST FLOATING WIND TURBINE

U OF MAINE LAUNCHES FIRST FLOATING WIND TURBINE

BY STAS MARGARONIS, RBTUS

A University of Maine (UOM) team launched the first American floating wind turbine, VolturnUS, on May 31^st incorporating innovations that could fast-track wind farms on the Atlantic and Pacific coasts as well as Hawaii.

Regional wind farms can be anchored off the shores of major U.S. population centers and connected to the land-side grid by transmission lines. This is the goal of the Atlantic Wind Connection project slated to begin construction off the New Jersey coast.

The Prototype

The prototype is a 65-foot-tall wind turbine and a one-eighth-scale version of a 6-megawatt full-scale wind turbine that UOM hopes to deploy off Maine’s coastline in 2016. The floating platform is designed to be anchored in deep water similar to offshore oil and gas platforms. Six megawatts can power 9,000 households.

“There are many firsts here today,” said Habib Dagher, director of the University of Maine’s Advanced Structures and Composites Center: “Not only is VolturnUS the first floating wind turbine in the U.S., it’s the first turbine tower to be completely made of composites, and the first concrete/ composite floating base in the world.” [1]

The VolturnUS unit was assembled at Cianbro, an engineering construction company that partnered with the University of Maine to fabricate the floating wind turbine.

Implications

The project has major implications towards fast-tracking a new floating wind industry in the United States:

• The semi-submersible tripod. The UOM design was found to be the most stable compared to designs such as the turbine-mounted-on-a-buoy or ‘spar buoy’ promoted by the Norwegian oil and gas giant, Statoil. The prototype will now be tested in Atlantic Ocean conditions. Stability is critical to reducing wear and tear on the turbine driven propeller blades and keeping maintenance costs low: “It’s like a tri-marine boat. It floats on three outer arms and the frame carries the load of the turbine. Our engineers made sure it could “breathe” in a balanced way so as waves hit the structure it has the flexibility to take on some of that impact,” said the chief engineer in charge of offshore structural design, Antony Viselli. [2]
• Concrete replaces traditional steel foundation. The semi-submersible base is made of concrete strengthened with composite materials, which eliminates the need for steel construction. Dagher said: “In Europe, offshore wind turbines have a life of about twenty to thirty years. The VolturnUS has a hundred year life expectancy. That’s why we developed the concrete base.” The concrete base reduces welding, man hours and uses a forming process that provides innate strengths that Dagher believes will be superior to a welded steel configuration. This approach has been used in composite materials for aircraft and is now being tested in a marine setting. A European designer noted that man hours for wind turbine fabrication in Europe are skyrocketing because of insurance and marine certification requirements for superior quality controls to insure structural integrity. The UOM Advanced Structures and Composite Center is providing a new paradigm for offshore construction that could help the United States regain the lead in offshore wind development.
• Composite tower. The composite tower also eliminates steel fabrication and welding. It creates the potential for a more stable and cost-effective structure.
• Floating wind turbines may replace fixed foundation structures. Initially, construction in Europe  focused on shallow water for the base of fixed foundation wind turbines. This requires construction of foundations in the water followed by installations of wind turbines. The vessels used to install wind turbines cost at least $100M. The shallow water foundation wind farm is proposed for several U.S. Atlantic coast projects. The UOM project may strengthen the case for building floating wind turbines and anchoring them in deep water.  Deep water semi-submersible structures are increasingly used in the oil and gas industry. Research shows that wind generation is optimized when moving further out to sea. Deep water structures open up wind farm opportunities on the U.S. Pacific coast and in Hawaii.
• Maintenance costs should be less. Dagher says the VolturnUS, secured by mooring lines with self-embedding anchors, floats like a vessel. It can be towed out to sea to drop its anchor and be plugged into the grid. Repairs require towing the wind turbine back to port for work rather than performing expensive maintenance work at sea needed for fixed foundations.
• Turbine integration with floating platforms. Concerns have been expressed that wind turbine makers are reluctant to support floating platforms because the wear and tear  is far greater than from fixed platforms. UOM hopes to improve confidence levels for wind turbine makers.
• Environmental Issues. Dagher told participants at a Maine Industry Initiative Webinar on June 5^th  that there had been extensive research on the environmental impact of the VolturnUS prior to launch. No negative impact was found. The floating turbine can be towed far enough out to sea so as not to be visible from land. This reduces opposition from people who do not want their views impaired.
• Cost issues.  Paul Williamson, director of the Maine Wind Industry Initiative based in Portland, Maine says the current cost of power generated by one offshore floating wind  project will be expensive and cost around 27 cents per kilowatt hour compared to the current 7 cents per kilowatt hour (KWH) for conventional power. However, as projects move towards commercialization, developers expect to reduce costs down to 10 cents per KWH, he said.
• Grid integration is the big unanswered question. The lack of power grid connections to wind farms has slowed development off the North German coast. Transmission operators need to build and pay for new transmission lines that connect offshore wind farms to German population centers which is costly.  In addition, offshore transformers are needed to transform Direct Current (DC) for long range transmission from wind farms to a land based power grid system using Alternating Current (AC).  A European designer who has worked on one such project says offshore transformers are proving to be very expensive to build  and deploy. In 2012, the German news service Spiegel reported major problems with transformers being built by Siemens in the North Sea saying delays are causing disruptions in bringing new wind farm electricity to land-side consumers.[3] High-Voltage Direct Current (HVDC) systems are used for bulk transmission of energy from distant generating stations. An HVDC system can transmit more power over a given right-of-way than an AC system, which is an advantage in overall cost.
• Siemens Moving Ahead With HVDC Installation. The German electronics giant, Siemens, says on its website that it expects to complete an offshore HVDC platform to connect to a North Sea wind farm by 2015:       “ The grid connection, designed as a high-voltage direct-current transmission link, has a rating of 690 megawatts (MW) and is scheduled to be operational by 2015. Amrumbank West will be built in the North Sea, about 55 kilometers from the mainland.”[4]

Background

According to a UOM press release:

“Tthe VolturnUS technology is the culmination of more than five years of collaborative research and development conducted by the UMaine-led DeepCwind Consortium. The DeepCwind research program is a unique public-private partnership funded by the Department of Energy, the National Science Foundation-Partners for Innovation, the Maine Technology Institute, the state of Maine, the University of Maine and more than 30 industry partners.

Data acquired during the 2013 deployments off Castine and Monhegan will be used to optimize the design of UMaine’s patent-pending VolturnUS system. The UMaine Composites Center has partnered with industry leaders to invest in a 12MW, $96 million pilot farm. The deployments this summer will de-risk UMaine’s  VolturnUS technology in preparation for connecting the first full-scale unit to the grid in 2016.”[5]