VolturnUS floating wind turbine. Image: Maine Aqua Ventus
It all started some six years ago when an investment banker specializing in oil and gas set up a think tank to help reduce dependency on fossil fuels. Recognizing the resource of strong winds off the coast of Maine, where he spent summers, the banker proposed some ideas to the University of Maine about harnessing the winds and creating a renewable energy source.
Today those ideas have evolved into the first offshore wind turbine built by the U.S., a demonstration model, approximately 1/8th-scale of the proposed 400-foot full-scale structure. Installed earlier this year with U.S. Department of Energy funding and based on the university’s VolturnUS turbine technology, the project is called Maine Aqua Ventus. It now is a collaborative effort, led by the university, Emera Inc., and Cianbro Corp. The goal is to reduce the cost of power considerably by connecting a wind farm to the existing power grid as well as to bring economic development to the state.
Jake Ward, vice president of innovation and economic development at the University of Maine, and a manager of Maine Aqua Ventus, says university experts, especially those in structures and composites, recognized renewable energy was a leading growth area for composites and that the amount of wind available off the Gulf of Maine is a huge resource.
In getting started, a team looked at bottom-mounted technology of offshore turbines in Europe but quickly realized that it would not work for Maine, where the turbines would be sited at least 10 miles offshore, further away than those in Europe.
The reasons for locating the farm further out, Ward notes, is because of the tremendous amount of activity in the first three-to-five-mile area from shore, including shipping traffic, commercial fishing, migratory bird and bat routes, marine mammals, wind jammer tours, recreational sailing, and for some people the turbines are a visual issue. Also, the further away from shore, the more consistent and stronger the winds are, but the downside is that the water deepens, and bottom-mounted technology would be difficult and expensive.
CAD rendering of a floating, offshore wind turbine. Image: Wikimedia Commons
So the technical challenge became: Is there a floating platform technology that can cost-effectively extract the wind and be durable enough to survive Gulf of Maine conditions? Ward’s answer: “We can. Absolutely.”
Using ongoing university research about wind and wave conditions in the Gulf of Maine, the team looked at different floating platform technologies and married them with new numerical models linking a wind turbine on a tower to numerical models simulating floating platforms for oil and gas. Since this was the first time such integrated models were used to predict structure behavior, proving accuracy of the predictions was among the first tasks, Ward said.
A 1/50th scale model was built and tested for a variety of things, including predicting survivability under extreme conditions and how much movement the turbine will undergo. The more movement on the turbine vertically, the less power is generated, Ward says.
Successful testing led to the installation of the 1/8th-scale model last summer. It was selected for DOE funding to demonstrate the use of concrete floating hulls and composite towers instead of steel structures for resistance and a longer life cycle than the 20-year life of a steel system.
The challenge now is going to full-scale, but Ward says these are different challenges about integrating everything from the environmental piece to the stakeholder piece to the permitting piece. Technically, the construction is similar to building and installing large concrete bridges or hydro electric plants, towing them out to sea and anchoring them.
The next critical step comes next spring when the DOE awards $46 million to three of six demonstration projects across the U.S. for the design and engineering of full-scale projects to demonstrate advanced technology to lower energy costs. The University of Maine’s submission is for two 6-MW turbines on top of two floating platforms as a test for the full scope of the plan to build a 500-MW wind farm that will feed into the existing power grid and considerably reduce energy costs.
Ward says he is very pleased with progress so far. “Like with any type of R&D commercialization there are days when you wish things would go better and faster and all that, but we are right on target,” he says.
The 1/8th scale model is about the size of a very large sailboat. “Even on the windiest days, it looks like a very calm stable structure,” he says. During a regular recent winter storm, winds and waves buffeting the structure gave the team an opportunity to collect data that would be comparable to an extreme weather event because of the scale of the structure. “We’re using that in designing the full-scale model,” Ward says.
On such days, Ward says it can be “extremely exciting seeing the equivalent of 60-foot waves crashing all over it.”
Nancy S. Giges is an independent writer.
Like with any type of R&D commercialization there are days when you wish things would go better and faster and all that, but we are right on target.
University of Maine