Power generation from marine resources is a small but growing segment of the energy market—and it’s one fabricators should watch
May 2012 - The earth’s surface is predominantly water, with the world’s oceans, lakes and streams accounting for 70.9 percent of the globe and land masses occupying 29.1 percent, according to the CIA World Factbook. For many, bodies of water represent food, hydration and other resources, but some people see power in their currents, tides and waves.
The United States uses roughly 4,000 terawatt hours of electricity annually, according to the Department of Energy. Generating power from water, including conventional hydropower and wave, tidal and other water power resources, potentially can provide 15 percent of the nation’s electricity by 2030. The DOE estimates one-third of the national total annual electrical usage—roughly 1,420 terawatt hours annually—could be produced from waves and tidal currents.
But converting waves and tides into usable power requires well-fabricated systems that can withstand the rigors of prolonged submersion. To achieve this goal, many researchers and companies are working with fabricators to create prototypes that will help determine the most-effective materials and designs to use in the long run.
While only a small sector of the energy market currently is working to generate power from the world’s water sources, it is a good area for fabricators to watch, says Ron Smith, president of Verdant Power Inc., a New York City-based developer of marine renewable energy. The modern marine power industry has been emerging for 15 years, he says. Now, it’s entering the commercial rollout period and is poised for growth. Fabricators and manufacturers “should be interested in this because there will be an industry that is going to be deployed around the world with these kinds of systems within the next decade,” says Smith.
Technology in development
Ocean Renewable Power Co.’s technology harnesses the power of oceans and rivers to produce electricity. The Portland, Maine-based company is installing the first grid-connected commercial tidal energy project in the United States using its proprietary TidGen Power System at a 60-acre site in Cobscook Bay off Seward Neck, Lubec, Maine.
The TidGen device consists of a turbine generator unit mounted via a chassis to a bottom support frame that is secured to the ocean floor, says Chris Sauer, president and CEO of ORPC. Moving water rotates the turbine’s foils, creating energy that powers a permanent magnet generator located in the center of the horizontal-axis device. An underwater cable transmits the power to an on-shore station from where the electricity is delivered to the grid.
The TidGen turbines are manufactured from marine composite materials. The chassis, generator and support frame are fabricated from structural steel.
Many of the system’s steel components are fabricated by job shops contracted by ORPC. The company typically works with fabricators near its project sites to support local supply chains, says Sauer. “Our philosophy is to push the economic benefits into the communities where we work to the maximum extent possible,” he says.
Newport Industrial Fabrication Inc., Newport, Maine, is a 15-year-old specialty fabricator that works extensively with exposed architectural structural steel, space frames and wide trusses. The ORPC project, which required working with steel tube, fell very much into the company’s wheelhouse, says Daniel Gerry, Newport Industrial’s president.
Using design software not typical to the industry, the company ensured tight tolerances for the ASTM A106 Grade B seamless pipe that comprised the structures. The model created from the software detailed not only the length and other overall geometric requirements of each piece of pipe but also the weld prep bevel angles, says Gerry. “The model gives us a precise look at what they would call the fish mouth where it’s the profile at the end of the pipe where it’s cut to meet the next piece of pipe,” he says.
Once fit together tightly, the system required full-penetration welds or fully fused joints carrying 100 percent of the component’s strength into the joint, says Gerry. The weld prep, as defined by the welding code AWS D1.1, includes the T, Y and K connections. With structural instead of process piping, the welder is fusing a piece of pipe onto another pipe that does not have a hole in it because there is no fluid that will be transferring to it.
“It’s a fairly sophisticated weld prep because it’s forever changing as it goes around this oval shape, the fish mouth,” says Gerry. “Then you’re applying it to this other part and you have no way of putting a backer ring in there like you would typically do structurally behind a full penetration or butt weld.”
The company used an open-root TYK connection, says Gerry. “This is all allowed by the code, but because the weld prep is constantly changing, your welder has to manipulate himself around the shape. It’s a real challenge to consistently perform that weld.”
Newport Industrial Fabrication also coated the structure for ORPC. When applying a coating, all surfaces have to be available for sandblasting. Otherwise, the coating will not adhere properly to the paint and ultimately will fail, compromising the longevity of the structure. Any connections or areas where the paint can’t reach have to be sealed off around the edges, says Gerry.
ORPC also is working with Alexander’s Welding & Machine Inc., Greenfield, Maine, on its power-generation systems. The job shop has worked on TidGen and, most recently, RivGen projects. RivGen is a system designed to generate electricity at river sites.
In 2009, the job shop was chosen to work on ORPC’s beta turbine generator unit. “We used our CNC equipment to cut pre-defined shapes from various metals and then we fabricated them with structural steel to create the TGU deployment system,” says Jimmy Alexander, owner and project manager.
For the TidGen Power System, Alexander’s was in charge of the precision machining portion. In this role, Alexander’s is creating all of the system’s drive line components, machined from 255 Duplex stainless steel, and the split bearing housings, fabricated and machined from A709 grade 50 steel.
Alexander’s role in ORPC’s RivGen unit began with the complete manufacturing of the chassis base. On its shop floor in Greenfield, Alexander’s personnel teamed with ORPC’s project manager and electrical engineer to assemble and align the foils and the generator to the chassis. Once the completed unit was delivered to Eastport, Maine, it was coupled with ORPC’s research vessel Energy Tide 2 for testing in Cobscook Bay.
Researching possibilities
Companies like ORPC aren’t the only ones researching marine energy. The DOE also has embarked on a program to advance knowledge on the topic and recently released two resource assessments showing that waves and tidal coastal currents could contribute to U.S. electricity production significantly. The West Coast, including Alaska and Hawaii, has especially high potential for wave energy development, while significant opportunities for wave energy also exist along the East Coast.
Congress requested the development of National Marine Renewable Energy Centers, and the Energy Independence and Security Act of 2007 determined the focus of the centers, says Jim Ahlgrimm, a team leader in the Wind and Water Power Program at the DOE. The Water Power Program is investing in three centers, which are located in Hawaii at the University of Hawaii, in the Southeast at Florida Atlantic University and in the Northwest at a facility shared by Oregon State University and University of Washington.
The centers research a range of topics, including everything from engineering and environmental effects to social considerations—“the whole suite of considerations for sustainable energy generation,” says Brian Polagye, co-director of the Northwest National Marine Renewable Energy Center.
“We’re not working with a specific developer. It’s a collection of researchers” and resources collaborating to move the marine energy industry forward, says Ted K.A. Brekken, a researcher with the Northwest renewable energy center. “It’s a collection of resources that spans everything from research to actual hardware work that’s intended to help the industry in general.”
Florida Atlantic University’s Harbor Branch Oceanographic Institute in Fort Pierce, Fla., has an in-house fabrication center used to build prototype equipment for the Southeast National Marine Renewable Energy Center. The resulting equipment has to stand up to harsh ocean conditions.
The institute has constructed a pair of monitoring devices that will be deployed in the Atlantic Ocean to test the Gulf Stream Current’s viability as a source of electricity: a moored telemetry buoy (MTB) with an underwater ocean current turbine (OCT) tethered to the buoy on the surface. The MTB is outfitted with a configuration of navigation, GPS, safety, communication, security and environmental sensors encased in a fabricated steel hull, says Geoff Beiser, project manager.
The MTB is fabricated with A-36 grade steel plate and bar, says Beiser. The hull’s plating is 1⁄4 in. thick to protect it against strong storms, while the keel plate is 1 in. thick to support the mooring and anchor forces.
“There are three watertight spaces and two watertight bulkheads,” which are ballast setups for optimum pitch and roll, he says. “All watertight seams were welded both inside and out using ER7018,” an AWS plate-welding process.
Ensuring solid, sealed welds is a top fabrication challenge. To test the seals, HBOI pressure tests the vessel like it would for any other pressure-vessel piece, says David Bourdette, research machinist at Harbor Branch. Avoiding thermal distortion in the metal during welding is crucial, so he and the other fabricators weld in a sequence to avoid warpage.
For many projects, “from a fabrication perspective, generally, what we are seeing is large steel structures with cutting, welding and rolling,” says Ahlgrimm. Because the projects are prototypes, the fabrication processes being used are not typically suitable for mass production, he notes. “Companies are more focused on demonstrating the technology at this point. Improved manufacturing processes would occur when we start getting into larger scale deployment. We expect there will be big opportunities to reduce costs in the manufacturing area.”
A look ahead
There is no single method for generating power from marine resources. “About 100 different technologies are being looked at worldwide,” says Sean O’Neill, president of the Ocean Renewable Energy Coalition, a national trade association dedicated to promoting marine and hydrokinetic energy technologies. “They will start to converge after awhile, but because the marine environment is so complex, there are going to be certain technologies that work in certain areas better than others,” he says.
The mix of systems includes a mix of materials, most prominently steel and composites. “We are still gaining a lot of experience about which materials work best,” says Brekken, noting different parts of a device may require different materials. The material also must be able to withstand corrosive salt water if it will be installed in the ocean. “What we’re seeing for the most part is the bulk or largest of the surface areas of these have tended to be made from fiberglass or in some cases steel that is properly coated or painted.”
At Verdant Power, most of the structural components of its Roosevelt Island Tidal Energy project are various steels and cast iron, while the rotor blades are glass fiber composites. Fasteners and sealing components utilize stainless steels, says Smith. Material is an important consideration because the systems will need to survive and perform underwater for years at a time.
“Right now, the spec is underwater operation for five years then retrieval, refurbishment and re-installation four times: 20-year life, five-year refurbishment cycles. Ultimately, we would love to have those systems operating for 20 years straight under the water, but obviously, we have to get there,” says Smith.
While marine hydrokinetic energy is among the newer renewable offerings, it has lots of potential. “We’re never going to be as big as wind or solar, but we are going to be a noticeable component of energy in the United States, particularly in coastal states such as Maine, Alaska and Washington,” says Sauer.
The marine renewable energy industry is on the cusp of widespread use, says Brekken. “The research and development phase has been building to this decade, 2010 to 2020,” he says. “From where I am sitting, I think it’s really the next 10 years that are going to give an indication of where things might go, because we’re really at the point now where there are several companies with devices that can be designed and built to an industrial scale.” FFJ
Nick Wright, associate editor of FFJournal, contributed to this article.
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