An object immersed in a wave field is subjected to complex motions – heave (up and down), surge (back and forth) and pitch (a rolling motion). Most devices extract only a small proportion of the total energy of a passing wave. The WET-NZ device is a point absorber that has been designed to extract as much energy as possible from all types of motion.
The device is floating but the majority of it is submerged so that as much of it as possible interacts directly with the passing waves. There are three main components:
- The power pod, which contains all the power conversion equipment
- The hull, which is flooded with seawater to add mass to the system
- The float, which pivots about a single axle between the hull and the power pod at the waterline
Because of the mass, the hull does not more vertically to track the wave profile, but can still capture surge and pitch motions. This allows the float to be excited by both vertical and horizontal motions of the waves and to rotate about the pivot, thereby creating relative motion between the two parts. By opposing this differential movement, work can be done and energy extracted.
The hull is approximately 18 meters long and 3.5 meters wide. Nominal wet mass (flooded) is approximately 50 tonnes and displacement volume is around 95% (i.e. the structure is almost fully immersed – the water line is nominally at the axle center). The float weighs approximately 4 tonnes with a displacement volume of 50%.
The project site is a 1-square nautical mile area at the Northwest National Marine Renewable Energy Center (NNMREC) wave energy test site. It is located offshore of Yaquina Head, Oregon, between Newport (and Yaquina Bay) to the south and Otter Rock (a coastal landmark) to the north. The project site is approximately 1.8 to 2.7 miles offshore, and is closest landward to the Yaquina Head Marine Garden. Water depths at this location are approximately 115 to 180 feet.
The test site is currently in Phase 1 of its development, which involves establishing a mobile berth at which developers like WET-NZ can test and analyze their wave converters. It is a ‘mobile’ testing berth because devices are connected to a nearby floating instrumental buoy, called the Ocean Sentinel, instead of being connected to the electrical grid onshore. In addition to load dissipation, the Ocean Sentinel monitored and recorded performance and environmental data transmitted from the WET-NZ device, which was the first device deployed at the site.
Fabrication of a second-generation half-scale device has been funded by the US Department of Energy. The device was tested off the coast of Oregon, US at NNMREC’s wave energy site for six weeks from August to October 2012, after which it was recovered before weather conditions deteriorated and the stormy season set in. Summer metocean conditions at the test site were characterized by moderate swell, morning fog, afternoon sunshine, and sea breeze. Typical wave heights during these months were 0.5 to 3 m with periods of 5 to 11 seconds – ideal for testing.
The project required authorization from Oregon Department of State Lands (DSL) and the Army Corps of Engineers (ACOE) for device deployment, in addition to National Environmental Policy Act (NEPA) compliance determination from USDOE. The DSL and Corp permits were obtained early August 2012. As both NNMREC and WET-NZ were using federal funding, the DOE prepared an environmental assessment for the project and released it for public consultation (this period closed on 18 July 2012).
There are no local (City of Newport or Lincoln County) biological resource laws or regulation specific to the project site. Appropriate federal regulations include:
- Endangered Species Act (16 U.S.C. 1533(c))
- Migratory Bird Act (16 U.S.C., Section 703, Supp. I, 1989)
- Magnuson-Stevens Fishery Conservation and management Act (16 US.C. § 1801-1884)
- Marine Mammal Protection Act
Appropriate state regulations include:
- Oregon Endangered Species Act (Oregon Revised Statutes [ORS] 496.171 to 496.192 and 498.026)
- Oregon State Water Quality Regulations (OAR 340-41 ODEQ)
The following measures address the impacts of the Proposed Project on biological resources:
- Any WEC device that was tested in other waters prior to shipment to the project site will undergo purging of contained water, cleaning, and drying to prevent the spread of invasive species.
- Umbilical cables will have at least single armor to reduce electromagnetic fields (EMFs).
- The umbilical cable connection on the WEC devices and Ocean Sentinel will be constructed of steel or other metal to discourage chewing, gnawing, or pecking and prevent electrocution by marine life.
- The connection node on the power cable will be filled with biodegradable seed-based oil.
- The Ocean Sentinel will be constructed with National Marine Fisheries Service (NMFS)-approved passive deterrents, such as bull rails and netting, to prevent its use as a marine mammal haulout.
- The Ocean Sentinel will use only TBT-free and copper-free antifouling paints and coatings, and NNMREC will require that all WEC devices to be tested as part of the Proposed Project use only TBT-free antifouling paints and coatings.
- All vessels engaged in activities to suppose the Proposed Project will comply with NMFS marine mammal viewing guides.