SURVEYOR'S NOTEBOOK

So What Does It Mean to have a 1000MW Wave Farm Offshore?

By Michael Raftery

Scale is a difficult concept when novel technologies are being introduced, especially when it comes to marine renewable energy projects.

Let’s assume we are talking about a 1000 Megawatt wave farm. It is quite interesting to visualize such a farm off the coast of New Jersey (see Figure 1).


 

Figure 1. A visualized 1000MW plate capacity wave farm off New Jersey to scale. The vertical white area is 1.2km x 16.8km (0.72 x 10.08 miles)  and contains 200 SurfWECs. The red line is a purposed 40km (24 miles) long submerged high voltage shore connector. 

The shore connection could be located at Oyster Creek where a 619 MW nuclear power plant was decommissioned in October 2018.

The visualized location consists of 14 aliquots from Bureau of Ocean Energy Management (BOEM), Outer Continental Shelf (OCS) permit blocks 6256, 6306, 6356, and 6406:

https://marinecadastre.gov/nationalviewer/#/B4E20A2A-B091-E211-A1F4-D067E5FDEE55/37.16031654673677,-71.982421875/6/esriocean

BOEM-OCS permit blocks are 4.8 kilometer squares. Each permit block contains 16 – 1.2 kilometer square aliquots. The visualized wave farm is to use the eastern most aliquots of the four permit blocks listed above. Each aliquot would contain 20 SurfWEC units, 4 rows deep, with columns running north and south. This equates to 10 aliquots with SurfWEC units and 4 aliquots for easements. At 20 units per aliquot, 600 meters of the 1200 meters of the north to south column would be covered by buoys offset 200 meters from each other. This allows a large safety margin for the watch circles (buoy range of motion) of individual units.

None of the units would be visible from shore.

Until recently, a 1000MW wave farm covering this small of an area off New Jersey ocean frontage was not possible, but wave energy research and development work at Stevens Institute of Technology has resulted in a wave energy converter (WEC) capable of concentrating the energy in offshore waves using a man-made beach called the SurfWEC concept. The SurfWEC can be safely anchored in depths of 30 meters (100 feet) or more and the depth and angle of the SurfWEC can be adjusted to make incoming waves the ideal shape for wave energy conversion.

Historical wave data (1991 – 2017) from the National Oceanic and Atmospheric Administration (NOAA), National Data Buoy Center (NDBC), buoy number 44025, shown northeast of the proposed SurfWEC project site, was used to project the performance of the wave farm for economic analysis. The wave climates from these two locations are nearly identical as they are at the same water depths. The 44025 buoy location is a bit more sheltered by Long Island, New York from waves coming from the northerly directions.

With the ability to concentrate wave energy by converting wavelength into wave height over the WEC, waves as small as 0.7 meters (2.3 feet) high, can be converted to 1 megawatt (1MW) of electricity. To convert the 0.7m high waves to 1MW of electricity, the incoming wavelength must be at least 40 meters long which equates to a 5 second period wave at this depth. The average wave period in this location ranges from 5 to 7 seconds depending on the time of year. The historical data shows the waves will enable over 1MW (1000kW) of electric power production per unit over 80% of the time on an annual average basis and production under 50kW per unit will occur less than 100 hours per year, or 1% of the time on an annual average basis (Figure 2).

Figure 2. Hourly Wave Data off New Jersey in 2017. Significant Wave Heights (Hs) are in meters (m), and the corresponding spectral period (Tp) is in seconds.

 

The visualized 1000MW wave farm, in average wave conditions 0.7-1.0 meter high (2.3 to 3.1 feet), will power over 200,000 homes and up to 1,000,000 homes in waves over 2 meters (6.5 feet) high depending on the wave periods. It will produce over 1.5 times the Oyster Creek Nuclear Plant maximum power output in waves over 3 meters (10 feet) high.

The average power production, for the same wave farm, 80km offshore would exceed 300MW or enough to power 300,000 homes. The seafloor cable required to deliver the electric power to shore costs approximately $1.2 million per kilometer ($2 million per mile) to install, and mooring prices increase with depth, so it is not a trivial issue going father offshore, but father offshore is economically viable and would likely reduce common use conflicts.

The installation cost for the units is projected to be $1.5 per Watt of plate capacity which equates to $7.5 million per 5MW unit with the Balance of Plant (BoP) (seafloor cables and grid connections) making up approximately 16% of the installation cost if this was a stand-alone project. If the units were co-located with an existing wind farm, the BoP would be approximately 2% of the project cost.

The naval architects and marine engineers at Martin & Ottaway are continuing to work on improvements in safety and efficiency while reducing overall project costs. There is still a great deal of testing to be done including sea trials, but we are confident the waves off New Jersey are now an economically viable renewable energy resource. Our confidence is based in the science and engineering research put into this project since 1992. Data from wave tank tests at Stevens Institute of Technology consistently demonstrated the SurfWEC’s ability to produce WEC prime mover velocities 10 times greater than existing WEC systems by creating surge-surf conditions over a near-surface platform. When offshore waves are converted to surge-surf conditions using a near-surface platform, larger buoys can be moved at much greater velocities than in typical offshore sea and swell conditions. We are able to control the exact depth and slope of the near-surface platform to optimize the shape of the surge-surf waves impacting the buoy in mild to moderate waves, and the platform autonomously lowers itself near the seafloor in large waves while the buoy stays on or near the surface to keep harnessing wave power which keeps the system operational and safe from extreme wave loads even during hurricanes. Events such as Tsunamis will have no structural affect on the units as very little kinetic energy will be input to the buoy or submerged platform at their offshore locations.

The logic for choosing this location included the existing grid infrastructure established for the 619MW Oyster Creek nuclear power plant which was scheduled to be decommissioned in 2018, the water depth, the seafloor composition, the distance from shore, and minimal impact on other uses for this area. This wave farm can replace a significant portion of electric power production of the decommissioned 619MW Oyster Creek nuclear plant.

Operationally, one major project goal is to provide jobs for the local marine industry including commercial boat captains and crew for routine maintenance operations such as mooring line and float inspections. Single-line fishing and dragnet operations will be available 750 meters (0.45 miles) outside the wave farm and scallop fishing will be allowed outside this perimeter. The wave farm will function as a nursery for plankton, seaweed, fish, scallops and other sea life. When the waves occasionally white cap over the platforms, they will oxygenate the seawater improving living and growing conditions for numerous forms of sea life.

SurfWEC LLC is interested in collaborations with OSW developers to maximize carbon-free electricity production from the BOEM OCS permit block leases available in the United States (Figure 3).

Figure 3. BOEM OCS – Mid-Atlantic Bight Offshore Wind (OSW) lease areas