SS Marine Renewable Energy – Ocean Current Turbine Mooring Considerations

Abstract

To assist in the development of mooring and foundation solutions for ocean current based electricity production, an overview of the resource and seafloor characteristics in three potential power production regions are presented. These regions are offshore Florida USA, North Carolina USA, and South Africa. Maximum measured flow speed off both the USA and South Africa were around 3.0 m/s and maximum temporally averaged energy densities were between 2.0 - 3.0 kW/m2. Water depths at considered locations range from 60-400 m, and bottom type varies greatly. Most evaluated locations contain occasional flow reversals and occasions when current speed approached 0.0 m/s (only locations near the core of the Gulfstream off SE Florida did not measure either event). While low current events are undesirable from energy production and mooring design perspectives, they might provide unique opportunities to install or maintain equipment.

Characterization of the mean flow field in the far wake region behind ocean current turbines

“…Ocean currents with time averaged kinetic energy fluxes above 0.5 kW/m 2 can be found along the western boundaries of most of the world oceans (VanZwieten et al 2013), with values exceeding 2.0 kW/m 2 in several areas (VanZwieten et al 2015). Multiple research teams are actively pursuing the extraction of this renewable energy resource.…”

“…However, OCTs will likely be attached to the sea bed using mooring cables and will operate in water column away from the boundaries (VanZwieten et al 2013;IHI Corporation 2014). Therefore, boundary effects will not significantly impact these systems.…”

“…Ocean current turbine (OCT) prototypes being developed to harness this resource are now approaching the offshore testing stage (VanZwieten et al 2014). Off Florida, these systems will likely be moored to the sea floor using compliant mooring systems in 300+ m of water, and will operate in the top 100 m of the water column (VanZwieten et al 2013). To enable rapid transition from single device testing to farm scale deployments, research directly related to turbine arrays is needed.…”

Marine Hydrokinetic Energy from Western Boundary Currents

“…Important engineering considerations include the type of turbine, mooring, and anchoring system to be used; the total water depth and bottom type where turbines will be installed; current variations with depth; and turbulence levels within the water column (Neary et al 2014b, VanZwieten et al 2015. Knowledge of these subjects has been increasing for several WBCs; however, as of the date of this article, large-scale electrical generation turbines suitable for deployment in a WBC are still in the development and prototype stages and have yet to be manufactured and commercially installed (Neary et al 2014b, Ecomerit Technol.…”

“…Section 4 describes MHK details in the Gulf Stream off Cape Hatteras, North Carolina, United States. This location has been well 40°N 30°N 20°N 10°N 0°1 0°S 20°S 30°S 40°S 90°E 135°E 180°135°W 90°W 45°W studied, the Gulf Stream there has many properties that will affect MHK energy extraction and that are found in other WBCs, and the region has characteristics suitable for possible commercial development of electrical power generation at some future time (Kabir et al 2015, Lowcher 2015, VanZwieten et al 2015. Section 5 looks ahead to the future.…”