Unique challenges in harnessing open ocean marine hydrokinetic energy

The oceans are a tremendous source of clean, renewable energy, yet the majority of this resource is located far from shore and the population centers that could benefit from the generated power. Tidal energy has been harnessed in various ways over the last few centuries, for both mechanical and electrical power generation. Presently, tidal energy is quickly becoming a viable alternative to conventional fossil fuel electrical generation, especially in the upper latitudes such as Europe and areas of North America. These sites tend to be close to shore, in relatively shallow water, and benefit from at least one period of reduced flow, or slack tide, during which certain installation and maintenance activities may occur. Open ocean marine hydrokinetic (MHK) power generation, however, poses many more challenges, while retaining the issues that tidal systems must overcome. Ideal MHK sites, typically within western boundary currents such as the Gulf Stream, Kuroshio, and Agulhas Currents, are tens of kilometers offshore, in hundreds if not thousands of meters of water. The ocean currents are relentless, flowing continuously and without significant velocity changes over periods of weeks to months. The hydrodynamic drag on generators, cables, and support equipment can be tremendous. Once moored in the currents, access to the generators for inspection, maintenance, and replacement is extremely challenging, and in some cases nearly impossible. Ocean Current Energy LLC (OCE) has developed equipment and procedures to address and overcome some of these difficulties. OCE has designed a novel device which utilizes generator “coins” which may be installed and removed while in the high current, similar to an aerial refueling operation. The OCE approach to these challenges demonstrate the required “out of the box” tactics of ocean engineering problem solving, while leveraging off the experience gained from similarities in tidal power generation.