Scaling up from the laboratory to open-water: Performance and Load Measurements for a Grid-Connected Tidal Energy Conversion System

Cross-flow turbines (CFTs) are inherently unsteady fluid energy conversion devices, even in a uniform, turbulence-free inflow, such as a towing tank. When CFTs are deployed in real tidal flows additional unsteady phenomena come into play, e.g., blade or rotor scale turbulence, or “tidal gusts” of longer time scales. Originating with the NSF-funded Living Bridge Project, a floating tidal energy conversion (TEC) system has been deployed since 2018 at the Atlantic Marine Energy Center (AMEC) Tidal Energy Test Site at Memorial Bridge in Portsmouth, NH, where tidal currents can reach speeds greater than 2.5 m/s during spring ebb tides. The TEC system consists of 3.2m diameter x 1.7m vertical axis CFT coupled to a direct drive PM generator, connected to the bridge grid via a rectifier and grid-following inverter. During a recent collaboration with the National Renewable Energy Laboratory (NREL) we made concurrent power performance, thrust load and tidal current resource measurements (via acoustic Doppler profilers and velocimeters), while the turbine operated in grid-synchronous mode. Results from these data sets will be presented, and operational characteristics analyzed. Spectral analysis highlights the importance of tidal gusts and turbulence on annual power production estimates.