Abstract
Much of the work to date on tidal energy resource assessments has focused on large-scale projects. For example, the first edition of the IEC technical specification (TS) for tidal energy resource assessment and characterization, TS 62600-201 provides a unified and internationally accepted methodology for commercial scale projects to estimate the velocity probability distributions at locations of tidal energy converters (TEC) for the purpose of computing the annual energy production (AEP). The methodology in the first edition TS includes two main approaches for determining the velocity distributions of tidal currents: a pure measurement-based approach, and a primarily modeling-based approach. For smaller projects, the direct measurement-based approach requires fixed instruments (FI) to be deployed at each TEC location for an extended time period. A new approach being included in the second edition is the so-called Hybrid Mobile Survey (HMS) approach. This method provides estimates of the velocity magnitude probability distribution at TEC locations by coupling one or more FI current profiler measurements with mobile vessel (MV) current profiler measurements. The full-length tidal currents time series at FI sites are used to infer the tidal current time series at the MV sites.
A field experiment testing the method was completed in Fall 2024 in the Savannah River in which two fixed instruments were deployed at multiple locations for a 40-day time period and mobile measurements were collected during a three-day time period. The locations of the FI deployments and the MV stations are shown in Figure 1. The vessel supporting the MV measurements held station at each location, staying within 20 meters of the target location for 3-5 minutes before moving to the next location completing the full cycle every 30-50 minutes. The ADCP measurement is used to build the regression model with the MV measurements and the Aquadopp measurement is used as validation. In addition to validating the methodology, we are evaluating several research questions such as how to treat time lags between measurements? What is the minimum duration of measurements at each site, controlling the station linger time for the mobile measurements? What is the best regression method for accurately inferring the velocity distributions?