Hydrokinetic energy assessment downstream of the hydroelectric dam from GNSS-tracked drifters: a new approach

The availability of river velocity data, crucial for assessing hydrokinetic energy potential, is often limited or nonexistent. This study proposes a rapid and cost-effective approach to evaluate river potential using Global Navigation Satellite Systems (GNSS)-tracked drifters. Field experiments were conducted in a downstream river stretch adjacent to a hydropower dam in Southeastern Brazil. These experiments included performance assessments of the drifters, with comparisons conducted against measurements from an Acoustic Doppler Current Profiler (ADCP) for dynamic analysis and a fixed reference point for static validation. The results indicated that the drifters provided speed and position measurements with an accuracy of approximately 6.7 cm/s and 2.6 m, respectively. A strong correlation (0.97) between drifter velocities and river discharge was demonstrated through field experiments. This enabled the derivation of velocity time series from historical river discharge data and their application to a power curve to assess the long-term hydrokinetic potential. Based on the velocity field and depth of the studied section, a configuration consisting of four turbines with a 5.0 m rotor diameter could generate an estimated 0.25 GWh annually, demonstrating the feasibility of utilizing residual energy to enhance the efficiency of a hydroelectric plant. Given that over 3700 hydropower dams with capacities exceeding 1 MW are currently operational worldwide, this methodology presents a replicable and valuable tool for global applications. Field validation in a Brazilian dam demonstrates its applicability as an alternative to conventional ADCP surveys. The method is particularly suitable for regions such as the Amazon, Congo, and Mekong basins, where off-grid communities depend on diesel generation, though it is less applicable in environments dominated by wind-driven currents.