•Multiple cylinders in FIM work synergistically for hydrokinetic power harnessing.•Peak power conversion efficiency was estimated at 88.6% of the Betz limit.•Power-to-volume density reached 874.7W/m3 at flow speed of 1.45m/s.•VIVACE can efficiently harness energy from flows as slow as 0.8m/s, with no upper limit. Horizontal hydrokinetic energy can be harnessed using Steady Lift Technology (SLT) like turbines or Alternating Lift Technology (ALT) like the VIVACE Converter. Tidal/current turbines with low mechanical losses typically achieve about 30% peak power efficiency, which is equivalent to 50.6% power efficiency over the Betz limit at flow speed nearly 3.0m/s. The majority of flows worldwide are slower than 1.0–1.5m/s. Turbines also require large in-flow spacing resulting in farms of low power-to-volume density. Alternating-lift overcomes these challenges. The purpose of this study is to show that the ALT Converter is a three-dimensional energy absorber that efficiently works in river/ocean currents as slow as 1.0–1.5m/s a range of velocities presently inaccessible to watermills and turbines. This novel converter utilizes flow-induced motions (FIM), which are potentially destructive phenomena for structures, enhances them, and converts hydrokinetic energy to electricity. It was invented in the Marine Renewable Energy Lab (MRELab) and patented through the University of Michigan. MRELab has been studying the effect of passive turbulence control (PTC) to enhance FIMs and to expand their synchronization range for energy harnessing. This study shows that multiple cylinders in proximity can synergistically work and harness more energy than the same number of a single cylinder in isolation. Estimation based on experiments, shows that a 4 PTC-cylinder Converter can achieve 88.6% peak efficiency of the Betz limit at flow speed slower than 1.0m/s and power-to-volume density of 875W/m3 at 1.45m/s. Thus, the Converter can efficiently harness energy from rivers and ocean current as slow as 0.8–1.5m/s, with no upper limit in flow velocity.