In addition to utility-scale power generation (e.g., rated capacities greater than 106 W), there are also possibilities for tidal current generation at the micro-scale (e.g., rated capacities less than 102 W) that could provide power to autonomous oceanographic instrumentation. This paper presents performance characteristics of a high-solidity, helical, cross-flow turbine rotor for a tidal current micropower system. Studies are conducted on a 1/4-scale turbine in a laboratory flume and a full-scale turbine prototype using open-water tows. Results suggest this type of turbine rotor can achieve efficiencies as high as 25% and can smoothly self-start at water velocities less than 0.5 m/s. The sharp peak around optimal efficiency displayed by the power performance curves suggests a need for generator control in a micropower system using this type of rotor.