Md. Meraz Hasan, MAH Shovon, Md. Mahmodul Alam
Wind energy use in low-wind regions depends on turbines that can self-start and maintain stable operation under weak and fluctuating airflow. Among the various designs, helical Savonius vertical-axis wind turbines (VAWTs) offer promising self-starting and low-speed performance. However, integrated assessments that link prototype performance to scalability projections, alongside cost of energy and net energy analyses, remain limited. In this study, we address that gap through an experimental and analytical framework. A two-bladed helical Savonius VAWT was fabricated using locally available materials to match the low-wind conditions typical of Khulna, Bangladesh. The turbine was evaluated through aerodynamic performance testing, economic analysis based on cost of energy, and environmental assessment using net energy analysis. In addition, geometric scaling projections were carried out to estimate power output and cost of energy at larger sizes. The prototype operated stably from 3.25 m/s and achieved a maximum power coefficient of 0.059 ± 0.004 at a tip-speed ratio of 0.48. This corresponds to a system-level efficiency of 9.24% relative to the Betz limit and is consistent with the typical behavior of drag-driven rotors. However, at the tested scale, the cost of energy was estimated at 925 BDT/kWh, and the energy payback ratio was 0.25, indicating that small-scale implementation is constrained by low annual energy production relative to material input. Importantly, scaling projections suggest that increasing rotor size by a factor of five could raise annual energy output by approximately 25 times and reduce the cost of energy by about 50%. Overall, results demonstrate that the primary limitation of micro-scale systems lies in geometric scale rather than aerodynamic performance alone. Consequently, scaling effects offer a viable pathway toward practical application in low-wind regions.