Comparative Analysis of Savonius and Darrieus Vertical Axis Wind Turbines for Off-Grid Application in Nigeria

This study compared Savonius and Darrieus H-rotor vertical-axis wind turbines (VAWTs) for off-grid battery charging across five Nigerian sites: Kano, Sokoto, Jos, Ilorin, and Warri. A quantitative, simulation-based approach was implemented in Python on Google Colab using entirely open-source tools. Hourly wind data for 2023 were drawn from NASA POWER and fitted to two-parameter Weibull distributions. Savonius aerodynamics were modelled via Blade Element Momentum Theory (BEMT); Darrieus performance used the Double-Multiple Streamtube (DMST) method with Gormont-Berg dynamic stall correction, calibrated to a measured Cp of 0.45. A constrained PMSG winding optimiser, ngspice circuit simulation, and an 8,760-hour battery simulation were run for all ten site-rotor combinations. The Savonius produced 152.7 kWh and 152.2 kWh annually at Sokoto and Jos, with loss-of-load probabilities (LOLP) of 13.5 percent and 14.6 percent respectively; the Darrieus delivered under 1 kWh at four sites and peaked at 15.5 kWh at Jos, with LOLP above 39 percent everywhere. The Savonius is the appropriate choice for off-grid charging at inland Nigerian sites where mean annual wind speed exceeds approximately 3.0 m/s; the Darrieus cannot function reliably as a standalone generator under current Nigerian wind conditions.