Design and finite element validation of a spring-assisted flywheel energy storage system for groundwater pumping in rural Uganda

Off-grid rural communities in Uganda lack reliable energy for groundwater pumping, with existing solutions constrained by high costs, limited lifespans, and environmental concerns. This paper presents the design and finite element validation of a spring-assisted flywheel energy storage system (FESS) developed for this context. The system was modeled in SolidWorks 2025 and analyzed using Ansys 2025 R2 STUDENT, incorporating a 50 kg mild steel flywheel (6.25 kg·m² moment of inertia), a spring-assist mechanism comprising two sets of three torsion springs (18.5 Nm/rad stiffness per spring, configured to deliver 35 Nm supplemental torque at the flywheel shaft when fully deflected to 120°), and a 2:1 belt-pulley drive. Static structural analysis confirmed exceptional structural integrity: the shaft exhibited maximum principal stress of 0.294 MPa (0.05% of yield strength) with factor of safety of 15, while the frame showed maximum deformation of 0.78 mm, von Mises stress of 18.5 MPa, and factor of safety of 13.5, substantially exceeding the recommended minimum of 3.0. Modal analysis identified critical speeds at 6,760 RPM, 9,762 RPM, and 17,593 RPM, establishing three resonance-free operating windows: below 5,700 RPM; 7,800–9,500 RPM; and 11,300–14,900 RPM. Based on human arm cranking literature, manual operation is expected to achieve only 95–267 RPM, well within the lowest and safest window (