Analytical Scaling Criteria and Feasibility Limits for Solar-Electric Aircraft

The feasibility of solar-electric propulsion is fundamentally constrained by the tradeoff between harvested photovoltaic (PV) electrical power and the aerodynamic and structural penalties of PV integration. An analytical framework was developed to assess the feasibility and performance scaling of solar-electric aircraft and to derive closed-form expressions, with particular emphasis on uncrewed aerial vehicles (UAVs). The shaft-power requirement was expressed in terms of wing loading, aerodynamic efficiency, and propulsive efficiency, yielding a fundamental scaling criterion for power per unit area. The incremental effects of PV integration were modeled using explicit weight and drag penalties, converted into equivalent electrical power-density penalties through the drivetrain efficiency. A unified feasibility condition was then obtained by requiring the harvested PV electrical power density to exceed these penalties. A nondimensional solar benefit parameter was introduced to quantify the effectiveness of solar augmentation across a range of configurations. The analysis also identified a crossover condition between shaft-power-equivalent solar input and required shaft power, defining the boundary between solar-augmented and pure-solar flight regimes. The resulting analytical framework provides compact design relations that link aerodynamic performance, structural scaling, and PV electrical energy capture. It offers practical guidance for the preliminary design of solar-electric aircraft and solar-augmented UAV systems.