High-altitude airships are being touted as the ideal aerial platform for long endurance applications for the next generation of communication systems. Such airships are usually powered by an electric propulsion system using solar cells mounted on upper surface of the envelope. Most existing studies related to such airships assume an axi-symmetric envelope shape, which has large drag and curved solar panels, both of which result in large size of solar panels. A possible solution to reduce solar panel area of a high-altitude airship is to use a multi-lobed envelope configuration on which flattish solar panels are mounted, which increases their power generation efficiency. This paper describes a methodology for conceptual design and sizing of high-altitude airships with a tri-lobed envelope, while incorporating the effect of parameters from four disciplines, viz envelope geometry, aerodynamics, operating environment, and solar irradiance. As a demonstration of the usefulness of this methodology, it is coupled to a particle swarm optimizer to obtain solutions that correspond to the minimum area of solar panels needed, while meeting all operating requirements and constraints for deployment on a specific day of the year. Compared to a baseline tri-lobed envelope, it is seen that the optimal solutions require 0.98–2.6% lower solar array area, while operating on four specific days of the year. Sensitivity analysis of area of solar array to a key parameter, viz fineness ratio (FR), is also carried out in this study. It is seen that as FR is increased from 3 to 6, the area of solar array required for operating on one specific day can be reduced substantially, due to reduction in the envelope drag and hence volume.