Since the recognition of the influence of human activity on climate change due to increasing use of fossil fuel energy, significant efforts are being devoted towards the development and implementation of renewable energy technologies that are harmless to the environment. One of the abundant energy sources is the sun. There are currently two primary ways of harvesting energy from the sun: through photovoltaic (PV) panels and through thermal collectors. With the evolution of unmanned air vehicles (UAV), as well as the growing interest in “Green Aviation,” the interest in investigating the usage of PV solar panels in certain category of aircrafts has increased in the last two decades. In a small UAV or low speed personal transportation aircraft, the wings of the airplane could possibly be covered with photovoltaic panels to harness sun's energy for propulsion. Most notably the success of “Solar Impulse” airplane has attracted the attention of general public as well as small aircraft enthusiasts. In this paper, we analyze the incidence of solar radiation over an airfoil/wing of an airplane. We show that, under some conditions, the incidence is independent of the shape of the airfoil. We develop a more complete model to compute the total solar radiation incident on the airfoil during a cruise flight using the solar tracking equations and geodesy for path creation. The model is based on the discretization of both the airfoil and the path. To illustrate the versatility of the model, we employ a genetic algorithm with migration to optimize the airfoil shape during some specific given flight conditions and discuss the results.