This Demonstration implements Hottel's clear-sky model to estimate the solar irradiance in at locations around the world. Integrating the curve over time yields the total solar energy received by a flat board in W h. This consists of two components: direct radiation and atmosphere-diffused radiation . Such a model can be used in various solar-related projects. It is computationally efficient and reasonably accurate during the summer in the middle latitudes. Altitude must also be taken into consideration in the design of a solar-powered vehicle.