Solar cooling is one of the most naturally appealing applications for solar energy. The resource availability and the demand are roughly in phase, both on seasonal and diurnal time scales, and it is a “high-value application”: That is, a British Thermal Unit (BTU) of cooling delivered by an electrically driven vapor-compression air conditioner costs the user substantially more than a BTU of heating supplied by burning natural gas. Why then, if the concept is so appealing, is solar cooling not already a fact of contemporary life? Why does the use of active solar cooling systems remain so limited? Clearly, there remain barriers to the practical implementation of solar cooling that are both technical and economic. In this section, we present a simple model (O’Gallagher and Winston, 1998) that helps quantify the economic factors and provides a basis for the comparison of different solar collector technologies.