A multi-purpose solar energy collector is disclosed. The collector is a flat plate type of collector that is designed to heat either air or water, or both, and is portable so that it can readily be moved from one place to another. In the air heating mode, the collector is ideally suited for drying grain. After the grain drying season, the collector can be converted to the liquid heating mode to heat agricultural process water or domestic water, for example. In the combined air-liquid heating mode, the collector can be used to provide both heated air and heated liquid.