Exemplary embodiments or implementations are disclosed of systems for drying materials and control apparatus and methods relating to material drying systems. In an exemplary embodiment, a control apparatus for a material drying system is configured to select one or more heat sources from a plurality of heterogeneous heat sources for drying the material. The selecting is performed based on one or more sensor inputs. The control apparatus controls the selected heat source(s) to provide heat to dry the material. In some configurations, a material drying system operates as a typical heat pump only when more cost-effective auxiliary heat cannot be provided to maintain a drying temperature.