In agricultural applications, the preservation of crops is essential. The most suitable method of preserving the crop is drying. The traditional methods used for drying include mechanical drying, where hydrocarbon fuel or burnable materials are used as a source of heat. The other method is open sun drying, where crops are placed in an open space. Both methods affect the quality and vital nutritious properties of the crops. The mechanical drying processes are costly, whereas the latter is dependent on the weather condition. To overcome these limitations, solar dryers are developed. Mathematical modeling is highly important for the perfect design and improvement of solar dryers. The performance of the drying system depends upon the different parameters that can be optimized using thermal modeling. This chapter covers the thermal modeling of greenhouse solar dryers for active and passive modes.