The development of research on the maximum power point tracking (MPPT) controller has increased significantly in this decade. The MPPT technique, however, is still demanding because of the ease and simplicity of implementing tracking technique on the maximum power point (MPP). In this paper, MPPT techniques and their modifications from various literature are classified and examined in detail. The discussions are focused on the main objective of obtaining the best possible MPPT technique with the best results at a low cost. The assessment for the selection of MPPT techniques is based on assessments from the previous literature. The discussion of the MPPT technique assessment is divided into two parts. In Part I, the MPPT technique based on constant parameters, and trial-and-error will be discussed in detail, along with its algorithm development in recent times.