Weathering and ageing effects often cause parameter changes in solar trackers. Such parameter variations lead to the degradation of the performance of model-based controllers used in solar tracking. This paper presents the design and performance validation of the model-tolerant intelligent proportional integral (iPI) controller, for sustaining the tracking performance of a polar-axis solar tracking system in the presence of model-parameter changes. The paper clarifies the stability and robustness requirements for the iPI controller, and also validates its performance by comparison with a classical PID controller derived using Nichol Zeigler tuning rules. Results show that the iPI controller is both easier to tune, and can better sustain control function in the presence of model parameter variations.