In this paper, an optimal control strategy is developed for managing a heat pump in an integrated solar thermal system. Solar thermal systems usually operate with both feedback and feedforward controllers. The focus of many existing studies in solar thermal system applications has been on the feedback part, while less effort has been made to improve the performance of the feedforward part. This paper introduces a novel robust feedforward controller as a sub-controller of an optimal controller for operating a heat pump integrated with the solar thermal system. In a simulation environment, the optimal control structure is implemented, and the performance of the robust feedforward controller is compared with a simple feedforward controller. Regarding the electrical power consumption, the simulation results demonstrate that the optimal control structure with the proposed robust feedforward controller outperforms the control structure with the simple feedforward controller. (C) 2019 Elsevier Ltd. All rights reserved.