Solar water heating system using flat plate collectors is an environmentally friendly system commonly used worldwide for low temperature applications. In this study, the main objective is to assess the economic and energy potential of flat plate collectors used in combination with modern, automatic pellet boilers for large hot water preparation in a commercial building (called Hammam or public bathhouse) under the weather conditions of Marrakesh, Morocco. Further, Annual simulations were conducted using TRNSYS software. Besides, the life-cycle savings method was carried out for the financial analysis. Further, the final configuration derived from the optimisation shows that the optimal collector area is found to be 213 m2, which provides an average solar fraction of about 48%. Indeed, the hybrid system can achieve a life-cycle savings of 82.7 k€ over the entire life of the system compared to the baseline system (Pellet boilers only). These results show that the implementation of solar thermal system in a traditional Hammam for the production of hot water has the better energetic and environmental performance compared to the reference system; therefore, the deployment of such a hybrid system will result in considerable reductions in CO2 emissions, substantial energy savings and significant progress in combating deforestation in Morocco.