The issue of power supply in hospitals is of special importance because of its direct effect on people's health conditions and vital treatment and care measures. Hospitals are among buildings with high energy consumption. The possibility of using renewable sources in their energy supply is one of the issues and challenges that specialists encounter. This paper discusses the possibility of installing a small solar power generation unit on a hospital rooftop to improve the quality of power supply systems. The case study is a hospital located in Tehran, Iran. For this purpose, the hospital energy system was modeled with the Design-Builder software. The obtained results were validated based on the actual consumption of the model specified in the hospital energy bills. According to the modeling step results, the annual consumption of the current energy system was ۳.۰۸ GWh of electricity and ۴.۲۳ GWh of gas. In the second step, a renewable power generation unit consisting of photovoltaic panels and battery was designed for the hospital's roof using PVsyst software. The designed power generation unit could produce ۱۳۲ MWh of solar energy per year, of which ۸۵ MWh may be sold to the main grid. The techno-economic and environmental feasibility study for the proposed system was performed using HOMER Pro software. The evaluation results revealed that considering the ۲۰-year lifetime of the project, the proposed system achieved a lower energy cost and lower net present cost than the current system. Environmental assessment of the model by considering emission penalty indicated that the proposed system emitted fewer pollutant gases into the environment than the current system. Sensitivity analysis was also applied to investigate the effect of discounting and diesel fuel price variation on the system’s energy cost. According to the results, a ۴ % increase in the discount rate leads to a ۱۴ % growth in the cost of energy for the project. Also, there was a direct relation between enhancement of the expected inflation rate and raising the net present cost of the project.