The integration of distributed renewable energy generation (DREG) has attracted great attention due to its technical and economic benefits to both consumer and utilities sides. This paper presents the impact of integrating renewable Photovoltaic (PV) based DREG using time-varying weather and time-varying load model in IEEE 33-bus and IEEE 69-bus systems. 13-years historical solar irradiance data are used and the PV output curve is generated using Beta-distribution to demonstrate the random daily solar irradiance. Results of the time-varying load model with and without PV placement are presented and discussed. Findings showed that integrating PV generation into the distribution system has significantly reduced the overall system losses by 32.71 and 43.80 for 33-bus and 69-bus respectively. The minimum bus voltage has improved from 0.9038 to 0.9719 for 33-bus and from 0.9091 to 0.936 for 69-bus system. © 2021 IEEE.