With the increased integration of photovoltaic(PV) power generation into active distribution networks, the operational challenges and their complexities are increased.Such networks need detailed characterization PV system sunder multiple operating conditions to understand true impacts. This paper presents a new mathematical model for a PV system to capture detailed effects of PV systems. The proposed model incorporates state transitions of componentsin a PV system and captures effects of insolation variations.The paper performs a reliability assessment incorporating PV systems at resource locations. The results suggest that there liability performance of an active distribution network atstressed operating conditions might be influenced by the high penetration of PV system. Reliability performance of distribution networks that are high penetrated with PV systemscan be affected by cloudy effects resulting from insolation variations. The proposed model can be used to quantify the level of reduction in reliability, resulting with cloudy effects.