The demand for mobile communication services has experienced astronomical growth in the past few decades and continues to grow steadily at a brisk rate. This is due partly to falling prices of user devices, the evolution of mobile applications, the widespread adoption of social media, and the recent advances in modern technologies such as the Internet of Things (IoT), cloud/fog computing, and Artificial Intelligence (AI). An expansion of mobile communication infrastructure to accommodate the rapidly growing demand and to migrate to new technologies (e.g., 4G/5G) have also resulted in a significant increase in the energy consumption of mobile networks. An attractive solution to reduce the carbon footprint of mobile networks and to reduce the energy bills of network operators is to deploy renewable energy systems(e.g., solar energy systems) to power base station sites. In this paper, we present a practical approach for dimensioning and evaluating renewable generation and storage systems for cellular base station sites. We use data collected from a base station site in Banda (North region of Cameroon) as input to the analytical model; we estimate the probability of service outage (when all the stored energy is consumed and the PV system is not able to generate energy).