The use of photovoltaic solar energy is a growing reality worldwide and its main objective is to meet electricity demand in a sustainable manner. The so-called Grid-Connected Photovoltaic Power Systems (GCPS) prevail in urban zones, together with Building-integrated Photovoltaics (BIPV); whose performance and energy efficiency depends on different factors. The main aspects include those related to the solar radiation available in the geographical location of the facility, the climate, the orientation and tilt of the used surfaces, the appropriate design of the system and the quality of the components. Therefore, several methods have been proposed to try to predict the influence of the aforementioned variables on the amount of electricity produced. However, the majority are very tedious to implement or do not take the specific characteristics of the system into account. This paper proposes a simple and reliable expression, which can be used in low latitude countries. The case study is likewise performed for Colombia, with a comparative analysis for different cities of the angular losses and due to dirt, the losses due to temperature, the DCAC conversion losses and the Performance Ratio of the system (PR). (C) 2014 Elsevier Ltd. All rights reserved.