In order to evaluate the impact of irradiance and temperature on the outdoor performance of solar devices, a monitoring system including electronic analyzers for measuring the I-V curve and a data management to store, synchronize and process the electrical and weather records were developed. With this system, the average performance as a function of irradiance and temperature of commercial solar panels was obtained in natural sunlight without tracker considering up to 4700 h of exposure and sampling time of 1 min. Besides, the data were processed considering the irradiance levels defined by each power rating conditions suggested by IEC 61853. The results indicated that in tropical weather the Standard Test Conditions (STC) are not as representative to evaluate solar panels, due that an irradiance of 1000 W/m(2) rarely occurs at 25 degrees C temperature of the panel. However, the Nominal Operative Cell Temperature (NOCT) was the most suitable condition to test outdoor performance according to the manufacturer data. Therefore, this condition could be considered to evaluate the status of devices and to define the maintenance guidelines of photovoltaic devices. Finally, the NOCT behavior over time suggested that between 200 and 600 h of exposure are more than enough to characterize and obtain reliable Power Rating Conditions (PRC) under the local conditions.