Every photovoltaic plant (solar cell power plants) has a sensor which is verifying the amount of radiation arriving on the panel. If the sensor is experiencing a failure due to snow, dust or a wrong calibration, then the efficiency measurement is giving a wrong interpretation of the energy production. Satellite information measuring the real solar radiation tells the correct amount at any given time and the correct amount of electricity which the plant should produce can be calculated, as a reference. This helps to detect possible failures and the need of plant maintenance operation.