The large-scale grid connected photovoltaic systems have become one of the most used renewable energy sources to support the conventional energy generation and one of the most cost-effective sources of energy, not only as a clean energy but also for the possibility to generate profit and create attractive opportunities of investments. From the operational point of view, the photovoltaic technology has different advantages with respect to other renewable energies because the solar resource is predictable obtaining trustworthy forecasts; the technology implemented is normally fixed reducing the maintenance cost and guaranteeing the long life of operation; scalability and quick construction. Those factors provide to the investors reliability to make a profit and, furthermore, they can predict the production of electricity of each PV system using models and compare them with the real values that are record daily implementing a monitoring system.