NOVELTY - The system (1) has photovoltaic panels (2) for outputting direct electrical current and/or voltage when the panels are exposed to incident solar radiation. A common generator (4) or an individual generator supplies alternating electrical current and/or voltage from the direct electrical current and/or voltage supplied by the panels. A measuring unit (6) e.g. wattmeter, measures the electrical power supplied by the generator. An adjusting unit (7) adjusts the impedance of an internal resistor of the generator such that the electrical power supplied by the generator is equal to a preset value.    USE - Photovoltaic system for supplying electric power equal to preset value, in a dwelling or an industrial building.    ADVANTAGE - The adjusting unit adjusts the impedance of the internal resistor of the generator such that the electrical power supplied by the generator is equal to the preset value, thus allowing the system to vary the impedance of the internal resistor of the generator according to the high or low losses of the output of the panels such that the electrical power supplied by the system is maintained equal to the maximum legal admissible power. The system determines the electric power supplied by the common generator or of the individual generator in an accurate, simple and rapid manner. The system enables electrical power equal to the maximum legal admissible power to be supplied constantly over time. The system is simple in design, easy to use and inexpensive.    DETAILED DESCRIPTION - The internal resistor is in the form of a potentiometer or resistors. The photovoltaic panels are in a form of plastic or metal plate and in shape of square, rectangle, hexagon or circular. The common generator or the individual generator is in the form an intensity or voltage inverter. An INDEPENDENT CLAIM is also included for a method for supplying electric power.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of a photovoltaic system.    Photovoltaic system (1)    Photovoltaic panels (2)    Photovoltaic cells (3)    Common generator (4)    Electrical power measuring unit (6)    Adjusting unit (7)    Control unit (9)