Safety device for photovoltaic installations

1. A safety device for photovoltaic installations comprising:

a first terminal adapted to connect to a first output terminal of a solar panel;

a second terminal adapted to connect to a second output terminal of said solar panel;

a first switching module connected between said first and said second terminal, said first switching module comprising at least a first switch and at least a first impedance connected in series, said first impedance having one terminal connected to said first terminal and said first switch having one terminal connected to said second terminal;

a control module adapted to read a control signal and drive the operation of said first switch based on the read value of said control signal;

power supply means adapted to supply power to said control module;

wherein in an emergency situation the control module closes the first switch of the first switching module to thereby short circuit the first and second output terminals of the solar panel.

2. The safety device for photovoltaic installations according to claim 1 , wherein said first impedance has a value adapted to keep the solar panel output voltage below a predetermined safe level and limit the inrush current on said first switch.

3. The safety device for photovoltaic installations according to claim 1 , wherein said first impedance comprises one or more stages and suitable by-pass means adapted to insert or short-circuit said stages.

4. The safety device for photovoltaic installations according to claim 1 , wherein said first impedance comprises a resistor serially connected to an inductor, in that said first switching module comprises a further switch having one terminal connected to said second terminal and the other terminal connected to the mid-point between said resistor and said inductor, and in that said control module is further adapted to drive said further switch to by-pass said resistor to limit power dissipation when needed.

5. The safety device for photovoltaic installations according to claim 4 further comprising a diode connected n parallel to said first impedance and adapted to limit the voltage spike across said first switch at turn-off.

6. The safety device for photovoltaic installations according to claim 4 , wherein said resistor is a variable resistor.

7. The safety device for photovoltaic installations according to claim 1 , further comprising:

a third terminal adapted to connect to a ground terminal; and

a second switching module connected between one of the first and second output terminals of said solar panel and the ground terminal, said second switching module comprising a second switch and a second impedance connected in series.

8. The safety device for photovoltaic installations according to claim 7 wherein said second impedance comprises a variable resistor.

9. The safety device for photovoltaic installations according to claim 7 , wherein said first switch and said second switch are of electro-mechanical or semiconductor type.

10. The safety device for photovoltaic installations according to claim 1 , wherein said power supply means comprise a power supply wherein the input voltage is the solar panel output voltage.

11. The safety device for photovoltaic installations according to claim 1 wherein said control module is provided with galvanic isolation between an input voltage side and a control signal side between the solar panel and an inverter.

12. The safety device for photovoltaic installations according to claim 11 wherein said power supply means comprise a further power supply wherein the input voltage is provided by said control signal.

13. The safety device for photovoltaic installations according to claim 10 , wherein said power supply is provided with input voltage hysteresis to minimize the hick-up frequency between turn on and turn off.

14. The safety device for photovoltaic installations according to claim 10 wherein said power supply is adapted to periodically turn off and on according to a predetermined temporization.

15. The safety device for photovoltaic installations according to claim 1 comprising an emergency switch, operable by a user through an external emergency button and adapted to force said control signal active.

16. The safety device for photovoltaic installations according to claim 1 wherein said safety device is integrated into said solar panel or into an inverter connected to said solar panel.

17. The safety device for photovoltaic installations according to claim 1 comprising a housing provided with an external enabling ON/STAND-BY switch and associated visual indicator.

18. The safety device for photovoltaic installations according to claim 1 comprising quick-plug standard connectors for photovoltaic applications adapted to connect to a solar panel and to a photovoltaic inverter.

19. The safety device for photovoltaic installations according to claim 4 wherein said further switch is of electro-mechanical or semiconductor type.

20. The safety device for photovoltaic installations according to claim 2 , wherein said first impedance comprises one or more stages and suitable by-bass means adapted to insert or short-circuit said stages.

21. The safety device for photovoltaic installations according to claim 1 , wherein said first impedance is variable with time or with temperature.

22. The safety device for photovoltaic installations according to claim 1 , wherein said first impedance comprises a PCT (Positive Temperature Coefficient resistor) or a NTC (Negative Temperature Coefficient resistor).