Question

Within a photovoltaic (PV) module there are three main parasitic capacitances: • Capacitance between the grounded support frame and the PV cells.
• Capacitance between the PV cells and the roof surface area.
• Capacitance between the PV cells and moisture on the surface of the glass.

The last capacitance, due to moisture is much higher than the other two capacitances (in wet conditions) and therefore the other two will be neglected for this problem. If there is sufficient moisture on the glass, we can make the assumption that the thin sheet of moisture forms one large conducting surface covering the entire area of the glass. Moreover, this conducting area touches the metal frame on the edge of the panel, which is grounded. Thus, the PV cells, glass, and conducting water form a parallel plate capacitor.

a) Assume that the glass relative permittivity is 6, the area of the panel is 1m2 and the thickness of the glass is 4mm. Estimate the parasitic capacitance of this module.
b) Assuming that the PV panel is connected (through the inverter) to the AC grid. The end result is that the potential of the PV cells oscillates at 120 Vrms, at a frequency of 60Hz, with respect to ground. Given this condition, what is the estimated displacement current to ground, which flows through the parallel plate capacitance?

c) Why are we concerned about this displacement current?

Answer 1