Measurement of Damages at Bypass Diodes by Induced Voltages and Currents in PV Modules Caused by Nearby Lightning Currents with Standard Waveform

In 1990 – 1993 and during an EU project in 1998 – 2000, the PV laboratory of BFH-TI has carried out tests about sensitivity of PV modules against lightning currents flowing in or close to the frame of a PV module [1], [2], [3]. For these tests, impulse currents with imax ≤ 120kA and di/dtmax ≤ 40kA/μs were used. It could be shown that even at moderate distances the voltages induced in a module by such lightning currents may go up to several thousand volts. Such voltages can easily destroy bypass diodes. Due to increasing cell dimensions and currents, more and more Schottky diodes are used as bypass diodes, which have only quite low reverse voltage ratings between 40 V and 100 V. In practical operation, such damages actually occur, but usually only at considerably higher peak induced voltages than the reverse voltage rating of the Schottky diode. In [5] and [7] the problem was analysed theoretically and the results of some first tests with short impulse currents (about 8μs/20μs) were shown. In this paper, the theoretical analysis is extended and results of many measurements performed in 2007 and 2008 with impulse current waveforms of about 6μs/350μs (di/dtmax ≤ 30kA/μs) at different modules and with different diode types are presented.