© 2019 IEEE. Recently, failures in photovoltaic systems (PVSs) caused by lightning damage have been increasing. When lightning strikes a PVS, the bypass diode (BPD), which is a protection element in the solar cell module (PV-MDL), breaks down and burns out, rendering the PVS inoperable. In this study, an impulse current test was conducted to clarify the lightning-induced BPD failure mechanism. The impulse current with a peak of 100 kA was employed to simulate a lightning strike traveling in the vicinity of a PV-MDL. The results indicated that a BPD fails because lightning (induced electromotive force) strikes in the bypass circuit of the PV-MDL as the impulse current passes in its vicinity. Furthermore, installing a metal frame in the PV-MDL was shown to reduce the negative impact of such lightning strikes.