2.1.3. Simulation Results and Analysis

The FEA software is used to solve the governing Equations (4)–(7). As shown in Figure 3a, the sharp corners of metal frame are easy to accumulate charges. The maximum surface charge density is 140 μc/m2. The minimum surface charge density is 6.89 μc/m2. As shown in Figure 3b, charges are more likely to accumulate on the border of BIPV modules, with the maximum surface charge density of 194 μc/m<sup>2</sup> and the minimum surface charge density of 0.11 μc/m2. In the electrostatic field formed by the lightning downward leader head, the space charge accumulates on the surface of the ground object

leading to the electric field. The upper edge of metal frame is easier to gather charges which can enhance electric field intensity.

**Figure 3.** Surface charge density of two PV modules (**a**) framed double-glass PV module; (**b**) BIPV module unit combination.

Through numerical calculation, the surface electric field strength distribution of the two PV modules is shown in Figure 4. It can be seen that the highest electric field strength of framed double-glass PV module is distributed at the four corners of the metal frame. The highest field strength of BIPV module is distributed on the upper edge of metal frame. In addition, the electric field strength on the two metal frames is much higher than that of the internal solar cells.

**Figure 4.** Surface electric field strength of different PV modules (**a**) framed double-glass PV module; (**b**) BIPV module unit combination.

Take different paths along the arrow direction on the metal frame, defined as a1–a4 and b1–b4. The measured electric field strength along different paths is shown in Figure 5. The maximum electric field strength is distributed at both ends of the metal frame. Those on the surfaces of framed double-glass PV module and BIPV module is 9.5 MV/m and 22.1 MV/m respectively. The electric field strength is increased by 132%. The locations of the PV modules surface with higher electric field strength are considered to have higher possibility of emitting answering leaders and intercepting the lightning stepped leader.

**Figure 5.** Distribution of surface electric field strength (**a**) framed double-glass PV module; (**b**) BIPV module unit combination.
