Thermal model in digital twin of vertical PV system helps to explain unexpected yield gains

The business case of novel integrated applications of solar energy is often regarded as a straightforward extrapolation of standard solar parks. But when the design of the solar park is remarkably different from typical solar parks, the operating conditions of the PV panels could also be changed. We have applied the digital twin to an R&D location with nine rows of eight bifacial PV panels in a vertical east/west orientation with varying row-row distances. We simulated the in-plane irradiances, based on measured GHI, which turned out to be in good agreement with observations of in-plane irradiances. But, using default free-standing PV heat transfer coefficients, the modelled module temperatures were too high and the simulated module powers too low. Applying an in-house developed method, we found that the heat transfer coefficient Uc is nearly double, and the vertically placed modules operate at a much lower temperature. The adjusted value for Uc leads to a 2.5% higher annual energy yield and higher performance ratio, partially offsetting the energy loss due to the less than optimal configuration. In conclusion, the digital twin increased the understanding of the vertical PV system and support future decision making, for instance for the application of vertical PV in combination with agriculture, where the low ground coverage ratio of vertical PV matches well with the needs from the agricultural sector.