Lauren Ngan et al. from First Solar presented a great poster at the 39th IEEE PV Specialists Conference in Tampa, FL on how “true” single axis tracking (without backtracking) produced more energy for First Solar arrays than the use of backtracking, which avoids row-to-row shading. As part of her study, she and her coauthors discovered a bug present in PVsyst related to their simulation of backtracking. I thought it would be good to provide a brief summary of the problem they discovered so everyone is aware of the issue. PVsyst has been contacted about the problem.

In short, when backtracking is selected in PVsyst, the diffuse and ground reflected (albedo) shading losses are set to zero along with the beam component shading losses. The authors believe it would be more realistic for only the beam component to be set to zero. Simulations run in PVsyst using “true” tracking include a non-zero diffuse and albedo shading loss. The result of this “bug” is that predicted energy from systems simulated with backtracking will be overestimated. The paper is entitled: “Increased Energy Production of First Solar Horizontal Single-Axis Tracking PV Systems without Backtracking.”  It is available now for registered conference participants and will be availible for others in the near future.