Huge Discrepancies between Power output in horizontal tracking bifacial system.

[Daisy]

Hello Support, 

I designed a fixed vertical agriPV system on both PVsyst and PVSOL Premium and got quite similar power outputs. I designed a horizontal N-S tracking bifacial agriPV on PVsyst and PVSOL (using the same modules and system input details as the fixed vertical one) but the difference in the power output was 70 MWhrs/year. In the design, the pitch was 10m, the elevation was 3.5m, the tracking was +/- 55 degrees. I understand that both software are different but I ensured that the time step, input data and losses from both were close to similar. How come the results differ so much? Is it due to the 2D design of tracking systems, or the use of both bifacial and tracking systems?

[hotline_oh]

Dear Daisy,

Please send the corresponding project files (*.pvprj) to hotline@valentin-software.com so that we can take a closer look at it.

[Daisy]

Dear support, 

I sent the files as requested. Looking forward to your response.

 

[hotline_oh]

Dear Daisy,  

Thank you for the files.

You have entered everything correctly in PV*SOL. We are not very familiar with PVsyst, but we have noticed a few differences:

• The climate data set is different. PVsyst uses a more up-to-date Meteonorm data set. We have created a new Meteonorm data set for the location. This increases the specific yield to 2002 kWh/kWp.
• The irradiation on the back of the module is only 114 kWh/m² in PV*SOL, but 214 kWh/m² in PVsyst. We do not know how PVsyst calculates this. We suspect that the different module arrangement has something to do with it. Unfortunately, we cannot map the rack system correctly. In PV*SOL, the modules are not arranged next to each other but on top of each other.
• In PVsyst, the PV module was selected from the database, but in PV*SOL, it was newly created. The standard low-light behaviour was selected. The software then calculates the low light behaviour using a model. These values are generally worse than if measured values from the manufacturer are used.

If you have any further questions, please do not hesitate to contact us.