How can a horizontal panel produce more per m2 of panel than a tilted panel (latitude value)?

[RicardoGomesIST]

Discussed in https://github.com/architecture-building-systems/CityEnergyAnalyst/discussions/3281

^{Originally posted by **RicardoGomesIST** January 27, 2023} Hi, I am using CEA to calculate PV panel potential. I am testing a very simple case for Lisbon (latitude =38º) - just one building with surrounding buildings lower than it.  I created two scenarios one with: - tilt=1º - (as 0 is not possible) so horizontal and other with: - tilt= 30º Assuming that the tilted panels face south, I was expecting that the PV production (kWh/m2) would be higher for the tilted than for the horizontal. What I get was: - tilt=1º - (as 0 is not possible) so horizontal Name | PV_roofs_top_E_kWh | E_PV_gen_kWh | radiation_kWh | PV_roofs_top_m2 | Area_PV_m2 -- | -- | -- | -- | -- | -- B1000 | 134821.9 | 134821.9 | 1046941 | 655.66 | 655.66 Doing the calculation: kWh/m2=E_PV_gen_kWh /Area_PV_m2= 205.6 -- - tilt= 30º Name | PV_roofs_top_E_kWh | E_PV_gen_kWh | radiation_kWh | PV_roofs_top_m2 | Area_PV_m2 -- | -- | -- | -- | -- | -- B1000 | 52345.78 | 52345.78 | 584711.3 | 365.92 | 365.92 Doing the calculation: kWh/m2=E_PV_gen_kWh /Area_PV_m2= 143.03 ------------------------------------------------------------- So I ran this and just changed the tilt angle: 

[martin-mosteiro]

I've been able to replicate the issue. The PV production per m2 of PV is higher for 1° than 30°:

I'll be looking into the cause for this.

[RicardoGomesIST]

Thank you Martin, is there any news on this?