Higher yield for flat modules than 13º east-west configuration?

[Ricardo]

Good morning,

I came across a funny result and I was wondering if you could help me make sense of it. I simulated two identical rooftops, one with an east-west configuration and the other one with the modules just laying flat (inclination = 0º) and guess what, the flat modules show a slightly higher yield than the others…

 

The main differences between both simulations are as follows:

 

• Flat modules: 1.066,73 kWp (3.879 modules), 111% sizing factor, 0’1% shading losses, 1.417,91 kWh/kWp
• East-west: 992,75 kWp (3.610 modules), 103% sizing factor, 2’7% shading losses, 1.360,51 kWh/kWp

 

Both have 16 inverters Huwaei SUN2000-60KTL-M0 (400Vac). The yield difference is 4’3% higher for the flat modules, while I would expect that east-west with inclination = 13º would produce more energy (even if it had a bit more shade).

 

Any idea why this is happening? Does PV SOL simulate soiling taking into account more soiling for less inclined modules?

 

I would really appreciate if you could give me some feedback. Thanks a lot!

[developer_mm]

Hello Ricardo,

the exact reason for that is pretty hard to say. I guess it's a mix of different reasons. For example, if you compare the yields without shading, you have 1398 kWh/kWp_eastWest and 1419 kWh/kWp_flat. The difference is now only around 20 kWh/kWp. Then the orientation of the modules in combination with the different configurations of your inverters (different sizing factors), which also influences the yield. I assume that your PV system is close to the equator due to your high yields. This means that modules with low inclinations or even without any inclination (directly at the equator) generate better yields due to the direction of the sun.

I hope this helps,

Marcel

[Ricardo]

Hi Marcel,

Actually, my modules are in Spain. I used the Meteonorm data provided by PV SOL when you choose a specific location (as opposed to the "standard" data provided by UNE EN 94003:2006 in PV SOL when you choose the main cities in Spain, which often leads to lower yields; the difference in climate data also surprised me some time ago but we discussed it in a different thread).

 

Please find below some screenshots of both configurations in case they help, east-west on top, flat below:

 

Does PV SOL simulate soiling taking into account more soiling (and thus less yield) for less inclined modules? Even if it doesn't, I'm still quite lost with this result, as even though the difference is not great, I would expect higher yields for east-west, never less.

[developer_mm]

Hello Ricardo,

PV*SOL does not consider soiling unless you define soiling losses in the options (under simulations).

I made a quick comparison myself for a location in Spain (same modules, same inverter configuration). It seems that the main reason for the higher yields of the flat modules is the higher irradiance.

Nevertheless, an east-west configuration may be a better option in matters of self consumption or losses due to soiling.

 

Kind regards,

Marcel