Roof-Mount is better than Open Rack?!

[EmeraldHex]

Alright, solar wizards, explain this one to me like I'm five. I run a PVWatts simulation for a 10kW system with premium panels at a 45-degree tilt, expecting my open rack setup to flex its superior airflow muscles… and what do I get?

Open Rack Output: 11,760 kWh
Roof-Mount Output: 12,263 kWh

Excuse me, what?! I thought open racks were the cool kids (literally) because of better ventilation. But now PVWatts is out here telling me roof-mount panels—aka glorified baked potatoes—are MORE efficient?!

Either I've entered the Upside Down, or there's some sneaky variable at play. Thermal modeling issue? Albedo effect? PVWatts just messing with us for fun?

Anybody else run into this? Someone tell me I'm not losing my mind here.

 

[Thongzai]

damn you must be my brother in problem as i had a similar situation that made me feel stupid and this is not my first solar powerd rodeo

 

[CarChemistry]

@EmeraldHex I think it depends on the context. In this case, open racks are better for ground mounted systems, while roof mounts are usually used for residential installations

 

[User1738]

Alright, solar wizards, explain this one to me like I'm five. I run a PVWatts simulation for a 10kW system with premium panels at a 45-degree tilt, expecting my open rack setup to flex its superior airflow muscles… and what do I get?

Open Rack Output: 11,760 kWh
Roof-Mount Output: 12,263 kWh

Excuse me, what?! I thought open racks were the cool kids (literally) because of better ventilation. But now PVWatts is out here telling me roof-mount panels—aka glorified baked potatoes—are MORE efficient?!

Either I've entered the Upside Down, or there's some sneaky variable at play. Thermal modeling issue? Albedo effect? PVWatts just messing with us for fun?

Anybody else run into this? Someone tell me I'm not losing my mind here.

Yeah, PVWatts can be weird sometimes, It assumes pretty basic conditions. these roofs can get a small albedo bump (light reflecting off the roof), and sometimes the temperature modeling isn't detailed enough to show rack cooling benefits properly. so you're not crazy, just limited by the tool.