PVsyst's forum

My firm just finished constructed a 17.5 MWP plant a few months ago and we are in the process of analyzing the measured vs PVSyst estimated production data.

Our Scada is giving us the Plane of Array Irradiance (POA) in w/m^2. Which of these PVsyst data is equivalent to the measured POA Irradiance? The "Global Incident in Coll. Plane" or the "Effective Global, Corr. for IAM and Shading"

Your measured value corresponds to the GlobInc value (Incident global), which is just the result of the transposition from horizontal to your tilted plane.
Th GlobEff value (Effective global) is the GlobInc, affected by the optical losses like Far and Linear shadings, IAM and soling losses.

It seems to me that GlobEff should be less than GlobHor 100% of the time, because GlobEff includes some losses like IAM and shading. Why would GlobHor be less than GlobEff?

GlobHor is irradiance measured in a horizontal plane. GlobInc is the irradiance that hits the actual orientation of your array. This will likely be greater than GlobHor as there are inherent benefits to tracking or installing modules at an angle. GlobEff is GlobInc after all optical losses are applied, as mentioned below.

For example, a single axis tracking system could see a GlobInc boost of 35% because it's facing the sun most of the day (ideally). After all optical losses are applied, the GlobEff boost could still equal 25% when compared to GlobHor.

The Global incident is just the result of the transposition of your meteo data GlobHor to your tilted plane.
With tracking arrays, when using backtracking, this could change when you change the width of the trackers or the pitch between trackers, because the backtracking conditions will vary.

In any other case, the Incident Global has no relationship in any way with the rest of the system, such for example the AC capacity.

Does anybody know how global incident in coll. plane could be negative? That's a new one for me. I just downloaded version 6.7.9, but it was able to successfully run some of my older tracker simulations just fine.

Ah, I just answered my own question. In case anybody else has this issue, I had accidentally tried to track from -45deg to -45deg, which admittedly is not a great idea.