Version 6.7.0 Soiling Losses on Report

[dtarin]

Hello,

In 6.7.0, when a monthly soiling profile is used, the yearly loss factor value is also being displayed on the report. It doesn't seem to affect the calculation, but is a little misleading when reading the reports.

[André Mermoud]

Some people will perhaps like to have an average.

[dtarin]

Replacing that with average would be good (and stating it as such).

[PVsystUser]

How does PVsyst calculate that yearly average?

Starting from monthly loss and calculating the POA-weighted average the yearly value is much lower than what PVsyst offers. Example is here: 

[André Mermoud]

I really don't understand what you mean.

The GlobInc value is the result of the transposition on the tilted plane, it doesn't include the soiling losses.

The soiling losses are taken into account in the GlobEff result  (effective irradiance on the collectors).

NB: The GlobInc is not an average, it is a cumulated energy.

[PVsystUser]

GlobInc has no relation to soiling.

What I wanted to understand is how PVsyst calculates the yearly average "Soiling" from monthly values?

For example, in January, we have an 11.8% soiling loss, but since January has low irradiation and thus lower generation, this 11.8% loss might actually be smaller in impact than a 6.8% loss in March. When we weight the monthly losses with GlobInc, the annual average results in 2.8%.

However, PVsyst suggests an annual average of 4.2%. How does PVsyst calculate this annual average, and how is the lower irradiance during winter reflected in this calculation?

[PVsystUser]

In other words: 4.2% is a normal average of monthly losses. Shouldn't this annual average reflect the lower irradiance/generation during winter?

[André Mermoud]

On this part of the report, the calculated average mentioned on the report is indeed the average of the soiling factors, not the soiling losses. It is not weighted by the effective irradiation. This indeed doesn't have much meaning when the soiling is highly inhomogeneous along the months.

However in the simulation, the soiling loss is calculated at each hour, according to the irradiance. It is quite correct.