Difference between runs of the same simulation

[MicheleANE]

Hi,

We encountered what looks like a bug while running a second time exactly the same project with the same data.

In the picture called "VCP losses" you can see the output of the first run of this simulation.

 

First run output

 

Then in the picture called "VCS losses" you have the output of the second run of exactly the same version just after saving, closing the software, reopening it and pushing simulation button again. You can see that shading related losses and the yearly Energy changed.

 

Second run output

 

I can also send the project file with the two versions saved, but I can't upload it here because it's a commercial project. In case it's needed, let me know where to send it privately.

Best regards

[linkeshd]

Hi! I can't help with a solution to this, but for someone who can, it may help to know what version of PVsyst?

[MicheleANE]

Hi,

You are right, I forgot to write it. I was on 6.75 version when outputting these but we also tried on a 6.74 PVsyst that we still had in the office and the same thing happens.

As said before I would like to share the project file with someone from PVsyst but I cannot upload it here, so please advice where to send it.

Best regards

[André Mermoud]

The difference is 0.004% (equivalent to 4 cents on a sum of 1'000 euros).

This may be a rounding effect, or an edge value in the shading's calculations.

Such differences may arise in simulations. We could pass some hours (or dozens of hours) for understanding such "problems", but we have more urgent priorities.

[MicheleANE]

Hi,

Regarding the original topic: the problem is not really the small difference in numbers but the fact that it always changes between the first run and all the successive ones. If it was a rounding it would happen for all the runs in the same way or more randomly in different runs.

Regarding the unexpected answer: this is the section of the forum dedicated to reporting bugs and this looks to me as a bug. I never said anywhere that this needs a high priority or anything similar and I didn't mean it as a critique. Usually bug reports from outside are welcome because they are free and bring improvement of the software, if it's not the case you can as well close this section.

Thanks for your time and best regards

Michele