Documentation of time shift application

[laurahin]

We've been confused by seemingly contradictory information about the application of time shift data to imported meteo files.  The question is what you have to do to get a time shift to be applied in the calculations, and whether it's sufficient to click on "Apply time shift correction" on the "Check data quality" window or whether the data must be reimported.  Differences in the documentation are as follows:

1) https://www.pvsyst.com/help/meteotables_graphsform_datacharacteristics.htm:  This page implies that you can just click on the "Apply time shift correction" button to use the time shift.  Note that no one in our group has ever found a way to save the MET file from the "Check data quality" window.

During the simulation PVSyst has the possibility to apply a time shift correction, expressed in minutes, to the calculation point which is always the middle of the hourly interval. Setting an adequate correction is extremely important to get good calculation results. The time shift defined in the .MET file is the result of an iterative process. The correction is considered as active when the user checks the box "Apply time shift correction" and saves the file. Once again, this correction shall not be confused with the values specified in the source file.

As an example, in the screen shot given below :   [Screen shot shows "Apply time shift correction" checked.]
- the user has first defined a -1 hour shift together with a + 2 minutes time shift in a PVSyst standard file
- he finally decided to set a +3 minutes time shift after considering the Check data quality tools of PVSyst.

- the +3 minutes time shift is the value written in the .MET file. It will be applied during the simulation.

[Screen shot follows, then]

In the screen shot given below [Screen shot shows "Apply time shift correction" unchecked.], the user decided not to apply the Time Shift defined in the source file. By doing so, PVSyst will not consider any minute shift during the simulation.

[Screen shot follows]

Both screen shots include the following, which seems to imply that a time shift has been recorded in the MET file in both cases.

 

2) https://www.pvsyst.com/help/meteo_notes_timeshift.htm  This page says that you have to reimport the data to apply a time shift:

-  First import the data without precautions. The program will guide you to the graphs for the assertion of the correct time shift.

-  Evaluate the effective time shift of your data.

-  Apply the observed TimeShift corrections in the format protocol, and re-import the data.

 

Toward the bottom of that page, a flow chart of instructions for adjusting time shifts is shown.  It has one place where it says to reimport the data to correct the time shift, but later says to re-adjust the data and save it.  What gives?  As mentioned, we have never found a way to resave the MET file after applying the time shift by clicking on "Apply time shift correction" and we have never observed a time shift to be noted for future use of a file using this method.

Of course, on https://www.pvsyst.com/help/meteotables_graphsform_importeddata.htm, we have

"Do not confuse between the time shift defined in the source file and the time shift used by the simulation, whose value is shown in the Data characteristics section of this form."

?

[Michele Oliosi]

Hi @laurahin

We just noticed the save button is missing... we'll add it in a next patch. In the meantime there is a workaround to save the file with the time-shift: instead of closing, change to another meteo file in the drop-down menu at the top of the window. You will see a notification that invites you to save the file. This can be applied to any MET file in principle, not just manually imported ones.

When you are importing your own data, you should rather reimport the data with a new time shift.

[laurahin]

Thanks!