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1 hour shift in weather data


a.nashed
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Hello

I have been trying to import a weather data file (TMY2 from TRNSYS weather library) and i followed the format in the PVsyst help file.

However, after converting the data within TRNSYS, the values are assigned to a hour-1 value for some reason (for example the GHI value for 8:00 is assigned for 7:00)

Does anyone know why this is happening?

I have attached the original TMY2 data CSV file (Marsa_TMY2) and the CSV file where i converted it to the PVsyst suitable format

Thank you so much

Regards,

Amir

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I believe the problem is because the original data is given for the end of the interval while PVsyst uses values with respect to the beginning of the interval.

So i tried to change the hours manually in the original file. This solved the issue but i got a warning that "The meteo values are shifted -60 minutes by respect to the time defined by the Timezone of your site"

Does anyone know why i get this warning?

Thanks

Amir

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The correct definition of the time stamp in imported data is a very important issue when importing external data.

It is explained in detail in the Help:

Meteorological data > Hourly meteorological data > Hourly meteo data quality check

Meteorological data > Hourly meteorological data > Time shift

The time stamp beginning or end specification is defined in the importing format of the "Import ASCII meteo files" option.

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Hi Andre

I fixed the hour shift header value to 1 and i also put the values in separate cells but after converting the data in PVsysts when i open the graphs/tables to see the imported data all the values disappear.

It also warns me that there is an error in the column headers (line 14, filed 8) and line indicating the units (line 15, field 8) and i cant really see anything wrong

What do you think is wrong?

I have attached the CSV file.

Thank you

Regards,

Amir

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Update: The disappearing values was mainly a file issue.

Now i am able to import the weather data but i still have the following issues:

1- If i did not skip the header lines, the values are assigned to 20:00 hour instead of 7:00 as if the header files are counted as values

2- If i skipped the header files, the values are again assigned to hour-1 not considering that the original values are with respect to the end of the interval

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Actually i knew what's went wrong after finding out the PVsyst manual. It would be also good if the PVsyst help can refer to the manual as the information regarding importing weather files are more detailed in the latter.

Thanks

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Hi Andre

After a revision, i realized that i still have the 1 hour shift problem.

To recap, as i explained the TMY2 data are given with respect to the end of the interval.

Now when i let PVsyst know that the original data are with respect to the end of the interval, it assignes all the irradiance value to "hour-1".

So for example, the value of the GHI at 8:00AM on the first day of January is 66 W/m2 and PVsyst assigns this value to 7:00AM which does not quiet make sense. I mean the value at 8:00 AM should be the same and all that should vary is that the value of the last hour of the last day of the year should be assigned to the hour zero (first hour of the first day of the year)

And if i ignored to inform PVsyst that the values are with respect to the end of the interval, the problem is solved but i get a warning under the data quality tab that there is a 1 hour shift in the values.

Any ideas what's happening?

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  • 5 months later...

Hi

I am having this same problem. I import a Helioclim file for a UK site. Helioclim data timestamps are in end format (07:00 refers to data between 06:00 and 07:00) and PVsyst works in start format (according to the Help). Helioclim is given in UTC and the site is in Britain so I set the meteo file time zone as 0.

But then I get the warning "The meteo values are shifted -60 minutes by respect to the time defined by the Timezone of your reference site".

Regardless of the number I enter for the Time Shift Correction, the data in the hourly GHI table does not change and the warning does not disappear. I.e. the value given for 7:00 in the Helioclim csv is quoted for 7:00 in the PVsyst table, even though it should be 1 hour different due to the timestamp format difference.

Can you see what is wrong?

Many thanks

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