Mismatch PVGIS TMY Time zone

Hello there,

I am not so experienced user but trying to use this good software.
It seems that I have a problem with usage of TMY PVGIS Weather file with SAM software. There is problem with time zone. Sun position is OK, but it seems that data in TMY not follow the sun position.
Analyzed location is in UTC+1, SAM reads time zone and make that Sun position proper to it. Weather data don't follow it, it seems that they are moved to the early hours. I have got more energy in eastern oriented array then western, 20% more.

When I read weather data DHI for example and Sun up over horizon and show them on time series there is mismatch in pictures. DHI data is full at the bigining (early hours) and empty at the later hours. As there is mismatch for an hour. My conclusion is the SAM uses UTC+1 time for sun position and UTC time for weather data.

I am trying to find on PVGIS website which time they are using when creating TMY but there is no info.

How to solve it?

Thanks in advance,
Sasa

Hi Sasa,

If you download a file using the "EPW" option from this page, re.jrc.ec.europa.eu/pvg_tools/en/tools.html#TMY , you should get a file with correct time stamps.

Otherwise, you can adjust the data in the file by copying the appropriate number of rows last day of the year to the first day of the year to shift the data. Usually this works because there is no sun in the night time hours, so shifting the rows does not affect the irradiance data.

Best regards,
Paul.

Hi Paul,
thank you for the reply.

If you download a file using the "EPW" option from this page,  re.jrc.ec.europa.eu/pvg_tools/en/tools.html#TMY  , you should get a file with correct time stamps.

Yes, indeed. "EPW" will change time stamps, every hour will be added by 1, but miss 00.00. When you check in text editor you will see that first data record starts with time stamp 01.00. There is a problem when EPW file is imported by SAM which ignore time stamps and put 00.00 time stamp at first data record. It is some incompatibility and it cancels changes made by EPW.

Otherwise, you can adjust the data in the file by copying the appropriate number of rows last day of the year to the first day of the year to shift the data. Usually this works because there is no sun in the night time hours, so shifting the rows does not affect the irradiance data.

I have already done by this way. I have saved CSV format form PVGIS and made macro to prepare new CSV file for SAM. 
Just for information convert macro already installed in SAM has some runtime error and had to make new one.

I will be free to mention some suggestions for the some of the next version of SAM:

• Option to define other currency then $, maybe € or better local currency from the list
• Option to choose average year file from NSRDB. As I see there are 2018 and 2019 years for Europe, and probably more by time. It would be useful to have possibility to choose average year made from the years data in the menu.

Best regards,
Sasa

 

Hi Saša,

Thank you for the suggestions.

As more years become available over time, the NSRDB may be able to generate typical meteorological year (TMY) data in addition to the single year files. For now, with only three years of data available, it is not possible to generate TMY files.

There are a couple of SAM macros that might help with the issues you are having with EPW files from PVGIS: The "Solar Resource File Converter" converts EPW to SAM CSV, and "EPW File Timestep Correction" which helps you adjust the time stamp.

To see a list of macros, click Macros under the Simulate button.

Best regards,
Paul.

Hi Paul,

for TMY we should wait for 10 years, shouldn't we. 

Yes, I was speaking about macro Solar Resource File Converter, for EPW works fine, but has runtime error when works with PVGIS CSV (as I saw code expects different format of file).

EPW File Timestep Correction also has a error. This macro expects that EPW file doesn't have minute column but it has. So, the result is empty one of the irradiance column.

I have prepared new macro and solve the problem as you suggested in last post. Just I would like to share my experience.

I am speaking about Mac version of SAM what I am using.

Best regards,
Sasa

Hi Saša,

Would you mind sharing a copy of your version of the Macro?

We haven't looked at the PVGIS CSV files in a while, so I'm not sure if there have been format changes since we wrote the macro. For example, the macro expects dates like "01/01/2013 00:00:00", but I see that PVGIS now returns dates like  "20130101:0000".

Best regards,
Paul.