PVsyst's forum

According to the PVSyst website: "The Time Zone is the difference between the local Legal time, and the UTC or GMT". Does this mean we have to change the time zone based on daylight savings? Ireland is GMT 0 in standard time but GMT+1 in daylight-saving or summer time. Projects in Ireland are automatically assigned Time zone 1 for some reason, is this just a bug?

Also, if I import met data based on either Time zone 1 or 0 then I get different results for the diffuse irradiation - why is this? This then changes the transposition gain.

Internally, PVsyst dosn't use the Daily Saving Time. As in most of PV softwares, the *.MET files always use the winter time.

Now when importing meteo data files which take the DST into account, you have to mention this in detail in the Importing protocol. See the help "Meteo Database > Import custom meteo files > conversion protocol"
Most of "official" meteo data don't involve a DST.

NB: It is very important that the Time shift is correct all over the year. You should check this using "Databases > Meteo Tables and Graphs > Check Data quality". And press F1 for getting the help "Meteo Database > Notes on Meteo > Meteonote9_Time shift in imported meteo files"

The Diffuse model is highly depending on the Time shift, as defined during the importing time: if this is erroneous, the diffuse is false.