Skip to content

Converting weather data

The instruction convert-meteo will convert CSV weather data into a MET file, useable in PVsyst or PVsyst CLI simulation.

In PVsyst the equivalent operation is Custom file import.

For more information on MET and SIT files, read the related PVsyst help page.

Preparing required files

The conversion requires a MEF file, which details the formatting of the file to be read, and a SIT file, containing necessary geographical information.

Preparing a MEF file

To build the MEF file, you can use the Custom file import PVsyst interface. In a workspace MEF files are located by default in the Meteo folder.

CSV data formatting

The formatting of the CSV file to be read is very permissive. The main requirement is that the data are organised as one time stamp per row.

Preparing a SIT file

SIT files can be generated from the Geographical sites interface. In a workspace MEF files are located by default in the Sites folder.

To aid with sizing calculations, SIT files also contain monthly weather data. This data is strictly speaking not necessary for the simulation, but is currently required. Using the PVsyst interface, it is simple to import data from several sources, or enter (placeholder) data manually.

Use cases

Example 1: Import third-party data files

The most common use case is to import a set of files from a third party service or tool.

  1. Group files and make sure that format is compatible (CSV, one time stamp per line)
  2. Use PVsyst to create a SIT file and a MEF file using the Custom file import interface, or obtain the SIT and MEF files from another source.
  3. (Optional) Import one file via PVsyst, to check the MEF definitions and data quality using the Meteo Tables and Graphs interface.
  4. Run PVsystCLI programmatically with SIT and MEF files as fixed inputs. As output path, use a workspace's Meteo folder.

Example 2: PV system performance testing

In this case weather data may be extracted as part of monitoring data. Once MET files are created, it is possible to run simulations (with PVsyst or PVsystCLI) and obtain simulation data that can be compared with the electrical measurements of your monitoring data.

MEF formats offer the possibility of importing POA irradiance data, which are common for PV system performance testing.

Procedure is similar to Example 1 but may involve more involved clean up and formatting steps in the data preparation.

Example 3: Pseudo-sub-hourly simulation preparation

Sub-hourly simulations can be approximated with the pseudo-sub-hourly simulation procedure. This consists in splitting data based on the minute time stamps, and running the simulation separately for each group.

  1. Process sub-hourly data to obtain one CSV file for each minute time stamp. For example, for 15-minute data, this means 4 CSV files (0,15,30, and 45 minute time stamps).
  2. As in Example 1 use one of the files to create SIT, MEF file and check the quality of the data and formatting.
  3. Copy MEF file for each minute stamp and adapt the time shift parameter. In a hourly simulation, PVsyst defines the sun position at the 30' mark (center of 1 hour interval). In the example this means that for the recording interval 0-15', with center at 7', the time shift needs to be -23', in addition to any other time shift present in the data. This step is best done programmatically.
  4. Once all CSV have a corresponding MEF file you can use these with the SIT file to run the PVsystCLI conversion procedure. This will generate all necessary MET files.

See this section for details on the simulation part of the procedure.

Output file

MET files are the main input for the simulation of a PV system. Because they contain horizontal global and diffuse irradiance data can be used with any orientation.

It may be convenient to define the output path for the conversion procedure as a workspace's Meteo folder. This will allow the files to be already present when using PVsyst to work in the workspace.

Output quality check

The PVsyst tool Meteo Tables and Graphs allows to visualize the content of MET files. Moreover, the Check data quality tab may help you detect any problems with data formatting definitions (MEF file) or with the data itself.

A typical example is a time shift in the time stamps. This can be fixed by selecting an appropriate time shift parameter in the MEF file.