Solar Resources

Use this section to load solar resource data to be used in energy yield calculation. Multiple datasets can be loaded though only one can be used at a time for an individual energy yield calculation.

You can import solar data from one of various supported file formats. Or download the data using one of the online APIs that we currently support.

Importing solar data from a file

File formats

The following file formats are currently supported by SolarFarmer:

  • Meteonorm PVsyst Hourly TMY (*.dat)
  • NREL SAM (*.csv)
  • NSRDB TMY3 (*.csv)
  • PVsyst standard format (*.csv)
  • SolarAnywhere format (*.csv)
  • SolarAnywhere TMY3 (*.csv)
  • SolarGIS database TMY (*.csv)
  • SolarGIS database multi-year (*.csv)
  • Solcast CSV (*.csv)
  • Tab separated values, free-format file (*.tsv)
  • Tab separated values, Date | POA | Temp | (WS) | (Albedo) | (Pressure) | (PW) | (RH) (*.tsv)
  • Tab separated values, Date | GHI | Temp | (WS) | (Albedo) | (Pressure) | (PW) | (RH) (*.tsv)
  • Tab separated values, Date | GHI | DHI | Temp | (WS) | (Albedo) | (Pressure) | (PW) | (RH) (*.tsv)
  • Vaisala TMY and long-term formats (*.csv)

Terminology

The following table defines the terms/acronyms used on this page:

Term Meaning
Albedo Surface Albedo (dimensionless) - optional variable
DHI Diffuse Horizontal Irradiance (W/m²)
GHI Global Horizontal Irradiance (W/m²)
NSRDB National Solar Radiation Database
POA Plane of Array (W/m²)
Pressure Air Pressure (mbar) - optional variable
PW Precipitable Water column height (cm) - optional variable
RH Relative Humidity (%) - optional variable
Temp Temperature (°C)
TMY Typical Meteorological Year
WS Wind Speed (m/s) - optional variable

Site meta data

When you select a file with one of the known formats, the latitude and longitude are displayed along with the time zone. You can adjust the time zone which is used to help SolarFarmer adjust the time stamps if necessary so it is valid for your site location. This is especially useful for tab-separated values files that do not contain latitude and longitude.

Solar resource resolution

You can use sub-hourly resolution for the energy calculation - you are not limited to hourly resolution.

Warning

The thermal model used in the energy calculation assumes steady state and may lose accuracy when it is less than 5-minute resolution. It is therefore recommended that you use at least 5-minute resolution.

This restriction will be addressed in future releases.

Be aware that using sub-hourly resolutions will also take the calculation longer to complete as the number of time-steps is greater than if you used an hourly resolution.

Validation warnings

You will be notified of any validation issues after the import is complete.

Tab-Separated values (TSV) files

There are four options to upload tab-separated values files. Read the directions in the upload window for required format and units. Here is a quick summary:

  • Header rows are ignored
  • IMPORTANT - Use the ISO 8601 date-time format YYYY-MM-DD hh:mm:ss (for example 2019-12-17 11:16:01)
    • Use hyphens between the year, month and day.
    • Use colons between the hour, minutes and seconds.
  • Timestamps should correspond to the beginning of the interval.
  • The order of the columns must be one of the following (the optional columns can be in any order after the required columns):
    • Date-time, POA, ambient temperature, (wind-speed), (albedo), (pressure), (PW), (RH)
    • Date-time, GHI, ambient temperature, (wind-speed), (albedo), (pressure), (PW), (RH)
    • Date-time, GHI, DHI, ambient temperature, (wind-speed), (albedo), (pressure), (PW), (RH)
  • Only use tabs as delimiters between the data columns; no commas or spaces.
  • Use a full-stop period for a decimal point; do not use commas.
  • You can specify the timezone after the file selection to make sure that the data, sunrise, solar noon, and sunset, are within expected tolerance.
  • If there are any anomalies in the data, such as diffuse greater than global, then they will be reported and/or corrected.

Supported column headers:

Header Property and Expected Unit Expected Range
Date or Time Date time stamp (YYYY-MM-DDThh:mm+OO:OO)*
GHI or SolarTotal or Glob GHI (W/m²) 0 - 1300
DHI or DIF or Diffuse DHI (W/m²) 0 - 1000
POA or Gpoa or Plane Plane of array irradiance (W/m²) 0 - 1300
TAmb or Temp Ambient temperature (°C) -35 - 60
WS or Wind or Speed or WindSpeed Wind speed (m/s) 0 - 50
PW or Water Precipitable water column height (cm) 0 - 100
Pressure or AP Air pressure (mbar) 750 - 1100
Humidity or RH Relative humidity (%) 0 - 100
Albedo Surface albedo (per unit) (only used by cloud calculations) 0 - 1
Note

The SolarFarmer value for missing data or invalid entries is 9999 or -9999. Use any of these values in your TSV file to consider any missing or Not a Number (NaN) values.

Video tutorial
Watch how to import custom solar data (sub-hourly, for any time period) using .tsv files. Follow along using the sample files or your own data!
Get sample files (.zip file, 6MB)

How to use Excel to reformat your date time column

If your date times are in a different format to the expected one you can use Microsoft Excel to reformat them.

  1. Load your text file into Excel

  2. Highlight the data in the date/time column (select the column header to select them all)

  3. Select 'Home' from the menu bar and then 'Number' from the ribbon: Home and Number in Excel ribbon

  4. Expand the Number Formats pull down menu and select 'More Number Formats...'

  5. Select Custom and enter Type as yyyy-mm-dd hh:mm:ss Custom Date Time

  6. Now use 'Save As' from 'File' in the menu bar to save the data as tab-separated: Save As Tab Delimited

Downloading solar data from online sources

You can download solar resource data from various online sources directly into your SolarFarmer workbook.

Note

Online sources that we support are currently a bit limited. Please let us know which other sources you would like to be supported and we'll do our best to add them soon.

Currently supported sources

Solcast API

Solcast (a DNV company) provides satellite-derived cloud estimates at 1-2km resolution, irradiance modelled at 150m. See Solcast's website https://solcast.com/ for more details, how to try their API for free, and their pricing options.

Their data is accessed using their API, and SolarFarmer allows you to use your Solcast API token to download data from their API directly into your SolarFarmer workbook, optionally choosing to save the data to a file at the same time.

Solcast API Download dialog

  • If you set a SOLCAST_API_KEY environment variable with your Solcast API token on the PC running SolarFarmer, there is an option to use that (the easiest way). Otherwise you can paste your Solcast API token in each time you use it (it is not stored in the workbook).
  • The location is automatically set from the workbook, though you may change this.
  • The time zone is also automatically set from the workbook.
    • Solcast currently only supports integer time zones. If your site has a none integer time zone (e.g., India with +5.5 hours from GMT) then pick the smaller integer zone (e.g., +5).
  • If requesting TMY data, the probability and GHI and DNI weight settings will be used.
  • If requesting historic data, set the time period required.
    • Solcast restricts the time period of each historic API request to 31 days. SolarFarmer will call the API multiple times and stitch the results together to form one file.
    • Not all file formats support historic data - see the table below.
  • The interval period options can depend on if you choose to select the TMY or Historic, and if you choose to save the downloaded data to a file, the file format chosen.
  • If you choose to save the downloaded data to a file, several file formats are available. See the table below.
  • If you choose to only import the data, Solcast CSV file format will be chosen, and the data will be imported into your workbook. There is currently no way of exporting the solar data from a SolarFarmer workbook.
  • If you choose to save AND import the data, it will only access the API once and download the data in the format you choose, and import using that. The Solcast JSON format cannot currently be imported.
Features available for each file format
File Format TMY TMY time periods Historic Historic time periods Can be imported
PVsyst standard format Yes 60 Yes 60 Yes
Solcast CSV Yes 15, 20, 30, 60 Yes 5, 10, 15, 20, 30, 60 Yes
Solcast JSON Yes 15, 20, 30, 60 No N/A No
NREL SAM Yes 15, 20, 30, 60 No N/A Yes
NSRDB TMY3 Yes 15, 20, 30, 60 No N/A Yes
Variables downloaded for each file format
File Format Columns downloaded (in addition to date and time)
PVsyst standard format (TMY) Tamb, GHI, DHI, DNI, WindVel, AlbedoDaily, Pw, Pressure
PVsyst standard format (Historic) Tamb, GHI, DHI, DNI, WindVel, AlbedoDaily, Pw, Pressure, relative_humidity
Solcast CSV (TMY) ghi, dhi, dni, wind_speed_10m, air_temp, albedo, precipitable_water, surface_pressure, relative_humidity
Solcast CSV (Historic) ghi, dhi, dni, wind_speed_10m, air_temp, albedo, precipitable_water, surface_pressure, relative_humidity
Solcast JSON (TMY) ghi, dhi, dni, wind_speed_10m, air_temp, albedo, precipitable_water, surface_pressure, relative_humidity
NREL SAM Temperature, Azimuth, Cloud Opacity, Dew Point, DHI, DNI, EBH, GHI, Pressure, Wind Direction, Wind Speed, Zenith
NSRDB TMY3 Several - too many to mention here!

PVGIS TMY

PVGIS is a free online source of solar data that now covers all of the world. It is implemented by the JRC (Joint Research Center) from the European Commission's in-house science services.

See their main website for more details: https://ec.europa.eu/jrc/en/pvgis and a map of areas of the world that they support: https://re.jrc.ec.europa.eu/pvg_tools/en/#TMY

A new version (5.2) was released in March 2022. This contains updated databases and coverage for the whole world. However, there is still a known issue for version 5.2 that some coastal areas can show values of zero (or close to zero) for variables such as temperature, wind speed, wind direction and humidity (see PVGIS 5.2 and scroll down to 'Known Issues').

It is recommended to use the latest 5.2 version. But if you see the above problems, use version 5.1 (if it is available) for your site.

PVGIS Download dialog

Solar Resource Compass

This is a DNV service (running in a web browser) that accesses and compares irradiance data from multiple data providers and allows you to see how they compare for your project location.

See https://src.dnv.com for more details.

Once you purchase and download your chosen data (currently in Meteonorm PVsyst Hourly TMY (*.dat) format) you can import the downloaded file into SolarFarmer via the Import button.