Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The IWEC weather files were developed by ASHRAE back in 2001 using a solar model developed in Germany (Kasten) that was found to give poor results in tropical and subtropical locations.
There is a newer IWEC2 weather file for Johannesburg, also developed by ASHRAE in 2012, using a different, possibly better, model (Zhang-Huang) that is available at cost at the WBT web site (weather.whiteboxtechnologies.com).
If you're just interested in seeing the solar radiation in Johannesburg, you can also get satellite-derived solar from CAMS https://atmosphere.copernicus.eu/, but expect a learning curve.
full disclosure: I'm the owner of White Box Technologies and the contractor to ASHRAE in developing the IWEC2 weather files.
