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.
Forgot to mention in case that wasn't known - the solar radiation data on virtually all the weather files around are calculated using some solar model. Solar radiation is not a parameter that is or was ever recorded at weather stations. Therefore, when you ask for the source data, there is none except what's shown.
Asked: 2018-01-15 04:34:50 -0500
Seen: 895 times
Last updated: Jan 15 '18
