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Johannesburg weather data

asked 2018-01-15 04:34:50 -0500

matilde's avatar

updated 2018-01-15 16:29:16 -0500

Hi there, there seem to be inconsistent direct and diffuse solar radiation data at 1pm on the 18th of Jan in the Johannesburg 683680 (IWEC) weather file. Is there a way to check the source data? Many Thanks Matilde

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answered 2018-01-15 16:09:08 -0500

Joe Huang's avatar

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 (

If you're just interested in seeing the solar radiation in Johannesburg, you can also get satellite-derived solar from CAMS, 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.

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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.

Joe Huang's avatar Joe Huang  ( 2018-01-15 16:11:57 -0500 )edit

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Asked: 2018-01-15 04:34:50 -0500

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Last updated: Jan 15 '18