Comparing different TMY/EPW providers : inconsistency of data?

Interesting to hear that you think this might be it:

But this does seem likely given that a half-hour offset looks consistent with those images of Los Angeles, @lionpeloux .

I know that it’s idiosyncratic and counter-intuitive to record radiation as a “total over the previous hour” but this is how EnergyPlus interprets the EPW radiation from the file and, considering that EPW was originally created for EnergyPlus and stands for “EnergyPlus Weather,” it seems pretty clear that this is the standard that EPW files should follow if they are to be considered valid.

If you want the official document that states this, @lionpeloux , you can see the description of the Radiation Fields in the EnergyPlus Docs here:

Field: Direct Normal Radiation

This is the Direct Normal Radiation in Wh/m2. (Amount of solar radiation in Wh/m2 received directly from the solar disk on a surface perpendicular to the sun’s rays, during the number of minutes preceding the time indicated.) If the field is “missing ( 9999)” or invalid (<0), it is set to 0. Counts of such missing values are totaled and presented at the end of the runperiod.

FYI, Radiance is thankfully very flexible in the way that you feed the radiation data to it and Ladybug does something very similar to this when it formats the EPW radiation for Radiance functions:

@Lukas 's suggestion of adjusting the time zone could be a suitable workaround for running correct Radiance simulations and producing visualizations like the radiation dome but I wouldn’t recommend this for EnergyPlus simulations. For that, you can build a new EPW with the hourly Radiation changed using the DF Create EPW component. You can shift the radiation values by a half hour using the LB Convert to Timestep to do a linear interpolation between the hourly values. Then deconstruct the data collection ad build a new hourly radiation data collection using every other value in the data collection.