Cumulus Support

I have been using Cumulus for about 18 months, and now want to understand the log files better.
The monthly log file contains a field (23, "W") which is described in the Wiki as :

Current theoretical max solar radiation (only valid if solar sensor on weather station)

I am using a WH1090 (and have ticked the correct station type in the configuration menu). It does not have a solar sensor, yet the "W" field contains a value.
Typically the values start 1 at about sunrise increasing to 121 (21 December) or 886 (1 July) at noon (UDT) then reducing back to 1 at sun-set. The value is 0 overnight.
What do these values mean?

See the FAQ: http://wiki.sandaysoft.com/a/FAQ#What_i ... playing.3F

The wiki is incorrect to say that it is only valid if you have a solar sensor, I'll correct that.