Help regarding solar calculations with Davis VP type sensors

Yes it all depends on your view but I used the same convention as some of the US Govt websites which say + for west and - for east on timezone. So yes +8 is what you needed, that’s how I coded it.

Before I put it up I did do some comparisons with the solar calculators at and it all worked out OK however I did notice that these calculations I am now using, which BTW are not exactly the same as the formulae I suggested to Brian, seem to work out to be closer to actual sunrise and sunset in the southern hemisphere. I would like to see if I can get better calculatiosn which come closer to the US Govt sites with non-zero values closer to sunrise and sunset, I think at present it can be up to 10 minutes each end of the day in the northern hemisphere.

The problem is that because, at least with the Bluewave sensor, you get low readings just at or before sunrise or after sunset the percentage calculation is very coarse and can easily give false positives for sunshine, and this is very noticeable if the non-zero values start a few minutes after sunrise and finish a few minutes before sunset.

I know that a Campbell Stokes recorder would probably not record at these low values so I think we need to have some kind of threshold below which WD ignores all values from both sensor and calculations, and I think this should be user adjustable to cope with differences in sensors and perhaps location, and to relieve Brian of some decisions as to what to set.

You may notice in my other thread that I seem to have a problem with the latest download where WD is getting non-zero values well after sunrise like some 40 minutes late today.