Cumulus Support

Hi
Have just added a Davis Solar sensor (6450).
The first day we had any real sun it gave me readings that were odd.
The calculated max Solar energy at the time was 441W/m2 but the sensor was recording 559, which seems somewhat high.

I used the default settings in MX.

I have now changed to BRAS as the calculation method, all other settings are as default.

Not really had any decent sunshine since to see which is better.

[Update] 12:35
OOh a sudden burst of sunshine.. now I have 645 of 454 (142%) Hmm

What settings do others use?

A lot of us got surprised when we first looked at solar sensor data to see spikes well above the "possible" line. When it is spiky, the issue is reflections from clouds. And, yes, the sensor really does get radiance well above what the sun can provide undisturbed because it is seeing not only the direct path it is entitled to, but some share for nearby locations that came to your spot instead.

So before even thinking of calibrating (again), wait for several hours of a smooth curve from nearly cloudless conditions.

Here in Albuquerque, the built-in algorithm gets the summer/winter difference a bit wrong, so I prefer to calibrate so that a cloudless stretch near either equinox matches the "theoretical Max" curve. Looking at the Solar sections of Station Settings in my copy of classic Cumulus, I find that I have the trans factor set to 0.8. That is probably not the default. It works well here in Albuquerque, New Mexico--probably not right for lots of other places. When I say it "works well", I'm accepting that near winter solstice a cloudless day beats the theoretical maximum by a bit less than 10%, while a cloudless day near summer solstice fall short by just less than 10%.

Two other factors influence your hours of sunlight per day reporting (but not the actual watts/meter value at any moment): I have mine set to Sun Threashold: 75%, and Sun Min: 20 watts per square meter.

The reflection spikes also give UV peaks well above the cloudless level.

Ah... Alberquerque

I feel I know it so well after 5 seasons of Breaking bad and now Better Call Saul

Thanks for your views on my issue.
Waiting for the sun to shine in a grey and damp UK