Detecting Cloudy or Clear night

Hi Brian

Thanks for this, can you confirm the operation, does it work with negative numbers.

i.e. if on a cloudy night the outside temp is 15.0 deg C and the Solar Temp is 14.9 deg C but on a clear night the Solar was 13.5 deg C

What would you enter in the 2 boxes + or - and what values

cant seem to enter -0.2 only -1.something

Re Brian

for cloudy night, then, set the first number as 0, the second as 1 (i.e 0.1 colder)
for the clear night, then, set the first number as 1, the second number as 5 (i.e 1.5 colder)

Hi Brian, thanks for sorting this, I am going to try this with my solar setup even though it
aint got any black on it and see how it goes, on the next mast maintenance i will be changing
my solar back to the light bulb and i will then add some black to the base of the bulb, but for
now i will see how it goes…

At the moment i can see the moon very clearly through the thin clouds my outside temp is 15.3C
and solar is 15.7C, just a little confused as to how to work out the settings that you have added

would it be 0.4 for cloudy and then wait for a proper clear night for the clear sky setting?

Outside temp 16.2, clear(ish) sky earlier Solar was 15.2 (1 Deg Diff)

Now gone cloudier Ouside = 16.2 Solare now = 16.1

Thats a good concise difference :slight_smile: are the settings changing the Icon for you?

you need to have a black body to get it coming up as colder Bashy…which you do not have, so its not going to work until you do

Yes Icon has changed

good news then

Are there degrees of cloudyness?

clear, partly cloudy, mostly cloudy, overcast

The average temperature in space is about 4 degrees Kelvin. If you infrared couple an object to the night sky, the sky will act as an infrared sink and the object will radiate its heat away into space. However, the object must be shielded from local things at normal temperatures, or the infrared that they radiate will be absorbed by your object and keep it warm. I have heard that the desert nomads made ice by placing water in the folds of a rumpled cloth spread out on the desert floor on a calm night. The humps in the cloth shielded the water from the infrared being emitted by the nearby sand dunes and let it cool down towards sky temperatures. A similar high school science demonstration involves putting a little water in a Dewar flask and leaving it outside on a windless night.

RE: black bodies.
Amongst my collection of useless tidbits that I have collected over the years was a short item I once saw in Popular Science or some similar publication. They said a reasonable approximation of a black body object had been made inexpensively by bolting a bunch of razor blades together side by side. Something about the way the blades narrowed in a curved manner towards the sharp edges, light would get trapped in the grooves formed by the assembly, and bounce back and forth many millions of times, thus having a high likelyhood of being absorbed and re-radiated. They said its spectra was close to the spectra of an ideal black body, although I think that they might have been talking about temperatures considerably higher than room.


i think the pelteir idea (i.e boltwood cloud sensor) has sheilding in place to stop the radiation from sideways sort of thing…

Attached is a shot of my ‘jar’.

To make this suitable for cloud detection as well as daytime solar, which bit do I need to blacken?

The probe itself?
The stem (an old pen body)?
Some part of the jar?
Some combination of those?
Something else?

Any hints appreciated. :slight_smile:

PS. The small ‘dots’ near the top right of the jar are not condensation - they are small bumps moulded into the glass for some reason…

try putting black tape around the bottom half of the jar…


Is it possible to add this cool feature also to us who use the 1-wire solarsensor too (that what use the diode and mv’s)? :wink:

My solarsensor has a tempsensor too and it is often colder than my maintemp at nights when clear nights.


if you can set that solar sensor temp sensor as a normal 1 wire temp sensor and get that set to be a extra temp sensor and then have that selected, then yes

Nice and straight forward. Sounds good to me. I’ll give it a try. Thank you. :slight_smile:

Ok, thanks Brian! Will do a test. Atm I have that tempvalues shown on WD’s maindisplay as %dallashumtemp2% :wink:

Just a little question, where in solarsetup should this new feature appear?

My solar-in-jar-screen is almost empty and I have now allocated the solarsensors temp as extrasensor #2 (see att.)

If your on about the cloud sensor settings then its in Setup (menu) then
advanced/Misc settings, then Boltwood Cloud Sensor, then its the bottom box :slight_smile:

Thanks Bashy! :wink: