Detecting Cloudy or Clear night

Hi all

I have noticed that an option for a peltier based cloud detector has been added?

Not sure where to find it?

But I have noticed that my Jam Jar Temperature Solar sensor is colder than my outside temperature sensor on clear nights and the same temperature on cloudy nights.

I assume that this is similar to a peltier sensor.

Could my temperature difference on a clear night be used to set the summary Icon & description?

Regards, Brian

Sorry I have just noticed that I have posted this in the wrong section. Oops

I aint sure how that would work dues to different temperature nightly

Its like solar in reverse, on a clear night regardless of temperature the Temp sensor in the Jam Jar is always lower than the normal outside temp sensor.

So you could look for the difference i.e. Jam Jar & Outside the Same = “Cloudy Night”, Jam Jar 1 Deg C < Ouside = “Clear Night” and somewhere in between is “Partly Cloudy”

Re Brian

Why would it be colder inside the jar at a clear night?

Best Regards,

A very good question, I don’t know, but it always is, if I take the lid off the class cover off the upside down Jam Jar so that the sensor is in free air then the temperature is the same.

I am assuming it the same / similar to how the peltier device works, both serfaces are in the same air.

Any body with a Jam Jam sensor noticed this?

Re Brain

I will let you know tonight :wink:

yes, thats the same principle,…i.e a black body gets colder at night (looses heat to space)
and so yes this could be used to set the cloud conditions at night as well, as being a simple night cloud detector
so, yes, I can add support for that (i.e a tick to say to use my solar in a jar sensor)

That sound great, I assume there would be an offset value as a difference?

Re Brian

Thanks for moving this thread…

Would it be possible to use a 1-wire temp sensor in this application Brian as say as a choice of extra temps (#1Extra or #2Extra or #3Extra etc) ? It sounds very interesting!


yes, I could add in the temperature differences to set each of the 4 night cloud conditions…

yes, Tokkiwi, any extra temp sensor can be used (albeit from 1 wire, labjack, or an actual weather station extra temp sensor)

I assume we would need two side by side - one in the black jar and one free/ventilated as per normal for a difference to be caculated from. Thanks.

I have just checked my readings, my Stevenson screen is showing 13.2oC and Solar in a Jar
is reading 13.6oC and currently we have high clouds about 3000ft (Mostly cloudy) and both
sensors were checked against each other before siting it on the mast…

So with this theory, if its the same temp or the solar is higher then its cloudy,
if the solar is colder then its a clear night?

As Brian said - the solar in a black jar is a “black body” and loses heat (gets colder than ambient) to a space/black sky. I think the two sensors would need to be in the same environment, not one on a roof and the other in the garden, then you could get unusual readings. But if the solar in a jar saw a warm tile roof (infra red re-radiated heat) then it could be warmer than a garden mounted ventilated unit at night time.

Hmmm, I see another project coming on!! :wink:

Hi Graeme, my solar has no black whatsoever its just white and glass, so I aint sure if this is going to apply to my solar :frowning:

Also mine is about 9m agl and the temp is about 2ft agl in the screen, so again, perhaps not the most ideal setup fcor this idea :frowning:

i thought that that solar sensor in a jar was that you painted the bottom black…

Hi Brian

no m8, all mine have been in a lab flask or a light bulb, the 1st 1 i made i painted the tube black
but that one is long gone lol

I recall seeing that some people have painted the probe black, though that wasn’t till after I’d sealed mine up and since I’ve seen no condensation over quite a few months of use I’m reluctant to disturbe it without good reason - my first (bigger sensor and bigger jar) attempt suffered a lot from condensation.

Has anyone tried painting the whole jar black?

Thoughts anyone?

Later: Maybe answering my own question - On reflection I think that painting the whole jar balck would not work because then the ‘black body’ would itself be exposed to the elements, instead of being in the protected environment of the jar…


Pour mon premier essai, sonde dans un verre noir.

Cette nuit:

Clair : 12,2

i think people could easily either create a black body device…i.e a black surface facing the sky with a temperature sensor on that surface, and then that is compared to the stations normal outside temperature reading, and the difference then determines the cloud cover
(i.e mount near your normal outdoor temp sensor)
an existing solar sensor in a jar with a blackened bottom can also then combine as a night time cloud cover sensor

i will add the ability to set the different temperture thresholds to the setup in wd…

in the latest .zip update you can now tick to use a difference in temperature between the selected extra temp sensor and the normal outdoor temp sensor
i.e a black surface with a temperature sensor on it will do the trick
or use your solar sensor in a jar, as long as it has a black bottom…

then set the thresholds, so that cloudy is the smallest temperature difference, and clear sky is the largest tempereature difference, that you see
then it should be bobs your uncle
I might have a go at setting this up myself…