WXforum.net
Miscellaneous Debris => Tech Corner => Topic started by: Jáchym on December 19, 2015, 12:16:25 PM
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OK, I appologize in advance as it might be stupid question but...
I personally don't have a weather station which would measure solar radiation so I cannot answer this myself.
A friend of mine was suggesting to me that you can actually determine the duration of sunlight based on the measurements from stations such as Davis VP2 or any other station that measures solar radiation. According to his view, in order to calculate the duration of sun shine you should simply look at the intervals at which the solar radiation measurements are not 0.
However, my understanding of how these stations work was that they actually measure the actual "amount" of light rather than sun shine so it only tells you when it is day/night, but it is not possible to determine the sun shine duration (to be precise, it is of course possible, but using a different device and not the solar radiation sensors that come as part of many weather stations).
As I said, I don't have a station measuring this myself so I would like to hear your opinions and if it is the case that I am correct, then if you know of any option how to measure the actual duration of sunlight in non-professional environment and ideally for some reasonable price.
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What EXACTLY is he trying to measure? Clear sky? Direct sunlight - as opposed to diffused like you would get with thin cloud or fog? http://www.pveducation.org/pvcdrom/properties-of-sunlight/measurement-of-solar-radiation
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Well measuring sunshine hours, which I believe is what your fried means, is not straight forward. Weather Display does it reasonably well. The Davis stations have a global solar radiation sensor which means that readings can go from 0watts/m˛ to over 800w/m˛ (possibly up to 1000w/m˛ because of cloud reflections etc) and that covers all lighting conditions from night through to bright sunshine. In order to calculate whether or not it is sunny you need to calculate the expected max solar radiation for your time of day, latitude/longitude, an allowance for the effect of the atmosphere (attenuation) and compare that with the Davis reading and calculate a % value, then set a threshold above which it is considered sunny (usually around 80%), you then count the minutes for where it is above threshold which gives sunshine duration.
Often quoted is a value of I believe 100w/m˛ for sunny conditions but that only applies to a solar sensor which measures direct radiation and is one which tracks the sun across the sky.
So it is not trivial as you can imagine.
Stuart
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Thanks for clarification, basically this is exactly what I thought... that either you would have to have a device which detects direct sun shine reaching it or you have to estimate it from the expected maximum.
Either way, the point is - it is not as easy as he thinks - i.e. the solar radiation sensors do not show 0 when it is overcast.
thanks
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What Stuart said, plus some of the weather programs (I know Cumulus and WD do it) will calculate the current theoretical value for you, and apply your desired percentage threshold to provide an indication of 'sunshine'. Is it as good as a dedicated sunshine sensor? No, but I have found it reasonably accurate, good enough to give a fair indication of the sunshine hours.
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Someone here wrote a little program to capture cloud vs. clear pixels on a sky cam. Another option...
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Sure, thank you all guys for replies and actually proving my understanding of it.
The bottom line is - it is possible to make a relatively accurate estimate, but the important thing is - the sensors themselves do not measure it and it is still just an estimate.
The question then remains what options are there of buying some sort of a device that would actually be able to detect direct sun shine and thus provide not an estimate but measurement.
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For me, the current best amateur kit is the Blake Larsen detector - http://www.sunrecorder.net/
You can fiddle around with temp sensors in jars etc, but the BL detects directly.
Instromet also make a sunshine detector/recorder too. http://www.instromet.co.uk/SunshineSensor.html
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http://www.metcheck.co.uk/acatalog/Sunshine_Recorder.html
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(possibly up to 1000w/m˛ because of cloud reflections etc)
Just a correction, 1200+ w/m2 during summers here on clear sky.
But..
I would say how any solution works depends lots on the location too.
As mentonied above i get 1200+ w/m2 on clear sky in June but only 60-80 w/m2 in December here at 60N. And again during overcast is the values like 300 w/m2 at summer and 0 w/m2 in December. So it would really need a "max value" to be calculated too before any solarhours can be calculated.
// Henkka
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For me, the current best amateur kit is the Blake Larsen detector - http://www.sunrecorder.net/ (http://www.sunrecorder.net/)
You can fiddle around with temp sensors in jars etc, but the BL detects directly.
and if it goes the developers' way it won't be "amateur" but it is a long haul!
Looks like some parts of Europe had great sunshine http://www.komokaweather.com/weather/sunrecorder/sunrecorder_display_v2_today.html (http://www.komokaweather.com/weather/sunrecorder/sunrecorder_display_v2_today.html)
but not much bright sunshine so far here today http://www.komokaweather.com/weather/sunrecorder/sunrecorder_display_v1.html (http://www.komokaweather.com/weather/sunrecorder/sunrecorder_display_v1.html):
LAT 42.9539
LON 81.4352
TZ -5
DST True
SRS 07:52:22 16:53:11
TOT 00:12:05 00:07:09
NRC 09:20:05 09:27:14
SUN 13:54:39 13:54:45
SUN 13:54:50 13:55:08
SUN 13:55:36 13:55:45
SUN 13:56:42 13:57:35
SUN 13:58:27 13:58:28
SUN 13:58:39 13:59:30
SUN 13:59:56 14:02:12
SUN 14:02:41 14:04:04
SUN 14:04:46 14:04:49
SUN 14:08:19 14:08:34
SUN 14:08:38 14:08:40
SUN 14:12:25 14:13:08
SUN 14:20:02 14:20:08
SUN 14:27:34 14:27:45
SUN 14:37:37 14:40:37
SUN 14:44:42 14:44:58
SUN 14:46:02 14:46:04
SUN 14:53:45 14:54:43
SUN 14:55:01 14:55:06
SUN 14:55:11 14:55:11
SUN 14:55:14 14:55:14
SUN 14:55:18 14:55:23
NRC 14:56:13 16:53:11
Paul
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http://www.metcheck.co.uk/acatalog/Sunshine_Recorder.html
This is exactly the link I found. So there probably is no cheaper alternative that might not be as accurate, but do the job. The question then is whether the 1300 price tag is worth it or if it the estimates are reasonably accurate... I guess he will have to decide himself, for me it does not really matter because my station does not measure SR, so I cant even make the estimates.
It is however something to consider to implement into my template, I will look on the internet at some papers about how exactly these numbers could be estimated (I guess it should depend on your latitude and time of the year).
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I have a max solar value calculator on my website at http://www.stella-maris.org.uk/maxsolar1.phtml (http://www.stella-maris.org.uk/maxsolar1.phtml) but it is only for testing purposes so people can see what they should be getting in something like Weather Display. Please note the comments about its use.
Stuart
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For me, the current best amateur kit is the Blake Larsen detector - http://www.sunrecorder.net/
You can fiddle around with temp sensors in jars etc, but the BL detects directly.
Instromet also make a sunshine detector/recorder too. http://www.instromet.co.uk/SunshineSensor.html
I mounted the BL SR today.
http://www.sunrecorder.net/googlemap/googlemap.php?mode=showstat&type=Today&serial=10112
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=D>
You're included Komoka Sunrecorder (komokaweather.com) (http://www.komokaweather.com/weather/sunrecorder/sunrecorder_display_v2_today.html)
Enjoy,
Paul
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Hi David,
For the 12 Months Sun Normal it looks like you are still on the default monthly sun hours of 1,449.0. You can edit that in SR program and use the normals from Environment Canada for their nearest to you - i.e. OttawaCanadian Climate Normals 1981-2010 Station Data - Climate - Environment and Climate Change Canada (weather.gc.ca) (https://www.climate.weather.gc.ca/climate_normals/results_1981_2010_e.html?searchType=stnProv&lstProvince=ON&txtCentralLatMin=0&txtCentralLatSec=0&txtCentralLongMin=0&txtCentralLongSec=0&stnID=4333&dispBack=0)
Click Normals Data, scroll down to and select Bright Sunshine, and that will give you the hours per month (year total of 2,083.7)
Good to see it recording again.
Have you been able to compare the B-L to your station(s) sensor or CMX calculation?
Enjoy,
Paul
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Thanks for the tip. Will check that out. I don't have any other sun sensor to compare to.
I may end up getting it a bit higher next summer. Another six or eight feet would clear up a bit of tree line at sunrise.
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I got the normals keyed in.
Having some trouble with it crashing all the time now.
02-10-2021 23:59:00 Midnight Break
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Hi,
Yes I had noticed that you have added the sunshine normals. Will be at the end of the month before you will be able to see how you compare.
I am not familiar with that logged status. Is that part of the current SR program?
Enjoy,
Paul
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I was looking around the Sunrecorder folder and in System folder I saw this file. I don't know what it all really means.
Could be related to the crappy computer its hooked to. I should try another to find out.
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H,
Can't help with that. My latest program is October 2018 and nothing like that in my file structure. Maybe a question for Ole.
Enjoy,
Paul
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Funny I have not touched the computer for a couple days and it runs fine. I'm thinking something with the super crappy video card or other fault with budget computer because I was on there checking charts and doing settings when it kept balking.
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Jáchym, you say you dont have a station that records solar, what about a station that can have extra temp sensors? If so and if you use a program like weather display, you could make your own solar sensor with the Solar in a Jar method, it works very well and i used it for a good few years and even experimented with the idea, such as a drilled out lightbulb, whilst very sensitive to sunlight, ie recorded every single subtle change, i changed to a laboratory flask shaped like a bulb and a temp probe and placed it upside down on my mast, i cant remember why i ditched the lightbulb idea now. Good thing is, it can also be doubled as a night cloud too.Ok, I'm rambling on and you may not even be able to use extra temp sensors...
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I have been interested in measuring sunlight too, and have several pyranometers to try to do so.
They basically measure incident light, and will start to show watts/meter/meter as soon as it gets 'light out' even if it is cloudy.
I know that various algorithms predict the amount of sunlight and intensity for a time of day. I think that Brian Hamilton uses the predicted max and you can choose if the measured value exceeds say 75% that it counts as 'sunny' rather than cloudy or whatever.
I've been using that setup for a couple years. since pyranometers measure light rather than sunlight, any sky illumination will generate a value, so I assume that one can just choose what level you want to exceed and integrate the measured value above that level for quantity of light.
I'm interested in the comments that allude to measuring cloudiness, even at night, to get even more information about sunlight. For solar panels, it would be interesting to know how the site evaluation meters work, or if they just measure the amount of both cloudy and non-cloudy solar radiation?
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Most hobby solar sensors will show 0w/m2 at night so to measure clouds at night you need a different solution, cetainly that's true for my old VP1 and my current GW1003 station. I have seen homemade solutions on forums in the past.
Stuart
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The Blake-Larsen Sun Recorder is now marketed alongside the Campbell-Stokes =D> Blake-Larsen Sun Recorder - Wittich & Visser (https://wittich.nl/en/product/blake-larsen-sun-recorder/)
Enjoy,
Paul
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How would you go about purchase? Direct contact?
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The last I've heard was that Wittich-Visser had made some significant changes to the product and is selling direct, but referring some program support to Ole, but I think that is also being reduced. I'd suggest an email to Wittich, or complete the contact form on the Wittich site.
Enjoy,
Paul
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Most hobby solar sensors will show 0w/m2 at night so to measure clouds at night you need a different solution
Stuart
For the solar in a jar it does not need much modification to do this, just a black bottom to the jar is all.
For the lab flask solar in a jar method is a little more tricky to add the black bottom bit its doable.
You need a sponge that's about an inch in depth cut in a circle to match the lower half of the lab flask.
cut some aluminium foil to match the size of the sponge, glue it to the sponge, colour using a permanent
marker, it will need a few coats to get it black., make a hole in the center for the probe to fit. Now for the
tricky part and why it had to be a inch thick and foil needed, the aim is to get it up the thin neck of the flask
and it to open up once inside, that's the sponge's job, so gently scrunch up the sponge so it will fit into
the neck of the flask and push it up, give it a moment to open up some, then using a long, thin tool, gently
press the sponge to the top of the flask to open the sponge fully, you can then use sommat like a crochet
needle to gently hook the sponge using the center hole and pull it back to the bottom of the flask, then just
fit the probe and stopper and there ya have a dual solar/night cloud sensor, I used that type for a good few years up on my mast and it work well.
Also used the upside-down jar method after i moved having lost the flask, just painted the inside jar lid
black, hence upside-down method :)
The above will only work with weather display or other software that can setup both homemade sensors.
They also need tweaking for the summer time temps and winter time temps.
I am currently using a homemade probe in a jar method for my night cloud on my Davis setup, its not actually
a jar, its a low bowl, colour black internally, added polystyrene as a layer that covers about 1/2 the depth
paint that black, made a small hole for the Davis probe, then covered with a phone screen protector and
stuck it in place with outdoor tape and fixed in place so it didn't blow away, this too works very well once
you get the settings right, you also need to tweak during winter/summer times due to temp change.
That method to can be used as a dual solar sensor if i needed it to.
Whilst quite crude methods they work very well :) See davis method graphs for day and night below
As long as the night cloud temp sensor goes about 1C below the air temp then you've got a night cloud
sensor, the 1C is so you have enough range for the few cloud types