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I am supposed to calculate the irradiation of the sun at a certain geographic location and to be able to perform further calculations. For this I need the maximum value at clear sky. To determine this value i user pysolar.

So far to work done. I can enter the day and the cooridnates of a place and it gives me the irradiation at this place from 00:00 o'clock to 23:59 o'clock of the local time. (The function takes timezone deviation so pysolar shows the values from 00:00am local time).

As an example the city Iranshahr with latitude: 27.2012 and longitude: 60.686582 with the -4:30 hours deviation from UTC has the following values in figure Iranshahr here.

For comparison in figure Berlin you can also look at the irradiation of the same day in Berlin.

According to bibliothek description, this value is "watts per square meter w/m²", where 1000w/m² corresponds to one sun.

My question is: what does the returned value in W/M² mean? is it for a second? for a minute? for an hour? or a day? Based on this number, how can I calculate the maximum irradiation for the whole day. or do I need further calculations to be able to use this value.

Fritz Gerlich
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  • Hi and welcome to stackoverflow. I'm no expert in this area, but I think you're correct - you will need to do some more calculations. AFAIK, the Watts per meter squared is the flux - a time-independent measure of how much of something goes through an area. You'd calculate that by lat long, because it would vary depending on the angle of the sun. (Lower angle, smaller W.) I'm guessing you'd need to multiply it by time to get to Watt hours - which are what usable energy (like a battery) uses. – morric Aug 10 '21 at 09:48
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    Hi @morric. Many thanks for your reply. In the meantime, I have looked at a couple of web pages that have explained the conversion from W/M² to Joule and then Joule to Watt Hour/M²/Day. My problem relates more to whether anyone has had experience with pysolar in this sense to be able to confirm that this unit that pysolar returns is per minute. – Fritz Gerlich Aug 12 '21 at 14:45
  • Understandable. I would have hoped that the documentation would have confirmed the units of the returned value. Best of luck. – morric Aug 13 '21 at 10:48

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