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I currently read a few papers and one of them stated to forecast solar irradiance using measures of solar radiation.
I hope this question is not trivial as I'm actually from germany, but if there is a specific difference between these two terms I would be glad if someone could explain it.

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2 Answers 2

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Technically (at least in solar energy industry):

  • Irradiance is the instant power of solar radiation per unit area, it is measured in W/m2 (it is instantaneous, therefore no time dimension in the units).

  • Irradiation is the quantity of solar energy per unit area, measured in Wh/m2/time (day or year or so; time dimension here is relevant).

Practically, the terms are often confused.

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    $\begingroup$ W = J/s, so I don't understand your statement of no time dimension in the units...? $\endgroup$ Commented Feb 22, 2023 at 12:56
  • $\begingroup$ @AtmosphericPrisonEscape right, very true correction. But I think what he's getting at is that the second one actually is a measure OVER a time. Similar to how velocity at any instant has the units of time (and tends to change over time of course typically)... but distance is actually more intimately linked to time because it's an integral over a chosen time period? I always have gotten too confused with W vs kWhr and such myself :-p $\endgroup$ Commented Feb 23, 2023 at 2:15
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    $\begingroup$ Wh/m2 has no meaning unless you include a time period, such as per day, per hour, or per year. But, of course, once you do that there is no difference between the two definitions. $\endgroup$
    – Mark
    Commented Feb 25, 2023 at 2:56
  • $\begingroup$ Thanks for all very relevant comments so far. Answer edited accordingly. Well, I still have things to study more here. $\endgroup$
    – jurajb
    Commented Feb 27, 2023 at 7:55
  • $\begingroup$ The definitions are now identical, except for a constant which depends on the value you choose for the time period in the second one. If you choose 1 hour, the definition becomes Whr/m2/hr - the hours cancel, leaving W/m2, which is the same as the first definition. $\endgroup$
    – Mark
    Commented Feb 28, 2023 at 20:42
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Solar irradiation is a measure of the energy delivered by the sun per unit area, watts or joules per square metre for example.. It is often recorded over a specific time period, so it is very much to do with solar radiation, but not exactly the same thing.

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  • $\begingroup$ that already explains a lot, but is irradiation and irradiance also the same? regarding [quora.com/… it seems that irradiation is not very much used. So what would you say is the actual difference between solar irradiance and solar radiation? in your answer you only refer to irradiation, it would be really nice if you could compare the terms if that's possible $\endgroup$
    – Marcel H.
    Commented Jul 18, 2019 at 23:01
  • $\begingroup$ I'm sorry, that link didn't show up correctly: quora.com/… $\endgroup$
    – Marcel H.
    Commented Jul 21, 2019 at 12:54
  • $\begingroup$ Solar radiation is the radiation emitted by the sun and without which there would be no advanced life on Earth. Nearly all living things depend on it. $\endgroup$ Commented Jul 21, 2019 at 13:02
  • $\begingroup$ okay, that helped a lot! thank you very much, so I guess solar radiation is just a term describing the radiation coming from the sun, whereas solar irradiation is a scientific term describing a power per unit area ratio $\endgroup$
    – Marcel H.
    Commented Jul 21, 2019 at 13:08
  • $\begingroup$ That's right, you've got it! $\endgroup$ Commented Jul 21, 2019 at 13:56

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