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What is "Light Soaking", as it affects pv production?

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  • What is "Light Soaking", as it affects pv production?

    Alright. I ran across this term today, and i'd not heard it before. A panel rep was telling me that his #'s would be higher because a given calculator "doesn't include the 3% gain from light soaking [and the power tolerance is wrong]."

    So I start looking into light soaking and all I find is tech papers when I want a simple explanation. Anyone got one? It seems it has to do with testing - specifically the flash test for base wattage? Any thoughts?

  • #2
    Term used by scammers to make there system sound better. Yes, the condition exists but does not produce enough extra power that can be calculated in. It's a panels ability to produce more power before it warms up to operating temperature. So the panel produces an extra 3% the first 10-15 minutes of the day. Not a big enough increase when the panels are under producing due to low sun angles.

    WWW

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    • #3
      @ Wy Wolf - huh. "a panels ability to produce more power before it warms up to operating temperature". huh. Panels operate at ambient, so... so how are we lower than operating temperature? unless your talking about noct values or mpp values of some definition or another? Is this documented somewhere? You happen to have any good links?

      What's more, if a panels production derate is soiling, angle of incidence, module mismatch, irradiance, temperatures, and a few other distinctions, how is this "light soaking" not accounted for already?

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      • Wy_White_Wolf
        Wy_White_Wolf commented
        Editing a comment
        When the sun first comes up they are at ambient temperature. But because of there dark color the sun quickly warms them up to higher than ambient. There normal operating temperature is 20 to 30F above ambient. It's well documented that panels produce more when cold.

        It's not accounted for because it such a small increase. A 3% increase that decreases to zero over 10 minutes will be about a 0.01% total production difference. That works out to less than 10WH a day per 1KW of array. Miniscule compared to everything else you listed.

        WWW

    • #4
      Originally posted by Rocksteady2R View Post
      @ Wy Wolf - huh. "a panels ability to produce more power before it warms up to operating temperature". huh. Panels operate at ambient, so... so how are we lower than operating temperature? unless your talking about noct values or mpp values of some definition or another? Is this documented somewhere? You happen to have any good links?

      What's more, if a panels production derate is soiling, angle of incidence, module mismatch, irradiance, temperatures, and a few other distinctions, how is this "light soaking" not accounted for already?
      It is a general characteristic of silicon PV panels that they run at a higher voltage (Vmp) and higher power for a given amount of light when they are cooler.

      Bench testing of panels, using flash light sources, takes place with the panels at a specified temperature and not allowing them to warm up from the light source before measuring.
      This is the technique generally used for the STC numbers.
      PTC testing adjusts these results to allow the panels themselves to warm up while controlling the ambient temperature. Those numbers are generally lower.

      So if you uncover a panel or the sun comes out from behind a cloud the panel will start to warm up above the ambient temperature and the output will decrease.

      I would not necessarily use the term light soaking to describe this, and it definitely would not increase the output.

      There may be a mechanism by which "virgin" silicon cells do not produce maximum output until they have been exposed to light for some time, but if so I have never heard of it before.
      They are not like lead acid batteries which require cycling of the active materials (commissioning) to produce maximum capacity.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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      • #5
        It's a B.S. term.

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        • #6
          J.P.M. , But why do you say that? What about it makes you discount it as relevant?

          inetdog Thanks! That starts to put things together for me.

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          • #7
            [QUOTE=Rocksteady2R;n333806]J.P.M. , But why do you say that? What about it makes you discount it as relevant?

            Since you ask:

            Because I think that, while I'm ignorant about most things, after returning to school 40+ years ago because of an interest in solar energy, getting multiple degrees in mechanical engineering, and subsequently devouring most everything I could find on the subject of solar energy while working as a mechanical engineer in various capacities and levels of responsibility and authority unrelated to solar, I've developed something of a B.S.ometer when, what may well be valid research is, to quote Kipling (slightly out of context) "Twisted by knaves to make a trap for fools".

            The use of the term "light soaking" lit up my B.S. meter.

            Light soaking, such as it may exist, seems to be, at this time at least, a small effect that may manifest by increasing the fill factor upon initial startup and be present after a few (20-50 ??) hours or so as the device settles in and has some molecular rearragement. This MAY result in a slight increase in efficiency over STC measured efficiency. The phenomenon, while it may exist, is not well documented in a quantitative way at this time.

            I write that it's B.S, because I have seen/read/watched shisters and conmen try and often successfully separate the ignorant from their money with twisting half truths and B.S. aided and abetted by that solar ignorance.

            I call B.S. because, to the degree that the phenomenon may exist, until it is better understood and mfg. processes devised to take advantage of it, it's necessary to assume it will exist in most every available solar PV device commonly available. Therefore, it's an advantage available to all, with no particular measurable and/or documentable advantage to any one mfg., except maybe
            as some peddler may conjure up to use as some bogus product feature.

            What does seem to be observable, however, is an initial "burn in" period for commonly available PV devices that lasts from a few months to a year or so during which device performance deteriorates slightly. Such degradation is not unusual and is expected. As an example only, I believe my array's panels lost very roughly about 2 - 3 % of their initial efficiency after about 12-14 months of operation and subsequently seem to have settled down to about 0.2% to 0.4% annual degradation or thereabouts. In general, it may be that such "light soaking" effects, to the degree they may exist at all, are 1.) Much smaller than the "burn in" degradation and therefore 2.) Already accounted for but masked or buried in with the burn in.

            Therefore, until documented and better understood, rather than discount light soaking as relevant, I dismiss it's use as IRrelevant marketing B.S.

            Take what you want of the above. Scrap the rest.
            Last edited by J.P.M.; 10-27-2016, 11:38 AM.

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