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  • Solar Panels

    Solar Panels 101

    I thought I would post this as I saw another thread today where the poster seemed confused as to what is the better solar panel, a mono or poly? http://www.solarwholesalers.com.au/s...-solar-panels/

    What is the best type of solar panels for my home, mono-crystalline or poly-crystalline?

    There is often great debate over whether you are better off with poly-crystalline cells in your solar panels or mono-crystalline solar cells in your solar panels.

    I think this question is one of the last things I would concern myself with if I were buying solar electricity panels and here is the reason why.

    When 2 solar panels are marketed at a particular wattage (say 250 watts) it means that (at standard test conditions) both will produce at least 250 watts, provided both of these panels have no negative power tolerance in their specifications.

    This is the case even though one of these panels may use polycrystalline cells and one of these panels may use monocrystalline cells.

    What is important to remember is that any slight differences in cell efficiency between polycrystalline or monocrystalline panels is already taken into account when they are rated and so is of little or no relevance to you as the end consumer.

    It may be that the mono crystalline panel in the example above is fractionally smaller than the poly crystalline panel that produces the same amount of power, because perhaps the mono crystalline cells used my be slightly more efficient but in the end both are going to produce the same amount of power.

    A better cell efficiency simply means that the mono crystalline panel might be fractionally smaller but if you look at the sizes of commercially available poly-crystalline panels and mono-crystalline panels of the same wattage (say 250 watts) they are very close to each other in size.

    Both types of solar cells usually have a similar temperature coefficient and so in practicality both are likely to produce an almost identical amount of power over time.

    Similarly, there is no evidence that either poly-crystalline solar panels or mono-crystalline solar panels decay at a different rate over time.

    This is why I would not be too concerned about whether the solar companies I talked too offered me mono-crystalline or poly-crystalline solar panels.

  • #2
    Amorphous (thin film) design, as used for almost all flexible panels, on the other hand are very different in their degradation over time (faster) but under some circumstances will not lose output as rapidly with partial shading when compared to crystalline cells.

    Most of the time the reduced output per unit area (efficiency) is low enough that their low light output still ends up worse than crystalline panels of the same size.

    If any forum members are (or were in the past) using thin film panels for a serious system, please jump in with your comments.
    Last edited by inetdog; 09-10-2015, 09:54 PM.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Originally posted by inetdog View Post
      Amorphous (thin film) design, as used for almost all flexible panels, on the other hand are very different in their degradation over time (faster) but under some circumstances will not lose output as rapidly with partial shading when compared to crystalline cells.

      Most of the time the reduced output per unit area (efficiency) is low enough that their low light output still ends up worse than crystalline panels of the same size.

      If any forum members are (or were in the past) using thin film panels for a serious system, please jump in with your comments.
      Good point about the thin films Dave. Sort of forgot about them, no one uses them any more in Oz

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      • #4
        I guess nobody is jumping in, but I'll do my part to reiterate the basics.

        Thin films are less efficient than mono/polycrystalline. That means a larger physical sized panel for the same given output. They may not have the 20 year lifespan that mono/crystallines do, especially when they are used full time. If your usage is temporary, or seasonally limited, then store them without any light striking them, as this will make them last longer.

        Unlike a mono/crystalline panel, where even small shadows from debris (wet leaves), overhead powerlines, flagpoles, and the like can essentially shut the panel down for all practical purposes, a thin-film only reduces its output by the part that is shaded. For a demonstration, you can cover half of a thin-film, and basically get only half the current output. You can put bullet holes in them, and only the missing "holes" are the part that has now reduced the output. At least this is the case with PowerFilm, which I own.

        Long term degradation is caused by *consistent* shadows that appear in the same place every day at the shadow edge particularly. Fortunately, the earth moves which can limit this problem to a degree. BUT, I would caution against anyone *planning* on using these panels with consistent shadows that don't move, or move very very slowly during the day. Mono / polycrystalline panels limit shadow degradation typically by using bypass diodes that electrically cut the panel into two or more halves, thus limiting the amount of shadow degradation upon the now reverse-biased cells. Thin-films typically don't have that because the reverse-bias is spread out and not concentrated to a single cell(s), but there may be exceptions.

        In the case of Powerfilm, Which uses A-SI, and NOT "cigs" I also noticed a pretty good output when high-heat was applied. That is, when laid down upon hot cement at 100F, the output did not drop significantly to my amazement, other than not being precisely aimed at the sun. Fortunately, under test during the middle of summer, the sun was for all intent pretty much directly overhead during the meat of the solar-insolation period. This was a limited test for about 4 hours per day, so I don't know about a permanent installation laid upon hot cement.

        (Note about powerfilm's voltage rating: you'll commonly see 15.4v as the "nominal" operating voltage, but in fact they DO get up to 18-22v like one would expect)

        For me, one would have to really find a way to justify thin-film for serious homeowner use. Maybe if you live in a war-torn area, have lots of flying debris that can damage a mono/poly crystalline panel, have limited shadows that you just have absolutely NO way of avoiding, or need the flexibility of a folding or "rollable" panel to fit specialized mounting requirements, then ... maybe.

        For SERIOUS portable use, Powerfilm being at the high end of quality would be my only choice if I had to charge gear up in a rough environment.

        But again, for household fixed installation - you'd need some real justification.

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        • #5
          Originally posted by solar pete View Post
          Good point about the thin films Dave. Sort of forgot about them, no one uses them any more in Oz
          Actually there are some very large Utility sized arrays (> 100MW) out in So CA that are using thin film (CdTe cells made by First Solar) along with single axis tracking.

          I imagine that having zero shade, the ability to face the sun all day and a very large array improves the economics of using thin film.

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          • #6
            Originally posted by SunEagle View Post
            Actually there are some very large Utility sized arrays (> 100MW) out in So CA that are using thin film (CdTe cells made by First Solar) along with single axis tracking.

            I imagine that having zero shade, the ability to face the sun all day and a very large array improves the economics of using thin film.
            Possibly, but the more rapid degradation from exposure to sunlight may still make them uneconomical in the long run.
            Some large solar installations were planned when crystalline Si was more expensive and got locked into thin film.
            Others were just investment opportunities to get tax credits and subsidies will little long term future.

            Materials other than Si may also make sense in concentrating solar systems or where multiple layer chemistries in one panel are used to harvest a larger part of the light spectrum, but that is not necessarily thin film.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #7
              Originally posted by inetdog View Post
              Possibly, but the more rapid degradation from exposure to sunlight may still make them uneconomical in the long run.
              Some large solar installations were planned when crystalline Si was more expensive and got locked into thin film.
              Others were just investment opportunities to get tax credits and subsidies will little long term future.

              Materials other than Si may also make sense in concentrating solar systems or where multiple layer chemistries in one panel are used to harvest a larger part of the light spectrum, but that is not necessarily thin film.
              I agree with you that pv cell material will continue to be explored in the search of finding a longer lasting, cheaper and higher output cells.

              I just wanted to point out that First Solar seems to have sold quite a few CdTe thin film panels for quite a number of large arrays around the world so someone has invested a few pennies into that technology.

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              • #8
                I've been through this before - because of the additional variables that thin-film introduces beyond mono/poly crystalline, those variables lead to an endless all out war of bench-racing specifications, and self-appointed keyboard CFO's that suddenly appear.

                Like LFP battery discussions, they are not for everybody, but in certain cases make total sense. It comes down to juggling all the ball-variables, and if it works for your needs, then go for it.

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                • #9
                  What are the thoughts/benefits on bifacial/PERC mono panels ?

                  Looks like solar world is also getting into them in addition to sunpreme.

                  Example bifacial 290W mono panel

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                  • #10
                    Originally posted by lanb View Post
                    What are the thoughts/benefits on bifacial/PERC mono panels ?

                    Looks like solar world is also getting into them in addition to sunpreme.

                    Example bifacial 290W mono panel
                    Bifacials are mostly a gimmick. Output from the backside of a panel is directly related to the input to the backside. a panel sittting 6" above a surface will have little to no input to the backside of a panel, hence little or no output from that side of the panel in that orientation. Nothing in - nothing out. It's that simple.

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                    • #11
                      If there was no/minimal price difference between a regular and bifacial panel, which would you choose and why ?

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                      • #12
                        Originally posted by J.P.M. View Post
                        Bifacials are mostly a gimmick. Output from the backside of a panel is directly related to the input to the backside. a panel sitttin g 6" above a surface will have little to no input to the backside of a panel, hence little or no output from that side of the panel in that orientation. Nothing in - nothing out. It's that simple.
                        I got see some of these in action at the Solar Decathlon a few weeks ago. I believe Cal Poly San Luis Obispo was using bifacials on their south facing deck awning. They said the downward facing panels collected an addition 20% output that was reflected off the deck. It's a nice idea, but just not very efficient. One PV technology I was impressed with was a 40% transparent panel that was used on Cal State Sacramento's deck awning. You saw thin black wire embedded on clear glass that allows for about 40% sunlight to shine through to the deck below, while collecting electricity. They didn't report the efficiency.

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                        • #13
                          Originally posted by maximizese View Post
                          I got see some of these in action at the Solar Decathlon a few weeks ago. I believe Cal Poly San Luis Obispo was using bifacials on their south facing deck awning. They said the downward facing panels collected an addition 20% output that was reflected off the deck. It's a nice idea, but just not very efficient. One PV technology I was impressed with was a 40% transparent panel that was used on Cal State Sacramento's deck awning. You saw thin black wire embedded on clear glass that allows for about 40% sunlight to shine through to the deck below, while collecting electricity. They didn't report the efficiency.
                          If you just let some of the light that reaches the back of the cell pass through rather than bouncing it back for another pass through the active junction region you are bound to lose some efficiency.
                          If the junction is very efficient at capturing light of the relevant frequency on the first trip and all that you are letting through is the useless frequencies, then the efficiency loss would be minimal. The light coming through would be blue-green tinted since the redder frequencies are the ones that the panel is using.
                          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                          • #14
                            solar panels

                            is solar world going out of business

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                            • #15
                              Originally posted by harleydee View Post
                              is solar world going out of business
                              As of today they are not....but there is "potential"

                              This article is dated November 3rd 2015 regarding a law suit that is pending. SolarWorld just had a key motion ro reconsider denied


                              *********
                              Indeed, in its 2014 earnings report, released this March, it stated, "If courts should decide that the silicon supplier is entitled to damages from our subsidiary SolarWorld Industries Sachsen GmbH [formerly Deutsche Solar GmbH], this would have a considerable negative impact on the company’s liquidity position, possibly even threatening the company’s continued existence."

                              Read more:
                              *********

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