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  • #31
    Originally posted by Wavelet8 View Post
    .... their info below:

    • DC losses in string inverter systems (including those with optimizers) are typically higher than in microinverter systems. This means that string inverter system simulations may show lower clipping losses at a given DC:AC ratio. However, these additional DC losses also impact the nominal DC:AC ratio and result in better nominal DC:AC ratios for microinverters systems for a given pairing.
    in a properly designed install, that is horse pucky. (an outright lie)


    • Clipping losses in systems are typically very low compared to other sources of losses, such as orientation factors, soiling, shading, and thermal losses. Additionally, clipping losses over time decrease as modules degradation takes place, while other loss factors such as soiling and shading generally increase.
    and their point being ??? Same losses over both systems, no win there.

    How about getting up on the roof to replace a failed microinverter, and having to take apart several panels to get to the dud ? Way easier to replace a string inverter on the ground, it can be done by the time you get the ladder and safety harness rigged.
    At year 12, when you get the warranty replacement micro and get up to the roof, you are going to find sized hardware, maybe incompatible connectors..... just too much fun for me.

    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister

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    • #32
      I guess getting up on the roof to fix them would be a concern after the 25 year warranty period expired on equipment and labor but the same connector changes could just as likely happen with the optimizer modules. However, the warranty period it's so far out the playing field may have completely changed by then.

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      • #33
        Originally posted by Wavelet8 View Post
        I guess getting up on the roof to fix them would be a concern after the 25 year warranty period expired on equipment and labor
        Or sooner if the warranty doesn't cover what you thought it did or the company is no longer in business.

        Originally posted by Wavelet8 View Post
        but the same connector changes could just as likely happen with the optimizer modules. However, the warranty period it's so far out the playing field may have completely changed by then.
        Yes, so why have either one if they are not needed? At least with microinverters you're not stuck with the same make/model if you need a replacement. By the way where are you getting the idea that DC from the panels is inherently less efficient than AC? The losses are managed by wire sizing and if you keep them the same, for the sake of argument, DC at higher voltage/lower current wins.

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        • #34
          Originally posted by Wavelet8 View Post
          The micro inverters do increase the number of failure points but they also limit the failure amount on your system. If you loose your string inverter you loose all your solar generation for however long it takes to replace it. If you loose a micro inverter your system generally continues to function with minimal losses for however long it takes to replace it. Replacement times do tend to very wildly from complaining on customer reviews I’ve read.

          The string inverters generally had a 10 year warranty that could be extended for for additional cost. The micro inverters had a 25 year manufactures warranty the same as the solar panels.

          I went with LG panels and micro inverters because I had tree’s along the side of my house and an enphase combiner box made sense in my application. At the time sun power hadn’t switched over to using the enphase micro inverters. I was told that the sun power micro inverters were less dependable and had higher energy losses than the enphase models? Do not really know if the reliability was really any worse? Just what I was told.

          So, i’m Interested in what you all think about the compared energy losses on a solar system using a string inverter vs micro inverters typically.

          So, if you don’t mind let’s skip the reasons between installing one type of system vs the other and keep it basic.

          if you had two solar systems side by side with the same number of panels each of the same wattage and type.

          Generally, Which system would have lower conversion energy losses?
          string vs micro’s?



          The reasons for one system over the other are basic and need to be not only not skipped over, but need to be one of the first considerations in the preliminary design phase of a project.

          With an average to large system, the output loss from 1 or 2 panels on, say, a 20 panel system may go unnoticed, maybe for some time. One thing I've seen in my HOA is that while most folks are quick to state individual panel monitoring as a big plus in the micro vs. string controversy, and one of the top reasons they chose a microinverter equipped system vs. a string inverter system, few, if any, ever look at their array's output, much less track it, after the novelty wears off after a week or two. Human nature. Possible/likely result: Without owners' keeping an eye on things, the advantage of panel level monitoring is mostly lost with system losses going unnoticed. If the single string inverter craps out, My guess is the effect is not subtle and quickly known - or at least/hopefully as quickly as the last POCO bill (if the owner bothers to look at it).

          A micro inverter equipped system can produce greater annual output than a string inverter equipped system. But, 2 points:
          1.) Any inverter system cannot restore output that was not there in the first place. An array that has its annual POA irradiance decreased by 20 % due to shade will probably have at least 20% less annual output than if that same shade was not present - micro or string inverter equipped. Micros can prevent the further loss due to shade that string inverters incur. Micros do have some advantage in that respect.
          2.) If annual shading shade is large enough to consider micros, maybe it's large enough that perhaps the application won't be cost effective. Micros can restore some of the shading loss - that loss mostly being from the inherent way the panels operate.
          PV is an expensive way to produce electricity. Putting arrays in any shade decreases cost effectiveness. That decrease needs careful consideration. Simply using micros will not address the question completely.

          Micros may be warranted for a longer period, but the warranties may not include labor or other costs such as shipping. And even if they do, getting at a micro in the middle of a poorly thought out or space limited (as many/most often are) may well require removal/replacement of one or several panels. Disturbing an array is never a good thing, with what's disturbed and how many things disturbed usually not adding to a system's future reliability. Then, there's the wear/tear on a roof which most folks never consider but can be consequential, especially if clay/concrete tiles are involved. And, what happens when the next micro craps out ? Answer: More of the same.

          On line losses: Most well designed systems on a roof or those with short runs to a string inverter will have relatively small line losses. Those losses will probably be a bit lower with string inverter equipped systems but I'm not sure the difference is enough to worry about, especially with a well designed system of either type with adequate wiring and design.

          So, if you consider "lower conversion energy losses" to be measurable by which inverter system will produce greater annual output for otherwise identical side/side systems, the answer is, it depends on shading.

          With no shading, either system produce about the same output. The argument that system reliability and maint. for a string inverter system will be better will tip the choice for a lot of informed people in that direction. String inverter systems have fewer parts and so fewer failure points. KISS applies. As the amount of annual production loss due to shade increases, microinverter equipped systems begin to have an advantage, or, perhaps to some, the disadvantages of micros are counterbalanced by possible increased annual production. But, to repeat, micros will not make more energy appear that was not present in the first place due to shading.

          An absurd but easily understandable situation: An array with no direct incident radiation will produce about the same amount of output regardless of inverter system used, string or micro. Micros will restore some of the energy lost due to the inherent characteristic of panels that make them somewhat all or nothing propositions as far as utilizing incident radiation in concerned, but not much more.

          The plusses/minuses of each method need to be considered on an application by application basis, and there is more than one thing to be considered in the analysis.

          Take what you may want of the above. Scrap the rest.

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          • #35
            Line losses between the panels and the PoCo meter will be there, even if ignored, in
            any system. I presume the original reason for micros was that system design becomes
            a no brainer. Preventing shading on a panel from affecting an entire string is an advantage,
            but a lot of shading is no way to build a PV array.

            A problem with micros comes with multiple orientation arrays. Strings can take advantage
            of using a reduced size inverter, micros must be fully equipped at every panel. Bruce Roe

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