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  • bcroe
    replied
    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

    Leave a comment:


  • J.P.M.
    replied
    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.) [U]Any[/U] 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 [U]further[/U] 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.

    Leave a comment:


  • sdold
    replied
    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.

    Leave a comment:


  • Wavelet8
    replied
    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.

    Leave a comment:


  • Mike90250
    replied
    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.

    Leave a comment:


  • Wavelet8
    replied
    Those are line or transmission losses. Most solar systems on roofs don’t have to deal with those problems. I’m more referring to conversion losses. Is it more efficient to have have one big inverter or several smaller converters. The efficiency of the inverters does matter but if you believe the micro inverter companies they believe they are generally more efficient. See 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.
    • 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.

    Leave a comment:


  • bcroe
    replied
    For efficiency, the micros will force you to 240VAC at the panels. My strings run at 400VDC over hundreds
    of feet, at far less power loss. This will probably over ride the inverter efficiency differences in the big picture.
    And its big buck difference for the extra copper and associated hardware.

    I have a problem with micro radio interference generators being spread over hundreds of feet. My
    string inverters can afford to spend more at just one spot to contain this. And if that was inadequate,
    I could afford to spend more at just one spot to contain remaining interference. Bruce Roe
    Last edited by bcroe; 05-24-2019, 09:07 PM.

    Leave a comment:


  • Mike90250
    replied
    Originally posted by Wavelet8 View Post
    ...

    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.
    Gotta read the specs on the inverters.. some are 98% some 97% some 99%

    Leave a comment:


  • Wavelet8
    replied
    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?




    Leave a comment:


  • J.P.M.
    replied
    Originally posted by MQGalano View Post
    the advantage of microinverts is that you have per panel monitoring of production.
    And as we've noted, the shine quickly wears off that apple for most everyone.

    Micros can help with shading but putting an array in partial or greater shade may make the whole thing non cost effective or at least make the time to breakeven longer to the point it's counterproductive to do PV in the first place. Some sites are just not good for solar applications. Besides, micros (or optimizers for that matter) can't produce electricity from nothing or create power where solar irradiation is not present.

    Leave a comment:


  • solar pete
    replied
    Originally posted by MQGalano View Post
    the advantage of microinverts is that you have per panel monitoring of production.
    Who cares, its simply not required, all micro do is add more failure points, they keep bringing out new models that are supposed to be better but I think the same issues applies, the roof is not the place to have sensitive electronics, give me a good old fashioned string inverter sitting in the shade any-day, you know what the real advantage of string inverters is.....they just work.

    Leave a comment:


  • MQGalano
    replied
    the advantage of microinverts is that you have per panel monitoring of production.

    Leave a comment:


  • J.P.M.
    replied
    Originally posted by solar pete View Post

    Yep I could not possibly agree more, crickey we actually agree on something
    So if we agree that adequate resource availability is one requisite for residential PV design, looks like we agree on the blinding flash of the obvious that micros are often and usually counterproductive to good design.

    Leave a comment:


  • solar pete
    replied
    Originally posted by J.P.M. View Post

    While product quality may, in all likelihood have a lot to do with the problem, I've got to see some of this having to do with the idea of doing something in more complicated ways than necessary with more parts when simpler ways would allow leads to more things failing. It's called KISS and probably been around close to forever.
    Yep I could not possibly agree more, crickey we actually agree on something

    Leave a comment:


  • J.P.M.
    replied
    Originally posted by solar pete View Post
    I just wonder how long it will be before they have to replace the current miro inverters with the next batch that are supposed to be better, well yes we are installers who made the mistake of getting into micro inverters and we have replaced hundreds of them, not anymore though we now refuse to use the crap things
    While product quality may, in all likelihood have a lot to do with the problem, I've got to see some of this having to do with the idea of doing something in more complicated ways than necessary with more parts when simpler ways would allow leads to more things failing. It's called KISS and probably been around close to forever.

    Leave a comment:

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