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  • #16
    You didnt mention Rapid Shutdown compliance which will become an issue as jurisdictions implement that part of the code. So far only microinverters and SolarEdge have that capability integrated. SMA has Tigo which can be installed with most string inverters.
    9 kW solar. Driving EVs since 2012

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    • #17
      Originally posted by mjlef View Post

      Actually, multiple points of failure are a great feature compared with a single point of failure. A single point of failure takes down the whole system. Multiple only takes out a small part of the system, which is a benefit to microinvertors.
      Design and build it fit for purpose with as few components that have sufficient quality for the duty will likely produce a system with the GREATEST MTBF - that is, lower failure rate/downtime.

      ore stuff, more goes wrong - but only if well designed and built in the first place.

      Aside from the idea that for most users who probably look at their output about as often as they look at their electric meter - that is - not much if at all, I'd wager that a zero output system problem will probably get noticed sooner than 1 or 2 panels under producing and gesulting in a few % penalty in output, particularly after day/day out put variation due to weather.

      Its' about probability. More stuff - higher probability of something going wrong.
      Last edited by J.P.M.; 01-13-2020, 12:19 PM. Reason: Clarified.

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      • #18
        Originally posted by mjlef
        As for a 700 foot line, voltage drop exists in AC or DC lines. No difference. In my case all lines are very short.
        The microinverters give us MPPT (Maximum Power Point Tracking) for each PV panel, increasing yield by typically 5-20% over
        simpler string inverters. String systems have had fires since panel voltages are summed and can be very high, causing arcing.

        "Design is a no brainer" is a great feature, allowing easy system expansion, and module level monitoring. It is a little more work since you need to mount more inverters and wire them, but that happens very quickly. And I do not have to worry much about a neighbor's tree getting too tall and causing shading on a few panels or the effect one one panel going bad. Without power optimizers, a string inverter system has a huge output drop because of shading. Microinverter systems just generate more power than string inverters, even when power optimizers are used.
        Not everyone needs be concerned with wire length. But if my farthest panel was connected to a microinverter,
        the wire loop to the meter would be 1500 feet long. Running that distance at 240VAC would require twice as
        much copper as running panel 360VDC for the same losses, I would NOT call that, no difference. But that is
        NOT the only issue. The PoCo loves to run the line at or above the legal maximum voltage. Any drop in the
        line fed by inverters adds to that, often enough causing inverter monitors to cause overvoltage shutdown. The
        DC line losses do not contribute to the effect, so it is minimized by running as much of the length as possible
        with panel DC voltage.

        Are string systems more fire prone, where is that reported? What about all those micros each a potential fire,
        especially if not individually fused?

        MPPT may be a point at any given instant, but the curve running very close to that same efficiency is
        somewhat broad. I have measured enough panel operating voltages to see that. The only way to approach
        20% loss in a string is with extremely mismatched panels or a fault. I doubt I exceed 2% anywhere.

        If shade is a serious problem, go with micros. Here I sometimes lose a string at a time sun is fading, the
        overall loss is only a few percent, and micros could only recover a fraction of that. Gaining a tiny bit more
        is pointless if more is burned up in the power transmission.

        In my case expansion was actually easier with a string system, because no inverters or
        consolidated power wire was added. Added strings aligned to peak at different times
        of day may share the same inverter(s), which also happens under cloudy skies. Micros
        are essentially unable to do this, resulting in much more idle equipment. Bruce Roe

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