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  • Grid tie in system advice

    At the moment I am getting ready to put together a grid tie in solar system and I was looking for some advice.
    I plan 15-330w panels specs:
    Max voltage- 37.8V
    Max current- 8.74A
    Max fuse rating- 20A

    Zeversolar 5kw, I havent got the inverter yet but I have some specs
    max DC-5300w
    Max input- 600V
    MPP voltage range- 100-520v/360v
    max input per MPP- 11A
    2 MPP

    I am guessing I would have to run 2 strings. String 1 is 8 string 2 is 7 panels. Would this be a problem not having an even number of panels? I could run 8/8 string but that would bring my
    wattage to 5280watt when Max is 5300w. I was also going to have a separate breaker box per string with each having 10A DC fuse,16A breaker, 1000V surge and about 5 -6 meters between breaker box and panels. On the AC side not sure what the breaker will be yet looking into local laws, but advice would be good. One thing is AC line would be about 200 meters from the the grid. Would this be a problem with putting power back in?
    Much appreciated for any advice you can give me.

  • #2
    Spec sheet on the inverter has 6500W DC for STC of panels. That's what your 16*330 -> 5280 would be compared against as they're rated under STC (Standard Test Conditions 1000W/m irradiance and 25C/77F with direct illumination. STC is the idealized test conditions, and not likely to actually ever hit it, let alone exceed it. You can get that amount amount of irradiance (or close to it, but if the air is 25C, then you're panels are more in the 50-55C range (about 25-30C above ambient air temps) and your efficiency drops ~0.5 for ever deg C above 25C (depending on the panels some may be 0.3% for ever deg C above 25C) So let's say a nice cool 20C day and it's 45C out there, that's 20C above or 10% efficiency loss do to temps.

    That said, that 'Maximum DC Power at cos (phi) = 1 is the maximum usable DC power. Anything above is waste, not that the panels couldn't have provided more, just that the inverter would clip if it did (hence the 6500Wp for STC of panels rating)

    Breaker should be at least 125% of current, so for 23A max AC current feed -> 30A breaker will suffice. Of course talk to your AHJ to make sure you do things according to their demand. Most want that breaker to be on the bottom of the panel (i.e. feed from Solar as far away from feed in from grid as possible in the panel.)

    You could have some line voltage drop, in that 200m, is that where the meter is? As long as your side's voltage level is slightly higher than the grid at the meter, you will feed towards the meter.