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High voltage inverters

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  • bcroe
    replied
    Originally posted by TheBearF8 View Post
    . bcroe Thanks for the feedback, I'm interested to know more
    of the details, like what wire size and inverters you used, esp.
    Charts may cater to the most common situations, but will not cover the optimum
    solution for every situation. Most wire will handle 600V, it is not hard to find the
    resistance of a loop and calculate losses. My pair of 7.5KW inverters deliver about
    60A at 250VAC to the PoCo net metering. The installation originally used the existing
    600 foot loop of 4 gauge wire, which at 0.00025 ohm per foot, came to 0.150 ohms.
    60A through 0.15 ohm gives a 9VAC drop, or around 3.6%. I considered installing
    a 2/0 copper wire loop, which would have cost $2600. Instead I get the same
    performance by going to 4/0 aluminum wire, which cost only $650. The triplex
    direct burial wire included a 2/0 aluminum neutral, which does not effect efficiency
    since inverter current flows in the 240VAC wires.

    This reduced losses to less than 1/3 the previous. If you are running less than 15KW,
    you can easily do even better. My boxes at each end needed to be able to terminate
    the big aluminum wire, any house service 200A box can do that.

    The DC runs are mostly individual strings capable of 8A through 10 ga PV wire, up
    to a 400 foot loop. There the combiner box brings them into two 6 gauge loops, each
    near 500 feet to the pair of inverters. Losses vary, but can exceed 1 %.

    Feeds can be combined at the array or at the inverters. Combining them at the array
    gives the option of easily using as large wire as needed (or smaller if not), instead of
    continuing with PV wire to the inverter(s). Another thing, if your panels do not receive
    identical sun at all times (like shading), a combiner feed will gain some efficiency at
    reduced current. Individual feeds not shaded will remain just as lossy at full current
    while the next one carries no current.

    600V is a safety limit generally used in consumer situations. Since panel voltages
    are much higher in severe cold, and will hit open circuit voltage near 25% more
    than MPPT operation, working backwards from the limit and not risking blowing up
    my 7 year old FRONIUS inverters, panel MPPT operation comes to about 420VDC
    at 20F below zero, about 340VDC in hottest summer. Bruce Roe
    Last edited by bcroe; 10-13-2020, 10:43 PM.

    Leave a comment:


  • nwdiver
    replied
    Originally posted by TheBearF8 View Post

    nwdiver Thanks for the feedback. Most wire sizing charts/calculators I have run across all mention 2 or 4 AWG for voltages around 480V. Thus I had to look at 600VDC+ to cater for the run length and remain within the 6 AWG range which is what I found is the max wire size specd on most of inverters I looked at. Could you please explain how you managed to use 8 or 10 AWG

    Thanks
    Wire size has absolutely nothing to do with voltage as long as your wire is properly rated and THHN wire is rate to 600v. It's all about current. #10 is 'rated' for 30A but de-rating can reduce that to <15A. ~10A is fine.

    Most inverters either have independent MPP channels or terminals for up to 6 strings. Instead of investing in a combiner box and fuses it's more cost effective to just run a separate circuit for each string. If you have 3 strings then run 6 #10s.

    Leave a comment:


  • TheBearF8
    replied
    Originally posted by nwdiver View Post

    ~400' is nothing. I would use a SMA inverter, they're a bit more cost effective than Fronius unless you like the ability to see DC Voltage and current remotely. All 240v inverters have the same max operating DC voltage ~480v. Just run each string on an independent 10 or 8 AWG circuit. The line losses @ 8A would be < 2%... and if you oversize the array they're 'free' when the inverter is saturated, which is exactly when line losses would normally be highest. With panels as cheap as they are it may be more cost effective to add more watts than upsize the conductors from #10 to #8.
    nwdiver Thanks for the feedback. Most wire sizing charts/calculators I have run across all mention 2 or 4 AWG for voltages around 480V. Thus I had to look at 600VDC+ to cater for the run length and remain within the 6 AWG range which is what I found is the max wire size specd on most of inverters I looked at. Could you please explain how you managed to use 8 or 10 AWG

    Thanks

    Leave a comment:


  • TheBearF8
    replied
    Originally posted by bcroe View Post

    I have 400VDC panel strings up to 700ft from the house, with AC & DC losses in the 1%
    range. There is some direct burial aluminum cable keeping losses down, cost no more
    than several panels. Bruce Roe
    bcroe Thanks for the feedback, I'm interested to know more of the details, like what wire size and inverters you used, esp.

    Leave a comment:


  • nwdiver
    replied
    Originally posted by TheBearF8 View Post
    Hi all

    sadly I can only have my panels a fair distance from my house +/- 400ft. So I need to do high voltage DC

    I found the Fronius Primo which allows for +/-600 VDC And they look like great inverters

    But what other inverters are there that can operate at 600VDC - 1000VDC ?

    thanks in advance
    ~400' is nothing. I would use a SMA inverter, they're a bit more cost effective than Fronius unless you like the ability to see DC Voltage and current remotely. All 240v inverters have the same max operating DC voltage ~480v. Just run each string on an independent 10 or 8 AWG circuit. The line losses @ 8A would be < 2%... and if you oversize the array they're 'free' when the inverter is saturated, which is exactly when line losses would normally be highest. With panels as cheap as they are it may be more cost effective to add more watts than upsize the conductors from #10 to #8.

    Leave a comment:


  • bcroe
    replied
    Originally posted by TheBearF8 View Post
    Hi all
    sadly I can only have my panels a fair distance from my house +/- 400ft. So I need to do high voltage DC

    I found the Fronius Primo which allows for +/-600 VDC And they look like great inverters

    But what other inverters are there that can operate at 600VDC - 1000VDC ?
    I have 400VDC panel strings up to 700ft from the house, with AC & DC losses in the 1%
    range. There is some direct burial aluminum cable keeping losses down, cost no more
    than several panels. Bruce Roe

    Leave a comment:


  • Mike90250
    replied
    Is your house off-grid or on-grid ? Off-grid battery systems are generally 48V max, because of the HV DC hazard.

    Battery based systems have several options for a 600V MPPT battery charger (Morningstar, Schneider and Midnight )

    Grid tie systems regularly use 300 - 600V inverters, up to 10,000 watts, often with 2 strings into 2 independent MPPT channels.

    Leave a comment:


  • TheBearF8
    started a topic High voltage inverters

    High voltage inverters

    Hi all

    sadly I can only have my panels a fair distance from my house +/- 400ft. So I need to do high voltage DC

    I found the Fronius Primo which allows for +/-600 VDC And they look like great inverters

    But what other inverters are there that can operate at 600VDC - 1000VDC ?

    thanks in advance
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