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  • #16
    Pablo - What is your background that makes you the expert to make the statements you made?
    [SIGPIC][/SIGPIC]

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    • #17
      background

      I'm an engineer with 30 years in the electrical power industry, primarily doing application and sales work. I also have about 20KW of solar installed, some at my house, some at my office. Systems at the house are tracked, office has fixed orientation.

      I definitely don't claim to be an expert, but I do know a few things.

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      • #18
        Originally posted by Pablodro View Post
        You can go to the higher DC voltages, but that means putting panels in series and protection of DC circuits is more troublesome. For my money, I'd rather not have ~400VDC running across my property. If you connect your panels in series, you do keep current down and elevate voltage, but safety is arguably compromised and a single bad cell (or bird mess) can bring down a whole string.
        I am trying to figure out, just what voltage you would recommend? AC or DC for 300'? I would
        definitely not want inverters out in a field somewhere, so mine would be DC. Voltage running across
        my entire property buried in conduit really doesn't worry me. The exposed PV array is my concern,
        and I have a comprehensive procedure for any work on that.

        A single cell isn't going to bring down a whole string, just reduce its output. The bypass diode will
        come into conduction, and in my case I have a 700 cell string instead of a 720 cell string. With
        multiple strings feeding an MPP circuit, it will find a compromise operating point between those limits.
        Here I have a panel with a known fault, its going to stay right where it is till this snow is gone. The panel
        is running about 12V low. My clamp on has seen this string deliver 7A at some 370 VDC, not down.
        Bruce Roe

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        • #19
          What it really comes down to is which configuration gives you the highest effective operating voltage over the long wire run (while staying below 600 V DC or RMS.

          If you go with AC, then for a really long run you have the option available of putting a transformer (~$1000 give or take) at each end of the run and transporting 600V AC.
          Compare the cost of the transformers considering the cost of the larger gauge aluminum wire for lower voltage and the risk of somebody stealing the inverters or the wire.
          I would avoid stringing a long run of copper where it might get stolen.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #20
            Trasformers

            Originally posted by inetdog
            If you go with AC, then for a really long run you have the option available of
            putting a transformer (~$1000 give or take) at each end of the run and transporting 600V AC.
            Compare the cost of the transformers considering the cost of the larger gauge aluminum wire
            for lower voltage and the risk of somebody stealing the inverters or the wire.
            I looked at transformers for my AC loop. Maybe an auto transformer style, a 5KW unit could
            boost 15KW by 30%, and back down. It could reduce peak wire loses 40%. BUT those 2
            units would be connected 24/7, and they use power ALL THE TIME. Boosting more than 30%
            will take bigger transformers, more standby power. A cheaper grade of iron will have much
            more loss. Considering that they are always on, they'd cancel any savings in wire loss. My
            conclusion; buy bigger wire. Bruce Roe

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            • #21
              For a remote array The only cost effective way to do it is to run DC from the array to the inverter and mount the inverter as close to the meter or house as possible.
              I will always do it this way. Although I will put a combiner at the array it is only to serve as a means to disconnect each string.
              I have found that it is easier and less costly to run individual strings and do the actual combining at the inverter.
              It is much easier to pull 8 #10 several hundred feet through a conduit than to pull #2 0r #4 the same distance.
              NABCEP certified Technical Sales Professional

              [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

              [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

              [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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