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  • AC or DC Solar Panels in Extreme Heat?

    I live in Palm Springs, CA where the temperature 4 months of the year is in the 100s, sometimes in the 110s. One solar installer wants to sell me DC Solar panels (Canadian Solar), and the other wants to sell me AC Solar panels (SunPower). I have done my research and have a good understanding of the difference between the two. My question: Would one type have preference over the other type under the extreme heat we experience here in the desert? Which panel, the AC or the DC, is likely to give me the least trouble here in the desert?

  • #2
    panel performance is going to be about the same.
    A dc Panel with the inverter in a nice cool place might perform a bit better.
    Ask the SP dealer about using a string inverter and mounting inside. SP panels have a very good temperature coefficient.
    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)

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    • #3
      Originally posted by Taylori View Post
      One solar installer wants to sell me DC Solar panels (Canadian Solar), and the other wants to sell me AC Solar panels (SunPower).
      There is no such thing as an AC solar panel. Everyone of them is DC. I suspect the one is bidding micro inverters on each panel.
      MSEE, PE

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      • #4
        Originally posted by Sunking View Post
        There is no such thing as an AC solar panel. Everyone of them is DC. I suspect the one is bidding micro inverters on each panel.
        Yes that would be the assumption.
        The industry has started to call modules with the micro inverters attached like Sunpower and Westinghouse AC panels. This probably started with gosolarcalifornia dot org calling them that.
        As Callifornia goes so goes the country.
        I know I know........................
        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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        • #5
          Originally posted by Naptown View Post
          panel performance is going to be about the same.
          A dc Panel with the inverter in a nice cool place might perform a bit better.
          Ask the SP dealer about using a string inverter and mounting inside. SP panels have a very good temperature coefficient.
          The SunPower dealer does propose mounting a string inverter inside the garage, which, although not in the direct sun, still gets quite hot in the summer. Everything I've read about the SP panels tells me that they are the "cadillac" of DC solar panels. I posed the question because I am concerned about the performance of AC solar panels, each with its own micro-inverter, in extreme heat year after year after year. Common sense tells me that the DC system with the inverter in the garage is going to survive better in the hot sun, but I don't really know. I'm unable to find any field data to either support or refute that belief . . . perhaps because the AC systems are so new.

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          • #6
            Originally posted by Sunking View Post
            There is no such thing as an AC solar panel. Everyone of them is DC. I suspect the one is bidding micro inverters on each panel.
            I believe you will find that solar panels with built in micro-inverters are called AC solar panels as a simple way of distinguishing them from DC solar panels, at least by some manufacturers, as well as others. See http://us.sunpowercorp.com/homes/products-services.

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            • #7
              Originally posted by Taylori View Post
              I believe you will find that solar panels with built in micro-inverters are called AC solar panels as a simple way of distinguishing them from DC solar panels, at least by some manufacturers, as well as others. See http://us.sunpowercorp.com/homes/products-services.
              Sales trash talk - nothing more - like on the playground in any big city
              [SIGPIC][/SIGPIC]

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              • #8
                Originally posted by russ View Post
                Sales trash talk - nothing more - like on the playground in any big city
                Perhaps, but as an uninformed consumer interested in buying a solar system, it makes a lot of sense to me: DC power leaves the DC panel, and AC power leaves the AC panel.

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                • #9
                  Originally posted by Taylori View Post
                  Perhaps, but as an uninformed consumer interested in buying a solar system, it makes a lot of sense to me: DC power leaves the DC panel, and AC power leaves the AC panel.
                  Might make sense to you but it is meaningless - by that definition any panel using a micro inverter would be an AC panel
                  [SIGPIC][/SIGPIC]

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                  • #10
                    Originally posted by jzchen
                    I know there is a concern about DC over long wire runs. That is why we use AC from the electric company. It can travel long wires without much degradation in power. The question is what is considered a long run for DC. [B]Actually DC is preferred for high voltages and long distance transmission
                    [/B]
                    There is also a safety concern over the voltage created by stringing the panels in series. This creates a very high voltage. The claim is that using a microinverter makes the wiring safer, ie. less likely to arc fault.[B]The moon or a star may fall on your house tonight as well - those concerns you mention are not really concerns - except possibly to a salesman who has a few trick words and no knowledge.[/B]

                    One last thing is that if one panel goes down for whatever reason, then the others, (at least on that string,) only work at that capacity. If it completely shuts off, so do the others. It is harder to diagnose which panel went bad..[B] You heard that from a solar pro like Naptown or KRenn or others here? Not a big deal.[/B]

                    Downsides to "AC panels," or panels with microinverters, is that you have a whole bunch of inverters that can go bad, as opposed to one, although they there is one enphase inverter warranted for 25 yrs[B] I would suggest you talk to solar companies and relay their points back here. When you are told you have found one that is not blowing smoke at you the guys will let you know.[/B]
                    [B]
                    Another suggestion would to be to stay totally away from green sites in regards to RE. They contain about 99.99% wrong information with youtube being even worse.[/B]
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                    • #11
                      Originally posted by jzchen
                      I know there is a concern about DC over long wire runs. That is why we use AC from the electric company. It can travel long wires without much degradation in power.
                      Incorrect. At the same voltages DC works better at long distances. That's why long distance transmission lines are all switching to DC.

                      However in solar power systems you generally have three choices:

                      Low voltage DC (i.e. 24, 48 volts)
                      Medium voltage AC (240 volts)
                      High voltage DC (300-500 volts)

                      High voltage DC is much better than low voltage DC or medium voltage AC. Wires can be smaller and losses lower.

                      There is also a safety concern over the voltage created by stringing the panels in series. This creates a very high voltage. The claim is that using a microinverter makes the wiring safer, ie. less likely to arc fault.
                      Both 240VAC and 400VDC are pretty high voltage, and present a safety issue when working around them. In general the system with the fewest connections is going to be safer since there are correspondingly fewer opportunities to access that voltage. In a modern system, built to code, there are very few risks with regard to shock.

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                      • #12
                        Originally posted by billvon View Post
                        Both 240VAC and 400VDC are pretty high voltage, and present a safety issue when working around them. In general the system with the fewest connections is going to be safer since there are correspondingly fewer opportunities to access that voltage.
                        My home is wired 230/408 3 phase - Outside of the US 240 is very common. Only the heat pump is on the 408 I believe.
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                        • #13
                          Originally posted by russ View Post
                          Might make sense to you but it is meaningless - by that definition [B]any panel using a micro inverter would be an AC panel[/B]
                          [B]Exactly![/B] That would still make a useful shortcut in terminology. The only difference between one way of getting there and the other is that in some cases the panel and micro inverter are sold as a unit (I just bought 5 "AC panels"), and in the other cases you buy a "DC" panel and a micro inverter separately and "build your own AC panel."

                          The risk, of course, is that people will misinterpret the terminology and think that there is something different about the PV cells themselves.

                          [FONT=Comic Sans MS](Rotating at 3600 RPM so that the light hits them alternately on opposite sides? )[/FONT]
                          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                          • #14
                            The vendors starting the new name are playing a game where they hope to get extra sales from people that don't understand they have the same product to sell as the next guy - not nice but normal.

                            I think the RPM's would have to reach somewhere in the 100,000 range to really get into the sweet spot
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                            • #15
                              Originally posted by jzchen
                              It was my understanding from EE class why AC is used instead of DC over long wires. Sorry if I was misinformed.
                              A long time ago that was true, but for a different reason. The reason: with 1940's technology you could boost AC voltage with a transformer, but could not boost DC voltage because the technology did not yet exist. Thus if you generated 480 volts AC you could boost it to 12,000 volts for efficient transmission, then drop it to 240VAC at the end for a user. With DC you had to either generate 12,000 volts, transmit it and use it (and it's hard to use 12,000 volts safely.) Or you could generate 120 volts DC and try to transmit that, but that's expensive and lossy.

                              So for a long time the ability to boost and drop voltage made AC the winner for long range transmission.

                              Now that we can boost and drop DC voltage, it wins for a different reason. To transmit an average of 1000 amps in an AC system you have to transmit a peak of 1400 amps, and to transmit an average of 12,000 volts you have to have peak voltages of 16,000 volts. However, to transmit 1000 amp/12,000 volts DC you need to handle only 1000 amps/12,000 volts. That means that towers have to be higher, wire spacing has to be greater and conductors have to be thicker to handle that power level at AC.

                              Since I am considering a centralized inverter system, I am considering the consequences down the road when I might personally try to change the inverter to save money. (I guess I don't want to accidentally fry myself.) It would be worse though if I had to get on the roof and change a microinverter as I'm not good with heights, and a pain to remove a panel to get at it....
                              That's a good argument for a HVDC array. Les stuff on the roof.

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