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  • Solar Panel wiring (diodes)

    Hey everyone,

    I have a few questions about the different wiring of solar panels. And how diodes are used to protect the panels. I would hate to blow one up!

    The specifications for the panels I purchased (Solarex MSX-64) are here:
    http://www.californiasolarcenter.org...arex-MSX64.pdf

    If I want to test a panel a voltage reading is easy enough to take but how do I measure amperage. Can you just connect positive to negative and take a reading or will this damage the panel? Do I need some sort of load between the positive and negative terminals?

    I have the general Idea how the diodes work but not how to size them. I have a few simple scenarios below with questions to help me understand the solar wiring better. I appreciate any help you can provide.

    If you have 4 12v/5A panels in series you will get 48V/5A.

    I understand that bypass diodes are used to protect the solar cells. If a cell becomes shaded the resistance increases. If there is no alternate path for the electricity to go and the voltage is high enough the electricity will force it way through the solar cell heating up the cell and causing failure.
    [LIST][*]What size diode should be used in a bypass configuration?[LIST][*]Since these panels are connected in series I assume the diode must be rated to handle at least 48V/5A with maybe slightly higher rating because electricity and components are not exact maybe 10% higher?[*]Is there a lot of loss if I use a diode rated at a much higher Voltage?[*]Is there a lot of loss if I use a diode rated at a much higher Amperage?[*]Will a diode that is rated higher reduce the heat on the component?[/LIST][*]What should a diode be rated for in a blocking configuration?[/LIST]

    If you have 4 12v/5A panels in parallel you will get 12V/20A.
    [LIST][*]Do you need any diodes in this configuration?[/LIST]

    If you have series string that puts out 48V/5A. Then place it in Parallel with another string that puts out 48V/5A. You should end up with 48V/10A.
    [LIST][*]Is there any diode protection so that under certain conditions that one string does not reverse current flow and fry the other string. [*]Is there a point where amperage in the system is too high by adding too many series strings of panels in parallel and frys the panels in the system?[*]In the example above is 10A flowing through all the panels?[/LIST]

  • #2
    >I have a few questions about the different wiring of solar panels. And how diodes are used to protect the panels. I would hate to blow one up!

    No diodes are usually needed. Yet I notice they are mentioned in the literature you cited. This literature is also dated 1998, and Solarex is all but vanished. Where did you get these panels? Do you realize you may never be able to get a replacement?


    >If I want to test a panel a voltage reading is easy enough to take but how do I measure amperage. Can you just connect positive to negative and take a reading or will this damage the panel? Do I need some sort of load between the positive and negative terminals?

    No load is needed. You can just short the terminals with your ammeter. Don't try this on a whole array - just on a single panel.

    Generally, there is no reason to use blocking and bypass diodes anymore, but with a panel that may or may not be from 1998, I am not sure.
    Lawrence Lile, PE

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    • #3
      I got the panels used for a decent price I was told that Solarex was bought out by BP a while ago.

      The panels do not have bypass diodes built in to them as they have a wiring diagram on the back of them. The only information about the size of the diodes needed are on the back is says minimum diode 5A

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      • #4
        What if you wire your panels in parallel and they aren't exactly the same voltage? Maybe then diodes would be necessary?

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        • #5
          Originally posted by jbarby View Post
          ..... the diodes needed are on the back is says minimum diode 5A

          Comment


          • #6
            Originally posted by Frank in PG View Post
            What if you wire your [B]panels in parallel and they aren't exactly the same voltage[/B]?
            Maybe then diodes would be necessary?

            Comment


            • #7
              panels of different voltages (17V & 19V) can be connected in parallel, and no diode needed. If the voltage is different by more that a couple volts, you will loose appreciable amounts of power, as the lowest voltage panel, will limit the array to it's voltage. So a 17v panel , in parallel with a 30V panel, will yeild 17V, and the 30V panel will loose half it's watts.

              Diodes only help steer voltage around shaded panels (bypass) or prevent nightime backfeed from the battery (only 1 dioded needed per string) Most charge controllers provide the nightime backfeed isolation, so a proper, unshaded system needs no diodes.
              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

              Comment


              • #8
                I know this is an old thread, but I was wondering about typical diode resistance.

                I notice a drop in voltage when reading on the load side of the diode and can definitely feel the heat (loss).
                I'm curious to know which diodes are built most efficiently and if going with a large diode is better than going with a diode that most closely matches the capabilities of the panel or string.

                Additionally, any recommendations on best diodes to use for solar applications?

                Comment


                • #9
                  Originally posted by Eric View Post
                  Additionally, any recommendations on best diodes to use for solar applications?
                  That is a no brainier answer, Schottky diodes.
                  MSEE, PE

                  Comment


                  • #10
                    Originally posted by jbarby View Post
                    I got the panels used for a decent price I was told that Solarex was bought out by BP a while ago.
                    There are going to be a lot of upset folks down the road. The solar bubble has busted. A large percentage of the solar manufactures are going to be gone very shortly.

                    BP did buy out Solerex a few years ago, and killed the company and discontinued all their products. They eliminated the competition. You are going to see a lot of this where the big companies like BP, Kyocera, Sanyo, Sharp, GE are going to buy out all these failing manufactures and bury them where no one can ever find them again, and take over any patent rights to their technology.

                    This is why you should only buy from one of the big companies because solar is such a small fraction or niche market of thier core biz, they can afford to loose money in them for quite a while, but they will always be there to back up warranty claims and still have the same product years from now if you need a replacement or expanding.
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by Sunking View Post
                      There are going to be a lot of upset folks down the road. The solar bubble has busted. A large percentage of the solar manufactures are going to be gone very shortly.

                      BP did buy out Solerex a few years ago, and killed the company and discontinued all their products. They eliminated the competition. You are going to see a lot of this where the big companies like BP, Kyocera, Sanyo, Sharp, GE are going to buy out all these failing manufactures and bury them where no one can ever find them again, and take over any patent rights to their technology.

                      This is why you should only buy from one of the big companies because solar is such a small fraction or niche market of thier core biz, they can afford to loose money in them for quite a while, but they will always be there to back up warranty claims and still have the same product years from now if you need a replacement or expanding.
                      I fear that you are correct. Hopefully we can benefit from what little competition remains. Cap and trade could be a game changer.

                      Comment


                      • #12
                        Originally posted by Eric View Post
                        I know this is an old thread, ........
                        Uh...hello myself... no it is not an old thread!

                        Comment


                        • #13
                          Originally posted by Eric View Post
                          Cap and trade could be a game changer.
                          Yeah that piece of legislation needs to be shot to death and put out of our misery.
                          MSEE, PE

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                          • #14
                            Originally posted by Sunking View Post
                            Yeah that piece of legislation needs to be shot to death and put out of our misery.
                            Agreed!

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