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  • Small PV system

    Hello,

    New here. I'm looking to install an small PV system. I already acquired an EpicSolar 40A mppt CC 1040W/150V.

    I have access to the following PV panels:

    Model: JKMS26P

    Specs STC NOCT
    Pmax 260W 191W
    Vmp 30.7V 28.0V
    Imp 8.47A 6.82A
    Voc 37.8V 34.7V
    Isc 9.11A 7.34A

    Now the question is, What values should I used to calculate how many panels? the STC o NOCT? Should I get 3 or 4 panels connected in series?

    In order to make it a 24V should I use 6V or 12V batteries?

    What size inverter can I use with that? 1500W or 2000W?

    Thanks
    Last edited by netstat; 06-04-2018, 08:23 PM.

  • #2
    Any input?

    Comment


    • #3
      If 3 panels then, 3 in series.
      If 4 panels then 2s2p, two series strings in parallel.
      Use STC values but bear in mind these controllers can be over paneled by a pretty good amount. The most important numbers to not exceed are the Voc. maximum.
      Manual, look on pages 8 - 9 https://www.i4wifi.cz/img.asp/?attid=315024
      4 6 volt GC2 (golf cart) batteries in series
      Your inverter shouldn't be any larger than required for your needs. Typically the larger the inverter the higher the idle power consumption.
      Last edited by littleharbor; 06-09-2018, 09:19 AM.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

      Comment


      • #4
        But based on the panel specs I could go with 4 in series right?

        Comment


        • #5
          No, 4 times 37.8 is 151.2. On a cold morning it would be considerably higher. As you can see the NOCT numbers don't include Voc. Obviously this isn't your panel. Just using the image as an example.
          Kyocera 265 2 (1).JPG
          Last edited by littleharbor; 06-09-2018, 10:37 AM.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

          Comment


          • #6
            netstat,

            I guess the best way to find out how many panels you need is to get 1 panel and test it to see how many amps it gets in real life.

            If the panel is rated 9 Amps do this:

            1-) Test how many amps produce in the best possible conditions, perhaps out of 9 Amps you are going to be surprised that you get 6 Amps only
            2-) Test how many amps produce in the average conditions, perhaps 3 Amps
            3-) Test how many amps produce in the minimum conditions, a cloudy day, maybe 1 Amp


            Once you actually know how many amps you get per panel you can start making your calculations as to how many panels you need, how to configure the panels, what charger would accommodate your panels production, what battery bank you would need and what inverter you need.
            Last edited by john95; 06-09-2018, 10:55 AM.

            Comment


            • #7
              4 in series gives you 151.2Voc @ 25C. Many (98%) charge controllers will be violated by this voltage. On a cold morning, the voltage will be higher, and your controller WILL be damaged.
              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
                Originally posted by john95 View Post
                netstat,

                I guess the best way to find out how many panels you need is to get 1 panel and test it to see how many amps it gets in real life.

                If the panel is rated 9 Amps do this:

                1-) Test how many amps produce in the best possible conditions, perhaps out of 9 Amps you are going to be surprised that you get 6 Amps only
                2-) Test how many amps produce in the average conditions, perhaps 3 Amps
                3-) Test how many amps produce in the minimum conditions, a cloudy day, maybe 1 Amp


                Once you actually know how many amps you get per panel you can start making your calculations as to how many panels you need, how to configure the panels, what charger would accommodate your panels production, what battery bank you would need and what inverter you need.
                Complete BS, ignore his post.

                With a Controller with a 150 Voc input and using th epanels you have specified the maximum number in series it can handle is 3 (three) end of story. Warning here do not use a PRIME number of panels except 1 and 3 because with a PRIME number you only have two configurations possible. Either all in series or all in parallel.

                This makes life real simple and a No Brainer. If you use 3 panels all in series. If you use 4 panels 2S2P end of story, no thought required.

                As for batteries you use whatever is required so you do not have any parallel strings. But lets make it a No Brainer for you. 6 VOLTS. Only thing left to figur eout is how many Amp Hours and that depends on panel wattage and battery voltage. With 3 x 260 watts will require roughly a 300 AH battery. With 4 x 260 watts wil require roughly a 400 AH battery. So now you go shop for 4 x 6-Volt 300 or 400 AH batteries.

                Now try to find 12 volt 300 or 400 AH batteries, good with that and if you do rent a fork lift to lift them up.
                Last edited by Sunking; 06-09-2018, 03:41 PM.
                MSEE, PE

                Comment


                • #9
                  Originally posted by Sunking View Post
                  Complete BS, ignore his post.

                  With a Controller with a 150 Voc input and using th epanels you have specified the maximum number in series it can handle is 3 (three) end of story. Warning here do not use a PRIME number of panels except 1 and 3 because with a PRIME number you only have two configurations possible. Either all in series or all in parallel.

                  This makes life real simple and a No Brainer. If you use 3 panels all in series. If you use 4 panels 2S2P end of story, no thought required.

                  As for batteries you use whatever is required so you do not have any parallel strings. But lets make it a No Brainer for you. 6 VOLTS. Only thing left to figur eout is how many Amp Hours and that depends on panel wattage and battery voltage. With 3 x 260 watts will require roughly a 300 AH battery. With 4 x 260 watts wil require roughly a 400 AH battery. So now you go shop for 4 x 6-Volt 300 or 400 AH batteries.

                  Now try to find 12 volt 300 or 400 AH batteries, good with that and if you do rent a fork lift to lift them up.
                  Thanks for the Info.

                  Another question, How you calculate this:

                  3 x 260W PV = 300AH battery
                  4 x 260W PV = 400AH battery

                  Thanks

                  Comment


                  • #10
                    Originally posted by netstat View Post

                    Thanks for the Info.

                    Another question, How you calculate this:

                    3 x 260W PV = 300AH battery
                    4 x 260W PV = 400AH battery

                    Thanks
                    Simple math using C/10 charge rate for a starting point.

                    3 x 260w = 780w / 24volt = 32.5 charging amps which is ~ C/9 for a 300Ah system
                    4 x 260w = 1040w / 24volt = 43.5 charging amps which is ~ C/9 for a 400Ah system.

                    Comment


                    • #11
                      Originally posted by SunEagle View Post

                      Simple math using C/10 charge rate for a starting point.

                      3 x 260w = 780w / 24volt = 32.5 charging amps which is ~ C/9 for a 300Ah system
                      4 x 260w = 1040w / 24volt = 43.5 charging amps which is ~ C/9 for a 400Ah system.
                      Thanks.

                      Based on this info, the inverter size should be around 2000W?

                      Comment


                      • #12
                        Originally posted by netstat View Post
                        .....Based on this info, the inverter size should be around 2000W?
                        The inverter should be the smallest that can manage your largest loads. The max size is 2Kw
                        Microwave, well pumps, irrigation pumps, septic grinder pump, Those are the usual large loads, and then if your fridge tries to start, the inverter has to have enough oomph left over to start the fridge.

                        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


                        • #13
                          Originally posted by netstat View Post

                          Thanks.

                          Based on this info, the inverter size should be around 2000W?
                          It depends on your loads. Just be aware that a 2000W inverter can draw close to 90 amps (2000w / 24v = 83.3a) so the cables between the battery and inverter need to be able to handle that current (even for a short time) as well as being fused properly.

                          Comment

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