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  • shorting out solar panels

    hi this is my first time on a forum so im new to all this
    I want to connect 2 100w solar panels to a 24vdc 300w water heater
    can this be done without a regulator but would this create a dead short on the solar panels
    with ohms law the heater has an impedence of about 2 ohms
    is this enough not to create a dead short ?????

  • #2
    Shorting solar panels does not hurt the panel, but the gold plate on the MC4 connectors will be spoiled if they are connected/opened under load.

    Water heaters generally have AC voltage thermostats, which will quickly be ruined with the DC from solar panels. If your heater has DC thermostat, you should be OK
    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

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    • #3
      iv just realised im six hours in front of you so thanks for replying
      I have a 240v water element and I want to replace the element with a 24v 300w
      so I can connect it up to the solar panles
      im told it can be connected up to a 24v solar panel
      would that be 2 in series or what

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      • #4
        On the panel, will be a value called Vmp=_____ That number is the max power voltage of the panel. you need a single panel or combination of panels, where that number adds up to 24V. But 100w panels will not work well, with a 300w load on them, their voltage will collapse and you will not get a lot of heating.

        And the thermostat in the heater, must be changed to a DC thermostat.
        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


        • #5
          the heating element is 24v 300w which will take about 12.5amps and is 1.92 ohms
          the solar panels vmp is 19.2v and the imp is 5.23 amps
          so in series 2 solar panels should give you about 10 amps which is what the heater will run on ???
          and there is no thermostat in the heater as it is only an element
          I might need to fit a over tempreture stat but as it is only like a pre heat system I don't think it will get that
          hot especially with our English weather.

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          • #6
            Is your plan direct-connection of the panels? I see no battery nor controller in your plans. That usually ends up going badly.

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            • #7
              yes pn junction no controller just directly
              my existing heater is 3ooow 240v and uses 12.5 amps
              all ac

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              • #8
                Originally posted by Nidge View Post
                the heating element is 24v 300w which will take about 12.5amps and is 1.92 ohms
                the solar panels vmp is 19.2v and the imp is 5.23 amps
                so in series 2 solar panels should give you about 10 amps which is what the heater will run on ???
                Perhaps you meant IN PARALLEL? Bruce Roe

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                • #9
                  Yes in parallel

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                  • #10
                    What are you expecting to do with this hot water? Nothing serious I hope. For most of the day the heating element will look like a dead short to the panels. Direct connect is popular because it is easy, it just doesn't work well. You have made about the best match with that element. I heat water off panel voltage with a power point controller and it is amazing how well it works.

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                    • #11
                      I all ready have a tiny system at home
                      iv got 2 very small panels one controller and one car battery this powers my 16inch tv in the dinning room
                      for ten monthes of the year I don't expect it to power the house
                      I all so don't expect the water heater to heat the water up to that degree
                      if it heats the water up by 40% it is still 40% more than it is now as we don't use the 240v one that is in there
                      I have not got a battery in this heater project as if I did then the heater would proberbly just drain the battery over night
                      Iv built control panels for 40 years so I know how to limit the time the heaters on but there is no need as the sun is a natural timer

                      iv since been looking into just getting one 275w solar panel all though the voltage on this is about 30v the currant output is
                      only about 9A
                      iv been talking to the tester at work and he seems to agree with me that the extra voltage should not hurt the 24v heater
                      its current that will kill it and 9A should not kill it
                      but if some one has all ready done this and it has not worked I could all ways get a 15A Dc to Dc step down buck converter
                      I know a controller does a simarlar thing but I thought that the heater would be more robust with it not needing a more controlled supply and charging currant
                      like a battery does

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                      • #12
                        I think this would help you with your quest:

                        https://www.youtube.com/watch?v=kVaxAfXQPDU

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