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  • Solar overflow to run water heater?

    So I've set up my system and it runs pretty good, most days it's in use, batteries are full or on trickle by 10am to 11am.

    I also have a 6 gallon electric water heater I currently run off a Genny. I'm thinking I'd like to use the over flow from the solar pannels once the batteries are full to run the electric water heater... If it's possible?

    Here's my set up
    https://www.solarpaneltalk.com/forum...-wiring/page11

    image_10129.jpg

    CC is a EPever 30A, inverter is a 1,500 with 3,000 peak load and it has a 110v plug on top that my fridge is plugged into, inverter is currently set to sleep after load is gone and kick on when it senses load.

    Water heater pulls about 13.75A (tested with kill-a-watt) and takes about 30 min to reach tempature. Based on this if I ran the water heater off the inverter it'd pull 1,650W (120vx13.74A). I can't remember all the math I had to do to set this up, but I'm thinking 1,650W /12v DC is 137.5A DC pulling from the batteries (+20% inverter conversion) is 165A DC for 30 min is 82.5Ah out of 214 total Ah on tbe battery bank would be 39.7% pull leaving me with 60.3% Ah left in a 30 min time frame.

    I see a couple things wrong with this:
    1) that's to deep of a draw down to be healthy for the batteries
    2) The discharge rate is way to extreme and will cook the plates/batteries.

    Since running the water heater off the battery bank does not seem to work ( unless I'm missing something), ...is there a way to run the water heater off the PV over flow once the batteries hit float charge and can this be done on some type of automatic switch so I don't have to be present to make it happen?


    Thanks
    Last edited by Carv; 02-09-2019, 12:06 PM.

  • #2
    I have one of those 6 gallon tanks and I run off excess solar and 900WH will get it up 60F to temperature. If already warm, a lot less power. Surprising what you can do with just 6 gallons. I have a 36V and 60V array, each drives a separate tank off the raw PV voltage thru a special controller you can't get. This leaves the batteries intact. If you could find an auto transformer, one with a dual 120V primary and enough current, it could be wired to produce 60V. That would be 1/4 of the rated wattage of the element and not present a large load on the inverter. I put less than 400W in my tank and have reliable results. Some use a big light dimmer, but this still presents a heavy load that won't make the inverter happy.

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    • #3
      I do the same thing but with a MidNite Classic CC. Works perfectly. I could link you to the thread where I set it up, but it is at the MidNite solar forum and this forum does not allow external links.

      If your CC has a Waste Not type feature (where it allows the use of excess solar power when available that is not otherwise used) it can be programed to only supply power to the water heater when certain conditions are met, say ... if the CC is in the absorb phase of charging at SOC 95% and the voltage is XX.Xv +/- .X volts the CC will supply a signal to power a water heater to the inverter using a SSR. So when the sun is out and the system is charged, if there is excess power coming from the solar only it will allow the inverter to power the heater. If the conditions are not met it does not. Then you never use battery to heat water, only solar. But I do not think your CC will allow that level of programing - you would need AUX outputs on the CC.

      There is another way. But will require more panels and a separate sub solar system. It would work with your current system to supply power to the relays, but the water heating would be done y a separate set of panels. Go to waterheatertimer (dot) org and look for the article Convert AC water heater to DC. This would also work, but would work independent of your current system.
      285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

      Comment


      • #4
        Also you can use a smaller element (as suggested). And remember, if you need to or can, you can use a 240v element in a 120v set up, and it will use 25%ish of the rated power. A 3600W 240v element when connected to 120v will only use 900 Watts.
        285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

        Comment


        • #5
          Originally posted by Matrix View Post
          I do the same thing but with a MidNite Classic CC. Works perfectly. I could link you to the thread where I set it up, but it is at the MidNite solar forum and this forum does not allow external links......
          [COLOR=#006400]You can put one link, in response to a direct question, so go on ahead. Mod[/COLOR]

          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


          • #6
            Thanks Mike,
            Matrix please put up the link. I'd like to read your thread as it looks like this might be my only option if I want to have my set up function like this.

            Ok so if I understand it, you guys are suggesting 3 different ways to do this;
            1) set up a new panel with separate system to power water heater
            2) Change my water heater element to run at 60V instead of 120V or to DC
            3) program the CC to direct the overage to the water heater, if my CC is capable.


            Guess I failed to give enough information, this is on a box trailer running 2 -60 cell 255W, 8.5A, 30V, grid tie panels in series and I don't want to add any more panels, it would just complicate things more and there's not a lot of room left. I also don't want to alter my heating element in the WH as I still need to be able to run the water heater off the Genny's 120V AC as a back up in case there's a problem with the solar.
            ​Here's the panel specs .https://www.solarpaneltalk.com/filed...9&d=1500058902

            My WH element is adjustable and I have it warming to approximately 130F currently. 60F is not exactly a nice hot shower plus the hotter the water is in the tank the less I have to use ( blending with cold) getting a shower.

            So I read up and I have the EPever 3215BN, I read the manual and it does not have any programing options for over flow. And from what I can tell the aux is just a low wattage pass through, looks like it's for a light bulb or phone charger, but I'm not sure on this?

            I do see a problem even if the aux load is enough, and that is I'm assuming the auxload is DC?

            Given my restraints is there another way pulling off the CC once batteries are on float? Even if I was able to do this, I'm thinking I'd still need to convert that feed from DC to AC?
            Last edited by Carv; 01-31-2019, 03:16 PM.

            Comment


            • #7
              The fundamental problem is that the WH element is a fixed resistive load while the excess power from the panels will be essentially variable current (as a function of insolation (being shined on)) at a close to constant voltage. It can never be the correct resistance to suck up all excess power, when the amount of excess power will vary.
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

              Comment


              • #8
                Its a long read, but I did add an index at the bottom of the first post:
                http://midniteftp.com/forum/index.php?topic=3881.0

                Originally posted by inetdog View Post
                The fundamental problem is that the WH element is a fixed resistive load while the excess power from the panels will be essentially variable current (as a function of insolation (being shined on)) at a close to constant voltage. It can never be the correct resistance to suck up all excess power, when the amount of excess power will vary.
                While true, if you use a small enough water heater resistive load, it will run a good bit of the time and use up a good bit of the excess power from the panels. And if you have some kind of programmable setting from the CC it will only run at user defined charge level points. There are several ways to program the set up with a MidNite Classic, none of which is ideal, but each having its own pros and cons. Most of that is discussed in various places in the link above.
                285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

                Comment


                • #9
                  Originally posted by Matrix View Post
                  Its a long read, but I did add an index at the bottom of the first post:
                  http://midniteftp.com/forum/index.php?topic=3881.0



                  While true, if you use a small enough water heater resistive load, it will run a good bit of the time and use up a good bit of the excess power from the panels. And if you have some kind of programmable setting from the CC it will only run at user defined charge level points. There are several ways to program the set up with a MidNite Classic, none of which is ideal, but each having its own pros and cons. Most of that is discussed in various places in the link above.
                  That makes it a good strategy if your goal is to avoid net export to the grid. It is less helpful when your goal is never to send power out to the net because of prohibitions or a single directional meter.
                  You can use a larger water heater load to consume more than your excess power to avoid feeding back into the net, but you cannot exactly match the power surplus.
                  SunnyBoy 3000 US, 18 BP Solar 175B panels.

                  Comment


                  • #10
                    This is on a box trailer so there is no grid to tie into or feed back to

                    Comment


                    • #11
                      Using the transformer method is probably your best method. The heating element is most likely 1400W and running it at 60V will produce 1/4 of that power. Like my 6 gallon heater you are never going to replace that element. I assume it plugs into something. Just plug it into a transformer when you want to heat water with solar. I didn't find anything cheap on ebay, 240V to 120V auto transformers rated at 750 to 1KW with cords and plugs already. What is your price point? My 6 gallon 1440W tank easily RAISES water 60F with only 900WH. That is two hours in mid day sun. If the water is somewhat warm it takes much less. Running off the panel voltage in an automatic system to harvest excess like I do is the way to go, but these systems aren't out there yet. Transformer is manual but doable.

                      https://www.ebay.com/itm/Simran-THG-...UAAOSwH2Ja0sfc
                      Last edited by PNPmacnab; 02-02-2019, 03:39 PM.

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                      • #12
                        Pnb, yes the WH has a 110v standard US plug.
                        I'll get the element specs too.


                        So if I was to do this I'd wire in the transformer to DC output side the CC then plug the WH in when batteries hit float? Basically how would this system be wired based on the photo above of my system?

                        Thanks

                        Last edited by Carv; 02-02-2019, 11:08 PM.

                        Comment


                        • #13
                          > So if I was to do this I'd wire in the transformer to DC output side the CC

                          NO !! Transformers only work on AC. Put DC into a transformer and you get smoke and a boat anchor.

                          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


                          • #14
                            So what am I missing here?

                            If transformers only work off AC then I'd have to wire it to run off the inverter as my CC only out puts DC, unless the Aux load is AC, does someone know on this CC?

                            This would mean I'm still pulling load off the batteries through the inverter and then stepping it down, basically doing exactly what I said won't work above.

                            So again what am I missing here?

                            Comment


                            • #15
                              Several years ago when I first got our camper and interest in solar for it, I followed a forum post on rv.net about a guy with a truck camper that dumped his excess solar via the "load" output of his charge controller to a dedicated 12V element in his water heater. I seem to recall him fabbing something up so that he could use an existing part of the water heater to house the dedicated element. I was interested because it was the same model Morningstar Tristar controller that I have; the Morningstar Tristar controllers have programming options to due this very thing. It did exactly what the OP is asking about, something useful to do with solar harvest if his batteries do not need further charging. Unfortunately, I cannot find this forum post. Sorry! I keep thinking it will be easy to dredge up but I'm not having luck. I recall that this was in no way a replacement for the propane heating of the water, nor a claim to heat the water to the setpoint via solar alone. But it was something useful to do with power that could still be harvested during daylight hours if batteries were already floating.

                              My google searching found an ebay link to "12 Volt 200 Watt DC Low Voltage Submersible Water Heating Element or Dump Load" if you'd like to search for that on your own, I didn't want to post a direct link here.
                              I'm an RV camper, mine has 280 watts of solar

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