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I need help for a Small system for a solar dummy.

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  • I need help for a Small system for a solar dummy.

    I wanting to run a composting toilet from solar. It's just a D/C fan that runs really. It uses .06kwh / day or 600 Watts a day? Can someone please tell me what I need. 4.5 hours of sun per day, want a 3-4 day backup battery, 12v DC. 150 watt panel would be good but I'm having trouble with the battery storage stuff? Thanks in advance for the help!

  • #2
    I guess that confirms it: SK is right again - solar is going in the toilet.
    Last edited by J.P.M.; 04-08-2017, 11:53 AM.

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    • #3
      Hahaha, nevermind guys, I'm going to run a small 7.0 cu ft fridge as well but need to find out the power consumption. Thanks

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      • #4
        Originally posted by Janachovsky View Post
        Hahaha, nevermind guys, I'm going to run a small 7.0 cu ft fridge as well but need to find out the power consumption. Thanks
        OK. Glad you can take a joke. Get a "kill-a-Watt" meter. ~ $20 or so @ stores, but know that beyond the educational and hobby value, it'll probably be cheaper $$ wise to run a 120V line to the hopper. Welcome to the neighborhood and the forum of few(er) illusions.

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        • #5
          Not sure what u mean by 120v line to the hopper? U mean just regular grid power?

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          • #6
            Originally posted by Janachovsky View Post
            Not sure what u mean by 120v line to the hopper? U mean just regular grid power?
            Yes. If that's possible, it may well be cheaper and more reliable w/a lot less hassle. Just sayin'.

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            • #7
              Yeah it probably is, but it can't b that expensive for a fan running all the time that uses .6kwh/day and a 115v 1.7amp chest freezer with externally controlled thermostat so I can use it as a fridge. Can it? I'm having a hard time calculating what I need, and just keep confusing myself more thoroughly.

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              • #8
                Originally posted by Janachovsky View Post
                Yeah it probably is, but it can't b that expensive for a fan running all the time that uses .6kwh/day and a 115v 1.7amp chest freezer with externally controlled thermostat so I can use it as a fridge. Can it? I'm having a hard time calculating what I need, and just keep confusing myself more thoroughly.
                Suit yourself, but yes, it can be a PITA and cost a lot of money relative to other ways of accomplishing the required tasks, especially if grid power in available. I'd run a 110 V AC line or maybe even an extension cord if not too far a distance and call it done until you learn more about solar and PV, especially if you are a solar neophyte. Hobby is one thing, a lot of fun and a good learning experience. Thinking you'll save money before you know what's involved is another.

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                • #9
                  Originally posted by Janachovsky View Post
                  Yeah it probably is, but it can't b that expensive for a fan running all the time that uses .6kwh/day and a 115v 1.7amp chest freezer with externally controlled thermostat so I can use it as a fridge. Can it? I'm having a hard time calculating what I need, and just keep confusing myself more thoroughly.
                  Well that freezer is going to draw about 200 watts (115v x 1.7amp = 196watts). But not continuously. So lets say it runs 10 hours a day at that load. That calculates to 2kWh.

                  I am still not sure what that fan draws but lets say you are correct and it is .6kWh/day or ~600wh.

                  Now add that 600wh to the 2000wh and you have two loads at about 2.6kWh a day.

                  To size your battery system, you need one that can delivery ~ 2600wh x 4 = 10400wh.

                  A 12volt battery system would have to be 10400wh / 12v = 870Ah.
                  A 24volt battery system would be about 10400wh / 24v = 435Ah

                  Depending on where you live you will need an 80A MPPT and about 1000 watts of panels for a 12volt battery. And about 1/2 that 40A MPPT and 500 watts for a 24v battery system.

                  Now that does not include any wiring, framework, inverter, fuses, etc. So go check out the prices of that battery system and lets us know if it would be cheaper than running a 110v AC line?

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                  • #10
                    I run a 7CF chest fridge and it takes me a KW of panels to do it and my system is far smarter than anything that can be dreamed up here. Where are you that 4.5 hours of sun per day is what you estimate? Usually people are overestimating sun.

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                    • #11
                      Originally posted by Janachovsky View Post
                      Yeah it probably is, but it can't b that expensive for a fan running all the time that uses .6kwh/day and a 115v 1.7amp chest freezer with externally controlled thermostat so I can use it as a fridge. Can it?
                      Yes 5 to 10 times more expensive. If you can use commercial power, do so. You should not take anything off-grid if other options are available and nothing is less expensive and reliable than commercial AC power.

                      Its the batteries and system efficiency that bites you in the butt and no way around it. Just in battery cost alone is what drives it to 5 to 10 times more expensive. If Sun Eagles guess is correct, and he is close at 2 Kwh per day is 20 to 30-cents/day, $6 to $8/month, $72 to $96/year and in 4 years of a good battery life $288 to $384. A good 4 year battery will weigh 600 pounds and cost you $1500 to $2000.

                      MSEE, PE

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                      • #12
                        I can get 2-12v batteries at 225ah in series to make 24v 450ah correct?

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                        • #13
                          incorrect. Batteries in series adds VOLTAGE Parallel adds AMPS 2, 12v batteries at 225ah in series = 24v 225ah
                          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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                          • #14
                            Got ya, so in series would need 2- 12v @ 450ah

                            ​​​​​

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                            • #15
                              And in parallel would need 2- 24 volt batteries at 225ah?

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