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System setup: Off grid solar, w/generator backup

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  • System setup: Off grid solar, w/generator backup

    Hey fellas. First time poster and new to the solar world.

    I've been working on a setup for my small remote cabin, and I'm trying to figure out how to wire a portable gas generator into my solar setup to act as a backup. I don't know if I can bring that power in through the charge controller, or if I bypass the charge controller. Anyone have any idea how I can make that work together?

  • #2
    Welcome.
    Some of the larger inverters, also have an onboard charger, and connects to your generator. This provides pass-through AC power, and charges the batteries when you run the generator.

    Otherwise, you buy a generator and a golf cart battery charger and charge your batteries with an external charger, and simply do the Bulk stage of charging to save fuel, and let the solar finish it when there is sun. You do not alter your PV or PV charge controller at all, you would simply wire in the other charger to the batteries. You do have to insure you have the voltage set properly.
    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


    • #3
      Originally posted by SD51555 View Post
      Hey fellas. First time poster and new to the solar world.

      I've been working on a setup for my small remote cabin, and I'm trying to figure out how to wire a portable gas generator into my solar setup to act as a backup. I don't know if I can bring that power in through the charge controller, or if I bypass the charge controller. Anyone have any idea how I can make that work together?
      No you can not attache a generator to the charge controller. Some (most good ) inverters have two or more AC connections and one can be set up for generator connections.
      OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

      Comment


      • #4
        Appreciate the feedback guys. One point I forgot to mention, my system will be primarily 12 volt, and only have a couple things inverted right at the point of usage, like the TV stuff, and the air conditioner. Does that change the advice at all?

        Comment


        • #5
          Originally posted by SD51555 View Post
          Appreciate the feedback guys. One point I forgot to mention, my system will be primarily 12 volt, and only have a couple things inverted right at the point of usage, like the TV stuff, and the air conditioner. Does that change the advice at all?
          so you plan to distribute 12V to dedicated inverters?

          It does NOT change the fact that you can not feed a generator out put into a Charge Controller. You can get a battery charger since you will have cheap inverters all over the place.

          Your bigger problem is 12V distribution. And trying to run an air conditioner from a 12V system.
          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

          Comment


          • #6
            You still need the generator for the Air Conditioner and you can use any automotive charger sized to your battery bank - about 10% of bank, so if you have a 200ah bank, you need a 20a charger, maybe 25a. At 14 charging volts, 25a x .5 FP means you need a 700W generator just for charging and then more to run the air conditioner. Most little inverter generators may not be able to start a air conditioner's compressor motor, likely 3kw needed for that.
            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


            • #7
              Originally posted by SD51555 View Post
              Appreciate the feedback guys. One point I forgot to mention, my system will be primarily 12 volt, and only have a couple things inverted right at the point of usage, like the TV stuff, and the air conditioner.
              Very very bad idea.

              Let's take an example. You have to run 50 feet of wire to your A/C which takes ~10 amps.

              120 volt case - 50 feet of Romex 14/2 (12/2 if you want to reduce drop a bit.) Fine for 10 amps. Voltage loss is about 1.5%, which is fine (most people target 3% max.) Cost - $30.

              12 volt case - 120 amps (120/12 with some inefficiency thrown in due to inverter.) To get to a 5% drop (which is still a bit high) you will need 4/0 wire. That's $1 to $2 a foot. Cost - $100 to $200.

              And that's just the wire. Everything else (protection, lugs, conduit if used) will have to be larger as well. Plus you'll be drilling enormous holes in your studs.

              Comment


              • #8
                Another user stuck inside a 12 volt toy box.
                MSEE, PE

                Comment


                • #9
                  Originally posted by jflorey2 View Post
                  Very very bad idea.

                  Let's take an example. You have to run 50 feet of wire to your A/C which takes ~10 amps.

                  120 volt case - 50 feet of Romex 14/2 (12/2 if you want to reduce drop a bit.) Fine for 10 amps. Voltage loss is about 1.5%, which is fine (most people target 3% max.) Cost - $30.

                  12 volt case - 120 amps (120/12 with some inefficiency thrown in due to inverter.) To get to a 5% drop (which is still a bit high) you will need 4/0 wire. That's $1 to $2 a foot. Cost - $100 to $200.

                  And that's just the wire. Everything else (protection, lugs, conduit if used) will have to be larger as well. Plus you'll be drilling enormous holes in your studs.
                  I should take a step back and describe the entire project. I am getting a 15x40' prebuilt storage shed. It will be split in half and be half attached garage, half living quarters. My power draw will primarily be LED lights, some USB charging outlets, a 12 volt ceiling fan, a 41 watt TV, an antenna booster, and perhaps one or two extra outlets for charging fish finder batteries. All appliances will be propane (furnace-no blower, oven, stove, fridge, freezer, coffee maker). There will be no toaster, microwave, electric coffee maker, etc.

                  I've done a power worksheet to see what my amps/day would be, and I've got it down to around 53. Now as far as the air conditioner goes, that would run right off the generator, it would not be hooked to the solar in any way. I've gone back and recalculated my array, and I think I can get it done with a 300 watt array to start, and a 400 amp battery bank.
                  ​​​​
                  I am in a weaker solar area being in the far north (Grand Rapids, MN). My power draw would be lowest when the solar power is the lowest (winter). I'm now reconsidering the backup charger all together, on the assumption that I can get upwards of 4 hours of good charging during my peak usage times (May-September). That would put me around 100 amps a day generating power, with a consumption of 55-70 amps/day.

                  As of now, I think i'll forget the backup charger. Worst case scenario, no tv for the day. Oh well, the whole point of this place is to be outside doing outside things. I've attached my floor plan for the fun of it.

                  cabin.PNG

                  Comment


                  • #10
                    Originally posted by SD51555 View Post
                    ....d I think I can get it done with a 300 watt array to start, and a 400 amp battery bank......
                    400Ah battery needs at least 40A for charging Best you will see from a 300w array is 21A Even 600W would be cutting it close.

                    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


                    • #11
                      Originally posted by SD51555 View Post

                      I should take a step back and describe the entire project. I am getting a 15x40' prebuilt storage shed. It will be split in half and be half attached garage, half living quarters. My power draw will primarily be LED lights, some USB charging outlets, a 12 volt ceiling fan, a 41 watt TV, an antenna booster, and perhaps one or two extra outlets for charging fish finder batteries. All appliances will be propane (furnace-no blower, oven, stove, fridge, freezer, coffee maker). There will be no toaster, microwave, electric coffee maker, etc.

                      I've done a power worksheet to see what my amps/day would be, and I've got it down to around 53.
                      Do your calculations in Watts and watthours
                      Amps is dependent on the voltage and easy to confuse someone

                      Originally posted by SD51555 View Post
                      Now as far as the air conditioner goes, that would run right off the generator, it would not be hooked to the solar in any way. I've gone back and recalculated my array, and I think I can get it done with a 300 watt array to start, and a 400 amp battery bank.
                      ​​​​
                      I am in a weaker solar area being in the far north (Grand Rapids, MN). My power draw would be lowest when the solar power is the lowest (winter). I'm now reconsidering the backup charger all together, on the assumption that I can get upwards of 4 hours of good charging during my peak usage times (May-September). That would put me around 100 amps a day generating power, with a consumption of 55-70 amps/day.

                      As of now, I think i'll forget the backup charger. Worst case scenario, no tv for the day. Oh well, the whole point of this place is to be outside doing outside things.
                      You need to do all your calculations on the lowest solar time of year, winter solstice. what you can make in summer is meaningless if you can't make it in winter.

                      worst case is you have no lights for a bit and your batteries sulfate.
                      OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                      Comment


                      • #12
                        Originally posted by SD51555 View Post
                        I've done a power worksheet to see what my amps/day would be, and I've got it down to around 53. Now as far as the air conditioner goes, that would run right off the generator, it would not be hooked to the solar in any way. I've gone back and recalculated my array, and I think I can get it done with a 300 watt array to start, and a 400 amp battery bank.
                        Well that was a nice Academic exercise. Just one problem, it will not work, especially in Grad Rapids. The battery needs to have at least a C/10 charge current and with 300 watts @ 12 volts is just 21 amps or C/19. To generate C/10 or 40 amps will take 600 watts in Grand Rapids. Use 300 watts and you will be replacing the battery every 6 months or less and spending a lot of time in the dark wondering how academics could be wrong.
                        MSEE, PE

                        Comment


                        • #13
                          Originally posted by SD51555 View Post
                          I should take a step back and describe the entire project. I am getting a 15x40' prebuilt storage shed. It will be split in half and be half attached garage, half living quarters. My power draw will primarily be LED lights, some USB charging outlets, a 12 volt ceiling fan, a 41 watt TV, an antenna booster, and perhaps one or two extra outlets for charging fish finder batteries.
                          OK. So that means you'll need an inverter. I would strongly suggest you get a decent inverter/charger so your generator can also charge your battery while you are running A/C. Your batteries will last a lot longer.
                          I've done a power worksheet to see what my amps/day would be, and I've got it down to around 53.
                          I assume you mean 53 amp-hours a day at 12V, which is ~600wh/day/
                          As of now, I think i'll forget the backup charger. Worst case scenario, no tv for the day. Oh well, the whole point of this place is to be outside doing outside things. I've attached my floor plan for the fun of it.
                          Well, no, worst case is a sulfated battery pack within a few months.

                          If I were you I'd treat the solar as a battery maintainer and rely on your generator to provide most of your power. Your solar will then keep the batteries from going dead and shorten generator runtimes.

                          Comment


                          • #14
                            That's why I came to you guys. Looks like I've got a lot more to learn. Appreciate all the help guys.

                            Comment


                            • #15
                              Originally posted by Mike90250 View Post

                              400Ah battery needs at least 40A for charging Best you will see from a 300w array is 21A Even 600W would be cutting it close.
                              Is that universal info? For example in an AGM battery vs a lead acid battery?

                              Comment

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