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Looking for guidance on off-grid solar setup for a she-shed trailer

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  • Looking for guidance on off-grid solar setup for a she-shed trailer

    Hi There,


    I am planning an off grid solar power setup for a She-Shed for my wife and would like some guidance on all the pieces I will need to make this work.


    She-Shed Summary:
    - Basically this is built as an off grid tiny-home trailer (8’x20’) for my wife as a she-shed little getaway on our large acreage property
    - Expected use is for 2-3 day overnight stays only (ie not full week and not a house replacement - just a little getaway)
    - Small 120V under-counter fridge expected to run during stay only
    - Small 120V ceramic wall heater for heat in the winter during stays
    - Small 120V water pump (runs only when using water)
    - 120v LED interior ceiling lights (~6w each)
    - Typical small kitchen appliances such as a 120v coffee maker/toaster oven/hot plate (not used at the same time and only used sparingly during the day)
    - Other small electric 120V devices: iPhone charger, laptop charge
    - Note: no DC appliances or devices planned

    Planned Solar System Setup:
    - 400W (4-panels) 12v Renogy Solar kit
    - 40A charge controller (whichever is sized for the 400W kit but allowing for growth)
    - Either 1x lithium ion battery 12v 170Ah -or- 2x lithium ion battery 12v 100Ah each (if two batteries will connect them in parallel for 12v 200Ah setup)
    - Honda EU2200i 2200W 120V portable generator (for non-battery power of high-wattage items and also for charging the battery as needed)
    - Based on the above she-shed summary, I’ve estimated a daily wattage load (based on running high wattage items off generator and the rest off battery/solar) somewhere around 2400 W/day - this should give me a 200A daily usage of the battery @12v in the worst case (i.e., assuming max usage of the items i’ve identified)
    - Note: This does not include off-setting power usage from the 400W panels (which should give 1600- 2000W charge power per day @5-6 hours of peak sunshine in our location

    Power System Connection Layout:
    - 400W panels mounted to the roof and wired into the charge controller
    - Charge controller wired to the battery(ies)
    - Batteries to a DC to AC 120v Power inverter (3000w or greater, 30A or higher)
    - 120V Appliances plugged in to the inverter (2x 15A outlets) - I have these mapped out to ensure correct circuit load for each outlet
    - Honda EU2200i Generator (2x 15A outlets)
    - 1st plug for separate dedicated outlet in the shed wired to the generator
    - 2nd plug wired to charge the battery (via AC to DC charger)

    Questions:
    1) Is it better to get a single 170Ah lithium battery now with potential to expand to a second 170Ah battery if needed, or start with 2x 100Ah batteries in parallel to get 200Ah?
    2) How should the panels be connected (series or parallel) given the 12V battery setup above?
    3) What is the best way to connect the generator into this setup so I can charge the battery either via solar or via the generator? i.e., should I use a combined inverter/charger setup or separate charger for the battery and an inverter for the 120AC appliances?
    4) If a separate charger and inverter, how should I connect the generator and solar inputs to the batteries? Do I need a transfer switch so only one input is charging the batteries at a time?
    5) Should I add any circuit breakers along the chain (if so, where)? - NOTE: for each of the 120v 15A outlets off the DC to AC inverter, I was going to hardwire these to separate 15A GFCI outlets to act as a breakers for the appliance end of things
    Last edited by asloren1; 02-07-2021, 03:01 PM.

  • #2
    My suggestions

    1: Fridge. Use an RV icebox and a $5 block of ice when needed Electric Fridge takes 24hr to self cool from a warm start and consumes >0.9kwh daily
    2: Heater. Electric is impossible, unless you only want it on for 10 minutes and flattened batteries. Look into "Mr Buddy" propane heaters.
    3: Batteries pass on the Li batteries, and use a pair of 6V 200ah golf cart batteries (wired in series) Flooded would be my first choice, AGM 2nd, Li last.
    Li batteries REQUIRE a BMS and integration with all charging sources, so the BMS can shut the chargers down when needed
    4: Inverter(s) 1 small one to power lights and chargers, small water pump: 300w Pure Sine Wave.
    1 large one (2000W mod-sine) which only powers the electric coffee pot/cooking appliance for 10 min, followed by a sunny day to recharge, and the inverter is only on, while the appliance is on, otherwise the self consumption will drain the batteries. Consider a Induction hot plate, much safer than glow coil, and 70% more efficient.

    Or wire up the 120Vac cooking outlets to your generator and avoid the hassle of a transfer switch and ground wire transfer.
    Lead acid batteries can charge simultaneously from multiple sources, Li becomes much more complicated because of the BMS interaction required

    With reduced load on solar, a single 300w panel, aimed properly, will support the rest. Unless you are in Ecuador, you would rarely have more than 5 prime solar hours a day. You might have 13 hours of daylight, but the noonish hours are the full power hours.
    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
      Hi Mike,

      Thanks for your reply!

      After some more thought, we have decided to go with a small wall mount direct vent propane heater (since we were going to have a propane tank anyway), so that now drops my overall power consumption basically in half (now about max 120A/day battery consumption @12v).

      Also, to clarify, the coffee maker, toaster and induction hot plate will all run off the generator directly and not off the batteries via the inverter. That leaves really only the lights, water pump and fridge running off the batteries via the 120v inverter. Also, we are only using the trailer for 2, maybe 3 days (2 nights) max and mostly need power for overnight vs. during the daytime.

      For the Fridge, this is a small 3.4cu ft 100W under counter dorm-size mini fridge that will only use 1.1A while running (we do plan to bring bags of ice when we first show up to pre-cool the inside to facilitate getting to temp).

      I also had some follow up questions to your comments:
      1) Regarding batteries, my understanding was that with normal type golf-cart or car batteries (i.e., non-lithium) you only get about 50% of the capacity and much less cycle life than with lithium (which allows for 100% capacity). If the solar kit I am buying has a charge controller anyway, what’s the main advantage of going with lead acid vs. lithium? Also, arent’t there concerns about venting/gas build up with lead acid?

      2) Depending on the battery type, I’m still a little confused as to how I connect the generator in to charge the battery. Per your comment, sounds like if I use Flooded or AGM, then I can just connect the generator via 120v to 12V inverter directly to the battery along with the output from the solar charge controller with no need for a transfer switch (which is only needed if using Lithium batteries right)?

      3) Regarding the inverter, I think I can now get away with only a 2000W 12v to 120V inverter to power everything given my reduced power needs. I’m a little confused as to your comment on the inverter drain as it shouldn’t be using much if any power just siting there if nothing is actively running?

      Thanks again for your help!

      -Adam

      Comment


      • #4
        > For the Fridge, this is a small 3.4cu ft 100W under counter dorm-size mini fridge that will only use 1.1A while running (we do plan to bring bags of ice when we first show up to pre-cool the inside to facilitate getting to temp).

        HA. That's about the same as my full size energy star fridge. The mini fridge has less insulation than normal, so it runs more.
        50% duty cycle = 100W x 12 hours = 1200wh. At 12 v that's 100ah, half your battery capacity. Or a block of ice, or dry ice, your choice.

        I'll let you look up the specs for idle draw and efficiency of your inverter. letting it run all the time, will suck a lot of power. Again - your choice. i still suggest the sure sine,
        only 450mA when on. ( 24 hrs = 11 ah consumed. ) compare that to your other inverter choices.

        Lithium cannot be used to 100%. Generally, you reserve the top and bottom 20% (40% of your capacity is now gone) for safety because Really Bad things happen when Li gets the least bit overcharged or drained completely. Below 40F, you loose half your capacity. Below frost, you cannot recharge or you destroy the battery,
        And with Li battery, you will need to carefully manage charging with solar & generator usage. No easy solution, the BMS must be able to interact with the charger.

        Generally, with a trailer, the batteries and propane are outside on the tongue. Batteries don't belong in living space.

        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
          Thanks - This is helpful info!

          For the fridge, I’m likely going to wire a generator outlet next to that outlet in case I need to switch it over to the generator source from battery. I also need to confirm the power draw as we are leaning towards a different fridge than the specs I gave you (smaller fridge).

          On the batteries, sounds like flooded or AGM are the way to go...why do you prefer flooded vs AGM?
          Also, why go with 2x 6v 200Ah in series which will give me 12v 200AH vs. 2x 12V 100Ah in parallel to get the same?

          Thanks!

          Comment


          • #6
            Flooded Lead acid. Cheap. Forgiving. good to learn on. Then after you get 5 years on them, go for the expensive ones. Just check water every 2 months
            AGM costs much more than flooded. overcharge leads to popping the sealed vents and venting H & O2, depleting the fluid in the battery. Shorter lifetime than flooded

            Batteries in series share the same current and stay balanced. Batteries in parallel seldom stay balanced, AGM even more sensitive. One battery does more work and ages faster.
            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
              Thanks!

              So, looks like my new setup should be as follows:
              - 400W panels mounted to the roof and wired into the charge controller
              - Charge controller wired to 2x 6V 200Ah lead acid batteries wired in series (for 12V 200Ah setup) - these would be mounted outside on the trailer tongue
              - Batteries to the DC to AC 120v Power inverter (2000w most likely but will confirm specs/drain per your comment above)
              - 120V Appliances plugged in to the inverter (2x 15A outlets) - these would be wired out from the inverter to 15A GFCI outlets to serve as breakers on each “circuit”
              - Honda EU2200i Generator (with 2x 15A outlets): 1st plug for separate dedicated outlets in the shed wired to the generator for non battery sourced power, 2nd plug wired to a 120V to 12V battery charger then wired to the batteries (connected in the same way as the solar charge controller - no transfer switch needed so they both charge the batts at same time if the generator is running)

              some remaining questions:
              1) what would you recommend in terms of fuses between the various connections?
              2) would you recommend going larger amperage on the batteries at all (ie >200Ah) for more capacity or stick with 200Ah for now?
              3) anything else I’m missing from the equation here?

              Thanks so much again for your help!

              Comment


              • #8
                some remaining questions:
                1) what would you recommend in terms of fuses between the various connections?

                Fuses depend on the wire size, because they protect the wires



                2) would you recommend going larger amperage on the batteries at all (ie >200Ah) for more capacity or stick with 200Ah for now?

                This is your calculation, From the loads you describe, if you skip the fridge and use propane, or ice, 2 batteries should be fine w/400W of PV


                3) anything else I’m missing from the equation here?

                What are you expecting to power with that big inverter ? Without the fridge and cooking appliances, 400w ballpark seems right.
                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

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