A/C with solar

HK91HK91 Registered Users Posts: 4
Here is what I have to work with 12- 100 watt renogy panels and a 100 amp mppt C.C. 6- t-105 re batteries to run a victron 500 watt inverter with a 450 watt 4.5 amp A/C. Question 12 or 24 volt on the panels to get the most solar power into the battery bank and wiring size and connector ideas, I can buy bigger wiring but not more batteries.The controller can use 4awg wiring so trying to get from 10awg to 4awg and solar connectors that I have seen only handle 10awg .Anderson powerpoles or?


  • BB.BB. Super Moderators, Administrators Posts: 32,998 admin
    I am a little confused... Is your question on how to build an efficient solar array with your 12 panels? Or is it to find a plug set that can take higher current?

    For the array question, it does depend on the specific charge controller (Vpanel-max, Vmp-min/max range, 12 or 24 volt battery bus).

    A "typical" higher end MPPT controller can take ~44 to 100 VDC Vmp-array input for a 24 volt battery bank (or ~22-100 VDC for Vmp-array on a 12 volt battery bank).

    For your 12 panels on a 12 volt bank, a minimum of 2 in series (6 parallel) to 6 in series (2 parallel strings) would work fine (Vmp-array~36 volts to 108). Note that 6x series may be a bit high if you get sub freezing weather (Voc-array goes up as ambient temperature drops). Note that MPPT charge controllers get a bit less efficient the higher Vmp-array vs Vbat voltage (ideal is probably around 2x Vbatt-charging--12 volt charging at 15 volts, Vmp-array-12~30 VDC "most efficient").

    For a 24 volt bank, you would probably want 3-4 panels in series minimum.... All in all, 4 series x 3 parallel strings is probably the best for your usage, unless you have have a very long wire run from the array back to the charge controller/battery shed.

    Regarding heavy current power connectors... They can get scary expensive. Anderson does make high current connectors too (use on aircraft/tanks/etc. for external start power).



    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,987 ✭✭✭✭✭
    I'd have to go back to the books to be sure, but if your 100 watt panels are rated for a series fuse of 15 amps, you are likely find having 3 strings in parallel with out using fuses or breakers on each string. @BB. likely knows the math and if derating is required, but 2 strings shouldn't be able to send more than 15 amps back through 1 string.

    Running an air conditioner on a minimal system will take some thinking. First a 500 watt inverter is not likely to meet the starting needs of a small window unit, most have a pretty high starting surge. Might try it now if you have the inverter, just be sure you have the batteries fully charged. 

    It will be seriously unlikely you will be able to run the air conditioner around the clock. I had a slightly smaller system when I started my adventure of running a small window unit. I had a 1000 watt array and 4 Golf Cart batteries. I ran them in a very well insulated tiny home 10x16, 6" thick walls, built in the shade. I ran a ran a window unit that used roughly 450 watts (the most efficient I could find locally, 5200btu Kenmore? from Sears) In the tiny home it would run 70-80% of the time for the first hour or so, then around 50% for the next couple hours and backed off usually to 30-40%. I live in Missouri where it often cools off at night even in the summer. I always set the timer to turn off the air conditioner by 2 am.

    Since this was draining the battery bank near 50% each night it was usually mid afternoon when I was reaching absorb, so I didn't try to run the system during the day. the following summer I added 300watts and 300 watts again the next year. The added array allowed me to run the air conditioner during the day some time after the battery bank reach absorb stage of charging. This reduced the early night time load as the home was already cooler to begin with. If you have a well insulated smallish area to air condition, you may find you can run some during the day. 

    If your home is in the sun the solar gain will be difficult to over come. Thin walled camper rougher still. I used a 1400 watt quasi pure sine wave inverter at first and a 1800 watt inverter later (ProSine). I used a 24 volt system which gave me a slight advantage, but a PWM charge controller (all fit on a 60 amp CC), your MPPT should give you a 10% advantage or so...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • EstragonEstragon Registered Users Posts: 4,496 ✭✭✭✭✭
    You would typically use something like this to go from 10ga pv wire to bigger stuff.

    There are various sizes depending on how you series/parallel wire the array.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • HK91HK91 Registered Users Posts: 4
    BB both efficient and wiring upgraded, it sounds like I would be better off staying at 8 panels, 4 batteries and skip the 100 amp C.C. and just get a quality dual fuel inverter generator
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