Off grid air conditioning help needed

treeleetreelee Registered Users Posts: 1
 hi all, need some help choosing an off grid air conditioner, my head is spinning! Trying to decide between window unit, split mini or portable. It is a small space, only 150sf, good insulation. Im in AZ so not worried about sun time. I have 4 panels 230w each and 6 batteries. My concern is do i go for lowest btu's or efficient mini split? There is a small portable designed for doghouses at 2500btu, window ac at 5000btu or lowest i 've seen split at 9000btu. Big price differences! I dont need to run all night. Should i just use cheap window unit or spring for the split mini?


  • littleharbor2littleharbor2 Solar Expert Posts: 1,135 ✭✭✭✭
    I put a 5000 BTU window shaker in my bedroom in Baja. Granted insulation was lacking but it barely lowered the temp of the room when it was in the high 90's. 

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • PhotowhitPhotowhit Solar Expert Posts: 4,782 ✭✭✭✭
    edited May 2018 #3
    If you don't intend to increase the size of your system, I might go for the mini-split. 

    I've used a window unit for a room about the size you are referring to, a 10x16 cabin with pretty much built to be air conditioned. Built in the shade, 6" thick walls, high roof to allow the air to stratify. Coming home with the room around 90 and humid it would take pretty much an hour to cool the room down. During this time the duty cycle (amount of time the compressor ran) was pretty much 100% after that it would continue to reduce from 70% to around 30%. I live in Missouri so I put it on  timer and had it shut down after I went to sleep. Missouri mostly cools off to around 70 in the evening.

    I don't know the capacity of your battery bank (6 batteries might be watch I ran a 24 volt system with 4 golf cart batteries, so was running them down to about 50% of capacity each night along with the other loads. I started with about a 1000 watt array. After the first summer I increased the size of array to 1200 and then about 1600 watts. This allowed me to run the air conditioner during the afternoon a bit after the batteries reach absorb. In this manner I could utilize the energy that the batteries couldn't use and cool down the cabin so the duty cycle was lessened in the evening.

    Batteries were pretty well stressed but lasted 4 additional years (they were already 1 year old).

    A mini split will be considerable more efficient than a window unit. The cost vs value is something you will want to decide. I think it is a near thing.

    A true sine wave inverter would be nice as the air conditioner will create some heat and use more energy running off a modified sine wave inverter. Also a high wattage continuous run will be handled easier with a higher voltage system, assuming a 12 volt system but could be 6 - 12 volt batteries.


    Most of original array and Power center.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do
  • jonrjonr Solar Expert Posts: 1,188 ✭✭✭✭
    edited May 2018 #4
    Consider the ones below.   Besides  insulation, make sure that the building is very well air sealed.

    You can calculate the load to know how many BTU you need.

    But inverter driven AC helps a lot with over-sizing issues.

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