Can someone review my plan - panels, controller, inverter, batteries - any input greatly appreciated

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blueskies
blueskies Registered Users Posts: 54 ✭✭

I am about to purchase four 355 watt (9 IMP/max amp at 39 VMP/ max power point voltage) panels (canadian solar / $179 each PLUS $295 TRUCK FEE) and a midnight solar classic 150 charge controller ($625). The primary goal is to run a small window a/c (4.9 amps continuous running / 520 watts at 115 alternating current). (I will find other uses when the a/c is not needed.) I have been told these panels will work well with the solar classic 150 if I wire 2 of the 4 panels series and then parallel them to the controller. I know there will be surge when the compressor starts which is why i am over-sizing (i hope). Then the next part of the plan is to get the needed 12v to 120v ac inverter. SO... when I can afford, I am planning on getting the AIMS pwri300012120sul 3000 watt pure sine wave sine inverter ($399/Amazon). (And hope it hold up so i don't have to purchase some gigantic inverter at an un-Godly price.) Then after I can afford more, I know I will need a large battery bank with big wires and fuses/breakers. I know that will be expensive and will be a pay as I can thing.) The remainder of my modest needs (tv, computer...) for my solar cabin will be powered on a separate system that I already have - the midnight kid (with an output that will use the dump load to heat some water). The cabin is insulated with reclaimed R-20 poly insulation so the a/c should not need to do a lot in the 12 by 8 foot space. Help me find my technical flaws and give me any advice, PLEASE. Note - I'm trying to keep all the panels on the roof pitched towards the south which limits me on panel choices. Blueskies.

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  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
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    PS this is the first time i got the nerve to post in a forum. Please be gentle and know that I appreciate all of the info I have received from posters.

  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    I would not consider a 3000 watt inverter on a 12 volt system. In fact when I wanted to run an air conditioner, I switched my system voltage to 24 volts. It really just not practical to run a large inverter off of a low voltage system. I am personally not a fan of running multiple system to serve the same building. Your well insulated I don't think you will have a lot of run time once you have cooled the place down. If your area cools at night and If that's your plan, to run mostly during the day, I think it's doable and reasonable. Running from stored energy will present some issues.

    I also don't like multiple strings of batteries. You haven't spoken as to your storage. You won't be able to run the air conditioner without batteries. Since the array of 4 x 355= 1420 watts should be close to maxing out the Classic 150 at 12 volts, producing 90+ amps in bulk and 74 amps at absorb, the array would support a 600 -900amp hour battery bank, That would be 3 strings of golf cart batteries. I think you could run it without fear on 4 golf cart batteries, particularly when running a load during the day, but I might throttle them back during 'off season' for air conditioning.

    I suspect you have read that there are NOT a lot of fans of Aims inverters. This is better than the last 3000 watt 12v Aims inverter I looked at which used 55 watts while on! I would suggest an inverter large enough to run the air conditioner, but small enough to run reasonable sized wire and less fear of voltage sag for the system if maxed out. Something like the Samlex PST 1500, it has the option of being hard wired. They make a cheaper one for around $365, but without this option.

    https://www.solar-electric.com/samlex-pure-sine-wave-inverter-pst-1500-12.html

    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.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
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    Please, do not purchase anything until you have a good pencil and paper plan for what your "final" system is planned to look like.

    It can be very difficult to "cost effectively" put a mix and match system together.

    Also, it is very difficult to cost effectively "grow" a system. Some parts can be reused on a larger system (solar panels, solar charge controllers rated for 12/24/48 VDC battery banks). Other items cannot (a 12 VDC AC inverter only works on a 12 VDC battery bus--And you cannot--highly discourage--mixing 12 volt loads on a 24 or 48 VDC battery bank). Also, mixing smaller/larger AH batteries and "old vs new" batteries on the same battery bus is something that should be avoided.

    Understanding your loads (watts, peak watts, Watt*Hours per day, etc.) is very important for system planning. Knowing if this is a summer or full time off grid system helps. And (roughly) where the system is to be installed helps us estimate hours of sun by season.

    You have a good size home system already... So you probably know much (or all) of what we are typing about here. Just want to make sure we on the forum understand your needs and intent before we go down a rabbit hole.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
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    Thank you so much Photowhit. I will definately reconsider the Aims inverter and do research to switch this system to 24 volts. These panels and the Classic 150 sound fine at 24v? Also, I saw a good test on a Samlex inverter as far as great efficiency - will research pst 1500.

    As far as the second system - I have collected so much that runs off of either 12 volt or 5 volt USB (easy plug into 12v cigarette lighter plug or hard wire 12 to 5 v adapter). and i have small panels that would not work well with the system I am working on. I would like to leave them separate for DC to DC only and secondary / tandem system for very modest usage. And the Kid I already have is wired for using excess from that system to heat water (have 12 volt water heater element (SMS from Germany, not a fake ebay 120 element with the numbers scraped off).

    Not to confuse that with the system I am working on now. In regards to the system I am working on, I think I'll take your advice, do my research and go 24v to converter and to inverter. On days / peak sun times when a/c is not needed, I have a tiny Haier washer that should perform without much less consideration than the air conditioning.

    Hope to hear more any time and thanks again!

  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
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    Thanks, BB! The old system is one I had on a one ton van when I traveled the country a bit. I learned a lot back then about how to ruin expensive batteries but I did have some great trips. I just think of the old system as an old grandfather clock in the corner. I would never connect it to a new system. (miss that van...)

    My pencil and paper have been busy for a long time but the whole 24 volt thru mppt and sine wave inverter is just starting to click.

    While I am in Illinois right now, I plan to move the cabin (some people want to call it a tiny house) within the sunbelt within a few years.

  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    I would think you would be a little undersized array to load, but time will tell.

    I ran a similarly sized array in my tiny cabin. 10 x 16 also with roughly R21 walls. I had 4 - 1 year old golf cart batteries from a earlier system and it was enough to keep me cool for sleeping in Missouri, where our nights tend to cool off. But I was 'push n' pull'ing the batteries pretty hard. Usually taking them down to 50% SOC(or less) every night. They hung in there for 5 years/4 summers. They were setup in a 24 volt bank and I was using a PWM charge controller. My cabin was in the shade as well.

    I don't know if you will be able to run the AC around the clock, even with 2 strings of golf cart batteries. I would set it on timer to turn it's self off after 3-4 hours and turn it back on when the sun hit the array fully. You should be able to run the AC and charge the batteries, particularly if you find the duty cycle (time the compressor runs) to be 50% or less.

    I miss my cabin, no chance of moving it, it was 14 feet tall;


    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.
  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
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    I love the picture, it made my day. my roof space is just short of using six of the 355 watt (9 IMP/max amp at 39 VMP/ max power point voltage) canadian solar panels instead of four. i could use a tiny porch over the door and use six. it would be a better dollar per watt value deal anyway, especially with truck shipping. do you think that would be a significant improvement in the array? again, wire every other panel in series for 24 volt output?

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    I'll concur with moving to a 24v system with your panels, and using only four Golf Cart batteries (6v 200ah) wired in series The batteries buffer the solar fluctuations, but late afternoon as the sun angle changes, you will have to shut down.

    Inverter size, as small as you can, while still being able to start the AC. A 2Kw inverter with good 2/O battery cables, should do it,

    Powerfab top of pole PV mount | 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 ,

  • blueskies
    blueskies Registered Users Posts: 54 ✭✭
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    Thanks, Mike! Info on batteries, and 1/o guage cables is especially helpful. Nothing needs to run off this system after sun-charging hours.

    Although I will only be using a 12v computer/12v led tv and accessories and 5v alarm at night, that does not need to come from this system.

    I guess there is no need to deviate from the manufacturer size cable coming out of the panels until the wires reach the MPPT so long as cable distance between panel and controller is less than 12 feet?