Newbie Here, Need Opinions on Inverters

H_GH_G Registered Users Posts: 16 ✭✭
Title says it all folks, I've already hooked up 4/100watt panels to 4/125 amp hr lead acid deep cycle batteries, they're fused, controlled and everything works fine. I'm not using this system daily but will be kept ready for an emergency and ideally I'd want to run a small office fridge (about 3ft high) and/or a small washing machine and maybe a fan at night but nothing else and one appliance at a time. 
Will a 1500 watt pure sine inverter be enough or would I need a 2000 watt one? Which brand?
I have looked at the xantrex and Aims online as I'd like one that's not super expensive but reliable in the long run.
What brand and power would you get for this set up?
Please bear in mind I see this as an emergency generator without oil, gas nor noise. 
I may have neglected to mention a 1200 watt square wave harbor freight inverter I already have and seems able to run this fridge or even the regular one. I've gotten these smaller appliances since becoming disabled and realizing that I'm alone and these smaller appliances would -in theory- draw less power while running on solar or off generators. Having them as back up also gives me peace of mind, knowing my cold stuff won't go bad. 


  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    1,200 to 1,500 Watt AC (TSW recommended) inverter should be enough.

    Your batteries, are they 12 volt @ 125 AH capacity deep cycle batteries (or Marine rated)? All 4 connected in parallel?

    If the bank is as I describe, that bank would be capable or "reliably" running about a 1,250 Watt inverter at rated load (and 2x surge current).

    If these batteries are flooded cell Marine type (not true deep cycle) or a communications/UPS battery designed for float service--They are not ideal for your needs.

    Next time--I would suggest getting "golf cart" deep cycle 6 volt @ ~225 AH--Put two of them in series time two parallel strings for a 12 volt @ ~450 AH battery bank (up to 3x parallel strings can work OK). They are usually cheaper and more reliable/rugged than other smaller battery types. And great for learning with (most people kill their first/second set of batteries). I prefer to not put a bunch of 12 volt batteries in parallel for a 12 volt battery bank (hard to see when one battery is having problems with just a volt meter).

    Solar panel wise, assuming 5% to 13% rate of charge:
    • 4 * 125 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 471 Watt array minimum (emergency, weekend, seasonal power)
    • 4 * 125 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 942 Watt array nominal (full time off grid)
    • 4 * 125 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,224 Watt array "cost effective" maximum
    So, I would suggest that your 4x 100 Watt panels are a bit on the small side--But an work for emergency power. If you where to go off grid for weeks/months at a time, I would suggest a 10% rate of charge minimum is a nicer system and your batteries will last longer.

    If you want to run (mostly) a small refrigerator--You are looking at around 1,000 WH per day... For someplace like San Juan PR (Guessing) you would need a minimum array of:

    San Juan
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 72° angle from vertical:
    (For best year-round performance)
    Jan Feb Mar Apr May Jun
    Jul Aug Sep Oct Nov Dec
    1,000 WH per day * 1/0.52 off grid system eff * 1/5.0 hours per day = 385 Watt minimum array

    I would suggest that you only "plan" on a fixed daily load of 65% to 75% of "predicted" output:
    • 385 Watt array * 1/0.65 solar capacity derating (i.e., use less genset fuel) = 592 Watt array "comfortable" year round operation
    So, for your system at 1,000 Watt refrigerator off grid, I would suggest 592 to 942 Watt array minimum/nominal for a full time off grid/minimum genset system.

    If you are in PR, it sounds like it is getting scary there with the power situation (government utility going bankrupt?).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • H_GH_G Registered Users Posts: 16 ✭✭
    edited October 2016 #3
    Your info is so complete and spot on, greatly appreciated. 
    Yes, batteries are in parallel and true deep cycle Duracell's, 12 volt. 
    Yes, I'm in PR but not in San Juan. 
    Yes, reality is finally catching up with culture here and that has turned me into a prepper of sorts. 
    I kinda read up and got this set up in a hurry after existing two days in that blackout and having to run around servicing generators when I can hardly walk nor stand, so getting ready for anything is my only hobby now. 
    Looks like I didn't make too many rookie mistakes and what I learned before pulling the trigger I got from this forum, you all provide an invaluable service to people like me and I can't thank you enough, so be proud you all. 
    Feels good to see I didn't do that bad for a first timer.  
    Thanks again. 

  • BB.BB. Super Moderators, Administrators Posts: 33,327 admin
    edited October 2016 #4
    A Honda eu2000i can be a nice backup for you... Uses around 1 gallon of gasoline every 4 to 9 hours (1,600 watt load to 400 watt or less). Also, since they have an internal fuel pump, you can buy/modify a fuel cap and it will siphone fuel from a 5 gallon gas can:

    Just change the oil every 25 hours (recommended)--Been looking for an external oil sump/filter that could make oil changes less often--but have not seen anything yet).

    Of course, need to ensure that don't have fuel leaks (draw fuel, and worry about fire) and you don't get carbon-monoxide into your home.

    Best wishes for you and your family... It is not a fun situation.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • H_GH_G Registered Users Posts: 16 ✭✭
    Those are really nice gennies but I already own a couple Chinese made ones that had me disappointed in changing the oil so often but now that I see Honda's are the same way I guess I should keep quiet about it, as they're not very noisy, were super cheap and so far have been very dependable provided you change plugs and oil almost every time you run them. I also add anti ethanol treatment to the gas I use in them as gasoline comes with crap in it nowadays.
    Didn't realize Honda's have a gas pump and again, that's fantastic info to remember next time I need one.
    Blackout aside, power has been reliable here in the last few years but I'm sure glad I kept gennies ready. Just over a week ago we had medium sized sun flares around here and that's one more thing to try and be ready for. I keep my inverters in a faraday cage I built myself. 
    Love learning new stuff here, much appreciated. 
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