Generator options

requiredwhenrequiredwhen Registered Users Posts: 7 ✭✭
edited November 2021 in Solar Beginners Corner #1

We're currently living in an off-grid cabin but are planning to build an off-grid house with a larger solar power system. We won't have the house for a year or two and our current battery bank is getting long in the tooth. 

Our current system is 48V with a 300 aHR battery bank. The new house will have a 550 aHR battery bank and also be 48V (Original post had wrong aHR amounts).

I'm anticipating needing a backup generator this winter to top up the batteries and it seems like we have a few options:

Option A - Use a construction 7500watt gas generator that we already own and add 2 IOTA 24V 25A or 40A chargers in series. The 2 chargers will cost about $800-1000 (Canadian Dollars). My rough estimate that they will take 2-3hrs to top up the batteries from 50% and the generator will use a lot of fuel. We'll use the system 60 times this winter I guess.

Once we have the new house, maybe I could re-use these chargers and run them off a small efficient diesel generator. Or sell the charges used.

Option B - Buy a new generator designed of off grid now. The supplier who gave us a quote for the new house system recommended a Winco 8KW system. They cost about $8,000 Canadian dollars. We'll need this anyway, so maybe just get it now.

Any advice or other options would be appreciated. Thanks!


  • wellbuiltwellbuilt Solar Expert Posts: 763 ✭✭✭✭
    600 hrs a season seams like a lot .
       My place uses a 430 ah battery and I use 10/15% over 24hours in winter with the solar turned off .
      I just run a 2800watt generator a hour or so a day and charge to full every 3/4 days 
      I run one frig/freezer and one freezer , tv  radio , cell booster  , lites , well pump 800/1000 watt 
      And really any thing I need . 
      4000ah plus battery seams like a lot .
     My place is 2800sf living space   3 car garage and 26x32 shop . Propane water heater,  stove , radiant heat floor 
      But I heat with wood .
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • wellbuiltwellbuilt Solar Expert Posts: 763 ✭✭✭✭
    There is a lot to be said for using Chargers and genarator to charge battery’s .
    but I would use the chargers off the generator you have and  buy a unit that works with 80% load 
     I think you could run off of 5500 watt generator  your inverter and battery’s will power your loads any way . 
      I think a absorb charge will take a long time you may want to use a small unit to absorb /eq 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Whoa !  That's a huge battery bank and you will need 440A DC to properly charge FLA batteries.   Are you really sure a 4400ah bank is needed ?

    Generator & charger.   Most larger 48V inverters are able to use a 240VAC generator to charge the batteries.  Generally they are high quality, good PF of .9 and in the 100A range .  Have you considered that option ?    100A @ 56V = 5,600watts and you want to allow for 50-75% surplus capacity in the generator since battery charging at high power for hours, is VERY demanding on a genset and alternator cooling.

      Unless Iota has told you specifically you can series a pair of 24V supplies, I would not try it, unless I was able to fully verify the outputs are totally isolated to a couple hundred volts.

    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

    gen: ,

  • Ralph DayRalph Day Solar Expert Posts: 1,018 ✭✭✭✭
    Really think about battery size.  While the "autonomy for x number of days" is great in theory, you have to be able to recharge the beast.  I've found it's better to have smaller battery size, more pv and a reliable generator (see mike95490 above).  
  • requiredwhenrequiredwhen Registered Users Posts: 7 ✭✭
    edited November 2021 #6
    Sorry, I just added up the aHR of each battery, forgetting that they are in series :) 

    I'll fix the original post for new readers. But the current system is 300 aHR and the new system will be 550. 
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