DukeCox: Looking for tips on buying a new genset

This discussion was created from comments split from: Need an expert.


  • DukeCoxDukeCox Registered Users Posts: 1
    Hi. This is my first time on the site. I am glad to find such a site. I moved into a home a while back that is powered by an off the grid solar system. I have many questions. The system was designed and built by very bright man who passed away without leaving detailed notes and instructions. I am preparing to purchase a new generator and the question arises, should I get an even larger generator? 
    The current generator, which seems to have been running everything pretty well when needed, but now needs service, is a 7,000 watt generator. It has begun to sputter, which seems to affect the steadiness of the current to the house. Is that inherently destructive to the system or appliances? Or , do I need a larger generator?
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Welcome to the forum Duke,

    I have split your question into your own discussion--Usually makes it easier to focus on your questions and answers and not mix them up with the original poster.

    You should probably first do a simple one line drawing of your system and label each component (i.e., 10x yyy Watt panels, ABC model xyz solar charge controller, 4 series x 3 parallel 6 volt @ 200 AH flooded cell batteries, brand X AC inverter-charger, etc.). And estimate how much electrical power you use summer and winter (Watts peak, Watt*Hours per day, etc.).

    You are going to be your own service person (unless you can find a friendly/knowledgeable person to service/train you on your system). Having a system design/parts list will be a big help when it comes time for repairs/replacements when things fail.

    You should also review settings like charging voltage and time for you battery bank.

    Have some tools like a hydrometer (if flooded cell lead acid batteries) and a nice AC+DC Current Clamp DMM for debugging and better understanding of your system:

    https://www.solar-electric.com/search/?q=hydrometer (Hydrometers--Make sure to rinse with distilled water before putting away)
    https://www.amazon.com/dp/B075ZHDQFP (low cost AC+DC Current Clamp DMM--Good enough for our needs)
    https://www.amazon.com/gp/product/B019CY4FB4 (mid-cost AC+DC Current Clamp DMM)

    My goal is to have a "balanced system design" for you...

    In general, your daily loads define your battery bank (for a typical off grid home, generally your battery bank is ~4x your daily load--Two days of storage and 50% maximum discharge for longer battery life). Then you design the solar array to "keep your battery happy" (roughly 10-20% rate of charge from solar), and size the array for hours of sun and daily loads (are you in Cheyenne Wyoming area?)...

    And you play with the numbers (larger solar array to save genset fuel in winter), choice between smaller genset that runs longer (if your peak loads are not very big). Fuel choices--Propane (nice if you have large propane tank for cooking/hot water/etc. anyway--Can be hard to start/freeze tank in very cold weather). Or gasoline (seems to be easier starting if very cold climates, but not great to store). Diesel--Harder to start in cold weather.

    For more gensets--Running them at 50% - 80% loading (typically charging battery bank) is most fuel efficient. A large gasoline/propane genset running at 25% electrical loading generally uses about the same amount of fuel (gallons per hour) as running at 50% loading. Inverter-Generators and Diesel genset do run more efficiently at lower loading (although, diesels should be run at heavier loads for better engine life and less service issues).

    So--The more you can tell us, the more help the folks here can be.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,581 ✭✭✭✭✭
    Generators have engines just like cars and trucks.  They require regular maintenance, which is far too often neglected.  The consequence is either you have to repair or buy a new generator, or your house goes dark and then you buy a new generator and replace ruined batteries.
    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 ,

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