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Generator vs batteries

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  • Generator vs batteries

    Im wondering what is more cost-effective:

    Suppose a house needs max 1Kwh per hour, max 6 hours per EVENING. Thus total +/- 6Kwh.

    What is more cost-effective?
    1. generator or
    2. deep cycle batteries charged with solar panels

  • #2
    You can do the math yourself but IMO for a 6kWh load a generator will always be cheaper to run.


    • #3
      Which one is more cost effective depends on the application, what factors you take into consideration in the cost analysis, and how long into the future you're planning takes the analysis, usually in terms of years.

      Short answer:
      Short term, the generator option will probably cost less.
      Long term, at some point, PV/batteries will be more cost effective.
      The questions are: What factors to consider in determining cost effectiveness ? And, for how long is the analysis to run in terms of time ?

      If you're interested, read on. If not, go the last sentence of this post

      Solar energy utilization is generally characterized (and justified) by (sometimes much) high(er) first/initial costs for the equipment with low(er) operating costs than for other, usually more conventional means of meeting a duty.

      One way to see that - and perhaps justify it - is to consider the high initial cost of solar equipment as sort of prepaying future operating (including fuel) and maint. costs associated with the alternatives to solar with perhaps an additional advantage for the solar option of some insulation from future price fluctuations in those future conventional (non solar) operating costs, particularly if those future costs are thought to have a higher probability of increasing rather than decreasing.

      So, in it's most basic terms, an economic analysis that involves solar energy equipment against other alternative methods to meet a duty is often done by comparing an initial known investment with estimated future operating costs.

      That analysis is then done for each method of meeting a duty. For such cost analyses - if the most cost effective method is the goal - the option with the lowest combination of in initial and operating costs on a NPV basis is chosen.

      When comparing solar as a means of meeting a duty with any other means of meeting the same duty (goal(s)), both alternatives (or all alternatives if more than two options are being considered) are compared using the same criteria. Sometimes there are many factors, sometimes few. Sometimes the analysis period is short, sometimes long. Whoever is footing the bill ought to be the one who decides the criteria for the analysis and how complicated it needs to be.

      The alternative that produces the lowest NPV in terms of all costs associated with that alternative is one way to define the most cost effective alternative.

      The common reality these days, and as its been for a long time is that for short periods of, say, a few years or less, and if the economic criterion chosen for the analysis make any sense and are not slanted in the solar option's favor - as solar peddlers and the greenwash media often/usually do - the solar option is not usually the most cost effective.

      For what you describe, given the relatively small load of 1kW, if you don't put a high $$ value on piece/quiet, short term, the relatively low(er) generator initial cost will probably make that option more cost effective than the PV/battery option more cost effective for any reasonably short analysis period.

      As the period of the analysis gets longer, the fuel for the ICE generator will probably be the biggest factor impacting the NPV of the long term costs of the generator option.
      As the period of the analysis gets longer, the operating costs of the PV panels and associated equipment will be pretty low, maybe --->>> 0$, but the batteries may have some operating/replacement costs, as well as perhaps some maintenance PITAs.

      The point in the future when the NPV of the costs for the two alternatives are equal is when they are equally cost effective.

      So, for the simple analysis described above, if your period of analysis (that is, how long, years maybe, you plan to be meeting a 1 kW load 6 hours/day) is shorter than the point in the future when the alternatives are equal, one option will be more cost effective - I'm guessing that's the generator option.

      If your period of analysis is longer than that breakeven point, the other option - I'm guessing the PV/batteries - will be more cost effective.

      One way to go might be to get a generator and see if the PV/battery option gets more cost effective

      Take what you want of the above. Scrap the rest.


      • #4
        i'd make a hybrid system. medium size battery bank, small PV array, and a generator. If you run out of solar, fire up the generator to run loads and recharge. After a year you will know your usage and costs and can decide to purchase more fuel or more solar PV.
        For this use, I'd get a propane conversion kit, the generator will run longer and cleaner from propane
        Powerfab top of pole PV mount (2) | 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



        • #5
          Thanks for all the replies above.

          In the country where I am now i can buy 3kg LPG for only +/- 1.50 USD .

          I have read another thread here, Honda 5Kw generator = 1 gallon lpg per hour.

          So, in an offgrid situation here perhaps wise to use a generator in the evenings for some heavy loads, like aircons just for a couple of hours.


          • #6
            Originally posted by GeorgeF View Post
            Thanks for all the replies above.

            In the country where I am now i can buy 3kg LPG for only +/- 1.50 USD .

            I have read another thread here, Honda 5Kw generator = 1 gallon lpg per hour.

            So, in an offgrid situation here perhaps wise to use a generator in the evenings for some heavy loads, like aircons just for a couple of hours.
            So, consider a modification to Mike's suggestion: Get a generator and a battery bank sufficient to meet your needs as you define them, but hold off on the PV until you've lived w/the generator/batteries for a year or two - or longer. I kind of doubt the price of PV will be going up much anytime soon.

            In the meantime, study up on off grid PV. Any system you then acquire will be better designed and constructed for the learning.