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Minimum battery sizing for PV system with prime generators

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  • #16
    Originally posted by Mike90250 View Post
    have you calculated how much solar & real estate you will need. I'd suggest GridTie inverters and shave load off the generators. skip batts.

    It is my understanding that grid-tie inverters do not play nicely with generators.
    It would only work if my PV < load. In that case, I would just be deloading my generators.

    Deloading a generator a few hours a day does save me some fuel, but it keeps my run hours high and only marginally reduces fuel consumption. Generators are most efficient at 100% load.

    Originally posted by Sunking View Post
    Puck me thinks you might be dealing with a low PF load. Battery Inverters and low PF loads do not play well together. So consider that so you do not shoot yourself in the foot like a DIY would do then wonder why it does not work.
    I think I know what you are worried about, but these are not low PF loads.
    We run them off of inverters already(UPS), so most of the issues are mitigated.
    Last edited by pucksr; 10-24-2017, 03:26 PM.

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    • #17
      A 5Kw solar inverter wont sync to a home size 8Kw generator. But utility scale 50-500kw generators are much more stable, and if you can generate enough solar to shut down 1 genset, you save fuel. If you add batteries, you more than double your expense.

      what is the scale of this install? A single 20kw cell tower? A 800kw village? 40 separate 20kw towers?
      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

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

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      • #18
        Originally posted by Mike90250 View Post
        A 5Kw solar inverter wont sync to a home size 8Kw generator. But utility scale 50-500kw generators are much more stable, and if you can generate enough solar to shut down 1 genset, you save fuel. If you add batteries, you more than double your expense.

        what is the scale of this install? A single 20kw cell tower? A 800kw village? 40 separate 20kw towers?
        A 100kW cell tower(essentially).

        While I have designed systems with parallel generators, normally the parallel is for redundancy, not to meet capacity. So, if I had two generators it would be for N+1 purposes.
        A 100kW generator is a small generator in the industrial world. We might get a little exotic and do a configuration where each generator is .5N and have 3 generators. However, that is about the extent of the array. That is a whole design debate which isn't really relevant here.

        One of the other advantages of a battery system that can operate for 4-8 hours is that you could hypothetically have all generators offline for certain types of maintenance. This has advantages. Imagine being at a Puerto Rico hospital right now. If you need to perform any scheduled maintenance on the main generator plant, you need to bring the main generator offline. If you have a two generator system, you have switched to the alternate.(which might be a closed transition, but probably isn't) If the alternate failed(which is shouldn't, but who knows if they followed NFPA 110), and you are lucky, you were able to temporarily connect a mobile generator. (which is almost certainly an open transition). You have to cross your fingers and pray that the nurses hooked all of the right equipment up to the orange plugs and that the battery doesn't crater. It is a UPS, so you only have 15 minutes if maintenance was done properly. Hopefully everything goes well. Even though all of these systems are designed to work, it is stressful for the people working on it. A 4-8 hour battery it a low-voltage alarm with a good amount of warning is a nice thing to have in your pocket. Even if the batteries are degraded, you still have hours instead of minutes. It discourages people from doing as much "hot work"

        So, besides all of the cost benefit, these systems tend to be better from a personnel perspective.



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        • #19
          I cant fathom the size of a 16000kwh battery, which would be needed to handle 8 hours load
          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

          solar: http://tinyurl.com/LMR-Solar
          gen: http://tinyurl.com/LMR-Lister

          Comment

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