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  • #16
    Originally posted by Living Large View Post
    For my particular low sun hour in winter application, I was drawn heavily by the high charge rate I could use from the genny, when needed. I didn't want 4, 6, 8 hours of gen run time. Every app is different, but this was one parameter that was attractive to me.
    For those who have not researched this area, the best use of the generator (short, high current run) is for part or all of the initial Bulk stage. Then stop the generator and let the panels contribute during the many hour Absorb and Float as well as picking up opportunity loads.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #17
      Originally posted by inetdog View Post
      For those who have not researched this area, the best use of the generator (short, high current run) is for part or all of the initial Bulk stage. Then stop the generator and let the panels contribute during the many hour Absorb and Float as well as picking up opportunity loads.
      Is it necessary to over-size the panels in order to provide extra amps for charging and running loads? A related question I have had but not yet articulated is this: I believe I read that one must put more than 100% into the battery for what is taken out. I have commonly seen ppl factor in the inverter inefficiency to balance panel input but don't recall the same being done for battery inefficiency.

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      • #18
        Originally posted by lkruper View Post
        Is it necessary to over-size the panels in order to provide extra amps for charging and running loads? A related question I have had but not yet articulated is this: I believe I read that one must put more than 100% into the battery for what is taken out. I have commonly seen ppl factor in the inverter inefficiency to balance panel input but don't recall the same being done for battery inefficiency.
        LFP batteries, if I recall right, are about 98% efficient, so you only need to return about 102% of what was used. Much better than my NiFe batteries at 70%, or lead acid at 80%

        You have harvest losses (your panels will generally only produce 80% of nameplate - this last week, I'm down to about 60$ of nameplate from heat on the panels - 102°F air temps and no breeze)
        inverter losses need to be added in, my 1Kw day time loads pull 1,400w through my inverter (at lower powers, it's not really efficient)
        Some more loss in the charge controller, so I'd be very tempted to have a nice cushion against losses.

        You take your expected daytime loads (I've got a 1KW water pump that runs about 3 hours a day) and subtract those from your charging currents, since that power goes to loads, not battery charging.
        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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        • #19
          Originally posted by lkruper View Post
          How do the numbers look for purely emergency backup?
          Heh, that depends on how much you are willing to spend / waste. Despite my love of lifepo4 for reasons other than just cycle life, I don't think they make financial sense as a backup that won't get active use frequently.

          Like mentioned before, you don't want to store them fully charged and sitting around forever. Unless you are a corporation that can take the 20% or more capacity hit yearly doing that, an even more in high heat conditions, it just doesn't make sense. One would have to compare that loss to a well-maintained lead based battery setup. I personally couldn't be able to willingly leave a lifepo4 battery at full charge at idle for more than a week or two.

          Details like these and how they differ operationally from an EV or RC model control standpoint immediately popped up. Unless you are doing one-day or possibly a weekend camping trip, designing around 80% DOD and a small bank can be a trap. For autonomy, you'll want to increase capacity just like you would with lead. On the other side is this standby / idle situation - you don't want to store at 100%, so you'll only charge your bank to 50 - 75% DOD, and then charge again when you return. Hope it isn't raining.

          Juggling the capacity of autonomy and idle/backup reduced storage capacity involves too many details to put a blanket statement on. Only the owner of the bank would be able to determine that. Keep calculator handy beforehand.

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