Maybe a dumb question...

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PauloScheidegger
PauloScheidegger Registered Users Posts: 1 ✭
in Solar Beginners Corner #1
I have two 330W PV and a 700W grid-tied 2-input microinverter that is yet to arrive. I have also a 324W lead-acid battery from my e-bike. Is it safe to plug this battery instead of one of the PVs? I'm aware the battery would be depleted in less than one hour, but will it be safe for the inverter? What about a much bigger 3kW battery bank? Will it hold for maybe 5~6 hours or could it damage the inverter?
I've already fried a 600W microinverter with this very same PV pair (no battery, of course), presumably by surpassing its 600W capacity with the 660W combined PV power.
It's just a theoretical question, I don't intend to risk another inverter to try it.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
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    I would never connect a voltage source like a battery, to a inverter that expects to see a current source (PV panels)
     It either works, or goes boom when the inverter cannot regulate the battery voltage to what it needs.
    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
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    What was the pv array Vmp and Imp for the 600 Watt gt inverters that fried?

    Ok general, an  MPPT input should work ok from a battery bank.

    But that is not always the case. And at least one designer/member here suggested a low value power resistor to "soften" the battery ability to surge high current a bit (solar panels are current sources, not voltage sources, so solar panels have almost no surge current capability). Depending on the working voltage and current required, adding a power resistor to drop a few volts at Mac load could work.

    But that is a guess, and probably no company will let you talk to a design engineer (and would not guarantee the results of something not tested).

    Generally it is over voltage, and possibly overheating that kills a GY inverter.

    There is also the possibly of a nearby lightning strike taking out electronics too (not your case?).

    Just out of curiosity, why battery and GT inverter? At typical utility power costs, 3 kWH is worth around $1. And gt inverters, if they work correctly, you will not see any effect on your home's AC power (other than the utility meter, another complicated/it depends post,

    Of you wanted to run test loads and long term cycling tests, I could see power savings (charge from grid and return most power back to the grid).

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • PauloScheidegger
    PauloScheidegger Registered Users Posts: 1 ✭
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    Thanks, mike95490. It is this kind of explanation I need to learn a bit more. As I said, it's just plain curiosity to help me understand what can and can't be done.
    BB, my PV Vmp are 37.5 VDC and Imp is 8.8 A each (https://www.enfsolar.com/pv/panel-datasheet/crystalline/39571). Regarding lightnings, although southern Brazil is the most lightning prone region of the world, it was a sunny and dry week when the inverter failed. Its case was VERY hot, to the point it was impossible to read input MOSFET markings after lifting thermal padding. All eigth input SMD MOSFETs were shorted out as well as most input transformers windings.
    It certainly makes no sense a battery feeding a grid-tied inverter, but I wondered if it could be an emergency alternative during a long term power shortage. It would also require a small inverter to supply AC to the microinverter as well as openning mains general power switch to avoid a short when power restablishes. Just wondering since I do have a battery bank to feed the e-Model T I am building.



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