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  • New in the Southeast US

    My primary use for solar power is a solar charged "backup generator" to provide "wait until daylight" power for the multiple outages we have each year. The outages are usually short (under 3 hours), with a few exceptions. The longest outage in more than 10 years in this location was 16 hours (straight line winds during a thunderstorm) with the next longest being 12 hours (snow) followed by perhaps 10 hours (freezing rain). The waveform of the co-op's power isn't as clean as my inverter but the power is generally reliable.

    The storage capacity (12 volts, 540AH AGM), the inverter (2000 watt pure sine wave) and the planned items in use (via a GenTran transfer switch and/or extension cords) provide an acceptable level of power for 16-18 hours if not heating (gas fired furnace) or cooling (5000BTU window unit) and 8 hours if heating or cooling (furnace or A/C on 1/3 of the time). This is to 50% DOD on the battery bank, which is acceptable if you consider the system as a big UPS. For long term use, I would limit DOD to 20% or less.

    The system is kept charged by a single 250 watt panel on an EPEver / EPSolar Tracer 3210A 30 Amp MPPT charge controller. There are no on-going loads on the battery bank but it does get regular "exercise" with enough power being drawn to drop the battery voltage to a level that puts the controller in "Boost Charge" mode. In the event of an extended outage, there is a 40 amp Tracer 4210A MPPT controller and another 30 amp Tracer 3210A MPPT controller to handle the additional 1250 watts of solar that is not yet installed. If the local electric co-op gives an estimated restore time, I can determine whether setting up one of the gasoline generators or putting more solar panels in service is the better option.

    The manufacturer specs the 12HX330 AGM batteries I have as 100% SOC at 12.72 to 12.84 volts after 24 hours rest. All but one of the five year old batteries still meet that spec, with the odd one being very close at 12.70 volts. I use the EPSolar software to monitor the system and, as I type this late on a day in August, the charge current is down to 0.01 amp, the battery is at 12.93 volts and the SOC is 55%. Obviously, this value does not match the battery specs so I just ignore the SOC display.

    All of the EPEver / EPSolar controllers seem to display SOC but none of the manuals I've seen offer a way to calibrate it. Instead, I just watch the battery voltage and try to manage loads to keep the voltage under load at an acceptable level.

    =================

    I write PAW fiction because the characters in my head keep having interesting conversations

  • #2
    Howdy notyoung and welcome to Solar Panel Talk, lots of people around these parts who know off grid, I only know enough about off grid to be dangerous, I stick to grid tied systems, cheers.

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