200 watt panels to Battery AH ?

Kevin10873Kevin10873 Posts: 2Registered Users
I have two 100 watt panels and will run them through a MPPT controller. I would like to know how big a battery do I need. I will be using the batteries as 12 volt without an inverter for a just in case the grid is hacked. I may run a small 12 volt TV or a 12 Volt scanner. I was thinking a 100 AH AGM would work; what do you think?


  • PhotowhitPhotowhit Posts: 4,764Solar Expert ✭✭✭✭
    edited March 30 #2
    That should be about perfect, 2 100 watt panels should reliable produce about 10-12 amps in the charging range for a 12 volt battery bank, or about 10-12 % of a 100 amp battery bank. That's in the range of 10-13% we like to recommend.

    If you are buying an inexpensive MPPT type charge controller, you should check to see that it really is an MPPT type! also the panels should be run in series for best results.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • Kevin10873Kevin10873 Posts: 2Registered Users
    Thanks Photowit; I purchased a EPEVER MPPT Tracer A series controller with a MT 50 remote meter.
  • mcgivormcgivor Posts: 2,390Solar Expert ✭✭✭✭✭
    The EPever is supposed to be a reasonable product, being a true MPPT controller. The battery capacity should be calculated by the loads and what they draw, amps multiplied by hours, remember a 100Ah battery has a usable capacity of 50Ah maximum, for longer life expectancy, less depletion is better. Have these calculations been done as it appears, from the outside at least, that this is a reverse engineered system, based on the question, don't want to see fundemental mistakes made, that's all.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    900W  3 × 300W No name brand Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal as a backup system. 
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergencies and welding.
  • littleharbor2littleharbor2 Posts: 1,093Solar Expert ✭✭✭✭
    For a beginner you might want to consider a couple 6 volt FLA golf cart batteries. They are inexpensive and will give you around 200 - 220 amp hours. A scanner sounds like something you would keep on continuously, probably more than a single 100 ah. battery can handle. That being said  and if this is going to be an everyday system you would want to add more charging power. Rule of thumb is 10% of your ah capacity for charging amperage in a daily use system.  which, in this case would be somewhere in the 20 - 22 amps of charging power. a third 100 watt panel should get you there.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

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