12v Solar to 24v Tesla batteries

LoCoSqurrielLoCoSqurriel Registered Users Posts: 2
Good day to All,

I am new here and new to solar. I have 4 100w Renogy panels (specs below), and I want to charge 2 - 24v 5.3kWH 250AH batteries. I will also have them being charged by the engine alternator while I am driving. I am wondering how is the best way to connect them and how long it would take to charge them. I was thinking 2 panels in series and then connected to the charge controller. I was hoping with the higher voltage connected this way would get the batteries charging sooner in the day. Just looking for thoughts and concerns.

Thank you for any assistance in advance! Cheers

Electrical Data Maximum Power at STC* Optimum Operating Voltage (Vmp) Optimum Operating Current (Imp) Open Circuit Voltage (Voc) Short Circuit Voltage (Isc) Maximum System Voltage Maximum Series Fuse Rating 100 W 18.9 V 5.29 A 22.5 V 5.75 A Module Efficiency 15.47% 600 VDC UL 15 A


  • mcgivormcgivor Solar Expert Posts: 3,274 ✭✭✭✭✭
    Being that the battery is 24V you would have to series the panels,  PV voltage muse always be greater than battery nominal. The 400W would produce ~ 320W which is extremely small given the capacity of the battery, for off grid about double that would be in the ballpark. The amount of time to charge would be in proportion to the amount they are discharged, given there are no figures it's impossible to speculate. Lithium-Ion batteries need a specific charge controller, with the exception of some drop in replacement type, others will need a battery monitoring system or BMS, to safely charge them as they are sensitive to overcharging and over discharge. Can you provide more details on the batteries as well as charge controller you intend to use, there are others here who have more experience than I do and will be able to assist in the specific niche of Lithium technology. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • LoCoSqurrielLoCoSqurriel Registered Users Posts: 2

    I was going to only use one of these batteries, however, I was just wanting the ability to stay off grid longer during the days with limited sun. Due to limited roof space, I was starting with 4 panels, I might be able to add more or adding a small wind turbine. A BMS will be used as well as a temperature monitoring system as they shouldn’t be charged or discharged within certain temps.

    The Charge controller I am looking to use:


    This is all I have for the details on the Tesla Battery:

    The modules consist of 444 Panasonic 18650 cells of about 3200 mAh nominal capacity. 

    The cells are configured 6s74p, Voltage range for the whole module is about:

    18.6V soc 0%

    23.1V soc 70%

    24.9V soc 100%

    capacity ~233Ah, ~5.2kWh


    length 27”/685mm

    total width with mounting fins 11 13/16”/300mm

    width without mounting fins 11”/280mm

    height 3”/75mm

    mounting fin at 2”/50mm

    terminals apart 9”/230mm

    tubing 5/16” 8mm

    weight about 55lbs / 25kg

  • EstragonEstragon Registered Users Posts: 4,451 ✭✭✭✭✭
    Properly tilted in full sun, the 2 strings of panels may produce ~10a, for ~40-50 amp-hours in a typical day.

    Wind probably isn't a viable alternative, unless you expect to park in quite windy (as in your hat needs to be tied on) conditions.

    Assuming consumpton is likely to be more than the solar will support, I'd consider a small inverter type generator, such as Honda eu2000i. The battery likely has a fairly high charge acceptance rate, so an hour or so of generator run time in the morning would probably get much of the charging done, with the solar finishing over the remainder of the day. These generators are relatively small, lightweight, quiet, and fuel efficient (as generators go).
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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