Need to figure out what I need for my houseboat. 36v li-ion battery pack.

I am trying to use solar off grid; n my houseboat. I have li-ion battery packs 10s about 150ah. I use a pure sine wave inverter that's 36 volt. There are some new sun power 425w panals with an open circuit voltage of 72v or so. How do I make this work if it will?  These panals have micro inverters built in. I'm really confused. I don't want to use the gas generator to charge my battery's.


  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    Welcome to the forum Iankscropio69,

    Just to clarify, the panels you have are:

    DC Electrical Characteristics

    • STC Power Rating 425W
    • PTC Power Rating 390.7W 1
    • STC Power per unit of area 18.3W/ft2 (196.6W/m2)
    • Peak Efficiency 19.66%
    • Power Tolerances 0%/+5%
    • Number of Cells 128
    • Nominal Voltage not applicable
    • Imp 5.83A
    • Vmp 72.9V
    • Isc 6.21A
    • Voc 85.6V
    • NOCT 45°C
    • Temp. Coefficient of Isc 0.06%/K
    • Temp. Coefficient of Power -0.38%/K
    • Temp. Coefficient of Voltage -0.231V/K
    • Series Fuse Rating 20A
    • Maximum System Voltage 600V

    Mechanical Characteristics

    • Type Monocrystalline Silicon
    • Output Terminal Type Multicontact Connector Type 4
    • Output Cable Wire Gauge 12 AWG
    • Output Cable Wire Type PV Wire
    • Output Cable Wire Length 27.6in (700mm)
    • Frame Color Clear
    • Backsheet Color data not available
    • Length 81.4in (2,067mm)
    • Width 41.2in (1,046mm)
    • Depth 2.1in (54mm)
    • Weight 56lb (25.4kg)
    • Installation Method Rack-Mounted
    The Voc for this panel is 85.6 volts (standard test conditions) and Vmp (voltage maximum power @ standard conditions) is 72.9 volts.

    I do not see panels with attached inverters, unless something like these kits:

    How far are you committed to this project as specified (purchased panels/parts/inverter(s)/etc.)?

    I guess you are in the USA (possibly middle California)? So your AC inverter is 120 VAC @ 60 Hz?

    In general, in USA, the micro-inverters are rated for 240 VAC @ 60 Hz nominal. And that would not "play" with a 120 VAC inverter (if you have a 120/240 VAC PSW/TSW inverter, it could work).

    In general, yes you can use micro inverters to "back drive" an off grid PSW 240 VAC inverter to share AC loads and recharge the battery bank (the off grid inverter needs to be larger than the sum of your micro inverters).

    And you need an off grid inverter that is designed for connecting to GT inverters such that it can turn off or limit the Micro Inverter output once the battery bank is full. Not many off grid inverters have that capability (especially older/simpler inverters)... And it would need to be setup for Li Ion battery set points.

    So, issues seem to be: 
    1. GT inverters to Off Grid inverter charging? Was that your intent?
    2. Off Grid inverter can manage GT inverter power output?
    3. Off Grid inverter can manage Li Ion battery bank?
    4. Off Grid inverter is 120/240 split phase, or 240 VAC?
    5. Off Grid inverter is 36 VDC battery bus... That is sort of non-standard these days (12/24/48 is typical for solar power systems)--Do you need 36 VDC for boat power?
    6. "Typical" off grid operation would use solar panels => Solar charge controller => Battery bank => AC inverter (standard DC to DC solar charging of battery bank)
    7. Are you planning on using a BMS (battery management system) for your Li Ion bank? 
    8. Do you plan on communications between BMS and solar charger and/or off grid AC inverter?
    9. Planning on using LiFePO4 or similar "safer" Li Ion chemistry for your bank?
    10. Vmp~72 Volt Vmp panels can be a bit of a "pain" to configure with "cheaper" controllers--Especially for 48 VDC battery bus systems.
    If you have not purchased any major equipment yet--Hold off until you have done some paper designs. 

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset