Minimum voltage for my MPPT controller

Options
SouthernBajaGuy
SouthernBajaGuy Registered Users Posts: 2 ✭
in PV Installers Forum - NEC, Wiring, Installation #1
Greetings, I live in southern Baja, Mexico so cold is never an issue. I'm buying a kit from SunGoldPower but deleting the solar panels (no room in car and they can cause a hassle at the border). The kit is a 5000 watt 48 volt hybrid inverter and 1 LiFePO 48 volt battery, 100ah.  The panels that would come with the kit are 6 x 200 watt, 12 volt each putting the voltage at 72 so I would assume it would be adequate for my system. I don't need nearly as much power as what's in the kit right now, I'm building a house as I go so I wanted to size the system inverter correctly.  I have 2 x 100 watt panels, 12v each and I'm wondering if I would have to get all the way up to 72 or if a little lower voltage would be OK.  I can't get ahold of the solar store near my house so I don't know the voltage of the panels.  Only the watts (550 watts or 340 watts).  Any insight would be helpful! 
· Share on Twitter

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #2
    Options
    From Littleharbor thread:

    For optimum results, you want the minimum Vmp-array to be (ideally) around 1.3x the battery charging voltage...

    For a typical LiFePO4 a 12 volt battery may take around 14.2 to 14.6 volts charging... Then the array minimum MPPT voltage rating should be:
    • 4 series LiFePO4 batteries * 14.2 volts nominal charging voltage * 1.3 MPPT voltage factor = 73.84 Vmp-array (STD)
    This allows for the array/panels getting hot in summer sun and Vmp-array falling as panel temperatures rise. MPPT controllers can only "drop" Solar Array voltage to Vbatt charging voltage. This will give you the minimum number of Vmp panels in series.

    There is another thing to watch out for... As panels get cold, the Voc (voltage open circuit) voltage rises... The minimum temperatures in Winter for Todos Santos are around 12C, so you will not see too much Voc voltage rise in winter... So you have to look at the Vpanel-max input rating for your MPPT controller to figure out the maximum Voc-array for the maximum number of panels in series.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,046 ✭✭✭✭✭
    #3
    Options
    Just saw here you are looking at a SunGoldPower inverter. I mentioned in the other thread about a low max Voc. inverter I recently came across. It was that inverter. It was blue, in case that means anything. Before you pull the trigger Look around for a nigher voltage mode for reasons I mentioned earlier. For example, Go over the specs on this. I have a 24 volt model and it is working great.
    PowMr 5000W 48V Hybrid Solar Inverter 110V/120V/208V/240VAC 100A MPPT Controller | eBay

    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,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

    · Share on Twitter

Categories