First Solar

Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
I was given this panel by a friend. It's new and never placed in service. I'd like to use it on my boat to supplement to draw on a 1000 ah ( 12V ) battery bank during the day. I have a 20 kw Generator that uses 2 gallon a hour to run. I keep the run time to 4 hrs a day or so to charge with a 150ah output xantrex sw 3000 inverter / charger.

@ $8.00 a hour to run, anything I can put back is a plus.

Model STP280-24/VB
Power (W) 280 Watts
Open Circuit Voltage (V) 44.80 Voc
Short Circuit Current (A) 8.33 Isc
Maximum Power Voltage (V) 35.20 Vmp
Maximum Power Current (A) 7.95 Imp
Dimensions (in)(LxWxD) 39" x 77" x 2"
Weight (lb) 60 lb
Connector MC-4

I need a charge controller of some kind. I'd like to know if this panel is even worth fooling with. Any advice is appreciated.


  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: First Solar

    You will need an MPPT type controller.

    Look at these:

    Realistically, you will need many more panels to reduce the genset usage.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: First Solar

    Could you tell me what the output of this panel would be for 12 v charging in ah ?? I was thinking of keeping it mobile so I could keep it oriented during the best sun hours .
  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Re: First Solar

    Using an MPPT charger with 0.77 derating and assuming a minimum of 4 hours of "full sun" per day (typically 2-6 hours per day depending on season):

    Maximum Power Voltage (V) 35.20 Vmp
    Maximum Power Current (A) 7.95 Imp
    • 35.2 volts * 7.95 amps * 1/14.5 volts charging voltage * 0.77 panel+chrgr derating * 4 hours of sun = ~59 AH per day nominal
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: First Solar

    And it will not have a significant effect on a 1000 Amp hour battery bank (about 1.5% charge rate). About 15 Amps peak current.
  • Blackcherry04Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: First Solar

    Thank you so much. Now I have a idea of what to expect, I was not sure in this case it would sense to use it or not. It looks like it could save a hour of running time over a 2 day weekend. There times my generator running schedule would change by just having the extra it would put in to allow me to wait on the charge and use shore power. Everything is a trade off.

    Thank You again,
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