4 x 175 watt 12v panels….Morningstar Prostar MPPT 25a enough?

1911
1911 Registered Users Posts: 51 ✭✭
in Solar Beginners Corner #1
Would a Morningstar Prostar 25a mppt charge controller be enough for 2s2p 175w 12v solar panels? 

this would be charging 2 x Sun Xtender 258ah in series.

i have a second Prostar mppt 25a if i need to use it.

thanks!
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,113 ✭✭✭✭✭
    #2
    That, being a 24 volt system, is a good fit.

    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.

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  • 1911
    1911 Registered Users Posts: 51 ✭✭
    #3
    is it advisable to oversize the charge controller?

    will using a cc at its upper limit of rated capacity harm the unit?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #4
    MorningStar does (in general) produce well designed and mfg. units. The typical "over paneling" for MPPT controllers is ~30%... Solar panels in warm to hot environments, in general, produce less power (voltage*current=power/Watts where Voltage or Vmp falls as panels rise above 25C--Standard test conditions.

    For example--A typical "max suggested array" for a 25 Amp @ 24 volt system:
    • 25 amps * 29 Volts charging * 1/0.77 panel+controller derating = 942 Watt approx max cost effective array
    Note that "good" MPPT controllers can manage their output current/power safely and reliably. If there is "too much current", the MPPT controller will throttle back on the output current (high equipment temperatures, low panel temperatures/large array, etc.).

    You are correct... Two things really kill electronics... High temperatures and thermal cycling. (moisture, dust, real bugs/insects, vibration are not great either).

    Temperature wise--For every 10C/18F over 25C/77F, the electronics will age 2x faster (i.e., 95F will have 1/2 the "life" of electronics). Keeping things "cool" (controllers, batteries, etc.) are very helpful to extend system/component life.

    Regarding, thermal cycling--Every transition for cold to hot and back to cold (i.e, cold room, heated by sun/electrical current during hot day, and back to cold) is also very hard on electronics (good design/assembly practices help a lot here too).

    In the end, keep the room cool and with good ventilation--And avoid lots of thermal cycling (i.e., room shaded/good venting, etc.).

    If you wanted to run the controller at 60% (or whatever) of rated array to keep it cooler--Won't hurt anything. However, it will cost you more controllers (or a larger controller)....

    Is it "worth it"--1/2 array size = 10C cooler (just pulling numbers from the air)? Use 2x the $$ (two controller for example) last 2x longer--Not bad... But 1x controller being replaced twice over time is the same "cost" overall... More up front cost and longer life and a 2nd unit that can keep you with power while repairing/replacing the first unit--Maybe important for you (i.e., "hot spares").

    Keeping systems "simple" is easier to maintain and repair. "Complicated systems" can be a pain to trouble shoot.
     
    Those are really questions you need to answer.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 1911
    1911 Registered Users Posts: 51 ✭✭
    #5
    Thank you for this detailed reply. Many good points.
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