is an MPPT worthwhile?

jdfnnljdfnnl Registered Users Posts: 15 ✭✭
I just started a different thread about battery capacity for a modest 2x100W panel solar system connected in parallel.

I would like to know if a MPPT would provide any additional power if the panels connected in parallel are already at a workable charging voltage for a 12V system (17-18V). There is a bunch of hype about how well MPPT track a panel's optimal voltage it has me wondering if I could squeeze a few more mAh out of the array.

Comments

  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    12V panels on a 12v system,  it's unlikely the MPPT conversion would activate
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Very general--Systems less than ~400 Watts are small and PWM can be most cost effective. 140 Watt "12 volt" panels are on the expensive side ($/Watt). And the PWM controllers are less expensvie.

    For systems over 800 Watts, you can use >200 Watt panels that can be down towards $0.50 per Watt. And much more expensive MPPT solar charge controller. Also, with larger arrays and arrays that are longer distances from the charge controller/battery shed, you can use a higher Vmp-array and smaller copper wiring (save money on panels and copper).

    I highly suggest that you do a few paper designs and see how the decisions/choices are made.

    First, define your loads (energy needs)--And remember that conservation is almost always cheaper than generating the power. When the system will be installed (nearest major city--Figure out hours of sun), is this a seasonal system or full time off grid. Use a genset for backup power or pure solar, etc.

    Once you have that information, then do a "cook book" paper system design. And lastly pick the hardware that supports your needs.

    There are always multiple answers possible--So designing several systems (cost vs options/needs). Then pick a design and buy the hardware.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PhotowhitPhotowhit Solar Expert Posts: 5,806 ✭✭✭✭✭
    You would have to connect your panels in series rather than in parallel, an perhaps you could squeeze out a few more ma. What would one cost you $100 more? You could buy a 100 watt panel for $80 delivered last I checked on Amazon. I personally wouldn't worry about a combiner box for 12 volt panels, but in theory you may need a combiner box as well. 

    As Bill said, lots of paper designs, I'd also write what you intend to do with your system and look to the future. 
    Will you end up at a higher voltage system?
    Will you never increase the size?
    Are you moving and want to maintain as simple a system as possible... etc

    Ran my tiny house on a 60amp PWM charge controller feeding a 24 volt battery. It worked fine, fridge a little air conditioning in the summer. I have a couple MPPT type charge controllers now and a bigger system and home...
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • SaggysSaggys Solar Expert Posts: 153 ✭✭✭
    I have two 80 watt 17vmp panels wired in parallel that was connected to a trace c12 pwm charge controller and it seldom reached panels Imp rating. Recently came across a morningstar sunsaver 15a mppt charge controller cheap and have replaced the c12 pwm, noticed about 10% more current in bulk charge. Not much difference, this is a casual observation, no test data to back it up.
  • mountainmanmountainman Registered Users Posts: 439 ✭✭
    edited October 2020 #6
    Adding an additional panel would increase the harvest 50% for $80
    A epever mppt controller $100 for a 10% increase.
    I ran 2 separate 12 volt 400 watt systems. 1 with pwm all in parallel.
    and 1 mppt all panels  in series.
    If your panels are close I would stay with pwm.
    If you find you need more power just add panels.
    Not saying it's the right way but I did not use a combiner box.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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