Pwm or mppt

With a 1kw array and a 24 volt 208 ah
4 GC batteries in series.

I can't decide between using 3 in parelell 
345 watt q cell panels.  38 vmp 47 voc and 9 imp.
With a TriStar pwm controller.

Or 4 250 watt Reno sola 2s2p 30 vmp 37.5 voc and 8.30 imp.
With a Morningstar mppt.

On mppt a single 40'  run of 10 awg ~2℅
On pwm 3 40'  runs of 10 awg ~2℅
I already have 150' of cable
Pros/cons thoughts anyone?

Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.

Comments

  • mike95490mike95490 Solar Expert Posts: 8,877 ✭✭✭✭✭
    My gut feeling is MPPT if you can swing the $ for a decent one.

    Here's my math with your systems:
    345 watt q cell panels.  38 vmp 47 voc and 9 imp.
    With a TriStar pwm controller.
    is 28V @ 27A  ( 756 watts)  (in PERFECT lighting conditions)

    Or 4 250 watt Reno sola 2s2p 30 vmp 37.5 voc and 8.30 imp.
    With a Morningstar mppt.
    is 28V @ 34.6A ( 970 watts)  (in PERFECT lighting conditions, 3% MPPT loss)







    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 ,

  • mcgivormcgivor Solar Expert Posts: 3,438 ✭✭✭✭✭
    mike95490 said:
    My gut feeling is MPPT if you can swing the $ for a decent one.

    Here's my math with your systems:
    345 watt q cell panels.  38 vmp 47 voc and 9 imp.
    With a TriStar pwm controller.
    is 28V @ 27A  ( 756 watts)  (in PERFECT lighting conditions)

    Or 4 250 watt Reno sola 2s2p 30 vmp 37.5 voc and 8.3With a Morningstar mppt.
    is 28V @ 34.6A ( 970 watts)  (in PERFECT lighting conditions, 3% MPPT loss)







    The results would differ depending on the ambient temperature, the following  is from Morningstar, an excerpt of the full text here  https://www.morningstarcorp.com/whitepapers/traditional-pwm-vs-morningstars-trakstar-mppt-technology/

    PWM Over MPPT:

    The preceding discussion of PWM vs. MPPT may cause some to wonder why a PWM controller would
    ever be chosen in favor of an MPPT controller. There are indeed instances where a PWM controller can
    be a better choice than MPPT and there are factors which will reduce or negate the advantages the
    MPPT may provide. The most obvious consideration is cost. MPPT controllers tend to cost more than
    their PWM counterparts. When deciding on a controller, the extra cost of MPPT should be analyzed
    with respect to the following factors:

    1. 1. Low power (specifically low current) charging applications may have equal or better energy harvest
      with a PWM controller. PWM controllers will operate at a relatively constant harvesting efficiency
      regardless of the size of the system (all things being equal, efficiency will be the same whether using
      a 30W array or a 300W array). MPPT regulators commonly have noticeably reduced harvesting
      efficiencies (relative to their peak efficiency) when used in low power applications. Efficiency
      curves for every Morningstar MPPT controller are printed in their corresponding manuals and
      should be reviewed when making a regulator decision. (Manuals are available for download on the
      Morningstar website).
    2. 2. As explained in the Environmental Considerations section, the greatest benefit of an MPPT regulator
      will be observed in colder climates (Vmp is higher). Conversely, in hotter climates Vmp is reduced. A decrease in Vmp will reduce MPPT harvest relative to PWM. Average ambient temperature at the
      installation site may be high enough to negate any charging advantages the MPPT has over the PWM. It would not be economical to use MPPT in such a situation. Average temperature at the site
      should be a factor considered when making a regulator choice (See Appendix).
    3. 3. Systems in which array power output is significantly larger than the power draw of the system loads
      would indicate that the batteries will spend most of their time at full or near full charge. Such a
      system may not benefit from the increased harvesting capability of an MPPT regulator. When the
      system batteries are full, excess solar energy goes unused. The harvesting advantage of MPPT may
      be unnecessary in this situation especially if autonomy is not a factor.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 30,752 admin
    If you have hot ambient temperatures and a cool FLA battery bank, the Vmp~38 volt array can get down towards ~31 volts Vmp-array-hot (104F with cells being ~36F higher than ambient under full sun). And you want to charge your battery somewhere around 29.5 volts or so.... The Vmp/Imp/Pmp curve is relatively flat, so it is not like the output goes from 100% to 0% at that point, but does fall a bit.

    That means possibly somewhat less harvest during the middle of a hot day (you have a couple of volts of wiring drop, a bit of drop across the PWM controller). Not the end of the world--But does reduce harvest some (of course, middle of summer with a large array--You probably have more harvest than you would need anyway).

    If you have longer wire runs, higher voltage on the Varray configuration makes wiring much easier and cheaper--Figure out your array to controller distance, and the wire AWG needed... It generally works out that you can get away with upwards of 6 AWG smaller wire diameter with a "higher Vmp-array" working voltage.

    As I always suggest, do a paper design with both options and see what works out best for you (cost, wiring issues, features like Internet/remote management that can be available on larger/more expensive MPPT controllers, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 30,752 admin
    Forgot to add... MPPT controllers will safely and reliably "throttle" the output curent... So you can "overpanel" an MPPT controller (~1.3x larger array) and all will be OK.

    PWM controllers cannot throttle their output like a MPPT controller can, so you should not overpanel a PWM controller.

    As always, check the manual for details.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mountainmanmountainman Registered Users Posts: 387 ✭✭
    edited April 23 #6
    Thanks all .  In my area summers 104f.
    These panels are local to me.
    4  250 watt panels cost .24/watt  $240
    3 345 panels 1035 watts are .50/watt  $525
    With a  Morningstar 30 mppt I can over panel
    800x1.3 1040 watts
     Morningstar 30 mppt $382 from naws
    My local dealer has a 45 amp Tristar pwm $75. 
    Pwm system cost~ $600
    Mppt system cost ~$622
    plus mppt shipping tax


    Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • mountainmanmountainman Registered Users Posts: 387 ✭✭
    edited April 23 #7
    @mcgivor information on the Morningstar
    Pwm vs mppt.
    From my understanding if you are using
     10-15℅ of your battery mppt has less advantage over pwm. Compared  to daily using 30-40℅.

    And if you live in a cold area  mppt is better.

    If its warm to hot all year a properly designed Pwm system would be cheaper. And work just as good or better than mppt.

    It states for 24 volt charging  no less than 30 vmp in the highest temp.
    And 34-36 vmp would be the most efficient.

    And For long distance arrays from the controller Mppt is cheaper than pwm because you have to use big expensive  wiring.
    The larger the array  the more mppt would Be the best cost effective choice.


    Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • mike95490mike95490 Solar Expert Posts: 8,877 ✭✭✭✭✭
    Regardless of temperatures or where you live, panel/battery voltage mismatch is wasted power.

    Higher voltage strings loose less power in small copper wires.  There are a lot of factors to consider on sizing a sytem
    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 ,

  • mountainmanmountainman Registered Users Posts: 387 ✭✭
    edited April 24 #9
    @mike95490 agreed there are a lot of factors. Higher voltage is more efficient in wiring. But the higher  the difference between array and bus voltage  the less efficient  the controller becomes.
    It's not a one size fits all. 
    the biggest challenge of solar is in winter   short  days  and  frequent overcast skies with my 3.59 January sun hours I need all the help I can get.
     The cost between mppt And pwm is not a factor at least not in my situation.
    So I'll spend the money on mppt and cheaper Grid  tie panels.




    Blue ridge mts. Renogy pwm 4 100 watt and 2 190 evergreen on Epever mppt 30. 4 Gc 208 ah @12 volts 300 watt psw inverter. 2 kw genny. Iota 45.
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