Increased PV Voltage Benefit

Anyone know if there is any amps into the batteries through a MPPT controller benefit from increasing the voltage by stringing multiple solar panels in series? As an example, if I connect two 24v nominal panels in series instead of parallel, will the series method give me any more amps into the batteries because the MPPT controller is able to work better? I am familiar with solar and MPPT controller basics.

Thanks, Dave

Comments

  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    Anyone know if there is any amps into the batteries through a MPPT controller benefit from increasing the voltage by stringing multiple solar panels in series? As an example, if I connect two 24v nominal panels in series instead of parallel, will the series method give me any more amps into the batteries because the MPPT controller is able to work better? I am familiar with solar and MPPT controller basics.
    If you can do parallel or serial, AND both arrangements will provide sufficient voltage headroom to operate the MPPT and hit the charge voltage on the battteries, AND your wiring losses are low, then lower voltages (i.e. parallel) is better. MPPT controllers are more efficient when the input and output voltages are closer together. (True of almost all nonisolated DC/DC converters.)

    However, if you can reduce wiring gauges by going to higher voltages, or you will see significantly lower wiring losses by going to the higher voltage, then the series arrangement might be cheaper and/or more efficient.

  • Dave McCampbell
    Dave McCampbell Registered Users Posts: 4
    Bill,
    Many thanks for that concise reply. We are installing a new system of 4 200 watt panels (Simax 36.8 vp) on a catamaran boat with a 12v electrical system and the shop is telling me I need to wire them in series in order to get the best output to the batteries from the MPPT controller. The implication is that the controller works better with a greater input vs output voltage spread. But we also will have some occasional shading from the mast and rigging so I am inclined to wire the panels in parallel in order to negate the shading issues (if one panel is shaded all lose power) with series panel wiring. With a Vp of 36.8v it seems that there should be enough headroom voltage from the panels to satisfy the nominal 12 v boat system. Right?
    Again many thanks. Dave
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    and the shop is telling me I need to wire them in series in order to get the best output to the batteries from the MPPT controller.
    That's nonsense. It is especially important to keep your input voltage down when you have only a 12 volt battery bank. Your instincts to parallel your panels are correct, for the shading issue as well as the overall operating efficiency.

    Regarding overall operating efficiency.... Yes, you can cut wiring losses with the higher voltage input, but you will just shift those losses into the controller where the extra heat will do harm. Unless you have extreme distances between panels and controller, there will be no overall gain in operating efficiency with the higher voltage input.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    One savings opportunity, at least in initial setup cost, comes from the fact that a single panel or string or two panels or strings does not require a separate fuse in each string.
    Three or more in parallel requires individual fusing, usually in a DC combiner box.
    SMA SB 3000, old BP panels.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    We are installing a new system of 4 200 watt panels (Simax 36.8 vp) on a catamaran boat with a 12v electrical system and the shop is telling me I need to wire them in series in order to get the best output to the batteries from the MPPT controller. The implication is that the controller works better with a greater input vs output voltage spread. But we also will have some occasional shading from the mast and rigging so I am inclined to wire the panels in parallel in order to negate the shading issues (if one panel is shaded all lose power) with series panel wiring. With a Vp of 36.8v it seems that there should be enough headroom voltage from the panels to satisfy the nominal 12 v boat system. Right?

    "The shop" is clueless, you have a better understanding of the situation.



    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.
  • Dave McCampbell
    Dave McCampbell Registered Users Posts: 4
    Many thanks for this information from all of you.  I will pass this on to the shop here in the Philippines so they will pass accurate info to future customers.  

    I will start a new thread on a question re Outback vs Morningstar controllers.

    Again many thanks,  Dave
  • 11JAGAN
    11JAGAN Solar Expert Posts: 34 ✭✭
    edited September 2015 #8

    "MPPT controllers are more efficient when the input and output voltages are closer together"
    what do you think about charge controller with 600 V as maximum input. are they less efficient?
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    11JAGAN said:

    "MPPT controllers are more efficient when the input and output voltages are closer together"
    what do you think about charge controller with 600 V as maximum input. are they less efficient?
    The only one I read the specs on, the schneider unit, has pretty decent efficiency specs. 

    I think the problem with efficiency occurs when you try to design too broad an input range.  The same unit can't be efficient at both high and low voltages.   The schneider high voltage controller won't work with the lower voltages that other controllers can use.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    11JAGAN said:

    "MPPT controllers are more efficient when the input and output voltages are closer together"
    what do you think about charge controller with 600 V as maximum input. are they less efficient?
    They are reasonably efficient - but even those controllers become more efficient as you drop their input voltage. 

    Often it comes down to "how much efficiency can I get for X dollars?"  And if a 500 volt system vs an 8 volt system means you can save a few hundred $ on wiring, combiner and conduit costs, it may be worth it.