When is MPPT most cost effective

slitzy
slitzy Registered Users Posts: 1
I have read that unless you have 500 watts or more of panels MPPT is not cost effective. Since panels produce only 70 to 85 % power does that mean your array must be 500 or more like 600 watts to compensate for various losses?

Comments

  • garlic
    garlic Solar Expert Posts: 43
    Re: When is MPPT most cost effective

    I believe it has to do more with the accumulative gain of MPPT over
    PWM meets cost effectiveness around 500 watts,actual panel output
    being equal between the two.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: When is MPPT most cost effective

    Welcome to the forum.

    MPPT starts to become attractive at about 400 Watts array size. That's before the derating. It usually will offer about 10-15% improvement over PWM. However, this will rise as the array gets bigger or the temperatures drop. There are other circumstances that makes MPPT attractive, such as long wire runs from the array to the controller where the ability to run higher array Voltage to overcome the V-drop of the wire. In some cases you may simply want to squeeze every last drop of power potential out of the panels, as in a boat or RV application where efficiency isn't going to be that good and there's a limit to the space available for panels.
  • Solar Guppy
    Solar Guppy Solar Expert Posts: 1,989 ✭✭✭
    Re: When is MPPT most cost effective

    Its a cost / benefit concern, at lower wattage's, the amount of watts to be gained by an mppt controller that is double in cost to a pwm.

    Say you use a $200 C40 vs a $400 dollar 45 amp mppt unit.

    In today's dollars, one could buy an additional 150 watt of solar using pwm for same total system cost.

    The Mppt with even a 30% gain, would need to be 500 watts to break even to the pwm using a 650 watt array to harvest the same net amount.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: When is MPPT most cost effective

    Also, MPPT controller have a very nice feature... Because you can run the Vmp-array to upwards of 100 VDC (roughly, some higher, many lower)--You can run a much smaller gauge copper wire from your solar array back to the battery shed/charge controller...

    If you solar array is right on top of your battery shed--then an MPPT does not do as much for you (a short run of 4 awg wire is one thing--200' of 4/0 wire is something else).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: When is MPPT most cost effective

    It occurs to me that with the ever-falling panel prices the traditional MPPT advantage array size is going up. If you compare the Morningstar 60 Amp PWM to the MPPT there's about a $300 difference in price: enough to buy around 185 Watts of panel. If you consider the MPPT minimum advantage to be 10%, that works out to an 1665 Watt array (nine panels instead of ten) - which would work well on a 24 Volt system maxing the controller at nearly 60 Amps.

    But like I said before, there's other things to consider.
  • Shadowcatcher
    Shadowcatcher Solar Expert Posts: 228 ✭✭✭
    Re: When is MPPT most cost effective

    I have to admit I haven't really tried it out yet, but… I bought the solar panel that normally sits on our teardrop trailer prior to doing my homework :blush: and ended up with one meant for grid tie system that puts out a good bit more voltage. That necessitated the use of an MPPT charge controller. The teardrop in many cases will be in places that are rather shady. I finished the install after school started and my wife started teaching again so the teardrop is put away for the winter. The location where the trailer is in our yard is shaded by large trees much of the day and the panel typically is putting out at least 35 V often in excess of 40. The 185 W panel is mounted flat on the top of the trailer and its view of the sky straight up is clear. The Sun Saver MPPT seems to be able to use lower light levels and still convert them into usable voltage for charging the AGM battery.