What if....

WebPower
WebPower Registered Users Posts: 86 ✭✭
in Advanced Solar Electric Technical Forum #1
So, people have asked in various posts on different forums:

-Can you hook up two enphase micro inverter inputs in parallel if you have a larger source than a sole microinverter can handle?

And I'm curious: 

-What if you hooked up an MPPT charge controller in parallel with an enphase microinverter?

Seems like inquiring minds want to know. At least I do. Anything out there that anyone can point to where these have been tried?
 
Pat
9000+W grid tied IQ7 22 panel rooftop and 6 panel ground combination with 1 additional IQ7 connected to 500W wind turbine+200w solar+2 IQ7s with 300W+600W on the RV grid tied when it's in the driveway.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    As a first approximation, if your MPPT input controller has equal or more capacity to the energy source, then paralleling MPPT will not work correctly. The MPPT controller is designed to "solve" the equation Pmp=Vmp*Imp by (more or less) adjusting the current the MPPT controller draws, measure the voltage, and figure out the maximum power for the Vmp*Imp=Vmp equation.

    When you have two or more MPPT input controllers, they will each be drawing current and monitoring voltage--And since the "other MPPT's" current draw is "invisible' to its "mate", they will be gathering faulty data, making faulty assumptions about Pmp=Vmp*Imp, and probably "oscillating" each unit's current draw as they try to hold (calculated optimum) Vmp voltage.

    Will is "damage" the controllers or the energy source--Probably not--You can try and see what happens. There are lots of variations in MPPT algorithms, so different brands/models may play differently with each other.

    An analogy... Imagine a car with two engines and two gas pedals... And two people controlling the pedals (or two "cruise controls") and not knowing what the other is doing... Trying to hold 55 MPH, up/down hills, wind, etc... It would be difficult to control a steady speed that way.

    When dealing with Grid Tied inverters... There are "transformer-less" models that would damage (for example) a MPPT solar charge controller in parallel with a "Transformerless" GT Inverter. Transformerless GT inverter solar inputs are not "ground referenced" (as I understand), and they will probably "fry" a solar MPPT charge controller.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • WebPower
    WebPower Registered Users Posts: 86 ✭✭
    #3
    Ok. So the MPPT hooked up to the battery to charge would be a renogy that uses a torroid. The enphase IQ7 would be the grid tie MPPT. I took an IQ7 apart once and dont remember seeing a torroid. I could open another one up as I have a couple of more bad ones. So bad things might happen with this combination. Good to know. If I did it, i'd monitor voltage and current on the inputs and outputs to see what's going on.

    So I might try to double up the IQ7s and see what happens. Probably using a power supply to start to see what happens. i'm curious mainly to see what happens with the "ON" point of each IQ7 thinking that their "ON" voltage will be slightly different. Maybe one turns "ON" while the other remains in standby until the MPPT point crosses the "ON" point of the second IQ7. Then the fun would begin!

    Pat

    9000+W grid tied IQ7 22 panel rooftop and 6 panel ground combination with 1 additional IQ7 connected to 500W wind turbine+200w solar+2 IQ7s with 300W+600W on the RV grid tied when it's in the driveway.
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