Mixing solar panels

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fca1
fca1 Solar Expert Posts: 124 ✭✭
in Off Grid Solar & Battery Systems #1
Hi there i now have 2 charge controllers one morningstar mppt60 and one midnite 150

i have the following modules:

mppt60: SuYANG 220 voc 53,7 vppm 47,5 ippm 4,63 isc 5,37 - 3 strings of 2 modules each giving me a vppm of 95v
midnite :Luxor 250w voc 37,57 vppm 31,13 ippm 8,08 isc 8,62 - 4 strings of 3 modules each giving me a vppm of 93.39v....

In my present configuration (24v) i have to keep both CC, but soon i will move to 48v and then the midnite will be able to manage all of them 4320w...
for what i read here for parallel connection i should take in consideration the vppm differences <10%, in my maths 93.39 to 95 is +/- 2% so i'm in the 10% rule...
So its this ok in your opinion ? should the modules difference in ippm be a issue ?


should i put a fuse before connecting in parallel both modules groups...
i.e the max ippm from the 220 modules group will be 3x 4,63=13,89 amps i can put a 20 amp fuse and on the side of the 250w module group i will have 8,08*4=32 amps i can put a 50 amp fuse ??
the 220w modules don't have now any fuse between the parallel strings, but the 250w have fuses between each 2 strings, not one fuse by string but for each 2 strings... so maybe no additional fuses on the 250w side...

now:
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future
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ps: how to calculate losses by using this mix ?


thanks for your attention.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Mixing solar panels

    The current difference between parallel strings will not be a problem.

    The Vmp's of the different strings is close enough to not be a problem either.

    You will of course need proper rated breaker on each and every string.

    The one thing that might trip you up is the different panel Voltages that make up the two very similar string Voltages: in some cases where the 'lower Voltage' panels get shaded the 'higher Voltage' panels can back-feed through them resulting in a loss of power and possible panel damage. If this is likely to happen you need blocking diodes on the lower panel Voltage string (I've written it that way just in case someone is reading this and adds up lower Voltage panels into a string that is higher Voltage than another made from higher Voltage panels - confusing enough?).

    If shading isn't an issue the diodes should not be needed. They will take a bit of Voltage themselves, but still the string Voltages should be close enough to work.

    With approximately 2 Volts difference I wouldn't worry about losses at all: the controller is going to pick the best Voltage and it may not match the actual Vmp of either string type.
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  • fca1
    fca1 Solar Expert Posts: 124 ✭✭
    #3
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    Re: Mixing solar panels
    Cariboocoot wrote: »
    The one thing that might trip you up is the different panel Voltages that make up the two very similar string Voltages: in some cases where the 'lower Voltage' panels get shaded the 'higher Voltage' panels can back-feed through them resulting in a loss of power and possible panel damage. If this is likely to happen you need blocking diodes on the lower panel Voltage string (I've written it that way just in case someone is reading this and adds up lower Voltage panels into a string that is higher Voltage than another made from higher Voltage panels - confusing enough?).

    If shading isn't an issue the diodes should not be needed. They will take a bit of Voltage themselves, but still the string Voltages should be close enough to work.
    i have some shading in one of the lower volt strings, but all modules have 3 bypass diodes, are you talking diodes in modules or between strings ?

    regards
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Mixing solar panels
    fca1 wrote: »
    i have some shading in one of the lower volt strings, but all modules have 3 bypass diodes, are you talking diodes in modules or between strings ?

    regards

    Between strings: bypass diodes are built-in to panels, blocking diodes go on the positive lead to prevent current flowing backwards through the panel. It usually only comes up with higher Voltage systems (has to be able to exceed the panels' reverse breakdown Voltage). Most of the time if the panels are all the same it still doesn't occur even with shading.
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