ProStar 30 Question

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monoloco
monoloco Solar Expert Posts: 103 ✭✭
in Off Grid Solar & Battery Systems #1
I am thinking about adding 2 235w panels to my system, they have an open voltage of 35 volts, I have a Morningstar ProStar 30 that I am not using, would it work for these two panels on a 24v system? The specs for the controller do not specify the maximum voltage it can handle.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #2
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    Re: ProStar 30 Question

    If that is Voc~35 VDC (voltage open circuit) for those panels, then that is too low for charging a 24 volt battery bank.

    Nominally, the "ideal" panels/array would have Vmp-array~35-37 VDC or so (that would be Voc-array~41-44 volts or so).

    A solar panel when hot can see its "spec" Vmp fall from 35 volts downwards to near 31 volts (hot sun, hot weather). And your battery bank needs around 29 VDC to charge quickly. That gives you a couple volts of head room for voltage drop in the wiring and charge controller.

    You could make an array with Vmp-array>35 VDC -- But then the overall efficiency of the panel/array begins to fall (a Vmp-array~70 VDC would have an "efficiency"/derating of 50% just because of voltage miss-match while using a PWM controller).

    Such a system (Vmp-array~70 VDC) will still work (albiet with lower efficiency), but then you need to look at the Vmax input of the charge controller and Voc-cold (could be well over 100 VDC)...

    So, do you want to do this? Or do something else? We can "do the math" to figure out the Vmp-array-hot and Voc-array-cold for your configuration and compare that with the controller's ratings.

    MorningStar does have an array configuration tool which may give you the answers directly:

    String Calculator Website

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: ProStar 30 Question

    "..........these two panels on a 24v system?"

    in addition to what bill said, you aren't being specific in your description for us to answer your question.
    is that the pvs that are to be a 24v system and/or the battery bank?
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  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
    #4
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    Re: ProStar 30 Question

    Thanks for the replies. To be more specific about my system, I am currently running 10 75w BP panels in two strings wired in series then paralleled into a FX60 controller to charge 8 305Ah Concorde AGM's. I would like to increase my solar charging capacity and the 235w panels are available here in Mexico at a decent price, Ideally I would add another MPPT controller and just wire them in series but that's not in the budget right now so I'm looking to get by with what I have.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #5
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    Re: ProStar 30 Question

    So what is the Vmp/Imp rating of the new panels? Also, what is the Vmp/Imp rating of the existing panels (may be able to series/parallel connect the old and the new--at least there is a chance).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
    #6
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    Re: ProStar 30 Question

    I'm trying to get more info on the panels from the vendor, I requested that he send me the make/model of panel so I could look up the Vmp and all he sent me was the open voltage. the Vmp of my existing panels is 17.
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  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
    #7
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    Re: ProStar 30 Question

    OK, I finally received the spec sheet for the panels, they are Renogy Rng-poly 235 panels, Voc.=37.08 Vmp.= 30.6 amp=7.66 I have never heard of this brand, the vendor's price is $2.09 a watt here in Mexico.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
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    Re: ProStar 30 Question

    ok 2 strings with a total of 10 12v nominal pvs would mean 5 pvs per string. the 2 pvs you just considered would be like 2 of the 12v nominal pvs in series for each pv or the total equivalent of 4 12v nominal pvs if you placed them in series. this does not work out right as each of your bp strings would be much higher in voltage by about 1 12v pv each.

    i know it sounds confusing, but look at it another way, a 12v pv typically has 36 cells to them. with 5 pvs in series you have 180 cells in series. the pvs you are considering most likely have 72 cells each and 2 of them in series is 144 cells in series. it could work if you took away 1 bp pv per string to bring the cell count in each string to be equal to one another. even if the vmp isn't exact on these cells, it really won't matter that much as it would most likely be close enough to use without any problems.

    this makes it look like 2 strings of 4 bp pvs in parallel to be paralleled with 2 of the new pvs in a series string. i hope i didn't confuse you.

    i should add that had you picked 3 pvs that have 60 cells in them to be placed in series that it might've flown as it would match the number of cells in series in the bp pvs. now i am not considering the max power capacity of the controller in this equation.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #9
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    Re: ProStar 30 Question
    niel wrote: »
    this makes it look like 2 strings of 4 bp pvs in parallel to be paralleled with 2 of the new pvs in a series string. i hope i didn't confuse you.

    i should add that had you picked 3 pvs that have 60 cells in them to be placed in series that it might've flown as it would match the number of cells in series in the bp pvs. now i am not considering the max power capacity of the controller in this equation.

    Niel, I think he wants to hook up those two new panels with an unused Prostar 30 that he has.

    Monoloco, yes, you can use your two Renogy panels with the prostar 30. You will want to hook the Renogys in parallel. You may find that with high temperatures the panel voltage is a bit low for absorb stage charging, but they will certainly contribute to bulk charging.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • monoloco
    monoloco Solar Expert Posts: 103 ✭✭
    #10
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    Re: ProStar 30 Question

    Thanks to everybody for your replies, I am thinking that I'll just import some panels with a higher Vmp. I don't think it will cost anymore and may possibly cost less to get the optimum panels.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #11
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    Re: ProStar 30 Question
    monoloco wrote: »
    Thanks to everybody for your replies, I am thinking that I'll just import some panels with a higher Vmp. I don't think it will cost anymore and may possibly cost less to get the optimum panels.

    Don't be too hasty... Your Renogy panels will give you full power during bulk charging which is the only time you can use full power. When you get to absorb stage charging you will not be drawing full power from your arrays.

    Your BP panels will be effective during bulk and absorb. During Bulk your Renogy panels will help out.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #12
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    Re: ProStar 30 Question
    vtmaps wrote: »
    Niel, I think he wants to hook up those two new panels with an unused Prostar 30 that he has.

    Monoloco, yes, you can use your two Renogy panels with the prostar 30. You will want to hook the Renogys in parallel. You may find that with high temperatures the panel voltage is a bit low for absorb stage charging, but they will certainly contribute to bulk charging.

    --vtMaps

    vtmaps,
    you're right and my mistake. i thought he wanted it all to go through one controller.

    yes, you cam feed the power from the new pvs into a separate prostar cc. the 35v vmp would be good for charging 24v batteries so the pvs will be paralleled.
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