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Thread: How Many 12v Solar Panels Needed To Charge 24v Battery?

  1. #11
    Join Date
    Oct 2010
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    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Quote Originally Posted by wwwindsock6 View Post
    I have a 48v solar system, can I mix a 36v 280 watt panel with a 12v 15 watt panel to get 48v ? I am new at this trying to learn, Thanks
    A 93 watt 12 volt panel would be a good match for the mentioned 280 watt 36 volt panel.
    1900 watts PV, (1000 watts PV feeding MidNite Classic 150; 900 watts PV + 160 watts micro hydro both feeding into a single shared Morningstar TS-MPPT-60) ; Xantrex Pure Sine 1800/12 for heavy loads; Xantrex Pure Sine 1000/12 on 24/7 for everything else; six Rolls Surrette 2 volt L16 @ 12 volts.
    Domestic hot water totally provided by the sun 8 months out of every year via thermal panel.

  2. #12

    Question Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    I just noticed something after deciding to go with 20W panels instead of 30W panels due to the overall size of the panels.

    The 24v 20W panel produces 0.61 Amps as can be seen here.

    Hooking two of those 24v 20W panels in parallel is going to double the Amps to give us: 1.22A total.

    ------------

    The 12v 20W panel produces 1.17 Amps as can be seen here.

    Hooking two of those 12v 20W panels in series is going to keep our Amps the same and still give us 1.17A total.

    So in this case, it's better to go with the 24v setup above correct? Again, I had to change from 30W to 20W panels because again I'm limited on space I found after measuring, the 30W panels would be a little too long.
    Me loves some solar

  3. #13

    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Vmp on the "24 Volt" panel: 33
    Vmp on two "12 Volt" panels in series: 34.4

    What this means in terms of charging a 24 Volt battery with a PWM controller: not much difference.

    The current the panel produces at its Imp is not necessarily the same as the current the battery charges at once the controller and all the wire is in place.

    Typically a "24 Volt" panel will have a Vmp of 35. The two "12 Volt" units in series come closer to this by 1.4 Volts. But that could make up for the Voltage drop through the wires.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  4. #14

    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Quote Originally Posted by Cariboocoot View Post
    Vmp on the "24 Volt" panel: 33
    Vmp on two "12 Volt" panels in series: 34.4

    What this means in terms of charging a 24 Volt battery with a PWM controller: not much difference.

    The current the panel produces at its Imp is not necessarily the same as the current the battery charges at once the controller and all the wire is in place.

    Typically a "24 Volt" panel will have a Vmp of 35. The two "12 Volt" units in series come closer to this by 1.4 Volts. But that could make up for the Voltage drop through the wires.
    So basically, you are saying it's better to go with 2x 12v 20W panels hooked up in series instead of 2x 24v 20W panels hooked up in parallel?
    Me loves some solar

  5. #15

    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Quote Originally Posted by rss2q View Post
    So basically, you are saying it's better to go with 2x 12v 20W panels hooked up in series instead of 2x 24v 20W panels hooked up in parallel?
    It looks that way to me. There's about .9 Watts difference in the choice.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  6. #16
    wwwindsock6 Guest

    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Quote Originally Posted by waynefromnscanada View Post
    A 93 watt 12 volt panel would be a good match for the mentioned 280 watt 36 volt panel.
    Thanks for the info, I was unsure whether to purchase a MX60 or solar panels to balance the voltage.

  7. #17
    Join Date
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    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Quote Originally Posted by rss2q View Post
    Part of me doesn't even know why I'm asking this question, but just need to confirm this with a few people.

    I have 2x 12v batteries hooked up in series to produce 24v, and I need to confirm that I only need 2x 12v solar panels in order to properly charge them? Of course I'll have a charge controller and etc., but I'm only focused on the question above.

    I remember when I asked someone how many panels I needed to charge a 36v battery, I originally thought I needed only 3x 12v batteries, but according to them that would not be enough, so that's why I'm double checking about this.

    Don't know why this wasn't a popular Google question
    normally 2 12v pvs of the proper current rating through a controller will charge a 24v battery bank. it really is governed by the vmp the pvs output and if not enough voltage is there to overcome resistive losses, operating losses of the cc, absorb voltage point of the batteries involved (and in the case of fla types the eq voltage), and temperature effects then putting another like pv in series can be done with at least trying to match up the imp ratings in the case of differing pvs. there are pvs out there that can put out enough to operate at a 24v potential without the need to series other pvs, but these are in the higher wattage range as well as expense range.

    i don't recall the question in the other thread going into the number of 12v pvs it would take to charge a 36v battery bank specifically and i believe if i'm remembering correctly that you wanted to split the batteries into differing voltage loads which you should not do on a battery bank. simply, if a pv can properly charge 1 12v battery then suffice it to say that 2 of the same pvs will charge 2 of the same 12v batteries. do realize too that when we refer to a pv as being a 12v pv that the output vmp of that pv is far above 12v and that 12v rating is for the typical charge requirements presented at that nominal 12v rating that is used by batteries.

    somehow, i feel you are leaving pertinent questions out of this like is a 20w pv enough to charge your particular battery and what these batteries are to power.
    NIEL

  8. #18

    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Quote Originally Posted by niel View Post
    i don't recall the question in the other thread going into the number of 12v pvs it would take to charge a 36v battery bank specifically and i believe if i'm remembering correctly that you wanted to split the batteries into differing voltage loads which you should not do on a battery bank. simply, if a pv can properly charge 1 12v battery then suffice it to say that 2 of the same pvs will charge 2 of the same 12v batteries. do realize too that when we refer to a pv as being a 12v pv that the output vmp of that pv is far above 12v and that 12v rating is for the typical charge requirements presented at that nominal 12v rating that is used by batteries.
    Well the method for charging that 36v system has come a long way since that thread and a solution has already been found as far as how to successfully charge that portion of the system.

    Quote Originally Posted by niel View Post
    somehow, i feel you are leaving pertinent questions out of this like is a 20w pv enough to charge your particular battery and what these batteries are to power.
    I can't remember who it was here, but these have been covered as well.
    Me loves some solar

  9. Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    Hello,

    I've got a system similar to the original poster's that I am trying to set up. I've got two 30W 12v panels wired in series that I'd like to charge two 12v 55Ah gel acid batteries, so it's really a 24v system on both ends.

    The problem I'm having is finding a solar charge controller that could handle this set up, does anyone have any recommendations? I have a cheap instapark 24v 10A one in place, and while it passes the battery voltage to my load, it doesn't seem to charge the batteries at all. The solar array is sending out ~38v.

    Thanks for any help you can give me.

  10. #20
    Join Date
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    Default Re: How Many 12v Solar Panels Needed To Charge 24v Battery?

    without more specs for the panels, one cannot give a definitive answer.... but... you are shy by at least 2 more panels probably as much as 4 short or more... that is why they are not charging, not enough amps total
    100% Off Grid @ 51* 46' N lat 124* 44' W long

    New House system: coming - 2 arrays @ 2240W
    CL150&Epanel 2 @140 W 12v PVs , 24V C&D AT-15P AGM @ 950Ah
    + CL150 2@120W 12 V panels, 24V C&D AT-15P AGM @ 950Ah
    Cotek ST1500W inverter, TBS 30a-24v Omni-charger, Honda Eu3000is,

    Guest cabin system: 3 - 70W panels to SB 2000e CC, with 2 - 100 ah 12v SAFT wet NiCd's , 600W TSW Inverter

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