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  1. #1
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    Aug 2005
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    Default Solar panels, 12v or 24v ?

    I have a 24v battery house bank and am looking to install Solar panels for the first time. Bearing in mind W/V = I, then on a 24v system one will need a panel twice the Watts as one needs on a 12v system in order to produce the same Amps : A 200w panel/24v = 8.33 amps, A 100w panel/12v = 8.33 amps : GIVEN THE SAME SUNSHINE/TEMPERATURE etc.

    Is that correct ??

    Since the object of the whole excercise is to recharge the batteries, i.e. put back into them as much Amps as possible (as efficiently as possible), does it not make sense to have a 12v panel connected to an MPPT charge controller which then 'steps up' the voltage to say about 28v, which necessary to recharge the 24v house bank ...?
    I have been told so many conflicting things e.g. to recharge a 24v battery bank one must use 24v panels and to recharge a 12v system one must use 12v panels.
    But others have said there is an MPPT controller which will do the 'step up' (12v stepped up to 24v).
    Given that 12v panels are a lot cheaper than 24v panels ...and if W/V = Amps, one only needs half the Wattage panel for 12v as one would need for 24v to get the same amps out.

    what about using two separate 12v , 100w panels connected sparately to two MPPT controllers which then all connected to the house bank.?
    Thoughts ??

  2. #2
    Hoolie's Avatar
    Hoolie is offline Registered User
    Location : Hants/Lozčre
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    You're not gaining anything by using an MPPT to step up the volts to 24v as the current output will be half the current input.
    I think your best bet is to run two 12v panels in series with a single regulator for your 24v battery bank.

  3. #3
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    If you 12v to 24v you will halve the amps. The best way to measure power is in watts, this will remain the same as you vary voltage.
    There are only a few MPPT regulators that will increase voltage and they will give a bit less than 1/2 the amps when converting from 12 to 24 v.
    For a 24v system you are better to pick nominal 24v solar panels.

  4. #4
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    Jun 2010
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    just buy a new battery every year it'd be cheaper, providing your alternator is ok.
    People got on ok up unitl now with solar panels

  5. #5
    VicS is offline Registered User
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    I would be looking at 2 12volt panels is series.

    You'll need a regulator or controller of some sort.

    The very cheap one s simply disconnect when the volts rise and reconnect when they fall again.

    Next step up in sophistication and price are "pulse width modulated" (PWM) regulators which control the charging rate rather than simply disconnecting and reconnecting.

    Next step from there if you want to get the maximum out of the solar panels are " maximum power point tracking" (MPPT) regulators which control the panel at its optimum terminal voltage and convert the extra volts into extra amps by electronic jiggery-pokery.

  6. #6
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    Quote Originally Posted by Hoolie View Post
    You're not gaining anything by using an MPPT to step up the volts to 24v as the current output will be half the current input.
    I think your best bet is to run two 12v panels in series with a single regulator for your 24v battery bank.

    Yes, good point, one would loose half the amps by stepping up from 12v to 24v....but there is a 'gain' financially rather than electrically speaking in the sense that the panels at 12v are cheaper than 24v panels.

  7. #7
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    Quote Originally Posted by PITCAIRN View Post
    Yes, good point, one would loose half the amps by stepping up from 12v to 24v....but there is a 'gain' financially rather than electrically speaking in the sense that the panels at 12v are cheaper than 24v panels.
    Yes, 12 volt panels are cheaper, but for the same wattage output are they cheaper, the calculation should be:- pounds per watt.
    For what its worth I use four 80w 12v (nominal) panels, wired in series, then parallel, using a cheapo regulator. That does me fine, I may go MPPT but not sure its worth it for me.
    If I agreed with you we'd both be wrong.

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