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Old 22-06-2010, 15:40   #1
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Solar Output

Hi,

I real world experience question here:
What Amp/H can I expect from 3 175W 24V panels connected in parallel and an MPPT controller, charging a 12V 900Ah bank in a Mexican sun.
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Old 22-06-2010, 15:54   #2
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some people use the formula of maximum hourly output times 5. let's see: you will have 525 watts divided by 25 volts which will give you a maximum output of around 21 Ah, which times 5 would give you 105 Ah per day.

of course, this all varies with orientation of the panels, latitude, time of year, and any shadowing you might have from your rig. For an energy budget, it might be best to go with a conservative 100 Ah figure, with the understanding that your mileage may vary.
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Old 22-06-2010, 22:10   #3
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A rule of thumb that I have seen published and have confirmed based on my own measurements is that an X watt panel will put out 1/3*X amphours (at 12 V) on a sunny day with the panel mounted horizontally. Obviously more in summer low lattitudes and less in winter high lattitudes and more if you point it at the sun all day.

Applying this rule of thumb to your 525 watts of panels gives 175 amphours at 12 V.

David
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Old 22-06-2010, 22:37   #4
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My setup is 2 x 175 watts, 840 ah of battery and MPPT.

I'm above the 49th parallel. Today I put 135 ah in the batteries even though I was sailing for 5 hours and it was cloudy at times. I put 175 on a decent day and 100 on a lousy one ... we are in the long days of summer.
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Old 23-06-2010, 10:06   #5
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If you're not trying to run air conditioning, I think you'll be fine.
On our previous boat while in Mexico, we had 470 watts worth of solar before MPPT's were available.
With a good reefer, HAM, watermaker, and lots of other toys we never wanted for power.
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Old 23-06-2010, 10:12   #6
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Quote:
Originally Posted by djmarchand View Post

Applying this rule of thumb to your 525 watts of panels gives 175 amphours at 12 V.
The OP is running a 24V system. He's certainly not going to get 175 Ah at 24 volts.
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Old 23-06-2010, 15:26   #7
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Quote:
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The OP is running a 24V system. He's certainly not going to get 175 Ah at 24 volts.
Did I say that? He is charging 12V batteries.

David
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Old 24-06-2010, 01:05   #8
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Thanks for all the input BUT, yes I have 24V panels charging a 12V batteries with an MPPT that can do the step down or up.

Do I get the same amps as you guys?
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Old 24-06-2010, 05:55   #9
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I saw an average of 62 amp hours for 24 hour periods over about 20 days of pretty close observation with 1 175 watt panel and MPPT controller. This was in the Caribbean in the month of May. This is with 24 volt panels feeding a 12 volt system. I used Link 2000 and Fluke VOM to measure output of panels.

Do you have a method of measuring your output? If you were putting amperage back into a 24 volt system your amperage would be half of that going into a 12 volt system. I think all answers were given at the 12 volt battery level.
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Old 24-06-2010, 12:33   #10
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I am going to use the Outback flex60 controller so will have a way of monitoring the amps
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