Frank asked in EnvironmentGreen Living · 9 years ago

solar panel to charge a deep cycle battery?

I have a 12 Volts, 125 AmpH deep cycle battery which I would like to charge using a solar panel. I am not looking for a trickle charge I actually need the solar to supplement and fully charge the battery from 50 percent or lower used state. What kind of 12V solar panel would I need for this job. I would like to charging to be completed in 24-48 hours if possible. I live in NorthEast of US with a south facing roof.

6 Answers

  • John W
    Lv 7
    9 years ago
    Favorite Answer

    Well, you'll need about 24 V to fast charge the batteries, you could probably get away with 15V for trickle charging or maybe 18 V. Lead Acid batteries are 50% efficient at charging and you're talking about trying to squeeze up to 1.5 kWh into the battery so if we assume that you want to do this during an 8 hour day, you would want 3 kWh / 8 h which is 375 W of 24 V panels. At the typical installed price of $10 per watt, that would be $3,750 of PV panels.

    Can't do 24 hour charge cause the sun won't shine for 24 hours regardless of how nicely you ask it to.

    You don't want to overcharge as that would just boil off hydrogen so you might want to wire up some FET's and zener diodes to cut off the charge when the battery reaches a certain voltage level.

  • 9 years ago

    Hey Q, you have two choices here. One is to get a panel that does not have the capacity to overcharge that battery. Basically, if the panels max amperage is below 2% of the battery's amp hour capacity, then it can be hooked up continously without causing any damage. In your case, 125 AH X 2% = 2.5 amps. A 50 watt panel would be the maximum size you would want for this. Instead of a charge controller, all that would be needed is a diode to keep the battery from discharging through the panel at night. Most panels today come with diodes already installed in the junction box, but if yours does not, they can be had at Radio Shack pretty easily. Look for a 6 amp silicone diode for about 79 cents.

    That size panel would take 25 good hours of direct sunlight to bring your battery from half full to full however, which may not meet your needs. 25 hours of good sunlight might take 5 days of pretty dry weather. If you need it to recharge faster, you can go with more solar, but you'll need the charge controller now to keep from overcharging your battery. The 50 watt panel might cost you $125 USD, a larger 120 watt panel about twice that amount, plus another $75 or so for a controller, something like a Morningstar 10 amp would work. The 120 watt panel would produce up to 7.5 amps in direct sun, which might bring your battery from half to full in one good sunny day.

    There is a great book at the library I would suggest reading, it's written by Richard Perez, who also happens to be the founding editor of Home Power Magazine, the only periodical that really gets into the nuts and bolts of renewable energy. I would suggest ordering the mag and checking out the book myself. We subscribed 13 years ago, our home is currently powered by the wind and sun. Most of the equipment we put in ourselves over time, so I fully understand how it all operates, that is where that magazine and some other sources have gotten us. Whatever you do, remember to keep that battery watered, at least once a month in warm weather. Take care Q, Rudydoo

    Source(s): The Complete Battery Book, by Richard Perez, (library) Home Power Magazine, Solar Energy International, Midwest Renewable Energy Association MREA.ORG
  • Anonymous
    6 years ago

    There is a step-by-step video guide online right now that can show you how to reduce your power bill by making your own solar panels.

    Take a look at it:

    Why pay thousands of dollars for solar energy ($27,000 average cost) when you can build your own solar panel system for just a fraction of the retail cost. You can build a single solar panel or you can build an entire array of panels to power your whole house.

    Some people are saving 50% on their power bill, some people are reducing their bill to nothing. But what’s most impressive is that just by following these instructions some are even making the power company pay them!

  • J.
    Lv 6
    9 years ago

    You don't want to discharge that battery that much, it will shorten it's life expectancy.

    With a charge controller, something as simple as on this blog, you would want a panel that is capable of putting out 10 to 15 Amps, so you would want a 120 Watt panel or 150 Watt panel for one battery, to charge in a 24 hour cycle. just go to their alternative energy section and take a look at what they have. Essentially a soup to nuts if you did not want to construct anything, just install.

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  • 3 years ago

    Guide To Solar Power :

  • 3 years ago

    102ah Deep Cycle Battery

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