12V Solar Panels for Deep Cycle Batteries Charging Systems

The Deep Cycle batteries used in cars, RVs or Boats are designed to be discharged and then re-charged hundreds or thousands of times. These batteries are rated in Amp Hours (ah) – usually at 20 hours and 100 hours. Simply stated, amp hours refers to the amount of current – in amps – which can be supplied by the battery over the period of hours.

For example, a 350ah battery could supply 17.5 continuous amps over 20 hours or 35 continuous amps for 10 hours.

To quickly express the total watts potentially available in a 6 volt 360ah battery; 360ah times the nominal 6 volts equals 2160 watts or 2.16kWh (kilowatt-hours). Like solar panels, batteries are wired in series and/or parallel to increase voltage to the desired level and increase amp hours.

The battery should have sufficient amp hour capacity to supply needed power during the longest expected period “no sun” or extremely cloudy conditions. A lead-acid battery should be sized at least 20% larger than this amount. If there is a source of back-up power, such as a standby generator along with a battery charger, the battery bank does not have to be sized for worst case weather conditions.

The size of the battery bank required will depend on the storage capacity required, the maximum discharge rate, the maximum charge rate, and the minimum temperature at which the batteries will be used. During planning, all of these factors are looked at, and the one requiring the largest capacity will dictate the battery size.

One of the biggest mistakes made by those just starting out is not understanding the relationship between amps and amp-hour requirements of 120 volt AC items versus the effects on their DC low voltage batteries.

For example, say you have a 24 volt nominal system and an inverter powering a load of 3 amps, 120VAC, which has a duty cycle of 4 hours per day. You would have a 12 amp hour load (3A X 4 hrs=12 ah).

However, in order to determine the true drain on your batteries you have to divide your nominal battery voltage (24v) into the voltage of the load (120v), which is 5, and then multiply this times your 120vac amp hours (5 x 12 ah). So in this case the calculation would be 60 amp hours drained from your batteries – not the 12 ah. Another simple way is to take the total watt-hours of your 120VAC device and divide by nominal system voltage.

UsingĀ  the above example;

3 amps x 120 volts x 4 hours = 1440 watt-hours divided by 24 DC volts = 60 amp hours.

Lead-acid batteries are the most common in PV systems because their initial cost is lower and because they are readily available nearly everywhere in the world. There are many different sizes and designs of lead-acid batteries, but the most important designation is that they are deep cycle batteries. Lead-acid batteries are available in both wet-cell (requires maintenance) and sealed no-maintenance versions. AGM and Gel-cell deep-cycle batteries are also popular because they are maintenance free and they last a lot longer.

24 thoughts on “12V Solar Panels for Deep Cycle Batteries Charging Systems

  1. Pingback: How to Monitor Your Solar Powered System

  2. Pastrick O Nwoko

    Dear Sirs,
    I want sand-alone solar inverter + charger that will invert 12 volts
    dc battery to 230 volts ac (50 hz). I want a system that could be
    used in rural areas in nigeria – it will be affordable to
    ordnary folks in the remote villages. Kindly give me
    recommendation as to which inverter and charger that will be ideal.
    Also the wright battery.

  3. carl

    Am looking for a way to power my well pump via solar. The reading on it is 230 volts. What size would I need?

  4. Ifeanyi

    I have a 1.4KVa 24V sukam inverter, and i want to use a solar panel to charge it. how do i get the right size of and the average cost

  5. Pingback: The Basics of Solar Power Systems to Produce Electricity

  6. john Oladiran

    Sir, I have a 3.5kva inverter+charger electricity to charge has always been a problem. Iwant to know if I can combine solar charging with electricity charging. Then also what rating or solar panels do I need to charge this 48 volt’4 number 200amps battery.
    Thank )ou

  7. Appachu

    i am working on a solar powered wheel chair. I need upto 240 w power which I will be storing in two 12V 18 Ah lead acid batteries. I need to power two PMDC Motors 12 V each. how should I go about selecting my solar panel and the corresponding solar charger and controller circuit. thank you

  8. ken hayes

    i have 6 solar panels that add up to 90 watts (bought at harbor fright) how many batteries would i need to run lights and small heater in my greenhouse also what kind of batteries will i need 2538432436

  9. deo

    I have a 90 watt solar system with a 12 volt deep cycle battery
    the ah 348 13.5volt,can i charge the battery up to 15 volt,
    i have a 26 watt light only ran for 6hr,thanks .DEO

  10. Mike


    W.R.T. you question about a 1 hp load, convert watts to watts, so to speak:

    105 Ah deep cycle (assuming 12 Volts) gives a capacity of 1260 W-hrs.

    Next, we know 1hp is 746 watts (if memory serves me)

    it follows: 1260 W-hrs/746 W yields 1.69 hrs. This assumes no losses, battery in fine condition, etc. etc. etc.

    In the event you supply your load through this entire cycle repeatedly, you will diminsh the life of your battery greatly.


  11. DrPorky

    I need to power the following:
    Fridge: 4.5A / 60W / 13.3V (running 24/7)
    Laptop: 1.5A / 85W / 56.7V (running 8 hours day)
    Fan: 2.5A / 14W / 5.6V (running 8 hours night)

    To get the volts for use in your formula I just used: Watts / Amps = Volts

    The inverter I’m looking at is a 600 – 1000 Watt Pure Sine Wave Power Inverter and has an output of 115VAC

    so would the calculation then be:
    amps x volts x hours = watt-hours divided by 12 DC volts = amp hours

    Laptop – 56.7 V (1.5A / 85W /56.7V)
    1.5 amps x 56.7 volts x 8 hours = 680.4 watt-hours divided by 12 DC volts = 56.7 amp hours

    Sorry, I’m a total newbie. I’m going to be vandwelling soon and am trying to figure out the most cost effective set up to power these items. So, I need an accurate calculation to determine battery size (going with AGM for sure) and solar array size.

    Thank you!

  12. kahlil


    im kahlil villareal and i invented my own motorized roller blades, my MRB is powered by a small deep cycle batteries .. but im only a 15 year old child so i don’t have money to pay for to much electricity consumption.. i use my motorized rollers for daily transportation for school.. i dont know how to make a solar panel connected to a deep cycle battery charger.. please help me.. please e-mail me.. :(

  13. William Carley

    To whom it may concern:
    What size solar pnl do I need to keep four ( 4 ) 12v deep cell batteries charged, to run my 5,000 watt 120v inverter. I’am using this to power my 24’x24′ cottage. I figure I use a total of 150ah at the most in a 24 hour period. I was thinking a 200watt 12v to a 240watt 12v solar pnl should do it. I’am using a 3500 watt generator right now, but gas gets expensive. I can run everything except fridge, airconditioner, and toaster on a 1,000 watt generator. Price also
    Thank you
    Bill Carley

  14. paul

    i have a camping trailer that i am going to set up with solar panels to charge my batteries. i understand how that part works. i have two solar panels and a controller. i would like to power up my 120v system in the trailer when i am camping so i dont have to plug into an external power supply. can i do this from my batteries and solar charging system?

  15. Kevin Pitman

    I need to install a video camera with no electrical but I do have a solar panel and batteries. The solar panel is large enough to fully charge a 12 volt battery, but I need the camera to operate continuously for 3 cloudy, 24 hour days. The camera draws .5 amps of current at 12 volts. How will I calculate this to determine what size battery is required. Thank you

  16. Chris

    I have an electric golf cart that uses six 8-volt deep cycle batteries. What would be the best source/item needed to keep these batteries charged?

  17. koh wan mow

    dear sir / mdm,
    i am planning to get 3 X 12VDC 120Ah AGM batteries and hook it all up pareller so it will be 12VDC 360Ah. i would like to know how to set up a solar panel to charge the above size power bank.
    What size and type solar panel is most reliable and effective to use in South East Asia region and what size controller to suit including is there equipment to monitor the batteries power remaining? what other equipment is require to set this up saftely?
    i know, the easiest and most convenience way to charge the batteries is generator with battery charger.
    i am trying to go green and save on long term.

  18. Miguel

    I have a 100 watt panel along with a 400 watt inverter and charge controller. What size battery do I need to use on this system ?
    Thank You.

  19. Sin

    I’m setting up the house for solar system.
    My max. wattage if i have everything running
    is 2450 Watts.

    I have a 3000 watt inverter with a 6000 watt peak.

    what my question is, I want to run the house for about 3 days
    off the batteries.

    what size batteries will I need to do this?
    and also what is the panel wattage I’ll need to recharge the batteries in a good amount of time?

    Also do you have any of these items in stock?

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