What Size Solar Panel to Charge 100Ah Battery?

What size solar panel do you need to charge a 100Ah battery? Enter your battery specs, solar charge controller type and desired charge time into our solar panel size calculator to find out:

Calculate Solar Panel Size to Charge 100Ah Battery

Error: This field is required.
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Error: Select a battery type.
Optional: If left blank, we’ll use a default value of 50% DoD for lead acid batteries and 100% DoD for lithium batteries.
Error: Select a charge controller type.
You can use our peak sun hours calculator to find out how many peak sun hours your locations gets per day.
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Estimated solar panel size:
watts
Warning: We estimate that a solar power system with these parameters would have a maximum charge current of . Many battery manufacturers recommend a maximum charge current of for lead acid batteries with this capacity. To maximize your battery’s lifespan, consider using a smaller solar panel or a bigger battery. Or increase your desired charge time.
Warning: We estimate that a solar power system with these parameters would have a maximum charge current of . Many battery manufacturers recommend a maximum charge current of for lithium iron phosphate batteries with this capacity. To maximize your battery’s lifespan, consider using a smaller solar panel or a bigger battery. Or increase your desired charge time.
Error: We estimate that it is impossible to charge your battery this quickly. The typical absorption time for batteries is around hours, which is greater than (or equal to) your desired charge time. Increase your desired charge time and try again.

Note: If you already have a solar panel size in mind and want to estimate how long it will take to charge your battery, check out our solar panel charge time calculator.

Calculator Assumptions

  • The solar charge controller is the only load connected to the battery

What Size Solar Panel to Charge 100Ah Battery?

To find out what size solar panel you need to charge a 100Ah battery, you’ll need to enter the following info into our solar panel size calculator at the top of this page:

  1. Battery Voltage (V): What is your battery’s voltage?
  2. Battery Amp Hours (Ah): What is your battery’s capacity in amp hours? We’ve gone ahead and entered 100 amp hours already, but you can always change it if your battery has a different capacity.
  3. Battery Type: Is your battery a lead acid or lithium (LiFePO4) battery?
  4. Battery Depth of Discharge (DoD): What level of discharge is your battery at? 100% means fully discharged and 0% means fully charged.
  5. Solar Charge Controller Type: Will you be using a PWM or MPPT charge controller?
  6. Desired Charge Time (in peak sun hours): How quickly do you want your solar panel to charge your battery, in peak sun hours?

Once you’ve entered the above info, click “Calculate Solar Panel Size” to get an estimate of what size panel you need to charge your battery at your desired speed.

Example

Let’s say you have a 12V 100Ah lithium battery and an MPPT charge controller in an off-grid cabin. You want a solar panel that will charge your battery from 100% DoD in 15 peak sun hours.

To find out what size panel you need, you’d enter the following into the calculator:

  1. Battery Voltage (V): 12
  2. Battery Amp Hours (Ah): 100
  3. Battery Type: Lithium (LiFePO4)
  4. Battery Depth of Discharge (DoD): 100%
  5. Solar Charge Controller Type: MPPT
  6. Desired Charge Time (in peak sun hours): 15

Turns out, you need a 110 watt solar panel to charge a 12V 100Ah lithium (LiFePO4) battery in 15 peak sun hours with an MPPT charge controller.

What Size Solar Panel to Charge 12V 100Ah Lithium Battery?

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT310 watts
10 peak sun hoursMPPT160 watts
15 peak sun hoursMPPT110 watts
20 peak sun hoursMPPT80 watts
25 peak sun hoursMPPT70 watts
5 peak sun hoursPWM380 watts
10 peak sun hoursPWM190 watts
15 peak sun hoursPWM130 watts
20 peak sun hoursPWM100 watts
25 peak sun hoursPWM80 watts

Summary

  • You need around 310 watts of solar panels to charge a 12V 100Ah lithium battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You need around 380 watts of solar panels to charge a 12V 100Ah lithium battery from 100% depth of discharge in 5 peak sun hours with a PWM charge controller.

What Size Solar Panel to Charge 12V 100Ah Lead Acid Battery?

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT220 watts
10 peak sun hoursMPPT100 watts
15 peak sun hoursMPPT70 watts
20 peak sun hoursMPPT50 watts
25 peak sun hoursMPPT40 watts
5 peak sun hoursPWM270 watts
10 peak sun hoursPWM120 watts
15 peak sun hoursPWM80 watts
20 peak sun hoursPWM60 watts
25 peak sun hoursPWM50 watts

Summary

  • You need around 220 watts of solar panels to charge a 12V 100Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You need around 270 watts of solar panels to charge a 12V 100Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with a PWM charge controller.

What Size Solar Panel to Charge 24V 100Ah Lithium Battery?

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT610 watts
10 peak sun hoursMPPT300 watts
15 peak sun hoursMPPT200 watts
20 peak sun hoursMPPT150 watts
25 peak sun hoursMPPT130 watts
5 peak sun hoursPWM760 watts
10 peak sun hoursPWM380 watts
15 peak sun hoursPWM250 watts
20 peak sun hoursPWM190 watts
25 peak sun hoursPWM150 watts

Summary

  • You need around 610 watts of solar panels to charge a 24V 100Ah lithium battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You need around 760 watts of solar panels to charge a 24V 100Ah lithium battery from 100% depth of discharge in 5 peak sun hours with a PWM charge controller.

What Size Solar Panel to Charge 24V 100Ah Lead Acid Battery?

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT430 watts
10 peak sun hoursMPPT200 watts
15 peak sun hoursMPPT130 watts
20 peak sun hoursMPPT100 watts
25 peak sun hoursMPPT80 watts
5 peak sun hoursPWM540 watts
10 peak sun hoursPWM240 watts
15 peak sun hoursPWM160 watts
20 peak sun hoursPWM120 watts
25 peak sun hoursPWM90 watts

Summary

  • You need around 430 watts of solar panels to charge a 24V 100Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You need around 540 watts of solar panels to charge a 24V 100Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with a PWM charge controller.

What Size Solar Panel to Maintain 100Ah Battery?

Maintaining a battery, also called trickle charging, is when you charge a fully charged battery at a rate equal to its self-discharge rate to keep it topped off.

Here are charts showing what size solar panel you need to maintain 100Ah batteries of various voltages using a PWM charge controller. I recommend PWMs for trickle charging because they generally have lower power consumption (which makes a small difference during long charging cycles). Also, MPPTs often require a PV voltage of 4-5 volts above battery voltage to start charging. That’s easy to achieve with a large solar panel, but not with a small one.

Note: Many factors affect a battery’s self-discharge rate — such as age of the battery and ambient temperature. To keep things simple I just used a desired charge time of 1000 peak sun hours for these calculations.

What Size Solar Panel to Maintain 100Ah Lithium Battery?

Battery VoltageEstimated Solar Panel Size
12V4 watts
24V6 watts
36V7 watts
48V9 watts

Summary

You need a 5-10 watt solar panel to maintain a 100Ah lithium battery.

What Size Solar Panel to Maintain 100Ah Lead Acid Battery?

Battery VoltageEstimated Solar Panel Size
12V3 watts
24V4 watts
36V5 watts
48V6 watts

Summary

You need a 3-6 watt solar panel to maintain a 100Ah lead acid battery.

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Alex Beale
Alex Beale
Hi, I'm Alex. I started Footprint Hero to help people reduce their environmental impact. My current obsession is DIY solar power projects, which I've been building since 2020.

2 thoughts on “What Size Solar Panel to Charge 100Ah Battery?”

  1. Hi Mr Alex,
    Thanking you much for your interesting web site.
    i have just installed two panels of 100w on my roof charging a 100Ah lead acid battery thru a MPPT charge controller.
    I have not started using the system, as I am still doing the wirings to my house.
    The controller is reading 157 Ah at 14.4 V, is this ok ?
    Thanking you for your reply.

    Have a sunny year !

    1. Hey Ali. I’m guessing the 14.4V reading is from the battery voltage screen? That sounds right, that’s a common boost voltage setpoint for lead acid batteries.

      My guess is the 157 Ah reading is from the total/accumulated Ah screen. That would mean your charge controller has charged the battery with a total of 157 Ah. If that’s the case, it sounds like you’ve discharged and charged the battery a few times already? If so, that reading sounds perfectly normal, too.

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