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: Enter a valid voltage
Error: Enter a valid battery capacity
Error: Select a battery type
Error: Select a charge controller type
Error: Enter a valid number of hours
Estimated solar panel size to charge your battery in peak sun hours:
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

  • Lead acid depth of discharge: 50% DoD
  • Lithium (LiFePO4) depth of discharge: 100% DoD
  • 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. Solar Charge Controller Type: Will you be using a PWM or MPPT charge controller?
  5. 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 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
  4. Solar Charge Controller Type: MPPT
  5. Desired Charge Time (in peak sun hours): 15

When you calculate it, you get the following result:

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 TypeEst. Solar Panel Size
5 peak sun hoursMPPT340 watts
10 peak sun hoursMPPT170 watts
15 peak sun hoursMPPT110 watts
20 peak sun hoursMPPT80 watts
25 peak sun hoursMPPT70 watts
5 peak sun hoursPWM430 watts
10 peak sun hoursPWM210 watts
15 peak sun hoursPWM140 watts
20 peak sun hoursPWM100 watts
25 peak sun hoursPWM80 watts

Summary

  • You need around 340 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 430 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 TypeEst. Solar Panel Size
5 peak sun hoursMPPT290 watts
10 peak sun hoursMPPT110 watts
15 peak sun hoursMPPT70 watts
20 peak sun hoursMPPT50 watts
25 peak sun hoursMPPT40 watts
5 peak sun hoursPWM360 watts
10 peak sun hoursPWM140 watts
15 peak sun hoursPWM90 watts
20 peak sun hoursPWM70 watts
25 peak sun hoursPWM50 watts

Summary

  • You need around 290 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 360 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 TypeEst. Solar Panel Size
5 peak sun hoursMPPT680 watts
10 peak sun hoursMPPT320 watts
15 peak sun hoursMPPT210 watts
20 peak sun hoursMPPT160 watts
25 peak sun hoursMPPT130 watts
5 peak sun hoursPWM860 watts
10 peak sun hoursPWM410 watts
15 peak sun hoursPWM270 watts
20 peak sun hoursPWM200 watts
25 peak sun hoursPWM160 watts

Summary

  • You need around 680 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 860 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 TypeEst. Solar Panel Size
5 peak sun hoursMPPT570 watts
10 peak sun hoursMPPT220 watts
15 peak sun hoursMPPT140 watts
20 peak sun hoursMPPT100 watts
25 peak sun hoursMPPT80 watts
5 peak sun hoursPWM720 watts
10 peak sun hoursPWM270 watts
15 peak sun hoursPWM170 watts
20 peak sun hoursPWM130 watts
25 peak sun hoursPWM100 watts

Summary

  • You need around 570 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 720 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 is a chart showing what size solar panel you need to maintain 100Ah batteries of various voltages:

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 500 peak sun hours for these calculations.

What Size Solar Panel to Maintain 100Ah Lithium Battery?

Battery VoltageCharge Controller TypeEst. Solar Panel Size
12VMPPT5 watts
24VMPPT8 watts
12VPWM5 watts
24VPWM9 watts

Summary

You need a 5-10 watt solar panel to maintain a 12V or 24V 100Ah lithium battery.

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

Battery VoltageCharge Controller TypeEst. Solar Panel Size
12VMPPT4 watts
24VMPPT5 watts
12VPWM4 watts
24VPWM6 watts

Summary

You need a 5 watt solar panel to maintain a 12V or 24V 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.
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.

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