What Size Solar Panel to Charge 12V Battery?

What size solar panel do you need to charge a 12V 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 12V 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 12V Battery?

To find out what size solar panel you need to charge your 12V 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? We’ve gone ahead and entered 12 volts already, but you can always change it if your battery has a different voltage.
  2. Battery Amp Hours (Ah): What is your battery’s capacity in amp hours? (If you only know its capacity in watt hours, first convert watt hours to amp hours)
  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 solar 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 12V battery at your desired speed.

Example

Let’s say you have a 12V 100Ah lead acid battery and a PWM charge controller in your campervan. You want a solar panel that will charge your battery in 10 peak sun hours.

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

  1. Battery Voltage (V): 12
  2. Battery Amp Hours (Ah): 100
  3. Battery Type: Lead acid
  4. Battery Depth of Discharge (DoD): 50%
  5. Solar Charge Controller Type: PWM
  6. Desired Charge Time (in peak sun hours): 10

Turns out you need a 120 watt solar panel to charge a 12V 100Ah lead acid battery in 10 peak sun hours with a PWM charge controller.

What Size Solar Panel to Maintain 12V 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 12V batteries of various capacities with a PWM charge controller.

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

Battery Amp Hours (Ah)Battery TypeEstimated Solar Panel Size
50AhLithium (LiFePO4)3 watts
60AhLithium (LiFePO4)3 watts
80AhLithium (LiFePO4)3 watts
100AhLithium (LiFePO4)4 watts
120AhLithium (LiFePO4)4 watts
140AhLithium (LiFePO4)4 watts
200AhLithium (LiFePO4)5 watts
50AhLead acid2 watts
60AhLead acid2 watts
80AhLead acid3 watts
100AhLead acid3 watts
120AhLead acid3 watts
140AhLead acid3 watts
200AhLead acid4 watts

Summary

  • You would need a 3-5 watt solar panel to maintain the most common sizes of 12V lithium batteries with a PWM charge controller.
  • You would need a 3-4 watt solar panel to maintain the most common sizes of 12V lead acid batteries with a PWM charge controller.

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

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 would 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 would 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.

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 would 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 would 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 12V 50Ah Battery?

12V 50Ah Lithium Battery

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT160 watts
10 peak sun hoursMPPT80 watts
15 peak sun hoursMPPT60 watts
20 peak sun hoursMPPT50 watts
25 peak sun hoursMPPT40 watts
5 peak sun hoursPWM200 watts
10 peak sun hoursPWM100 watts
15 peak sun hoursPWM70 watts
20 peak sun hoursPWM50 watts
25 peak sun hoursPWM40 watts

Summary

  • You would need a 160 watt solar panel to charge a 12V 50Ah lithium battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You would need a 200 watt solar panel to charge a 12V 50Ah lithium battery from 100% depth of discharge in 5 peak sun hours with a PWM charge controller.

12V 50Ah Lead Acid Battery

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT120 watts
10 peak sun hoursMPPT60 watts
15 peak sun hoursMPPT40 watts
20 peak sun hoursMPPT30 watts
25 peak sun hoursMPPT30 watts
5 peak sun hoursPWM140 watts
10 peak sun hoursPWM70 watts
15 peak sun hoursPWM40 watts
20 peak sun hoursPWM30 watts
25 peak sun hoursPWM30 watts

Summary

  • You would need a 120 watt solar panel to charge a 12V 50Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You would need a 140 watt solar panel to charge a 12V 50Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with a PWM charge controller.

What Size Solar Panel to Charge 12V 120Ah Battery?

12V 120Ah Lithium Battery

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT370 watts
10 peak sun hoursMPPT190 watts
15 peak sun hoursMPPT130 watts
20 peak sun hoursMPPT100 watts
25 peak sun hoursMPPT80 watts
5 peak sun hoursPWM460 watts
10 peak sun hoursPWM230 watts
15 peak sun hoursPWM150 watts
20 peak sun hoursPWM120 watts
25 peak sun hoursPWM90 watts

Summary

  • You would need around 370 watts of solar panels to charge a 12V 120Ah lithium battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You would need around 460 watts of solar panels to charge a 12V 120Ah lithium battery from 100% depth of discharge in 5 peak sun hours with a PWM charge controller.

12V 120Ah Lead Acid Battery

Charge TimeCharge Controller TypeEstimated Solar Panel Size
5 peak sun hoursMPPT260 watts
10 peak sun hoursMPPT120 watts
15 peak sun hoursMPPT80 watts
20 peak sun hoursMPPT60 watts
25 peak sun hoursMPPT50 watts
5 peak sun hoursPWM330 watts
10 peak sun hoursPWM150 watts
15 peak sun hoursPWM100 watts
20 peak sun hoursPWM70 watts
25 peak sun hoursPWM60 watts

Summary

  • You would need around 260 watts of solar panels to charge a 12V 120Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You would need around 330 watts of solar panels to charge a 12V 120Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with a PWM charge controller.

What Size Solar Panel to Charge 12V 200Ah Battery?

12V 200Ah 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 would need around 610 watts of solar panels to charge a 12V 200Ah lithium battery from 100% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You would need around 760 watts of solar panels to charge a 12V 200Ah lithium battery from 100% depth of discharge in 5 peak sun hours with a PWM charge controller.

12V 200Ah 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 would need around 430 watts of solar panels to charge a 12V 200Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with an MPPT charge controller.
  • You would need around 540 watts of solar panels to charge a 12V 200Ah lead acid battery from 50% depth of discharge in 5 peak sun hours with a PWM charge controller.

How to Charge a 12V Battery with a Solar Panel

You’ve got your 12V battery. ✔

You’ve got your perfectly sized solar panel. ✔

Now you need to connect them together to start solar charging the battery.

Here’s a quick tutorial:

Note: For more in-depth instructions, check out my full tutorial on how to connect a solar panel to a battery.

Parts

  • 12V solar panel
  • 12V battery
  • Solar charge controller (one that’s compatible with 12V batteries)
  • Battery cables
  • Solar panel to charge controller adapter cables

Step 1: Connect the 12V Battery to the Charge Controller

Insert the stripped end of the negative battery cable into the negative battery terminal on the charge controller. Screw the terminal shut with a screwdriver. Repeat the process for the positive battery cable.

Connect the ring terminal on the negative battery cable to the negative terminal on the 12V battery. Repeat the process for the positive battery cable.

Your charge controller should turn on to indicate the battery and charge controller are properly connected. Mine has a battery indicator light that turned on.

Now you need to program your charge controller for your battery type. This lets the charge controller know which voltage to charge the battery to.

Consult your instruction manual for how to do this. In this example, I’m using a sealed lead acid battery, so I programmed my charge controller for that battery type.

Check!

Step 2: Connect the Solar Panel to the Charge Controller

Connect the positive solar panel adapter cable to the positive solar panel cable. Repeat the process for the negative solar panel cable.

Insert the negative solar cable into the negative solar PV terminal on the charge controller and screw the terminal shut. Repeat the process for the positive solar cable.

Your charge controller should indicate that the solar panel is properly connected. Mine has a PV indicator light that turned on.

Done!

Step 3: Put the Solar Panel Outside in Direct Sunlight

Your solar panel and battery are connected…

…but the solar panel isn’t charging the battery yet because the panel isn’t in direct sunlight.

That’s an easy fix.

Take your solar panel outside and angle it towards the sun.

Once you do, your charge controller should indicate that the solar panel is charging the 12V battery. For example, the PV indicator light on my charge controller starts blinking green when the battery is charging.

There ya go!

You’re charging a 12V battery with a solar panel.

(Simple, no?)

Now all you have to do is wait for the solar panel to charge the battery. The charge controller will automatically stop the charging once the battery is fully charged.

Solar Charging 12V Batteries FAQ

What Size Solar Panel Do I Need to Charge a 12V Battery?

A 100W solar panel (left) next to a 5W solar panel. Both are 12V solar panels and both can charge a 12V battery. But the 100W panel can output up to 20 times the power of the 5W panel, so it will charge a 12V battery much faster.

Short answer: Use the calculator at the top of this page.

Long answer: What size solar panel you need depends mainly on 2 things:

  1. Battery capacity in amp hours (Ah)
  2. Desired charge time in peak sun hours

If you want to charge a big battery quickly, you’ll need a big solar panel or solar array. Like how you’d need a big hose to quickly fill up a big bucket.

Alternatively, if you want to slowly charge a small battery, you can use a small solar panel. A small hose will eventually fill up a small bucket.

Want to charge a big battery slowly? Or a small battery quickly?

Your solar panel size will fall somewhere in between.

There is no single solar panel size that will be perfect for every scenario. Depending on your battery size and how fast you want to charge your battery, you could get away with using a small 5W solar panel, or you might need a 400W solar array.

How Many Solar Panels Do I Need to Charge a 12V Battery?

Me happily charging a 12V battery with one 100W solar panel

You only need one 12V solar panel to charge a 12V battery.

For instance, a 100 watt solar panel is a common solar panel size you could use to charge some of the most common 12V battery capacities.

But if you have a big battery and you want to charge it quickly, you’ll likely need to buy multiple solar panels and connect them together to create a solar panel array.

If you just want to maintain a 12V battery, you can get away with a small 12V solar panel, such as a 5W or 10W panel. That’s right — a 5W solar panel will charge a 12V 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 12V Battery?”

  1. Hi. Thanks for the clearly presented information. Your calculators helped me understand something useful about battery capacity. I use my 12v 50Ah battery to power an LED strip-light (1.6 Amps) but I only do this for a few minutes or an hour, once a month or less. Once this year, I used the light for 3 or 4 hours. So my system’s capacity is underused. I wanted to know if I added another 12v 50Ah battery, could the system could support it. And it appears it can. At an average of 2.76 peak solar hours daily, (London, UK) it seems my 50w panel would manage. It seems that just in December and January there would be a deficit of peak solar hours and recharging. Ta!

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