What Size Solar Panel To Charge A 12v Battery, & How Many Panels Are Needed?

12v lead acid or lithium ion batteries are common in vehicles like Rv’s, marine boats & yachts, cars, bikes – the list goes on!

But, what size solar panel do you need to charge a 12v solar re-chargeable battery?

And, after determining size, how do you figure out how many panels you need?

The answer is that it depends – on both the battery, and the solar panel set up you are using.

Below we have listed the types of solar panels you might use to charge a 12v battery, and informational guidelines for the size of solar panel required.


*You should always check the battery, and solar panel manufacturer instructions for exact charging requirements & compatibility.


What Size Solar Panel To Charge 12v Battery, & How Many Panels Required?

What type of solar panel to charge a 12v battery?

Before we identify the size of solar panel needed to charge a 12v battery, it makes sense to know the type of solar panels you might use.

In some situations where you’ll be charging a 12v battery – like when out with an rv for example – you’ll be off grid.

In these instances, more portable solar panels will be a better choice.

You can read more about both mounted/fixed solar panels and portable solar panels for 12v batteries here.


What size solar panel to charge 12v battery?

Short answer:

One or multiple 100-120 Watt rigid, flexible/bendable or large folding solar panels will usually be a suitable size panel for charging a 12v battery.


More Detailed Answer:

Size could mean two main things with a solar panel – the surface area dimensions, or the size of output (Watts & volts) that it has.

Whilst surface area is important for knowing whether and how many solar panels you can fit on a surface, output is far more important as far as battery charging.

A 12v battery will have two main pieces of information you need to know in order to find out what size panel is required to charge it:

1. How many volts it needs  – a standard 12V re-chargeable battery needs roughly 13.6 volts to charge.

2. How many A/h (amp hours) it needs replaced each day to be fully charged – the battery manufacturer should also tell you the A/h of the battery.


Once you know this information, you can then figure out how many Watt hours you need to fully charge the 12v battery:

1. Estimate how many hours of sunlight you have available to shine on the solar panel/s

2. To get the Watt hours that you need, multiply the battery voltage by the A/h – e.g. with a 110 A/h 12v battery, it would be 110A/h x 12v = 1320 Watt hours

3. To find out how many Watts of solar panels you need, multiply the Watt hours by the hours of sunlight available e.g. if you have 6 hours of sunlight available to you in a day (take into consideration cloud cover too), it would be 1320 Watt hours/6 sunlight hours = 220 Watts of solar panels


So, how do you use that information?

Well, we know that we need 220 Watts of solar panels, but we should also be aware that solar panels in reality don’t produce full output compared to the marketed numbers. So, it’s wise to up that number by 10-20% – to 240-260 Watts of solar panels.

If you want say a flexible solar panel, they come in mostly 50 Watt and 100 Watt models.

A 100 watt flexible solar panel will output roughly 17-19 volts while operating.

3 x 100 Watt flexible solar panels would be suitable in this instance to meet the 260 Watt requirement.



Due to the difference in voltage, a solar controller/regulator should be used with these solar panels to charge the battery to prevent damage to it

Most reputable solar panel manufacturers suggest 3 or 4 stage charging protection between the panel and the battery


How many solar panels to charge 12v battery?

Refer to the answer above – it depends on how much power the battery you have is using per day.


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