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

Solar Panel System

Photo by Marufish/ CC BY

The 12v battery has become very popular and is now used in bikes, cars, boats, recreational vehicles etc.

And now these batteries are being used in solar panels as well. But what’s the right solar panel needed to charge a 12V battery? Apart from the size you also need to determine how many panels are required.

What Type of Solar Panels Do You Use?

The short answer is it depends on the type of solar panel set up you have and the battery’s design. The following information gives you an idea of how 12v battery charging works with solar panels.

If you’re off the grid – use batteries or on a solar-powered RV – you’ll want solar panels that are compact and portable. Majority of RVs come with 12v batteries, and you can use mounted/fixed, flexible or folding solar panels.

What is the Right Size Solar Panel to Charge a 12v Battery?

The right size is one or more bendable/flexible/rigid/folding solar panels in the 100 to 120-watt range. This is usually enough in most cases.

Keep in mind that size may also refer to the volts and watts (output) and the surface area size.

Knowing the surface area size is necessary to determine how many solar panels you can install on it. For 12v battery charging however, the output is more vital.

To find the correct solar panel size for a 12V battery, two things are needed:

  • How many amp hours (a/h) it must replace daily to charge fully. You can find the battery’s a/h on the manufacturer website.
  • How many volts are required? A typical 12v battery requires about 13.6 volts for a full charge.

How to Find the Watt Hours Needed to Charge a 12v Solar Panel Battery

Now that you know these figures, you can determine the number of watt-hours that is required to charge a 12v battery. There are 3 steps.

  • Determine the number of sunlight hours that shine on the panels.
  • Multiply the voltage of the battery by the amp hours. So if the amp hours is 110, the formula is 12v x 110 A/h = 1320 watt-hours.
  • To figure out the number of solar panel watts you need, divide the number of available sunlight hours with the watt-hours. So if you get 6 hours of sunlight the formula 1320 divided by 6 = 220 solar panel watts.

So you require 220 watts solar panels. But majority of solar panels don’t generate maximum output in spite of what the numbers claim.

So if the figures say you need 220 watts, get 240 to 260 solar panel watts to make p for any shortage. Here are some options to get those 220 watts.

  • 3 x 100-watt flexible solar panels is sufficient to get 260 watts
  • A single 100-watt flexible solar panel generates approximately 19 volts as it runs
  • Majority of flexible solar panels come in 50 or 100 watts

Off-Grid Solar Panel 12v Battery Charging

Three options are available, fixed, flexible and folding. We went over this a bit earlier, but now it’s time to look at them in detail.

Folding Solar Panels

Folding Solar Panels

These are available in small and large sizes, though the right size depends on your needs..

The big folding panels have about 80 to 20 watts. A steel stand keeps it up and is designed to fold out. These solar panels are equipped with a solar controller to charge a single 12v battery.

Small folding solar panels cannot charge a 12v battery as they only have about 6 to 30 watts. You can find 20-watt models and that should be enough to charge lights, smartphones, tablets and USB devices.

Folding solar panels are ideal because they’re easy to setup, portable and mostly assembled already. The connectors, cables and controllers are easy to configure.

Mounted/Fixed Solar Panels

Fixed solar panels can’t be bent. You mount them on rooftops or RVs, anywhere with a flat surface.

A 100 watt fixed solar panel has sufficient voltage for one 12v battery. Like folding solar panels you’ll want to use a solar controller with four-stage cycling to safeguard the battery.

They’re usually made from poly-crystalline or mono-crystalline with aluminum framing. Fixed solar panels are also widely available and cost-effective.

Flexible Solar Panels

Flexible solar panels are portable and flexible, usually up to a 30-degree arc. This makes it the ideal choice for irregular surfaces.

Some flexible solar panels have 100 watts with up to 18 volts, more than enough for a 12v battery charge.

If you’ve got a solar controller you’ll be able to use the battery on home roofs, cars, RVs, boats and cabins. The biggest benefit of flexible solar panels is how quickly you can install it.

Why Use a Solar Charger Controller?

A solar charger is ideal if you’re going to use a panel with more than 5 watts. A charge controller also prevents battery discharges in low lit environments.

A solar charger controller also enhances charging quality and prevents overcharging.  A well-designed solar charger controller also comes with pre-installed blocking diodes to improve performance.

A solar charger controller has many functions, but basically, it works like an on/off switch. It allows power to get in the battery and cuts off access when the 12v battery is charged.

Photovoltaic panel ratings are in watts while solar controller ratings are in amp. So if you have a solar controller at 6 amps, it’s compatible with solar panels up to 70 watts.

Solar panel output is measured in watts. On the average, a 15-watt solar panel produces 3600 coulombs (1 a/h) with an hour of sunlight.

Solar powered shed: Basic solar setup

Final Verdict

In the end, figuring out the solar panel size to charge a 12v battery comes down to numbers. As shown here it’s not really hard to do once you know what figures to work with. You can avoid a lot of potential problems by figuring out in advance how much watts or amp hours you will need.

1 comment… add one
  • GARY FRANCE Feb 29, 2020 @ 13:00

    This has greatly simplified a subject I know nothing of! Thank you.

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