What Size Solar Panel To Charge A 12V Battery?

Renewable solar energy provides an environmentally conscious setup that can power up your electricity needs. 

Whether you plan to run off-grid in an RV, camping, or for a cabin, solar energy can meet your power needs. But understanding what size solar panel you require charging your 12V battery helps you run an efficient setup.

To get you started, this article will address:

  • What size solar panels charge a 12V battery?
  • How long does it take to charge your battery?
  • What equipment will you need to run efficiently?

Find out all you need to know to charge your 12V battery properly and to keep your eco-friendly solar setup running smoothly and efficiently.

100 watt solar panels

How Big of a Solar Panel Do I Need to Charge a 12v Battery?

The type of solar panel required to charge a 12V battery depends on the capacity, or amp-hours (Ah), of the device you wish to power. You can find the Amp-hours listed on your battery or in the description of your battery before you purchase it.

Of course, your exact solar panel needs vary, depending on the following factors:

  • Weather: Sunnier weather makes the charging cycle quicker.
  • Panel setup: Optimum angles and direction increase the speed of charging.
  • Lost efficiency: The less efficient your charger and inverter, the more you lose efficiency as power flows through them.
  • Battery effective capacity: The higher the capacity, the larger your needs.

For most setups, solar panels with wattage between 100 and 120 provide enough wattage to charge a 12V battery.

Technically, you can use any size solar panel to charge your 12V battery but less powerful solar panels take much longer to charge your battery fully. The bigger the surface of the panel, the quicker the charging cycle.

How Do I Charge a 12V Battery With Solar Panels?

Solar panels collect energy from the sun, which stores the charge in your batteries. Your battery capacity determines just how much power you can store.

The higher your capacity, the more energy you store. If you plan to use batteries as part of your solar setup, you need solar panels, a charge controller, and an inverter.

You must first connect your solar panels to a charge controller. The controller does two things:

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  • Monitors how much energy you’re storing so that the batteries don’t overcharge 
  • Shuts down a system if the batteries become too depleted

Before powering your appliances, you need to connect your batteries to an inverter. This is important!

The inverter converts DC energy collected from your solar panels into AC energy that your appliances and other electronics can actually use.

What Solar Panel Setup Terms Do I Need to Know?

Before you get started, understanding a few key terms helps you navigate your solar panel setup. To do the math to figure out your solar power needs, a better understanding of these terms makes the calculations much simpler.

  • Amp-hours (Ah): refers to the number of amps offered in one hour
  • Voltage: lists the potential output of your solar panel or battery
  • Wattage: the operating power of your solar panel or battery
  • Power inverter: connects to the panel to convert DC energy to useable AC power
  • Charge controller: a device that controls when your solar battery charges
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Do I Need a Deep Cycle Battery?

Although you can charge a 12V car battery with your solar panels, we have specifically designed deep cycle batteries for solar energy needs. Where a car battery provides a burst of energy to start a car, deep cycle batteries provide a power bank to run your electronics.

Designed to handle the repeated charging and discharging that happens during solar power use, a quality deep cycle battery has been designed to be an essential part of your solar energy setup for running electronics.

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

Figuring out how many solar panels you need to charge a 12-volt battery depends on a few factors and you can perform the calculations to fit your solar setup exactly. The battery capacity affects your setup the most.

If you have a 200Ah 12-volt battery, you would need 3, 100-watt panels or 1, 100-watt panel to charge your battery.

To understand and calculate your needs, consider the actual capacity of your battery first. Just to make life easier, check out this list of common battery capacities and approximate panel needs:

  • One 50Ah battery needs a 90-watt solar panel.
  • One 80Ah battery needs a 140-watt solar panel.
  • One 175Ah battery needs a 100-watt solar panel.
  • One 120Ah battery needs a 210-watt solar panel.
  • One 200Ah battery needs a 300-watt solar panel.

How Does the Actual Capacity of My Battery Affect the Charging?

First, note the actual capacity, or Amp-hours (Ah), of your battery. Although Amp-hours listed on batteries reflect the battery’s capacity, we must use a lower figure for the actual capacity.

Because of lost efficiency and depletion, you calculate actual capacity based on 80% of the capacity (Ah). For example, if your 12-volt battery capacity was 200Ah, you would determine your needs based on 80%, or 160Ah (200 x 0.80 = 160). 

How Does Battery Depletion Affect Battery Capacity?

Remember, no battery holds its charge completely, and manufacturers recommend never allowing a battery to deplete past 50%.

So after you have figured your actual battery capacity, you simply take that number and divide it in half. Using the example of a 200Ah battery, the true capacity would be 160Ah.

So the genuine needs of the battery for charging should never be more than 80Ah (160Ah / 2 = 80Ah).

Will a 100-Watt Solar Panel Charge a 12-Volt Battery?

If you don’t use any amps for long periods, a single 100-watt solar panel could charge your 12-volt battery comfortably.

But the duration for recharging a battery depends on many factors, including how depleted the battery has become, the battery capacity, weather, and more. Having a general idea of your needs can help you optimize your setup.

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You can figure the answer by using the formula: 80% x (battery volts) x (capacity) / number of daylight hours.

So if you had a 100Ah 12-volt battery and 5.5 hours of daylight, you would need 175 watts, meaning you would need two 100-watt solar panels.

How Long Will a 100-Watt Solar Panel Take to Charge a 12V Battery?

Consider several factors when judging the time it takes for a solar panel to charge a battery. You want to think about the weather, panel wattage, battery capacity, battery depletion, controller efficiency, and more.

However, you can also focus simply on battery capacity, solar panel watts, and sunlight hours. Estimate the time it takes for a 100-watt panel to charge a 12-volt battery by using this simple formula to calculate your charging time: (battery capacity in Ah) x voltage/panel wattage.

In most cases, when the battery capacity (Ah) matches the amps produced by the solar panels, fully charging a drained battery takes five to eight hours.

To make your life easy, you can use this simple cheat sheet to know how much time you need for a 100-watt panel to charge common 12V battery capacities:

  • One 50Ah battery takes about 4.8 hours.
  • One 80Ah battery takes nearly 8 hours.
  • One 100Ah battery takes about 10 hours.
  • One 120Ah battery takes approximately 12 hours.
  • One 200Ah battery takes just over 19 hours.

How Many Amps Do I Need to Charge a 12-Volt Battery?

Typically, a 12-volt solar panel rated at 100 watts charges a capacity of around 5 amps per hour (Ah). On a typical solar day, with 6 hours of sunshine, your solar panels can charge to a 30Ah capacity (6 hours x 5 amps).

The amps you need depend on the capacity of your battery, the size, or wattage, of your solar panels, and how many amps you intend to use.

How Many Volts Should My Solar Panel Be to Charge My 12v Battery?

Ideally, the voltage of your solar panels should match the voltage of your battery. Technically, however, you can also use panels with different voltages to charge your 12V battery. But using panels and batteries of different voltages complicates your setup. 

The following sections give useful tips to create a workable solar setup with higher-voltage panels for your 12V battery.

Can I Use a 24V Solar Panel to Charge a 12V Deep Cycle Battery?

It is true, you can match voltages between your solar panel and battery making for an ideal setup. But you can also use a higher voltage solar panel to charge a 12V deep-cycle battery by selecting one of these workarounds, although each comes with a downside:

  • Use a DC-DC converter to step down the 24V in your panel to 12V for your battery. This option makes your setup less efficient.
  • Wire two 12V batteries in a series. This option becomes more expensive.
  • Use an MPPT charge controller. The expense for this option makes it unlikely to be used in smaller configurations.


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