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3 Steps To Determine What Size Solar Panel You Need To Charge a 12V Battery

If you are wondering what size solar panel to charge a 12v battery, there are a few things to consider. Solar panels come in a variety of sizes, and the size you need will depend on the wattage of your device or appliances, the number of batteries in your system, and the conditions where you will be using them.

In addition, solar panels can be used to charge a variety of devices and electronics, so you will need to think about what you will be using the solar panel for in the process before you make a purchase. 

Whether you are charging a 12v battery for an RV or for home use, the larger battery bank, the higher wattage your solar panel should be.

Now let’s get down to answering the question:

What Size Solar Panel To Charge 12v Battery?

To know the size of the solar panel you need. Follow these 3 simple steps:

Step 1: Know your battery capacity. This is measured in ampere-hour or amp-hour (Ah). The battery capacity will determine how long the solar panel can charge the battery.   

Step 2: Know the average number of sunlight you can get in your area. The sun is the source of solar energy. The amount of sunlight will determine how much solar energy the solar panel can produce.  

Step 3: Calculate solar panel size. The size of a solar panel to charge a battery can generally be calculated by multiplying your battery voltage on the value you get in step 1 and dividing the results by the value you get in step 2. In this case, we already know the information about the voltage rating of our battery. To summarize, calculations go down to simple math like this:

Solar Panel Size = (Battery Capacity x Battery Voltage) ÷ Ave. sunlight hours per day

For example:

Let’s say you live way South Western region of the United States where we get something around 6 hours of peak sun hours per day and we have a 12 volt, 50Ah battery that we need to charge using a solar panel.

Then how many solar panels to charge a 12 volt battery would be:

(50Ah x 12Volts) ÷ 6h = 100 Watts

How many watts of solar panel are needed to charge a 50Ah battery?

With that answer, you need at least one 100-watt solar panel to fully charge this 50Ah deep charge battery. 

Factors To Consider

There are a lot of other factors to consider when deciding what size solar panel to charge a 12v battery. We listed some right down below.   

Solar Panel

1. Power Output of the Solar Panel 

This is determined by the solar panel’s size, the amount of sunlight it receives, and its efficiency. A solar panel’s power output is measured in watts.   

2. Solar Panel’s Efficiency 

The solar panel’s efficiency will determine how long the solar panel can charge the battery.   

3. Type of Solar Panel  

There are two types of solar panels: monocrystalline and polycrystalline. Monocrystalline solar panels are more efficient than polycrystalline solar panels. Some solar panel systems come with cables and other parts included, while others do not.

4. Number of Solar Panels 

The more solar panels you have, the more power you will need to charge the battery. These can be connected in parallel or in series. During the cabling, you need to use connectors like MC4.  

5. Energy Output of the Solar Panel

This is measured in watt hours (Wh). The energy output will determine how many hours the solar panel needs to charge the battery.

6. Amp Rating 

Solar panel amps or amperage is a measure of the electrical current produced by the panel. Its amperage is not a measure of the power output of the panel, but rather the amount of current that the panel can produce.   


1. Type of Battery

There are two main types of batteries that can be charged with solar panels: Lead acid and lithium-ion. Lead-acid batteries are less expensive, but lead acid batteries are not as efficient as lithium-ion batteries.

There is also rising popularity of another modern type of battery called lithium iron phosphate batteries.

2. Number of Batteries

The more batteries you have, the more power you will need to charge them. The fifth factor is the battery cycle. Batteries can be a cycle battery or a deep-cycle battery.

Cycle batteries are designed for short-term use, while deep-cycle batteries are designed for long-term use. 

3. Car Battery

Car batteries require DC solar power. The solar panel must be able to produce enough DC solar power to charge the car battery.  

4. Battery’s Efficiency

The battery’s efficiency will determine how long the solar panel can charge the battery.  

5. Battery’s Voltage

The number of volts will determine how long the solar panel can charge the battery.   

Other Factors

1. The Weather

The intense temperature in summer, the snow and cold wind in winter, and too much water on a rainy or stormy day. In many terms, the weather throughout the course of the year can affect the solar panel’s power output.

Cloudy days will reduce the solar panel’s power output as everything solar needs a good amount of sunshine. However, solar panels can still absorb light and heat at a certain temperature in the air though it’s not that sunny.

2. DC to AC Inverter

The inverter converts DC solar power into AC solar power. The inverter’s efficiency will greatly affect how much solar power discharge the solar panel can produce.   

3. Charge Controller

The charge controllers regulate the flow of electricity from the solar panel to the battery. The charge controller’s efficiency will determine how long the solar panel can charge the battery. They can also help extend the life of your battery.

There are 2 types of solar charge controllers. These are the PWM (Pulse Width Modulation) charge controller and the MPPT (Maximum Power Point Tracking) charge controller. 

Final Thoughts

There, we have given you an idea of what size solar panel to charge 12v battery. You should be able to make your own estimate by now. Hope we answered your question and you find all the information you need in this article, it’s time to start shopping around for solar panels. 

There are a lot of great options out there, so take your time and find the one that’s right for you. Be sure to compare the quality, prices, features, and warranties before making your final purchase.

Follow the instructions that come with your solar panel to ensure proper installation of each part and operation. In the end, if you have questions in mind, be sure to ask a professional for help.