Can Solar Panels Charge Car Battery?

Solar energy can be used in most places nowadays. It’s fast, cheap and most importantly environment friendly. So the question is: can you charge your car battery with a solar panel?

To charge your car battery with solar panel your car battery need to be Deep Cycle batteries (used in marine vehicles or RV). Other car batteries can’t withstand deep discharge, so the solar panel is inefficient in that case. So deep-cycle battery is mandatory.

Also, another thing to be careful of is Solar Charge Controller. Do not connect your panel and battery without it otherwise, you can accidentally ruin your battery.  A Solar Charge Controller is quite cheap so there is no reason not to get it. Along with that be sure to connect an inverter too.

Knowledge regarding battery, voltage, car battery function, and solar panel functions is important if you are planning to use a solar panel during charging a car battery. Otherwise, you may run into various small problems and in the worst-case damage your car battery. 

In the following article, we will discuss important things regarding charging car batteries with solar panels and how to properly do it with proper equipment and requirements. Hopefully, it will clear up many of your questions regarding this topic.

What Car Batteries Can You Charge With Solar Panel?

Not all car batteries can be charged with your everyday solar panel. Reasons include the battery’s design and functions of charging and discharging. 

There are three important types of batteries you need to know about for this case:

Can you Charge Car Starter Batteries?

As the name suggests these are used to start up your car. What these do is provide high bursts of power to the engine for a short time then is recharged by the alternator.

As you can see, the batteries are not designed to handle multiple discharges or recharge cycles so try to drain these and your battery life will shorten significantly.

So due to their design limitation, they can’t be charged using solar panels.

Can you Charge Marine Batteries?

This one is a hybrid of both Deep Cycle and Starter Battery. They can handle discharge to some level without damage. So in this sense, they are a bit better but still, these are not recommended to charge using a solar panel due to various problems and their variety and design complexity.

Can you Charge Deep-cycle Batteries?

These ones are completely the opposite of Car Starter batteries. They provide low amps to the engine. So keep in mind that a deep-cycle battery is not quite good for starting your engine. Do note that these batteries provide amps for a longer period and without immediate damage.

Deep-cycle ones last longer if you recharge them properly. Take Gel or AGM batteries for example. Do not discharge them more than 50% before you recharge them. (The percentage is near 15 in the case of starter batteries). And if you follow this tip your battery will last longer.

Due to their design and ability to withstand high amounts of discharge or recharge cycle, it is highly recommended that you use this type of battery for charging with a solar panel.

What Solar Panel do you need for Charging Car Batteries?

When you charge your car battery with a solar panel you have to be careful about things like amps, voltage, and other electrical terms. In modern days most automobiles have 12V batteries so you have to use a solar panel according to that measurement.

Take a look at the back of the solar panel. The most important ones are Load Voltage and Max Amps. Let’s take an average 100w panel. Load Voltage is generally 18v and the max amp is 5.56. (Try multiplying those numbers you will get 100). Why 18v?

Your panel can be 16 volts or 15 volts but 18 volts generally works well in my opinion.  

Before we proceed you need to know some additional info regarding the battery to avoid damage. 

AGM and Gel Batteries are generally good with charge current up to one-quarter of their own capacity. So for example take a 100 amp hour battery. You can charge it with up to 25 amps. Use any more than that so that your power will be wasted and at worst the battery will warm up and get damaged.

Also with this 25 amp limit, you can use lower amps than this. It will still charge but you will need more time to do it.

Now to the main topic, how to find the best size and spec for your panel? 

First, find the voltage you will charge your battery at. (Let’s say 12 volts). And then find out your battery’s amp-hour (Let’s say 100 amp-hour). Then decide at what amp you will be charging your battery (For Example we take 20 amps.

Now what you do here is multiply the voltage you will charge your battery at with the amp. (In our example it is 12 x 20 = 240 watt) And it is done! The resulting number will be the watt of the solar panel.  

How Long Will It Take to Charge Car Battery with Solar Panel?

One important factor in everything is time. How much time this needs and that. Generally, most people need to know the time it takes to charge batteries.

To be frank, finding charging time is simple math. Take your battery capacity (Say 100 amp hours) and at the amp, you will be charging your battery at (Say 20 amp). Now divide the former with the latter. (In our example we do: 100 / 20 = 5 hours). And you would get how long it will take to charge your panel.

Do I need a Solar Charge Controller to Charge Car Battery?

Yes, you need it. Otherwise, your battery will get overcharged and get fried.

As stated earlier, if you use an 18-volt panel on a 12-volt battery. More charge voltage would result in overcharge. And overcharge will lead to disaster. 

And if you want a more scientific explanation of what happens if you don’t use a solar charge controller and overcharge battery, here it is:

At high voltage, the battery would start producing hydrogen and oxygen. In layman’s terms, your battery will start to leak gas. And soon electrolytes on your battery will start bubbling. And this is how your battery will die a painful death.

So please consider using a solar charge controller. It’s really cheap.

What type of Solar Charge Controller for Charging Car Battery?

There are two types of Solar Charge Controller: PWM (Pulse width Modulation) which is cheap and very affordable and MPPT (Maximum Power Point Tracking): Which is more efficient and costs more than its counterpart.

So what should you choose? Let’s look at both of them in more detail.

Think of PWM as a switch. Say your solar panel is increasing its voltage. Once it reaches a certain point PWM will come and stop it. This switch-type mechanism lets the panel hover around a voltage that won’t fry your batteries.

So what is the con of this? Simply it is inefficient and wastes any voltage higher than the charge limit voltage. But it’s still considerable when you look at its price.

MPPT on the other hand looks at the available wattage (which is volt x amps). The MPPT charge controller can control both volts and amps to maximize the charge a battery receives. So with saving your battery it gives you the added efficiency. 

The choice of these is personal. One rule of thumb I follow is to use cheap products for casual work and efficient products while doing serious work. So choose either of them based on how serious you are and how much you are willing to spend.


Charging your Car Battery with a Solar Panel is something you need to be careful about. Otherwise, you may make unwanted mistakes. For that not to happen you must have proper knowledge regarding which type of battery you are using, the specification of your panel, using solar charge controller, and other precautions.

The key takeaways here are-

  1. Always use a deep-cycle battery if you are planning to charge it with a solar panel. Because if you use other types like car starting ones it won’t work.
  2. Don’t forget about recharging your battery at the 50% mark regularly so that your battery remains healthy and gets a long life span.
  3. Always look at the electronic unit and try to learn more about it. Sometimes simple math regarding them can solve a lot of problems. The key thing to remember is volt multiplied by amp equals watt.
  4. Choosing proper Solar Panel size, quality and features are very important. Overpowered solar panels will cost much and under-powered solar panels won’t perform well. So be sure to choose the optimal ones.
  5. And most importantly use a charge controller while charging with a solar panel. Solar Charge Controllers will prevent various disasters. And it is a great safety mechanism.

To wrap it up, you can charge your car battery very well provided that you have the correct battery type, right panel specification, and a good charge controller. With sufficient knowledge about this equipment, you will be good to go.