What Size Solar Panel to Charge a 12v Battery?

Charge a 12v Battery with Solar Panel

There’s no better way to recharge your battery than by harvesting clean, free renewable energy from sunlight.

When it comes to charging deep cycle batteries using solar panels, some of the frequently-asked concerns are: What is the best size solar panel needed to charge a 12v battery?

If you’re seeking an answer in detail on this issue, you’re at the right spot.

How Many Watt Solar Panels To Charge A Deep Cycle Battery?

Car battery
Car battery.

The answer to this question isn’t easy. I want to throw my hands up and say, “it depends,” and leave it at that. However, if I did that, you’d be mad at me, so we’ll look at how we can determine the size of the panel.

Typically the dimension that a solar panel needs that can charge a battery is determined by using this equation:

\(\text{Panel size} = \frac{\text{Batarry Capacity}\text{ * }\text{Battery Voltage}}{\text{Average hours of sunshine per day}}\)

How to calculate the solar panel size.

Let’s say, for instance, we reside in Texas, in which we can enjoy approximately 5 minutes of maximum sun time every day. We also have a 12-volt, 100 Ah battery that needs to charge with solar panels.

Then, the number of solar panels needed to charge a battery of 12 volts could have to be:

\(\frac{\text{100Ah * 12Volt}}{\text{5 hours}}=\text{240 Watts}\)

How many watts of the solar panel is needed to charge a 100AH battery.

Also, it is necessary to have at least two 100-watt and one 20-watt solar panels to fully charge this 100AH deep-charge battery.

This is all there is to it, I guess? All I have to do is purchase these solar panels, hook with my batteries and then enjoy my off-grid life.

If you sat down and decided to go immediately to purchase the three solar panels, then you’ll be wasting your money.

This is because all batteries, including lithium-iron-phosphate batteries and car batteries, possess a “depth of discharge.” which is the amount of energy that you can effectively drain from your battery without risking permanent damage and decreasing its life.

The majority of high-quality deep cycle batteries are around 80percent DOD. This means that you must take the 100Ah battery the same way as one of the 80Ah ones because you do not want the charge to drop lower than 20 percent, and keep this in mind when you are looking for a new battery.

We must now consider the capacity to discharge when calculating the size of the solar panel.

\(\frac{\text{80% * 100Ah * 12Volt}}{\text{5 hours}}=\text{192 Watts}\)

How many watts are required to charge a 100Ah deep cycle battery that has an 80% discharge depth.

To charge the 12 volts, 100Ah battery, you’ll only require one 175-watt solar panel.

How Many Solar Panels To Charge A 12V Battery?

To help you save time and make your life more simple, we’ve compiled an overview of the most commonly used 12v deep cycle batteries and the number of solar panels required to charge these batteries.

Battery Capacity (12v)Solar Panel Size
50Ah Battery90-watt solar panel
80Ah Battery140-watt solar panel
100Ah Battery175-watt solar panel
120Ah Battery210-watt solar panel
200Ah Battery350-watt solar panel
How many solar panels to charge a 12v battery cheat sheet.

NOTE: These panel sizes were calculated using 5 hours of direct sunshine per day. So be sure to verify the local time for sun hours to get more precise panel sizes.

How Fast Will Solar Panels Charge A Battery?

Many variables determine how long it takes to charge a battery of 12v by using a solar panel, including the capacity of the battery and solar panel watts. The average sun-hours per day and how intense the sunbeam’s intensity is, the solar controller’s efficiency, temperatures and humidity in the weather, and many more.

But, in the interest of simplicity, we’ll concentrate on the three most important variables: solar panel capacities, watts, and the average peak hours of the sun.

Calculating the speed of charging your battery is quite simple. All you have to do is use this simple formula:

\(\text{Full charge time} = \frac{\text{Battery capacity Ah * Voltage}}{\text{Panel power}}\)

How quickly will the solar panel charge a battery?

If, for instance, we wish to charge the 100Ah battery (12v) by using the 100-watt solar panel, it will take about 12 hours of direct sunlight, which is also known as 2-3 days.

But, this isn’t true since we did not consider the discharge level.

If we assume that DOD is 80% is, the amount of time needed to fully recharge the 100AH deep-cycle battery using the help of a 100-watt solar panel is about nine and a half hours.

\(\frac{\text{80% * 100Ah * 12Volt}}{\text{100 Watt}}=\text{9.6 Hours}\)

How long does it take to charge a 12v battery using the 100-watt solar panel?

We compiled an inventory of the most popular 12v battery capacities and how quickly the capacity of a 100-watt solar panel charge them:

Battery Capacity (12v)Full charge time with
100W solar panel
50Ah Battery4.8 hours
80Ah Battery7.68 hours
100Ah Battery9.6 hours
120Ah Battery11.52 hours
200Ah Battery19.2 hours
How many solar panels to charge a 12v battery cheat sheet.

How Much Power To Charge 24 Volt Battery?

In general, 24 volt rated car batteries aren’t that popular since they cost more than 12v batteries and aren’t used for many purposes.

If you need a 24v battery, you could make it by linking two 12-volt batteries together, and it’ll function as a 24-volt battery.

Calculating the power needed to charge a 24v battery is very similar to the calculation for its 12v equivalent.

\(\text{Required power} = {\text{Battery DOD * Capacity * Voltage(24Volt)}}\)

How much power is required to charge 24 volt batteries?

Therefore, if we had a 24 volt, 200Ah battery with a DOD of 80%, the power required to charge the battery is 3840 Watt.

To determine how many watts solar panel to charge the battery of 24 volts:

\(\text{Watts} = \frac{\text{DOD * Capacity * Voltage}}{\text{Average hours of sunshine per day}}\)

How many watts of solar panels are needed to charge a battery that is 24v

To supply our 24 voltage battery with sufficient power, we’ll need about 700 Watts from the solar panel (assuming 5 sun hours per day). Also that we require 7 100-watt solar panels to recharge this battery to deep charge.


1. Can You Use A 24V Solar Panel To Charge A 12V Battery?

Yes, but not in a direct way.

In general, it isn’t possible to connect the solar array to the battery since this could charge too much and permanently damage the battery.

To safeguard your battery, connect a charge controller to the panel on the sun and your battery.

This controller converts the solar panel’s output of 24 volts into a 12v voltage that is more appropriate that allows you to charge your battery without permanent damage to it safely.

2. Can You Charge A 24 Volt Battery With A 12 Volt Solar Panel?

The simple answer is you can. However, you’ll need to make use of a charge controller to transform the solar panel’s output to an appropriate current rating so that you can recharge the battery without harming it.

It is important to note that it’s not advised to recharge deep cycle batteries using a solar panel with a different voltage rating because it will cause an excessive loss of power.

3. Do I Need A Charge Controller To Charge A Battery Using Solar Panels?

The issue of solar panel systems is their power is dependent on the sun’s rays. This means that it is variable throughout the daytime. For instance, the output is the highest during the sun’s peak hours (noon) and then is at its lowest around dusk.

It is essential to have a charging controller required to ensure that the panels are not charging too much the battery. This can permanently damage the battery and decrease its life span and result in the battery being ignited and exploding.

It is important to note that you do not require solar chargers in the event of solar panels that are small and maintenance-free, like trickle charge panels, since the output of the panel would not be enough to charge the battery.

In general, if the panel generates lower than two watts each 50Ah, that means you don’t require an electronic controller.

4. Will A Solar Panel Charge A Dead Battery?

The right size solar panel can completely charge your battery in just five to seven hours.

This kit will give your battery sufficient power to stop drying too fast, yet it will not overcharge it.

5. Why Does My Solar Panel Not Charging My Battery?

There are several couples of causes that could be the cause of this kind of failure like:

  • Broken wires
  • Faulty rectifier diode
  • Charge controller settings
  • The wrong configuration
  • The battery has gone down

Last Words

As stated in the article, we have provided you with an in-depth solution to the solar panel size needed to charge a 12V battery. We also provided several frequently-asked questions on solar panel charging of batteries.

We genuinely hope that you enjoyed this article as much as we enjoyed writing it.