What Solar Panel Size to Charge an 80ah Battery?

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Recharging an 80ah battery using solar panels is straightforward, but how long does it take? And how many panels do you need and what size? We will answer those questions and related topics in this guide using simple teems and concepts.

A 300W solar panel can recharge an empty 80ah battery in 4 to 5 hours. If the battery is partially discharged at 50%, charging time will take 2 to 3 hours depending on how much sunlight is available.

How Many Solar Panels to Charge an 80ah Battery?

Solar panel sizes are often measured by how many watts it produces, not the physical dimensions. To find out how many panels you need, we have to determine how many watts an 80ah battery has.

An 80ah 12V battery is equal to 960 watts, so a 960 watt solar array is the minimum required to fully charge it from 0% to 100%. How many solar panels you need depends on how quickly you want to charge the battery.

Solar panel arrays to recharge an 80ah battery in one hour:

  • 3 x 350W
  • 2 x 500W
  • 4 x 250W
  • 4 x 300W
  • 5 x 200W
  • 7 x 150W

If you want to recharge in five hours or less, your solar system must generate at least 200 watts an hour (200W x 5 hours = 1000W).

Solar panel arrays to recharge an 80ah battery in one hour:

  • 5 x 200W
  • 1 x 300W
  • 2 x 100W
  • 1 x 350W

300 and 350 watt solar panels are the most commonly used in homes, RVs and even mobile homes. The fewer solar panels you have to install, the easier the installation is. We suggest the Huajin 300W Flexible Solar Panel as it provides the power you nee and is also waterproof.

The number of solar panels needed will depend on the power output. The higher the panel watt rating, the fewer panels required. In terms of physical dimensions these PV modules are not too different either.

You can opt for 150, 200 or even the Renogy 100W Monocrystalline Solar Panel and connect several of them to produce 960 watts. But installing several panels is going to occupy a lot of space on a rooftop. Even on a ground mount installation those modules will require lots of room.

The more solar panels you use, the heavier the combined weight. This is very important if you live in an old house. An average solar panel weighs 40 lbs. so imagine having several of these on the roof as you charge the battery. In short, the fewer the panels used, the better.

Once you have chosen the solar panels, the next step is to charge the battery. How long that takes is what we will cover next.

How Long to Charge an 80ah Battery?

The charging time depends on how much power the solar panels produce, sunlight and battery depth of discharge.

A solar PV system consisting of 4 x 300 solar panels can generate 1200 watts an hour and charge an 80ah battery. This can happen in perfect weather though. By perfect that means no clouds or anything that could block the sun.

Even if the conditions were not perfect, a 1000W PV system can still fill the battery in an hour given its capacity. It is another matter with smaller solar systems.

Theoretically, any solar panel size can work, but it will take longer. A 300W solar panel can be used to top the battery in 3 to 4 hours depending on the weather. With smaller PV modules the charge time will take longer.

But even with a good sized solar array, it might take more than a few hours if the sky is overcast. And if the sky is clear a small PV system will charge faster than you might expect.

In other words the charge time depends on the weather and not just the solar array size. It takes a combination of the solar panels and the sun to charge batteries as fast as possible.

How Depth of Discharge Affects Charge Time

In the calculations above the assumption is that the battery is fully depleted. However that is unlikely or should not be the case if you are using lead acid batteries.

Lead acid batteries should not be discharged below 50%. If the battery is discharged at 50% it only needs 480 watts to get filled. Instead of a 1000W solar array, two 250W solar panels will be enough.

Most lead acid or FLA batteries have a 50% DOD, but some AGM and gel batteries have a higher capacity at 70% or so. Lithium batteries are even higher at 90% to 100%.

The reason we did the calculations for an empty battery is because it does happen in real life. Ideally you should recharge lead acid batteries at 50%. But there are many cases where the battery gets drained down to zero.

Whether it is due to an emergency, poor weather or something else, there will be times you may not be able to recharge the battery at the recommended level. So it is important to know the numbers and how the calculations work just in case.

While the 50% depth discharge is common among lead acid batteries, with lithium it varies somewhat. Most are good enough for a 90% DOD, but for others it is lower. You should check the specifications so you can charge it properly.

How Long Does an 80ah Battery Last?

This will depend on the size of the load and how many amps are drawn from it. This rule applies to all solar batteries regardless of the size. The voltage and presence of solar panels determine how long you can run the battery.

To find out how many watts a battery has, multiply the amp hours (ah) with the volts (v). 80 x 12 = 960, or if it is a 24V battery, 80 x 24 = 1920 watts.

A 12V 80ah battery has 480 usable watts if you follow the 50% depth of discharge. The battery can run any of the following:

  • A laptop computer for 1 to 2 hours
  • A DVD player for 12-15 hours
  • A 42 inch TV for 4 hours
  • A game console for 1 to 2 hours

These calculations are based on the assumption these electronics run on their average power consumption. For instance, this battery can run for 1 to 2 hours if it is 200W. A 100W laptop will run longer. A 700W desktop is out of the question unless you let the battery drain below 50%.

Another way to calculate battery life is the amps per hour. Batteries are rated at 5 amps per 20 hours, so if the load is 10 amps an hour, the battery is good for 8 hours or so. It is difficult to be more precise because batteries lose charge faster when you draw more power.

However there are ways to make an 80ah battery run more than 480 watts without letting it drop below 50%, use batteries with better DOD or connect it to solar panels.

80ah Lithium Batteries

As mentioned earlier, lithium batteries have a superior DOD compared to lead acid. An 80ah lithium battery lasts longer than an 80ah FLA. If you have to run appliances for long periods, lithium may be worth looking into.

Another way to increase the runtime is connect two or more batteries together in series or parallel. This boost battery capacity but you have to use more solar panels to charge the battery bank.

Connect Batteries to Solar Panels

Let us go back to our 12V 80ah battery. The usable wattage is 480 watts after which you have to recharge the battery. But if you connect solar panels to the battery you can keep the battery running.

With a 500 watt load, the battery drops to 50% in an hour. But what if you have a 500W solar array connected to the battery? You can let the solar panel run your load during the day and when the sun goes down, let the battery take over.

The battery will still be full come sundown because it was never used during the day. You can run a 480 watt load at night and next day, charge it with the solar panel. As long as the load does not exceed the capacity, you can keep the battery going.


The bottom line is there are many ways to charge an 80ah battery, and with plenty of sunlight it will not be a problem for a good sized solar panel array. Just like with anything solar, careful planning will save you a lot of time and effort.