How to Charge Two Batteries with One Solar Panel

It is a question that a lot of those new to solar power will ask. Can a solar panel charge 2 batteries? If you run a lot of appliances for instance, they might require more than one battery, but can your solar panel charge them both? And how long will it take?

A single solar panel can charge two batteries if they are connected in parallel. A charge controller is needed to ensure the batteries will receive the proper current and not be overloaded.

How to Set Up a Solar Panel to Charge Two Batteries

You are not limited to two batteries actually. You can charge as many as you want as long as the batteries are connected in parallel and the solar panel is large enough. The charge time will depend on the solar panel size and how many sunlight hours are available.

Example, you have two empty 12V 100ah batteries and a 200 watt solar panel. Each battery requires 1200 watts to fill. Make sure the batteries and solar panel voltages are compatible before charging. A standard 200 watt panel has an 18-21V circular voltage, enough to charge a 12V battery.

To charge the two batteries:

Step 1. Place the batteries side by side and connect their negative terminals. Do the same with the positive terminals. Positive to positive, negative to negative.
Step 2. Connect a charge controller to the batteries and to the solar panel.
Step 3. Position the solar panel so it receives as much direct sunlight as possible.

Now you just have to wait for the solar panel to recharge the batteries. In perfect weather a 200W solar panel can produce 1200 watts with six hours of sun.

Having a good solar panel is essential to charge two batteries. For these tasks we like the Newpowa 200W 12V PV module, as it has a high efficiency rating and will charge batteries fast.

For the charge controller we recommend the EPEVER 30A MPPT solar controller. It works with 12V and 24V batteries and will optimize the charging process without overloading the battery. .

Since the panel is charging two batteries, it can theoretically take two days to fully charge both. However that is assuming the weather stays perfect for two days and the panel generates 200 watts an hour every day. More likely though it will take 3 days to charge the batteries.

In reality however, a lot of factors can affect the performance of a solar panel. So instead of 1200 watts a day you will probably get 900 to 1000 watts. Depending on the weather it might be less, which is why we say 3 days is what you can expect.

But of course it will also depend on the size of your solar panels, as we explain next.

How Many Solar Panels Do I Need to Charge Two Batteries?

Technically you can use any solar panel size to charge two batteries. But the smaller the solar panel the longer it will take to charge.

Example you have two 100ah 12V batteries and a 100 watt solar panel. Both batteries are empty and require 2400 watts. With 5 hours of sun, a 100 watt solar panel can generate up to 500 watts a day.

It will take a 100 watt solar panel 5 to 6 days to fully charge two 200ah batteries, with an average of 5 hours of sun and 400 to 450 watts a day.

But if you have three 100 watt solar panels, you could get up to 1500 watts a day. Even if the output is only 1200 watts daily, a 300 watt solar array can charge the batteries in two days.

This is based on the assumption that the batteries are 100% empty. Most deep cycle batteries have a 50% depth discharge rate. If you do not fully discharge the batteries, they will take less time to recharge.

Bottom line: it takes one solar panel to charge two batteries, but having more panels – or a single large one – is going to make a lot of difference. If you want the batteries to charge faster you should get a large solar panel or several small ones joined together.

Remember that solar panels and batteries are only two components. You also need a charge controller to ensure the batteries do not get overcharged. To find the right charge controller, divide the total solar panel watts by the battery voltage and add 25%. Round the answer off.

How Many Batteries Can You Charge with a Solar Panel?

Technically there is no limit to the number of batteries you can charge with a solar panel. However, you should restrict it to two batteries, though a large solar array can handle several more. Too many batteries can make it harder to fully charge.

A 200 watt solar panel can charge up to two 100ah batteries. You can connect more batteries with higher capacities, but charge time will take several days.

If you have a large solar array – 400 watts and higher – you can connect several batteries at the same time. And you will need the extra solar power if you have to recharge large batteries.

When a solar panel charges several batteries, it has to distribute the current for each one. If you connect several to a small panel, there will not be enough current for each battery.

This means some batteries will be fully charged, while others do not get filled. This cold lead to an uneven performance and affect the appliances you run with the battery bank. The more batteries you charge the longer it will take. Keep this in mind if you need those batteries charged over a specific period.

If you have two empty 12V 100ah batteries and want them charged in one day, you need two 300 watt solar panels. If you can wait a day or two, one 300 watt panel is enough. A 100 watt panel may take up to a week to charge both.

There is no hard and fast rule on how many batteries should be charged with a solar panel. Check your solar panel manual for specific information on its battery charge capacity. You also have to consider the inverter size if you want to run several AC appliances.

How Do I Know if a Solar Panel is Charging a Battery?

Since solar panels can take a while to charge a battery, how will you know if it is charging? This is where a charge controller comes in handy again. Aside from protecting the battery from overloading, charge controllers provide other useful pieces of information.

Look at the charge controller display screen. It will show the current going into the battery as well as the voltage. If you have lead acid batteries for instance, the voltage will be 14.4 volts. For an MPPT controller it will depend on the solar panel voltage.

You can also write down the battery voltage before charging. Connect the battery to the solar panel and let it charge. After several hours, take a look at the battery indicator. If the battery was charged the volts will be higher.

If your solar panels have a good warranty you can have it fixed or replaced at no cost if they are not charging. Your batteries also have warranties and so do controllers. If there is a problem with the charge you can contact the manufacturer, but you may want to try the following solutions first.

Why is My Solar Panel Not Charging the Battery?

There are many possible reasons why your battery is not being charged. These can be due to the charge controller, the solar panel or the batteries themselves.

First check the cables connecting the panels, batteries and the charge controller. Any loose or frayed wire will disrupt or prevent a charge. If the wires are fine, reset the charge controller according to the manufacturer instructions.

Resetting the controller usually fixes the problem. If it does not, check the solar panel if it is shaded, or there are cracks or other issues. You can also check the batteries. Problems with charging can occur if the battery is old. If you are still unable to get the battery to charge, you may have to do some troubleshooting.

Conclusion

What we have shown here is that you can charge any number of batteries, provided the solar panel is powerful enough. A solar array with several thousand watts of power can handle a large battery bank. It all comes down to your system specs.