Can You Charge a Lithium Battery with a Solar Panel?

Because lead acid batteries need a lot of maintenance and have a 50% depth discharge, lithium batteries have become more popular for solar systems. But can you charge these with solar panels? Is the process any different from lead acid batteries?

Solar panels can charge lithium batteries, but an MPPT solar charge controller is required. More current goes into the battery when an MPPT controller is used, which leads to faster battery charging.

How to Charge a Lithium Battery with a Solar Panel

This is a step by step guide to charging lithium batteries with solar panels. This is a simplified, general approach. Your solar panel kit might have a different procedure so check the instructions.

Step 1. Get a Charge Controller

There are two basic types of charge controllers to choose from, MPPT and PWM. We recommend an MPPT charge controller for lithium batteries. The EPEVER 40A Solar Controller is going to run most solar systems and provide the best possible results.

If you use a PWM controller, it will reduce the solar panels voltage until it matches the battery. The solar array will not be able to use its full power, wasting current and of course dollars.

An MPPT charge controller increases the current just as the solar array voltage is reduced. The controller adjusts the current automatically to ensure maximum current goes into the battery.

There are many other differences between an MPPT and PWM controller, but the most important is MPPT controllers are more efficient in lithium battery charging.

Step 2. Set up the Charge Controller

Charge controllers should be installed in a waterproof location. The distance between the controller, battery and solar panels have to be sufficient for the cables.

Make sure the solar panels and other electrical components are grounded. You can mount the controller on any surface except metal.

Step 3. Configure the Lithium Battery Cables

If you haven’t already, remove the lithium batteries from its packaging. Should the wires be already plugged in, move to the next step.

If the wires are not connected, plug them into the appropriate slots. These wires are color coded so you can distinguish between positive and negative.

Make sure the wires are in the proper inputs, otherwise the battery will not charge. Secure the wires. If you need help with solar panel and battery wire sizes, here is a guide.

Step 4. Plug the Battery Wires into the Charge Controller

Take the two loose battery wire ends and insert them into the charge controller. Thee are positive and negative ports on the controller. Insert the wires in the appropriate location.

Designs vary, but usually you just slide the battery wires into the controller. When the wires are in place, secure them with a screwdriver.

Step 5. Put MC4 Connectors on the Charge Controller Wires

Hold the charge controller wires and put MC4 connectors on the ends. If your solar kit did not come with MC4 connectors, you can buy these in any solar power supply shop.

Step 6. Connect the Controller Wires to the Solar Panel

You should have the charge controller wire ends fitted with MC4 connectors. Take these two and plug them into the solar panel connectors.

Solar panels also have MC4 connectors. Match the male and female solar MC4 connectors with those of the charge controller. The male MC4 controller should be connected to the female solar panel MC4 connector. Do the same with the other controller and panel connectors.

Step 7. Test the Charge Controller

Give all the wirings a light tug to make sure they fit. Now turn on the charge controller. If it hasn’t done so automatically. If there are no error messages, the installation is successful.

Step 8. Give the Battery Time to Charge

Now all you have to do is wait for the battery to charge. How long it takes depends on the solar array size, sun hours and how much power is left in the battery.

A 300W solar panel can charge a 12V 100ah lithium battery in 4 hours. This is based on the following calculation:

100ah x 12V = 1200

A 100ah 12V battery has 1200 watts. So it follows:

300W x 4 sun hours = 1200

It takes 4 hours to charge a 100ah battery. But this calculation is based on the assumption the solar panel produces 1200 watts in four hours. If ouare charging LiFePO4 batteries, make sure the settings are correct.

For that to happen the panel must generate 300 watts consistently for 4 hours. This is possible in ideal weather but if clouds build up, the output will be reduced.

In less than ideal weather it might take 5 hours or longer. And if you have a large battery bank, charging will take more time. So we recommend a large solar array so you can charge batteries faster.

Do I Need a Special Charger For Lithium Batteries?

You can use an MPPT or PWM solar controller. but as we explained earlier, an MPPT controller is the better choice.

MPPT solar controllers cost more, but you will get more current from your array. When it comes so solar power it is all about getting maximum usage from the panels, batteries and inverters.

PWM controllers are ideal for small batteries, but for lithium you are better off with MPPT. A PWM controller will drop the solar array voltage to match the battery, which is going to waste the solar panels’ energy production.

With an MPPT, the solar panel operates at near maximum level and increases the amount of energy that goes into the battery. This is why an MPPT is ideal for lithium and any other large battery capacity.

Lithium vs. Lead Acid Batteries

Lead acid batteries have a 50% depth discharge rate. So if you have a 100ah lead acid battery, only 50ah should be used. Once the capacity reaches 50ah, it is time to charge. This can be frustrating if you run a lot of appliances on solar. It might also seem like you are not getting your money’s worth since you only get to use half the capacity.

With lithium batteries you can use up to 85% or more. Each charge lasts longer and you can use more, which is ideal for heavy duty applications.

Lead acid batteries also have to be refilled with water every few weeks. Again this can be a burden especially if you have a large battery bank. With a lithium battery, this is not necessary.

Lithium Battery Frequently Asked Questions

How many solar panels do I need to charge lithium batteries?

It depends on how many batteries you are going to charge. The more batteries, the more solar panels needed. Unlike lead acid batteries however, you can use almost the full capacity of lithium.

How long does it take to charge a lithium battery?

A 300W solar panel can charge a 100ah battery in 4 to 5 hours. This is possible if the sky is clear and the sun is out. Cloudy skies, shading and rain will lead to slower battery charge times.

Some lithium batteries claim to have an 85% DOD, while others are 90%. Which is it really?

The depth discharge rate varies. Some manufacturers claim a full discharge of 100% is possible. Other brands take a more conservative approach and go with 85%. You should check the instructions that came with your battery and use that as a guide.

Why are my solar panels not charging the battery?

The most likely reason is there is not enough sunlight. A solar array big enough for a house is not going to work without sunlight. Make sure the solar panels are in the proper position to receive maximum sun.

Why is my charge controller not working?

Go over the installation steps in this guide. Make sure to follow them correctly. The most likely reasons is a loose or frayed wire.

Do I need an inverter to run appliances with a lithium battery?

If you run only DC powered devices, an inverter is not required. But if you want to use any appliance that runs on AC, an inverter is a must. The inverter capacity must match or exceed the total watts you want to load. This is especially true if you run air conditioners on large systems.

Conclusion

In other words, solar panels can charge lithium batteries just fine. Provided of course there is enough sunlight and a quality MPPT charge controller is part of the system. Once set up, you can leave everything to the sun.