How to Charge LiFePO4 Batteries with Solar Panels

In this tutorial, I’ll show you 2 ways to charge lithium iron phosphate (LiFePO4) batteries with solar panels.

(No solar experience necessary.)

In fact, I use both of these ways to solar charge my own LiFePO4 batteries.

This tutorial will focus on solar charging 12V LiFePO4 batteries, but I’ll also share some tips on how you can do it with lithium batteries of different voltages, such as 24V, 36V, and 48V.

Let’s get started.

1. How to Solar Charge LiFePO4 Batteries with a Simple Charging Setup

In my opinion, this is the easiest way to charge LiFePO4 batteries with solar panels.

This method requires no tools or prior solar experience. It’s relatively cheap. And it’s as plug-and-play as it gets.

Video Walkthrough

This method is so easy I made a 60-second video showing you how to do it. Check it out and consider subscribing to my YouTube channel if you like DIY solar videos like this!

Parts

• 100W 12V solar panel — I’d recommend a 50 to 100 watt solar panel for this setup. The max solar panel size for this setup is 120 watts.
• 12V LiFePO4 battery — I’m using a 100Ah battery, but you could use a smaller or bigger one as long as it’s still a 12V battery.
• Allto Solar MPPT charge controller — This isn’t your traditional-looking MPPT charge controller, but it’s designed to be great at one thing: solar charging 12V batteries.
• MC4 to SAE adapter cable — Most 12V solar panels have MC4 connectors. If yours does, you’ll need this adapter cable to connect the solar panel to the charge controller. You may also need the included polarity adapter.
• SAE to battery alligator clips — This adapter cable lets you connect the charge controller to a battery. It even comes with an inline fuse which is an important safety practice when solar charging batteries.
• SAE extension cable (optional) — This extension cable would make it easy to place your charge controller and battery inside while charging.

Step 1: Connect the Solar Panel to the Charge Controller

Connect the MPPT charge controller to the solar panel, using an MC4 to SAE adapter cable, if needed. Your charge controller should automatically turn on once you do. If it doesn’t, try using the included SAE polarity adapter to get the solar panel’s polarity to match the charge controller’s.

Note: This charge controller is a bit of an exception, in the sense that connecting the solar panel first is not the normal order for most charge controllers. Most often, you’ll connect the battery to the charge controller first. It’s always important to read your charge controller’s product manual for its recommended connection order.

Step 2: Select Your Battery Type

Select your battery type using the charge controller’s MODE button. I’m using a lithium iron phosphate battery, so I pressed the MODE button until the “Lithium” battery setting was selected.

If you’re using a different type of battery, such as an AGM or sealed lead acid battery, select that type.

Step 3: Connect the LiFePO4 Battery to the Charge Controller

Connect the battery to the charge controller using SAE to battery alligator clips. Connect the positive charge controller cable to the positive battery terminal and the negative cable to the negative battery terminal.

Look at the charge controller’s screen to confirm that the solar panel is charging the battery. The charge controller’s screen should show you the charging amps and volts. (You may have to wait a minute for the charge controller to track the maximum power point.) Mine showed a current of 6.6 amps at 14.0 volts, which works out to 92.4 watts from my 100 watt solar panel.

And just like that…

…you’re charging your LiFePO4 battery with a solar panel!

Now all you have to do is wait until your battery is fully charged. The charge controller will automatically stop charging the battery once it’s full.

This setup is so easy to put up and take down that I just put the parts in in my shed when I’m not using it.

Tip: If you want to keep your battery and charge controller out of the elements while charging, you can get an SAE extension cable and place it between the solar panel and charge controller. That way your solar panel can be outside while your battery and charge controller are safely inside.

2. How to Build a Small DIY Solar Power System with LiFePO4 Batteries

This second method isn’t nearly as easy to set up, but it’s the best route if you want a more permanent and expandable system with LiFePO4 batteries. It forms the basis of a basic DIY solar panel setup that you can use to power devices in a vehicle or off-grid system.

Parts & Tools

Note: A lot of the solar components listed below are included in the Renogy 100 Watt Solar Panel Kit. Last I checked it’s cheaper to buy them as part of the kit rather than all separately.

Here are the parts and tools I used for my setup. The wiring and equipment is sized for use with a 100 watt solar panel, with lots of room to grow in terms of current ratings in case you want to add more panels later on.

• 12V LiFePO4 battery — I’m using a 100Ah battery, but this setup will work for nearly any size 12V battery
• 100W 12V solar panel — I’m using a 100W solar panel, which is a good size for slowly charging a 100Ah battery over the course of a week (included in kit)
• Lithium-compatible PWM charge controller — I’m using the Renogy Adventurer 30A, but a cheaper alternative is the Renogy Wanderer 30A (included in kit)
• Solar adapter cables — for connecting the solar panel to the charge controller (included in kit)
• Battery cables — for connecting the charge controller to the battery (included in kit)
• 30A ANL fuse set — a 30 amp fuse is the right size for the charge controller linked above. If you’re using a different charge controller, look in its product manual for its recommended fuse size
• Fuse cable — for adding the fuse between the battery and charge controller
• Screwdriver
• Optional: Wrench or ratchet — for tightening bolts

Step 1: Understand the Wiring Diagram

First, let’s quickly run through the wiring diagram and understand the important parts of it.

Here are the main things to understand about it:

• Do not connect your solar panel directly to your LiFePO4 battery. Doing so can damage the battery.
• Instead, connect the solar panel to the LFP battery via a solar charge controller. A charge controller regulates the voltage and current to safely charge the battery. It also stops charging once the battery is fully charged.
• Use a charge controller that is compatible with lithium batteries. When shopping for a charge controller, look at the compatible battery types. Make sure the one you get is compatible with lithium batteries (sometimes listed as “Li” or “LFP”). Many cheap charge controllers only support lead acid batteries — such as sealed, gel, AGM, and flooded batteries.
• Place a fuse on the positive cable between the battery and charge controller. This is a safety best practice in DIY solar setups. Look in your charge controller’s manual for the recommended fuse size.
• You may need to fuse your solar panels. This will usually apply if you’re using multiple solar panels and decide to wire them in parallel. Watch this video to learn whether or not you need to fuse your solar array.
• You almost always first connect the battery to the charge controller. Only once that’s done do you connect the solar panel(s) to the charge controller. Consult your charge controller’s manual for the manufacturer’s recommended connection order.

Now that you understand the basics of how charging LiFePO4 batteries with solar panels works, it’s time to start building.

Step 2: Connect the LiFePO4 Battery to the Charge Controller

First, put the fuse in the fuse holder. Then connect the fuse cable to the fuse holder. Use a wrench or ratchet to tighten the bolts, if needed.

Connect the positive battery cable to the other end of the fuse holder.

Just like that, your positive battery cable is properly fused. Hooray for safety!

Locate the battery terminals on your charge controller. They’ll usually be labeled with a battery icon or the word “BAT” or “BATT.”

Connect the positive battery cable to the charge controller’s positive battery terminal. For most charge controllers, you use a screwdriver do this. Open the correct terminal on the charge controller with the screwdriver, insert the stripped end of the wire, then screw the terminal shut.

Connect the negative battery cable to the charge controller’s negative battery terminal.

Time to connect!

Connect the positive battery cable to the positive terminal on your LiFePO4 battery. To do so, simply unscrew the bolt on the battery’s positive terminal, slide the cable’s ring terminal onto the bolt, then re-screw the bolt to the terminal.

Connect the negative battery cable to the negative terminal on your LiFePO4 battery.

Look at your charge controller for an indication that it’s powered on. Your lithium battery and charge controller are now connected, so your charge controller should automatically turn on. If it has a screen, the screen should turn on and start displaying system specs like battery voltage. If it doesn’t have a screen, it should have LED indicator lights that turn on or start blinking.

If your charge controller has turned on, your battery and charge controller are now connected. Aww yeah!

Here’s what my setup looked like at this point:

If your charge controller doesn’t turn on, check for loose wires. Also double check that you inserted the battery cables into the correct terminals on the charge controller. If neither of these is the issue, your LFP battery may be in sleep mode, and I’d recommend following our tutorial on waking up LiFePO4 batteries.

Step 3: Set the Battery Type as Lithium on the Charge Controller

Note: Every charge controller has different steps for setting the battery type. Follow the instructions in your charge controller’s manual. These instructions are for the charge controller I’m using in this tutorial.

Many charge controllers work with multiple battery types, so you need to tell yours which type of battery you’re using. This is an important step because different batteries have different charging parameters. If you’re using a lithium battery but your charge controller thinks you’re using a lead acid battery, it won’t charge it optimally.

For my charge controller, the Renogy Adventurer 30A, I pressed SELECT until I got to the battery voltage screen. If using the Renogy Wanderer 30A, I run through the steps on setting battery type in my Renogy Wanderer review.

Then I held ENTER until the battery type started flashing. As you can see, it was set to “Sld” which stands for sealed lead acid batteries. I pressed SELECT to cycle through the options until I got to the “Li” option, which indicates lithium batteries.

I then held ENTER while the lithium battery option was on the screen to confirm my selection.

That’s it! Your charge controller now knows it’s connected to a LiFePO4 battery, and it will charge it to the right voltage levels for that battery type.

At this point, some charge controllers may ask you to set certain charging parameters, such as charging/absorption voltage and float voltage. Consult the charging parameters listed in your battery’s product manual or our article on LiFePO4 battery voltage charts for guidance.

Step 4: Connect the Solar Panel to the Charge Controller

Your charge controller and battery are properly connected. Your charge controller is properly programmed for LiFePO4 batteries. All that’s left to do now is connect your solar panel and start solar charging your LiFePO4 battery.

Cover your solar panel with a towel, or flip it face down, to prevent it from generating power.

Connect the positive and negative solar panel cables to the solar adapter cables. Make sure the exposed wire ends don’t touch! ⚡️

Locate the solar terminals on the charge controller. They’ll usually be labeled with a solar panel icon or the word “PV.”

Connect the positive solar cable to the positive solar terminal on the charge controller, and connect the negative solar cable to the negative solar terminal on the charge controller.

Your solar panel and charge controller are now connected! And you’re so close to being done!

Here’s what my setup looked like at this point:

Just one little thing left to do…

Step 5: Place the Solar Panel in Direct Sunlight

Uncover or flip over your solar panel and place it in direct sunlight. For best results, angle it towards the sun.

Look at your charge controller for an indication that the solar panel is charging the LiFePO4 battery. The indication is usually in the form of a blinking LED light, a battery charging icon, or a positive number on the PV/solar current screen. On mine, I confirmed by going to the PV current screen, which displayed the number 5.1A. That means my solar panel is charging my LiFePO4 battery at a rate of 5.1 amps.

You’re now charging your LiFePO4 battery with solar power!

Now you just need to wait for the solar panel to fully charge the battery. Charge controllers automatically stop charging once the battery is full. Your charge time will vary considerably based on factors like weather, battery capacity, and solar panel wattage.

If your solar panel doesn’t start charging your battery, here are some common issues:

• Your solar panel may not be receiving enough sunlight. Make sure it’s in direct sunlight and no part of the panel is shaded or covered. You can also mount it at the optimal tilt angle and azimuth angle for your location.
• Your system may have loose connections. Double check all your wiring connections, especially the terminals of your charge controller, to make sure no wires have come loose.
• Your battery may be fully charged. Charge controllers automatically stop charging once a battery is 100% charged. Discharge the battery a bit and retry.

How Long Does It Take to Charge a LiFePO4 Battery with Solar Panels?

A 100 watt solar panel produces around 300-500 watt hours per day, so it usually takes about 3-4 sunny days for one to fully charge a 12V 100Ah LiFePO4 battery. Though the exact number will vary quite a bit based on weather, location, and time of year. (For instance, on very cloudy days a 100W panel can produce less than 100 watt hours.) Try out our solar panel charge time calculator to get an estimate of your particular setup.

If you’re wondering how that charge time compares to a standard LiFePO4 battery charger, you can estimate your charger’s charge time using our battery charge time calculator.

Of course, you can always speed up or slow down the charging rate by picking a different size solar panel. Our solar panel size calculator can help you estimate what size solar panel is right for your desired charge time.

Charging Multiple LiFePO4 Batteries with Solar Panels

To solar charge multiple LiFePO4 batteries at the same time, you need to first connect the batteries in series or parallel.

Batteries connected together should be identical with the same age, BMS, voltage, and capacity. They should also have been purchased from the same brand around the same time. If your batteries aren’t identical, I recommend solar charging them separately.

Solar Charging LiFePO4 Batteries Wired in Series

Wiring batteries in series sums their voltages and keeps their amp hours the same. So two 12V 100Ah LiFePO4 batteries connected in series will produce a 24V 100Ah LiFePO4 battery bank.

In this case, in order to solar charge your LFP battery bank, you’ll need to make sure your solar panel or solar array has a nominal voltage of 24 volts or higher.

You achieve a 24V solar array by using a 24V solar panel or wiring two 12V solar panels in series.

Solar Charging LiFePO4 Batteries Wired in Parallel

Wiring batteries in parallel sums their amp hours and keeps their voltages the same. So two 12V 100Ah LiFePO4 batteries connected in parallel will make a 12V 200Ah LiFePO4 battery bank.

In this case, you can continue charging your battery bank with the setup I built in this tutorial. It will just take longer for it to fully charge.

If you have an MPPT charge controller, you can speed up the charging process by connecting more solar panels in series or parallel. If you have a PWM charge controller, you can speed up the charging process by connecting more panels in parallel.

4 Tips for Charging LiFePO4 Batteries with Solar Panels

1. Don’t charge a LiFePO4 battery below freezing (32°F or 0°C). Doing so can reduce your battery’s capacity and even cause it to develop internal shorts which cause irreparable damage. The exception to this rule is if you have a LiFePO4 battery with low-temperature charging protection.
2. Don’t exceed the battery’s maximum charge rate. The recommended max charge rate in amps is usually listed on the battery label or in its product manual. Most often it’s a 0.5C rate, meaning the number of amps is equal to half of the battery’s capacity in amp hours. For example, a 50Ah LiFePO4 battery will likely have a recommended max charge rate of 25 amps. For a 200Ah LiFePO4 battery, it’ll likely be 100 amps.
3. When disconnecting the battery from your solar charging setup, you almost always disconnect the solar panels first. Most charge controllers recommend disconnecting the solar panels first, then disconnecting the battery. As always, consult your charge controller’s manual for its specific recommendations.
4. Place or mount your battery and charge controller inside. I took pictures with all my equipment outside because of the better lighting. But batteries and charge controllers aren’t usually waterproof like solar panels are, so you’ll definitely want to bring those inside when raining.