These instructions will show you, with step-by-step videos, one of the foundational skills of building DIY solar power systems: how to connect a solar panel to a battery.
By the end, you’ll be charging your 12 volt battery — or higher — with free solar energy.
(If that doesn’t get your blood pumping…I don’t know what will.)
Alright. Let’s get to it!
Materials & Tools
Note: I’ve listed the sizes I used and linked to either the exact materials I bought for my setup or materials that are compatible with it. Feel free to copy my setup. Otherwise, adjust the sizes of your components for the amount of current that’ll be flowing through your system.
- 100 watt solar panel
- 12 volt battery
- 30 amp solar charge controller
- 12 gauge wire
- 12 gauge wire connectors
- MC4 solar adaptor cables
- MC4 solar extension cables (if necessary)
- 15 amp MC4 inline fuse
- Inline fuse holder with 20 amp fuse
- Heat shrink tubing
- Safety glasses
Step 1: Understand the Wiring Diagram
Here’s the wiring diagram showing how to connect a solar panel to a battery:
It’s important to understand the following:
- Don’t connect a solar panel directly to a battery. Doing so can damage the battery. Instead, connect both battery and solar panel to a solar charge controller.
- It’s recommended you fuse your system. Safety best practices, y’all! Place one fuse between the positive battery terminal and the charge controller. Place another between the positive solar panel wire and the charge controller.
Step 2: Make the Battery Cables
I didn’t have pre-made battery cables lying around. So I decided to save some money and make my own.
Turns out it’s pretty easy. Here’s how I did it:
Cut two pieces of wire to the length you want and strip both ends. (I made one a little shorter to account for the fuse I’m going to attach to it.)
Put the fuse in the fuse holder. Use our fuse size calculator to find the right fuse size.
Connect one of the fuse holder’s wire leads to your shorter battery cable with your wire connector of choice. (I used a 12-10 gauge butt splice connector.)
Shrink wrap the connector with heat shrink tubing and a heat gun.
Slide a piece of heat shrink tubing onto each battery cable (before crimping the terminal connectors…don’t forget until after like I did 😅).
Then crimp the battery terminal connectors onto the battery cables and shrink wrap the connections. Look at your battery terminals to know which size connectors to use. Mine uses 1/4″ ring terminals.
Battery cables complete!
Now they’re ready to be connected. ⚡
Step 3: Connect the Battery to the Charge Controller
Note: At this point I put on my gloves and safety glasses because places like Advanced Auto Parts recommend wearing them when working with batteries.
Follow the instructions in your charge controller’s manual for connecting it to the battery. I’ll show you how to connect the charge controller I used, the Renogy Wanderer:
Connect the negative battery cable, the one without the fuse, to the “-” battery terminal on the charge controller.
Connect the positive battery cable, the one with the fuse, to the “+” battery terminal. (Renogy recommends connecting the battery cables to the charge controller before connecting them to the battery.)
Connect the battery cables to the battery terminals — negative first, then positive. Before connecting the positive cable, I like to touch it to the positive battery terminal because sometimes there will be a little spark.
Your charge controller should turn on or light up to indicate the battery is properly connected. For instance, mine has a light that turns on.
The battery is now connected!
At this point, your manual may tell you how to program the charge controller for your battery type, voltage, etc.
Mine has a button which I can press to indicate battery type. It defaults to sealed lead acid, which happens to be the type I’m using. So I just kept it at the setting it was on.
Step 4: Connect the Solar Panel to the Charge Controller
Next up — connecting the solar panel!
Most solar panel cables come with pre-attached MC4 connectors. To connect a solar panel to a charge controller, you need MC4 solar adapter cables.
(These are basically a length of solar PV wire that has an MC4 connector at one end and is stripped at the other. For my setup, I made my own by assembling a male and female MC4 connector. I also bought MC4 solar extension cables. The extension cables are optional based on how far apart your solar panel and charge controller are.)
For the panel’s positive cable, connect the MC4 inline fuse, positive extension cable (if using), and then the MC4 adaptor cable.
For the panel’s negative cable, connect the negative extension cable (if using) and then the MC4 adaptor cable. Don’t let the exposed wires touch!
Follow the instructions in your charge controller’s manual for connecting it to the solar panel. I’ll show you how I connected mine:
First connect the negative solar cable to the charge controller, then connect the positive. Your charge controller should turn on or light up to indicate that the panel is properly connected.
Everything is now wired together!
Just one more step…
Step 5: Put the Solar Panel in the Sun
Once you do, your charge controller should indicate that the battery is charging. Mine has a light that flashes when the battery is charging normally.
Just like that, you’re DONE. 🥳
Now you know how to charge a battery with a solar panel!
Sit back and let the panel collect all that free solar energy. The charge controller will stop charging the battery once it’s full.
How Long Does It Take to Charge a Battery with a Solar Panel?
Use our solar battery charge time calculator to find out. The answer depends on a lot of factors.
As an example, here are the specs for the setup I used:
- 100 watt solar panel
- 12V, 33Ah lead acid battery
- PWM charge controller
According to our calculator, with this setup it’ll take about 7 hours of direct sunlight to charge the battery from 50% (the recommended depth of discharge for lead acid batteries) to fully charged.
But change any part of the setup — e.g. swap in a 50 watt solar panel, a lithium battery, or an MPPT charge controller — and the charge time will be different.
So yeah, definitely recommend the calculator for that question.
Give it a go:
DIY Solar Power Projects You Can Build Now
What you effectively just built was a small DIY solar power system. That’s a big deal!
Now that you’ve passed that milestone, here are some more projects I think you’d be interested in building:
These solar-powered LED lights use essentially the same system you just built. All you need to do now is connect some LED strip lights to your battery, and your good to go.
You’ve just learned how to charge a 12 volt battery with a solar panel…
…why not learn how to charge phones, power banks, and other handheld electronics?
This is a 5 volt solar charger, and it uses different skills and components than a 12 volt solar charger. Think soldering and circuits instead of fuses and wire connectors.