These instructions will show you, with step-by-step videos, one of the fundamental skills of building DIY solar energy systems: how to connect a solar panel to a battery.
In the end, you’ll be charging your 12-volt battery, or more, with free solar power.
(If that doesn’t get your blood pumping…I don’t know what will.)
good. 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 12 volt solar panel
- 12 volt battery
- renogy wanderer 30a solar charge controller
- 12 gauge wire
- 12 gauge wire connectors
- mc4 solar adapter wires
- mc4 solar extension wires (if needed)
- fuse 15 amp mc4 inline
- 20 amp inline blade fuse holder
- heat shrink tubing
- safety glasses
- Wire stripper
- Wire crimper
- Wire cutter
- Heat gun
step 1: understand the wiring diagram
here is the wiring diagram showing how to connect a solar panel to a battery:
It’s important to understand the following:
- Do not connect a solar panel directly to a battery. doing so can damage the battery. instead, connect the battery and solar panel to a solar charge controller.
- It is recommended that you fuse your system. best safety practices, y’all! place a fuse between the positive terminal of the battery and the charge controller. place another one between the positive cable of the solar panel and the charge controller.
step 2: make the battery cables
I didn’t have any pre-made battery cables lying around. so I decided to save some money and make my own.
Turns out it’s pretty easy. this is 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 take into account the fuse I’m going to put in it).
Place the fuse in the fuse holder. use our fuse size calculator to find the correct fuse size.
Connect one of the wires from the fuse holder to the shorter wire on the battery with the wire connector of your choice. (I used a 12-10 gauge butt splice connector).
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 later, like I did 😅).
then crimp the battery terminal connectors onto the battery cables and wrap the connections with heat shrink film. look at your battery terminals to find out what size connectors to use. mine uses 1/4″ ring terminals.
complete battery cables!
Now they’re ready to be connected. ⚡
step 3: connect the battery to the charge controller
Note: I’m wearing my gloves and safety glasses right now because places like Advanced Auto Parts recommend using them when working on batteries.
Follow the instructions in your charge controller’s manual to connect 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 a fuse, to the battery “-” terminal on the charge controller.
Connect the positive battery cable, the one with the fuse, to the “+” terminal of the battery. (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 terminal of the battery because sometimes there will be a little spark.
Your charge controller should turn on or illuminate to indicate that the battery is properly connected. for example, mine has a light that turns on.
battery is already 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 that I can press to indicate the type of battery. the default is sealed lead acid, which happens to be the type I’m using. so I kept it in the configuration it was in.
step 4: connect the solar panel to the charge controller
next: connect the solar panel!
Most solar panel cables come with mc4 connectors pre-installed. 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 positive panel lead, connect mc4 in-line fuse, positive extension lead (if used), then mc4 adapter lead.
For the negative cable from the panel, connect the negative extension cable (if used) and then the mc4 adapter cable. don’t let exposed wires touch!
Follow the instructions in your charge controller’s manual to connect 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 one. your charge controller should turn on or illuminate to indicate the panel is properly connected.
now everything is connected!
just one more step…
step 5: put the solar panel in the sun
position your solar panel in direct sunlight at the best tilt angle for your location (this is easy to do with my $11 DIY solar panel mount).
once it does, 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, that’s it. 🥳
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 is 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 many factors.
As an example, these are the configuration specifications I used:
- 12v 33ah lead acid battery
- 50% battery depth of discharge
- 100w solar panel
- pwm load controller
According to our calculator, with this configuration, the battery will take about 4.5 hours of maximum sun to fully charge.
but change any part of the configuration, e.g. swap a 50 watt solar panel, lithium battery or mppt charge controller, and the charging time will be different.
so yes, I definitely recommend the calculator for that question.
3 DIY Solar Power Projects You Can Build Now
what you actually just built was your first solar panel setup. that’s a big deal!
Now that you’ve passed that milestone, here are a few more projects I think you’d be interested in building:
1. solar car battery charger
By connecting a solar panel to a 12V battery, you’ve actually made a solar 12V battery charger. Car batteries are 12V batteries, so you could just as easily use the system you just made — or the near-identical one described in this tutorial — to solar charge your car battery.
2. diy 12 volt solar powered led lights
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 you’re good to go.
3. solar charger for electric bike
You can build a modified version of the solar charging system you just made to solar charge an electric bike. Or, just connect an inverter to your 12 volt battery and plug the ebike charger in like normal.