Will a 5W Solar Panel Charge a 12V Battery?

Yes, a 5W solar panel can charge a 12V battery.

In fact, I recently did it myself:

Then, after doing it, I saw that Google isn’t exactly giving the best answer to this question:

Huh?

And I decided to write this article to set the record straight.

So, once again, for the people in the back:

Yes, you can charge a 12V battery with a 5W solar panel. You just need to make sure it’s a 12V solar panel. Anything less, such as a 6V or 9V solar panel, won’t work.

Here’s how I did it:

Materials & Tools

Materials

Tools

Step 1: Connect the 12V Battery to the Solar Charge Controller

Connecting a battery to a solar charge controller requires wires, wire connectors, and an inline fuse.

You can use your own wire and connectors, or you can buy some to make the process a little easier. I ended up buying something called the NOCO GC018. It’s a 12V plug adapter that comes with an inline fuse and ring terminals — the right kind for my 12V battery.

To start, I cut the 12V plug off the NOCO GC018 with my wire cutter.

Then I just pulled the wires apart a little bit and stripped the ends. (I’ll be sticking the stripped ends in the charge controller’s terminals.)

Now my wires are ready. I can connect them to the battery terminals using the ring terminals. And I can connect them to the charge controller terminals using a screwdriver.

So that’s what I did:

I first connected the positive and negative wires to their respective battery terminals. Like so:

Then I used a screwdriver (a precision screwdriver, in my case) to connect the stripped wire ends to the charge controller’s battery terminals. My controller’s terminals have a battery icon on them, as well as a plus and minus, to help me know where each wire goes.

When all the wires were connected, my charge controller turned on to indicate that it was properly connected to the 12V battery.

Consult your charge controller’s manual for instructions on how to program it for your battery type. Mine defaults to sealed lead acid batteries, which is the battery type I was using.

Step 2: Connect the 5W Solar Panel to the Solar Charge Controller

My 5W solar panel came with wires that had stripped ends. This made it simple to connect it to my charge controller.

I simply connected the positive and negative solar wires to their respective terminals on my charge controller. Once again, the terminals have a solar panel icon on them and are marked for positive and negative which makes it easy.

Now your solar panel is connected…

…and you’re done!

Here’s how mine turned out:

That’s really all there is to it.

However, because my solar panel was inside, at this point it wasn’t getting enough sunlight to actually charge the battery.

Time to take it outside.

Step 3: Test Your 5W Solar 12V Battery Charger

You’ve effectively just built a 5W solar 12V battery charger. Not bad!

To test mine, I took everything outside (making sure no wires got disconnected in the process) and put the solar panel in direct sunlight.

I then cycled through the system specs on my charge controller until I got to the PV current display.

It indicated that my 5W solar panel was charging my 12V battery at a rate of 0.2 amps:

There you go — proof that a 5W solar panel can charge a 12V battery.

I can now just leave my charging setup outside in direct sunlight. The panel will continue to charge the battery as I go about my day.

The charge controller has overcharge protection, meaning it will stop the charging once the battery is full.

5W Solar 12V Battery Charger Wiring Diagram

Here’s the circuit diagram for using a 5W solar panel to charge a 12V battery:

And here’s what I call the “real-world wiring diagram”, which shows what it looks like in real life:

Notes about this wiring diagram:

  • Safety best practices are to place a fuse between the charge controller and both battery and solar panel. (However, for this project, because my solar panel is so small, I left out the fuse between the solar panel and charge controller.)
  • For most charge controllers, you connect the battery first and then the solar panel. Consult your controller’s manual for the manufacturer’s recommended connection order.
  • Make sure to get a 12V 5W solar panel. If it is a lower voltage 5W panel (like 6V or 9V) it won’t work with a 12V charge controller.
  • Make sure your charge controller is compatible with your battery’s chemistry. For example, some charge controllers only work with lead acid batteries. Others work with lead acid and lithium batteries.
  • I recommend a PWM charge controller for this project because they’re cheap

Tip: This circuit diagram would work for many other solar panel sizes (e.g. 10W, 20W, 50W, 80W, 100W) as long as it’s a 12V solar panel and you use the appropriate wire gauge and fuse size for the current.

How Long Does It Take to Charge a 12V Battery with a 5W Solar Panel?

According to our solar panel charge time calculator, it takes around 155 hours of direct sunlight for a 5W solar panel to fully charge a 50Ah 12V battery.

Here’s what I plugged in to the calculator:

And here are the estimated charge times for 5 other common solar panel sizes:

  • 10W solar panel: 78.4 hours
  • 20W solar panel: 40.2 hours
  • 50W solar panel: 17.3 hours
  • 80W solar panel: 11.5 hours
  • 100W solar panel: 9.6 hours

Of course, these estimated charge times vary depending on battery capacity.

What Size Solar Panel Do You Need to Charge a 12V Battery?

You can charge a 12V battery with many different solar panel sizes.

Knowing this, the question then becomes:

“How fast do I want to solar charge my 12V battery?”

Based on the above charge times, we can draw some conclusions:

5W and 10W solar panels are good for slow, trickle charging 12V batteries. They’re a good size solar panel for maintaining a 12V battery’s charge, and will slowly charge it up over the course of weeks — maybe even months depending on the weather and size of the battery.

20W and 50W solar panels are good for fast charging small 12V batteries. For example, a 20W solar panel can charge a 20Ah 12V battery in around 17 hours of direct sunlight. A 50W panel can do it in around 8 hours.

80W and 100W solar panels are good for fast charging large 12V and car batteries. If it’s a 50Ah battery, they can fully charge it in around 12 hours or less of direct sunlight.

For more help on finding the right size solar panel for your solar charging setup, check out my post on what size solar panel will charge a 12V battery quickly.

Tip: You can reduce these charge times further by upgrading from a PWM to an MPPT charge controller. MPPT charge controllers are much more efficient, but they’re also much more expensive.

2 More DIY Solar Charging Projects You Can Build Now

Like I said, you just built a solar 12V battery charger.

You connected a solar panel to a battery via a charge controller. And the solar panel is now charging that battery.

Using what you just learned, you can build even more solar chargers.

Here are some ideas for your next project:

1. DIY Solar Car Battery Charger

Car batteries are also 12V batteries. So, using the same solar panel and charge controller, I was able to make a solar car battery charger.

2. Solar Ebike Battery Charger

You’re also just a few parts away from solar charging an electric bike. Don’t be fooled by how complex it looks — you just need a bigger solar panel and a small inverter.

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Alex Beale
Alex Beale
Hi, I'm Alex. I started Footprint Hero to help people reduce their environmental impact. My current obsession is DIY solar power projects, which I've been building since 2020.
Alex Beale

Alex Beale

Hi, I'm Alex. I started Footprint Hero to help people reduce their environmental impact. My current obsession is DIY solar power projects, which I've been building since 2020.

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