3 Ways to Solar Charge an Electric Bike

I recently made solar chargers for both my electric bikes.

Here’s the first one for my Specialized ebike:

And here’s the second for my converted ebike:

As you can see, the solar ebike chargers I made are each a little different. That’s because there are multiple ways to solar charge an electric bike.

(And because some ways don’t work for certain ebikes. 😬)

If you’re set on making a solar charger for your ebike — or a full-on solar bike — here are 3 ways to do it.

1. Make Your Own Solar Ebike Charger

Pros:

• Most efficient (least amount of energy is lost during the charging process)
• Lightweight relative to other methods

Cons:

• Doesn’t work for many off-the-shelf electric bikes
• Can be complex

Best for:

• Bikers who want to build a solar bike — i.e., mount a solar charger to their electric bike and solar charge it while riding
• Electric bikes whose batteries can be simultaneously charged and discharged
• Electric bikes whose chargers don’t have data pins

Materials

• MPPT boost solar charge controller for your ebike battery’s chemistry and voltage — I used the Genasun GVB-8-Li-41.7V-WP, designed for 36V nominal lithium batteries
• Solar panel — if you’re mounting it to your bike, consider a flexible panel with SunPower solar cells (the most efficient available)
• Adapter cables — I used an MC4 to Anderson adapter cable. Get the right adapter for your charge controller.
• MC4 inline fuse — the right amp rating for your panel

Step 1: Plug in Your Ebike and See What Happens

For this method, we won’t be using the charger included with your ebike. We’re going to be making our own.

Because this method is best for solar charging an ebike while riding it, let’s first see if you can charge and ride your ebike at the same time.

(Many off-the-shelf ebikes cannot be charged and ridden at the same time. The bike’s BMS disables the throttle or electric assist when the charger is plugged in.)

Plug in your ebike charger and see what happens to your bike. See if the throttle or pedal assist still works.

For example, you can see my Specialized ebike enters a “Charging” mode when the charger is plugged in. In this mode, the electric assist is completely disabled.

If your ebike works like normal while charging, great! You can ride and charge at the same time.

If the electric assist on your ebike is disabled while charging, then I have some bad news:

You won’t be able to solar charge and ride your bike at the same time — at least not without modifying the BMS, which I don’t know how to do.

But you can, of course, still solar charge it while NOT riding it. You can use any of the 3 ways described in this article to do so.

Now we need to find out how hard it will be to make our own charger.

Step 2: Look at Your Ebike Charger

Next, look at the charger that came with your ebike — specifically, the part that plugs into the battery.

For example, here is the plug on my Specialized charger:

The two big bottom pins on my charger are its positive and negative power pins. You’ll also notice a third tiny pin in the top right. This is a data pin, also called a signal pin, that transmits data from the charger to the battery.

Look and see if your bike charger has any data pins.

If it does NOT have data pins, you’re in luck — it will likely be easy to solar charge your ebike via the existing charging port. You can jump straight to Step 3.

If it has one or more data pins, you have two routes you can try out (both are for DIY experts and neither is guaranteed to work):

• Mimic the data signal: For charging via the existing charging port
• Use different power pins: For charging via a charging port that you hack together

Mimic the Data Signal

First, make sure the data pin or pins are necessary for charging. Test this out by covering up a data pin with electrical tape and plugging in the charger. Repeat for any other data pin on your charger.

As you can see, when I do this with my Specialized charger, the battery won’t charge:

From this little test I know the data pin on my charger is necessary for charging.

This means, to solar charge the ebike using this method, we need to mimic the data signal coming from the data pin.

Note: At this point, you might be thinking: “Mimic the data signal…how the heck are we gonna do that?!” Now you can see how tricky this solar charging method can get. Now’s a good time to consider whether or not you want to look into one of the other methods detailed in this article.

Now measure the voltage of the charger’s data pin with a multimeter:

You’re looking for something that would be easy to replicate. In this case, my Specialized charger’s data pin outputs a steady 5 volts.

This is encouraging. It means I may be able to ‘trick’ the data pin by applying a steady 5V to it. For instance, I could wire a 5V buck converter inline to the data wire.

(If you have a Bosch battery, here’s a video showing how you can trick it to accept a charge by applying 5V to the data pin.)

At this point, I can unfortunately no longer help you. I’ve never tried to mimic a data signal myself. I just know that others have had success before with certain bikes.

You’ll have to test and figure out the rest yourself. I recommend trying to replicate the data signal before building out the rest of your solar charger.

Also, be warned that you may now be in uncharted territory.

It’s possible that no one has figured out (or documented) how to mimic the data pin signal for your particular bike. If you go this route, know what you’re doing, take proper precautions, and be prepared to try a bunch of different things.

Use Different Power Pins

If you can’t or don’t want to mimic the data signal, you won’t be able to solar charge your ebike via the existing charging port.

Your last option is to try to hack together your own charging port.

Some ebike batteries have a second set of power pins between the battery and motor controller that you can use to solar charge the battery.

For example, for my second ebike (the one I converted), I worked with an ebike shop that soldered some battery cables to these power pins, which are accessible by removing the motor controller’s housing.

This is what it looks like:

Needless to say, don’t try this at home. Lithium batteries are dangerous. And explosive. Get professional help if you’re considering going this route.

Step 3: Buy or Make Your Adapter Cables

At this point, you should know:

• Whether or not you can solar charge your ebike while riding it
• Whether you plan to solar charge via the existing charging port or via a charging port that you hack together

We’ve made it through the hardest part. Congrats!

If you know how to connect a solar panel to a battery, you know it’s as simple as connecting some wires. We just need to buy or make the right adapter cables to connect everything together.

Here’s the wiring diagram:

My solar panel came with MC4 connectors, the solar industry standard. And my MPPT boost solar charge controller came with Anderson Powerpole connectors.

Here’s what they look like:

To be able to connect the solar panel to the charge controller, I got an MC4 to Anderson adapter cable.

As for connecting the battery to the charge controller, mine both already had Anderson connectors so I didn’t need an adapter cable.

Buy or make the adapter cables for connecting your charger together. You may also want to put an extension cable between the solar panel and charge controller so you can place the solar panel outside while your bike is inside.

Tip: Some common connectors for ebike battery chargers include a 2.1mm barrel jack, XT60 connectors, and Anderson Powerpole connectors. You can find many of these wire connectors and pre-made adapter cables online, especially on ebike websites such as Luna Cycle and Grin Technologies.

Now it’s time for the easy part — connecting everything together.

Step 4: Connect the Solar Panel to the Ebike Battery

This is the easiest part of the whole build.

Here’s a quick video overview of the process:

Consult your charge controller’s instructions for the recommended connection order. Most charge controllers I’ve worked with recommend connecting the battery and charge controller first. But the one I used for this project, the Genasun GVB-8-WP, recommends connecting the solar panel and charge controller first.

So I first connected the solar panel to the charge controller using my MC4 to Anderson adapter cable. Then, I connected the charge controller to the battery. (Once I do, you can see the charge controller’s LED blink green, indicating it’s in standby mode.)

(If I wanted, for extra protection I could’ve added an inline MC4 fuse between the solar panel and charge controller. You’ll notice my charge controller has a built-in fuse between the charge controller and battery.)

Now it’s time to take the charger outside and give it its first real-world test.

Step 5: Test Your DIY Solar Ebike Charger

I moved my solar panel outside and placed it in the sun. My solar charge controller started quickly blinking green, indicating that the battery was being charged.

What this means is…

…my solar ebike charger works!

Now I can sit back and relax while the battery charges up.

If yours isn’t working, consult the troubleshooting section in your charger controller’s manual.

Step 6: Mount Your Solar Charger to Your Ebike (Optional)

You’ve just made a solar charger for your electric bike. At this point, you’re probably thinking:

Can I mount the charger to my bike so the battery charges while I ride?

It’s definitely possible. In fact, I recently did it myself:

To do so, you need to decide on a way to mount your solar charger to your bike.

Here are the most common ways I’ve seen:

• On a bike trailer
• On top of the bike (to create a solar roof of sorts)
• Over the front or back wheels

I decided to mount mine to a bike trailer. With the help of my engineer friends, we designed a custom solar panel mount.

After a couple iterations this is what I ended up with:

Which I mounted to my bike trailer like so:

Now I have a full-on solar bike. As I ride, the solar panel charges the battery which powers the motor. It’s pretty great. But I’ll warn you — it’s a lot of work.

It’s also entirely optional. Most people don’t need a solar powered electric bike. If you don’t want to bother with this step, you can just leave your solar bike charger at home.

The mount you build will be customized for your specific setup, so I can’t tell you how to do it. I’ll just leave you with some photos and videos as inspiration for your design:

• Solar roof and solar bike trailer
• The Sun Trip’s Instagram
• A longtime solar biker’s design changes over time

2. Use an Inverter and 12V Battery

Pros:

• Uses the charger included with your ebike
• Works for all ebikes

Cons:

• Less efficient
• Heavy

Best for:

• Solar charging an ebike while NOT riding it (though you could still mount this system to your bike)
• Ebikes that have hard-to-replicate chargers (such as chargers with data pins or uncommon connectors)

Materials

• 12V solar panel — I used a 100 watt panel
• 12V solar charge controller
• 12V battery — I used a 12V 33Ah battery
• Inverter — I used a 150W inverter. Get one with a power rating capable of handling the energy demands of your bike charger.
• Adapter cables and fuses

Step 1: Connect the Solar Charge Controller and Inverter to the Battery

Here’s a wiring diagram for how to make this solar charger:

This charger stores the solar energy in a 12 volt battery, then uses an inverter to convert it into AC for using the charger included with your ebike.

It’s not as efficient and lightweight as the first method, but — depending on your bike — it may be easier to make. This method also works with all electric bikes.

Let’s get started.

First, connect the solar charger controller and inverter to the battery. Best safety practices are to place a fuse on the positive leads between the battery and both the charge controller and inverter.

As you can see in the video, my charge controller and inverter both turn on, indicating that they are properly connected.

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

Next, connect the solar panel to the charge controller. Best safety practices here are to include a fuse on the positive wire between the two.

Note: I used a 100 watt solar panel, but feel free to use whatever size you want as long as its nominal voltage is compatible with your charge controller.

My charge controller now displays a number for the incoming PV voltage, indicating that the solar panel is properly connected.

However, the solar panel isn’t charging the battery yet because it’s in low light. Time to put it in the sun.

Step 3: Test Your Solar Ebike Charging System

First, put your solar panel in the sun and look at the PV current on the charge controller to make sure it’s charging.

You can see mine is charging the battery at a rate of 0.8 amps.

This means the solar panel is successfully charging the battery. Now I need to plug in my ebike charger to the outlet on the inverter.

When I do so, my bike’s computer indicates that the bike is in charging mode:

My solar ebike charging system is working!

Here’s a video walkthrough of the whole thing:

If I want, I can leave the solar panel outside so that the 12 volt battery is topped up and ready to charge my ebike battery whenever it needs it.

Note: You could also mount this setup to your ebike to make a solar bike. It is a less than ideal way of solar charging an electric bike while riding, though, because of the added weight of the 12 volt battery and inverter and the energy losses incurred from converting DC to AC, then back to DC.

3. Use a Solar Generator

Think of a solar generator as essentially a small, self-contained solar power system.

It has a solar charge controller that regulates the incoming solar energy, a battery that stores it, and an inverter that converts it to AC for when you want to plug in your AC devices. It makes solar powering and solar charging as simple as possible.

Of course, you’re gonna pay extra for that convenience. A lot extra.

Pros:

• Simplest method
• Can use your ebike’s included battery charger
• Works with all ebikes

Cons:

• Expensive
• Less efficient
• Heavy

Best for:

• Bikers who want a done-for-you solar electric bike charger

Materials

• Solar generator
• Compatible solar panel

Step 1: Connect the Solar Panel to the Solar Generator

I don’t have a solar generator to illustrate this part, but it’s super simple.

Connect the solar panel to the solar generator following the instruction manual. Make sure the panel is compatible with your generator.

Step 2: Plug in Your Ebike Charger

Plug in your included ebike charger to an outlet on the solar generator. Your ebike should start charging.

Easy.

How Long Does It Take to Solar Charge an Electric Bike?

You may now be wondering: “How long will it take for my solar panel to charge my electric bike?”

You can find out using our solar battery charge time calculator. I input the following specs for my solar bike:

• 36V 26.5Ah lithium battery
• 170W solar panel
• MPPT charge controller

According to our calculator, it will take around 6.9 peak sun hours for my solar panel to fully charge my ebike battery.

Try it out for yourself:

Note: The calculator is designed for solar power systems that solar charge a battery directly, instead of by using an intermediary 12V battery and inverter.

2 More DIY Solar Chargers You Can Build Now

You now know how to solar charge an electric bike. Pretty cool.

Here are some more DIY solar chargers you may be interested in building:

1. DIY Solar Car Battery Charger

Solar charging a car battery is a lot easier than solar charging a bike. You just need to connect a 12V solar panel and the car battery to a 12V solar charge controller. And you can use whatever size solar panel you want depending on how fast of a charge you’re looking for.

2. DIY Solar Phone Charger

This homemade solar charger has a USB port for charging 5V electronics such as phones, tablets, and portable battery packs. It folds up for easy storage and, if you want, you can install eyelets in the corners for attaching it to your backpack.