Running an Ebike on Solar Energy: The Sheddy Kilowatt Story

Five minutes after I installed a solar panel on the roof of my bike shed it began to rain. Since this was April in Oregon, the rain was not an unusual or unforseen event and in fact the next five days were rainy and mostly cloudy. But even on those damp days my solar system managed to generate enough power to not only charge my ebike, but also my phone, Android tablet and radio batteries. After that first week, I knew that I had pieced together a workable system. It's not fancy or particularly elegant, but it gets the job done.

Sparky, my eBike, runs off a 36 Volt, 12.5 AmpHour Lithium-ion battery Since Watts equal Volts times Amps, Sparky's battery holds 450 WattHours of power. Sparky's stock wall charger plugs into a U.S. standard 120 Volt AC outlet and puts out 42 Volts DC at 2 Amps so it puts out 84 Watts in an hour. To completely load Sparky up with 450 Watts takes about five and half hours if I plug into the wall. Charging off the sun is a different story.

The hundred Watt solar panel I got from eBay only puts out 100 Watts in some theoretic, perfectly sunny world that I certainly don't live in. And even if the panel were to miraculously put out 100 Watts, it would do so only at a maximum voltage of 18 Volts. I needed to get that up to a steady 42 Volts to charge Sparky.

My first thought was to get what is called a "boost controller." This is a device which will take a variable voltage input (like what a solar panel puts out) and boosts it to a constant voltage. Like damn near everything these days, the Chinese make an inexpensive one you can buy on eBay, so I ordered one to go with my solar panel.

The device is marvelously complicated and came with a manual that had obviously been translated into English by a not too bright robot. Here is an actual paragraph from that manual:

The controller uses advance software algorithms initiative rope move, quickly and accurately tracking the maximum power point of photovoltaic panels module voltage, active tracking work at the maximum power point of the solar cell module in order to get more solar energy. Enhance the charging current and power generation.

After reading that I decided to initiative my own rope move and I went on YouTube and found some guy with a British accent who had messed around enough with one of these controllers to figure it out and explain it in such a way that even a dumb American like me could use it. Following his instructions, I set up my boost controller put out the 42 volts I needed to charge Sparky's battery.

While that system worked, the flaw in my plan quickly became apparent, I had to have Sparky parked in the shed and plugged in to get the power off the panel. The panel doesn't generate power at night and in most of the daylight hours, Sparky is at work with me. While I could just charge Sparky using the main power at work and have my employer pay the power bill, that is not at all what I wanted to do. I want to run Sparky on sunshine.

Sir Robert Watson-Watt, the inventor of radar, once said "you get one idea today, you get a better idea tomorrow, and the best idea...never." My next idea was to add an intermediate storage battery to the system and as I researched and thought my next, next better idea was to get a little integrated battery/inverter Power Bank unit. I found a good one, again made by the Chinese and available on eBay.

I also got a little recording Watt meter which is not needed for the system to work, but useful in that it tells me how much power the panel is generating and how much has been stored. The Power Bank has a little 4 LED power meter but the Watt meter gives me a clearer picture of what is going on.

The Power Bank has built-in circuitry that lets it take power straight off the solar panel, so I no longer need to use the green boost converter. The solar power, up to 220 WattHours, gets stored in the Power Bank's internal Li-ion battery. The Power Bank charges up during the day while Sparky and I are at work.

You might have noticed that the Power Bank has roughly half the capacity that Sparky does. That means that if I came home at the end of the day with Sparky completely depleted, even if the Power Bank was fully charged, I could only charge Sparky's battery half way. If that actually happened, I'd need a second day to charge the Power Bank and then transfer that power to Sparky. In practice, I'm a pretty frugal ebike rider and in a week of commuting and errands, I only use a few hundred Watts.

My typical charging pattern looks like this: I get home Friday night and Sparky is down to around 50%. I plug Sparky's standard wall charger into one of the 120 VAC inverter outlets on the Power Bank. The next morning, Sparky is full and the Power Bank is empty. I spend the weekend riding Sparky around and the Power Bank spends the weekend in the shed charging up. Sunday night I again connect Sparky to the now full Power Bank. Monday morning the Power Bank is again depleted and Sparky is ready to take on the work week at full strength.

The actual truth of things is that even with less than great weather and the inefficiencies of various intermediate batteries and inverters, my little solar system gives me more than enough power to keep Sparky humming along. In fact, I have more than enough power so I also use the power bank to keep my phone, tablet, and radio charged up. All the words and pictures in this post come are here thanks to solar power.

If you want to build a system like mine, the only two parts you really need are a Solar Panel and a Power Bank. The prices of these things tend to fluctuate. I paid about $100 for my 100 Watt panel and $131 for my Power Bank. I consider it money well spent.

Keep 'em rolling,

Kent Peterson
Eugene, Oregon

The Real Secret

I didn't need or want an ebike, but now I'm glad I've got one!

While ebikes have been a growing part of the bicycle business for several years, I'd always figured I didn't need one and frankly, I didn't want one. For decades I've managed to get around just fine on a bike where I'm the only motor and I didn't see any reason to complicate matters. It was somewhat ironic then when Bike Friday started doing more and more ebikes for our customers that I became "the ebike guy." While Alan Scholz, our company's founder, did the bulk of the preliminary research and development for Bike Friday's new line of ebikes, my job in the service department involves adding electric motors to customer's existing bikes and troubleshooting bikes with problems. As I've been known to grumble now and then "adding a bunch of electronics and a motor to a bike doubles the universe of potential problems." I also may have said the ebikes are "bikes for lazy folks." Statements like this are why Bike Friday doesn't have me working in the sales department.

As I got to work with more ebike customers, I saw that I was very wrong about the "lazy folks" comment. In many, many cases a person gets an ebike so that they can keep riding. One 80 year old customer wanted to keep riding with his slightly younger, faster pals. Another wanted to bike to work instead of drive and the motor took care of the one big hill in her way. A mom uses the extra oomph of an ebike to help her carry her two kids to school on the back of her Haul-a-Day. These are not lazy people.

Still, I have a flat commute to work. I'm no longer young, but I'm reasonably fit. I sure didn't (and don't) need an ebike. But Alan, who is a bright guy, kept bugging me. "You won't really get it until you have one. Test riding customer bikes isn't the same." And Alan kept giving me stuff. "This motor was one I was checking out for research, but it's a bit heavier than what we'd want for a customer's bike. You should put it on your bike." The next week we had a warranty issue with a battery because of a cracked mounting bracket. "We can't sell it to a customer, but I bet you could make it work on your bike." Eventually, the pile of parts was either going to bury my workbench or get put on a bike. I installed all the various bits on my Pocket Companion.

My first commute was a couple of miles per hour faster, but it wasn't life changing. Riding an ebike is like riding a tandem with a strong partner. With the pedal assist system we use on the Bike Fridays, the motor only kicks in when you are pedaling. You select how much (or how little) of a boost you want. With e-assist I'm quicker getting across an intersection when the light turns green. My top speed isn't changed. Ebikes by law have a regulator that stops the motor from applying power at a certain speed. You can pedal faster than that speed, but it is you doing the work, not the motor. But my average speed went up because where ebikes shine is helping you at times when conditions would slow you down. On my flat commute, in addition to the intersections, I noticed the boost most on days when I was riding into a headwind.

But it was on my days off that I really began to bond with my ebike. I've always been a strong climber, but with the ebike I really don't even have to think about hills. Yes, I gear down and pedal, but Sparky (as I've renamed my bike!) is like a little pal saying "let me help you with that." Hauling a couple of big boxes of books to the thrift store with the bike trailer? No problem, Sparky is there to help.

They did a study in Norway and they found that in general ebike riders get about 80% of the workout they would riding a non-electric bike over a given distance. But they also found that ebike riders tend to ride about 20% farther on average and their average speed is about 20% faster. My own experience echoes this. I'm having fun, riding more and riding farther.

I've told my friends that I've gone from being an ebike skeptic to being an ebike enthusiast and I'm dangerously close to becoming an ebike evangelist. Alan was right, I had to own an ebike to really get it. I still don't really need an ebike, but I'm damn glad I've got one!

A Little Story for Earth Day

Now various folks call people like me who try to reduce their environmental impact on the earth "Tree Huggers". Most times I take the reference as a badge of honor. But sometimes, depending on the context, I'm not always thinking Bob Ross style happy thoughts about trees.

I recently built myself up an electric bike and even more recently pledged that I was not going to charge it off the main power grid. With the help of my son Peter, I assembled a small bike shed in our back driveway and a few weeks ago I installed a 100 Watt solar panel on the shed's roof. Since then all the power for my ebike, radio, phone and Android tablet have been generated from sunlight.

Late yesterday afternoon, while it was still bright and sunny, I was puttering around in the shed and I noticed the Watt meter was showing a lot less power than I'd expect. I stepped out and looked at the shed's roof. A tree at the edge of the yard (which I'd always thought of as quite lovely) was casting its leafy shadow on the solar panel.

"You stupid tree!" I grumbled.

I guess I'm a bad tree hugger.

Kent Peterson
Eugene, Oregon USA