by Laurence Clarkberg
Every spring Judy and I like to go on a week-long ebike tour around Cayuga Lake. It’s really quite enjoyable: leisurely gliding past the scenery, buying vegetables at a farmstand, soaking up local history, and staying in a series of campground cabins as we make our way around the lake. We take our time, going about 30 miles every other day. We travel at about 15mph, so that’s only two hours of biking every other day.
There are only a couple of drawbacks to traveling by ebike. One is that it can be kind of lonely while biking because it’s hard to bike side-by-side with one’s companions. Another is that a sudden downpour can make the experience miserable. And lastly, it can sometimes be a burden trying to find an outlet to recharge the ebike batteries.
Enter the Sun Pony. The Sun Pony is a two-seater tricycle to which I’ve added crank drive ebike motors, batteries, and solar panels. The Sun Pony solves many of our problems with touring by ebike: my life partner and I can sit together and enjoy each other’s company as we travel; the overhead panel provides some rain protection; and we can easily recharge our batteries anywhere the sun is shining. But the Sun Pony is more than just a great touring machine. It is a game-changing vehicle that can potentially solve many problems with our transportation system in general, as I’ll describe below.
Sad History of Solar Cars
There is a certain allure to solar powered vehicles. Surely it should be possible to power a car from the sun. On a bright day, the sun produces about a kilowatt of power per square yard of surface area. As an ebiker, I know that a kilowatt is capable of propelling my ebike up a hill in excess of 15mph, and up to 30mph on the flats. As an engineering problem, a solar powered vehicle seems totally solvable. It’s simply a matter of figuring how to mount a square yard of solar panels on a bicycle-sized vehicle. And the consequences of getting it right would be huge: human society could finally free itself from its addiction to stinky gasoline, which is incredibly toxic on so many levels. Shouldn’t society make solving this problem a priority?
For a brief period in 1987 a group of engineers at no less than General Motors did make designing a solar car a priority. They created the Sunraycer as a contestant in the World Solar Challenge, a week-long race across Australia. I remember following the race when I was a college student, and it filled me with optimism. The Sunraycer triumphed: it finished the race in five days, two days ahead of the competition. Solar cars had arrived, though the $2 million price tag left them out of reach for all but large corporations. The Sunraycer led to the development of GM’s EV1 electric car, the first production electric car, in 1996. The main problem with the EV1 was that it was too successful. The cars were fast and quiet, and the 90 mile range was not an issue since most people drive less than 30 miles a day. As chronicled in the movie Who Killed the Electric Car? GM and others in power feared that the EV1’s success would damage the gasoline-powered car business. GM rounded up all of its EV1’s and sent them to the crusher.
This was a sad time for the electric car, let alone the solar powered car. However, several other car manufacturers saw the potential of electric cars, and so in the early part of the new century they began development of their own production models, including the Nissan Leaf and the Tesla Roadster. Even GM relented and got back in the EV game, developing the Volt, as described in the 2011 sequel movie Revenge of the Electric Car. Not described in that movie, a team of engineers also began development of a solar powered EV called the Aptera. The Aptera is ultra-lightweight and aerodynamic. Hopes are that it can go 100 mph and have a 1,000 mile range. After some funding difficulties during the 2008 recession, the team is back together and the Aptera is back on track towards production. Another notable solar car from this period is the “Stella,” the world’s first solar-powered family car. Built by a team of engineering students from the Eindhoven University of Technology (TU/e) in the Netherlands, the Stella was, like the Sunraycer, first created for the 2013 World Solar Challenge solar car race in Australia. The car is capable of a top speed of 75 mph with a full load of four people and has a range of 500 miles at speeds of 43 mph. Not bad! Take that, solar car naysayers.
Around this time ebikes also blossomed as a practical technology, first in China, then in Europe, and lastly in the United States. Three developments came together to make ebikes possible: lightweight powerful lithium batteries with electronic battery management, powerful and efficient brushless electric motors with stronger magnets, and computer control of those motors using advanced electronics. I built my first ebike, a Surly Big Dummy cargo bike fitted with the StokeMonkey mid-drive motor, in 2010. It seemed an obvious next step to attempt to power my Stoked Dummy with on-board solar panels. Solar vehicle technology had finally reached the garage of the home hobbyist!
I paid $900 for three 65 watt portable solar panels, for a total of 195 watts, and mounted them to the back of my Stoked Dummy. At that time I was unable to find a charge controller for my lithium batteries and so I used the panels to charge a 36v pack of lead acid batteries directly from the solar panels. Needless to say, this was not very efficient and produced only about 40 watts of charging power on a sunny day. Then I planned and executed a three-day test trip from Ithaca, NY to Silver Bay, NY (about 300 miles). The solar panels provided about one quarter of the power on that trip. I decided that it wasn’t yet worthwhile to mount solar panels on an ebike. I postponed my dream of creating my own solar powered vehicle.
Recently, however, solar and ebike technology have both improved to the point where it is worth reconsidering a home-built solar vehicle project. A 200 watt portable solar panel can be had for less than $300, one-third the price of a decade ago. Charge controllers for 52v lithium ebike batteries are readily available. And since 2010, lithium ebike batteries have halved in price while doubling in power and capacity. Judy and I became inspired by ebike uber-hobbyist Justin Lemire-Elmore who in his Youtube video Solar Ebike Basics describes how simple it is to add a small solar panel and a charge controller to an ebike. Justin also describes his own ebike odyssey that he made with his fiancé in 2018 in the context of the Sun Trip solar ebike race across Europe. We were hooked!
Last year we purchased two 200 watt portable solar panels with matching mppt charge controllers (coincidentally sold by Justin’s company Grin Technologies). We used the panels to power two of our trips in 2022: we carried them on a bike trailer for a week-long trip around Cayuga Lake, and we took them to Burning Man to recharge the folding ebikes we had brought to the event. The panels not only charged our ebikes, we used those ebike batteries to power an induction hot plate that we used to cook our meals and we used solar power to recharge our lights and phones. Except for a perplexing connector failure, everything worked great!
The trip to Burning Man was an energy eye opener. We love burners, they are 99.9% wonderful enlightened people. And we love Burning Man, we had a great time at the event. But last year we found that we were deeply disturbed by our fellow burners' unapologetic reliance on stinky noisy fossil fuels, not only at the event itself, but to get to the event. As one walks down a typical street in Black Rock City (a temporary city of 80,000 people), one is greeted by the smell and noise of diesel generators huffing away to power all the glitz. A burner aphorism is “Bring All the Stuff,” and bring it they do. People fill large trailers and RVs to the brim and drive them cross-country thousands of miles to get to the event. Those who don’t drive fly to the event. Only a handful of the 80,000 participants bike to the event. Granted, it would be a difficult bike ride across hundreds of miles in the scorching desert sun. But wait! Could not that very sunshine be used to power a vehicle, perhaps an art car designed to both be at the event but also to get to the event? We had had an epiphany, as one often does at Burning Man. We became determined to build such a solar art car and to drive it from New York to Black Rock City in 2024. We started by sketching the Sun Pony (and coming up with the catchy name) on the train ride home from Burning Man.
EVs Aren’t the Answer
Electric vehicles are not a complete solution to our transportation woes. Yes, you read that correctly! You smug Tesla owners aren’t quite so green as you think you are. Your personal vehicle weighs four thousand pounds, dude! My ebike only weighs 40 pounds! And if you think you are going to go 0 to 60 mph in 2.3 seconds down my street, where my kids are playing, you are sadly mistaken!
EVs, as the car manufacturers are currently conceiving of them, only solve one class of problems with our current transportation paradigm, the problems associated with using a toxic substance for fuel. Mainstream EVs all continue the stupid paradigm of unnecessarily fast, heavy and wide vehicles. They all continue the paradigm of forcing you to drag around three unoccupied seats (and sometimes an unfilled truck bed) wherever you go. As bicyclists, Judy and I are used to challenging the assumptions of car owners. One assumption is that you need to carry around a heavy steel and glass enclosed space wherever you go. Bicyclists achieve the same transportation functionality simply by dressing for the weather. Another assumption is that you need a vehicle capable of speeds over 30 mph that can go distances over 300 miles. This may be true for travel between cities, but most people most of the time travel at less than 30 mph for less than 30 miles a day within their own city. A typical car is designed for long distance travel at high speeds but is actually only used for short distance travel at low speeds. The tool does not match the job. Current car use is like using a sledge hammer to hammer in nails. This is shameful and will lead to disaster.
Another assumption is that cars need to be wide. Consider that every inch of width of cars adds millions of miles of cement and asphalt to our transportation infrastructure for roads and parking. Since concrete is one of the major sources of greenhouse gasses, halving the width of cars could solve the climate crisis while providing the same functionality. Note that car speed is linked to width and weight, since cars need to be heavy and wide in order to be stable at high speeds. Limiting the speed of cars could also solve the climate crisis, since slower cars can be much lighter and narrower than fast cars.
In order to survive, the automobile industry needs to change its assumptions that cars need to be large, heavy and fast. It makes sense for our car-centric civilization to instead design and use two different kinds of cars: cars for “between city use” and cars for “within city use”. In an ideal world our large gasoline-powered multiple passenger cars would be kept in garages at the periphery of our cities and only be used for “between cities” travel. They wouldn’t be allowed within cities so as to spare us their toxic fumes, noise, and deadly speeds. After gasoline powered cars are outlawed (I’m guessing by the middle of this century), large fast EVs like the current Tesla or Volt would be parked in these peripheral garages. They can be charged by nearby solar farms. This transportation infrastructure might be a great use for former malls.
Smaller cars for “within city use,” in contrast, can easily be powered by on-board solar panels, as the Sun Pony demonstrates. This class of cars would be perhaps 40 inches wide and six feet long. They would have a range of 30 miles at up to 30 mph. Such a car can easily weigh less than 200 pounds, carry four people, and be powered by a small (less than five horsepower) electric motor. Its 25 pound battery could easily be charged in a sunny afternoon by a square meter of solar panels mounted on the top of the car. The solar car solution exists now, but it requires us as a society to bifurcate our ideas about what a car is.
EVs aren’t the answer. A new class of cleaner, lighter, slower and narrower vehicles for use within our cities is the answer.
Filling the Personal Transportation Size Gap
Have you ever noticed that there is a huge size gap in our transportation system between large and small personal vehicles? There are ways of getting around that weigh zero to dozens of pounds (like walking, bikes, skateboards and scooters) and vehicles that weigh thousands of pounds (cars). There are very few vehicles that weigh hundreds of pounds. Why is that?
A lot of the reason for the size gap has to do with the assumption that a car needs to go highway speeds, which, as we’ve just discussed, requires a vehicle to be heavy and wide even though highway driving may only be a small part of how people use a car.
The car size gap makes our cities unsafe. We are so used to this fact that we tend to take it for granted. Large vehicles threaten small vehicles and pedestrians. Large vehicles fill the limited space in our cities. The pollution from large vehicles is changing the weather itself. Isn’t this enough reason to use smaller machines for getting around our cities?
We need to fill the car size gap. We need medium-sized vehicles. There is a great opportunity for the entrepreneurs of America to fill this gap. Ebikes have closed the size gap a bit, bringing up bicycle technology to be a little bit faster, heavier, and more powerful (at a higher cost). Car manufacturers have the potential to close the size gap by producing cars that are smaller and lighter and perhaps solar powered, but consumer expectations of highway speeds and long ranges, and government regulations that define what a car is, have prevented them from doing that. (Note that the Sun Pony very purposefully has three wheels instead of four. Having pedals and only three wheels makes it legally a bicycle.) So don’t expect the auto manufacturers to produce a practical solar powered car. It is up to the ebike industry, and ebike hobbyists such as you and me, dear reader, to close the size gap.
Here are some figures for you to contemplate. Think about how these seven vehicles differ in usefulness for personal transportation within a city, and then compare their width, weight, power, speed and cost. Which ones would you like to drive? Which ones would you prefer other people to be driving in your neighborhood?
How to Build Your Own Sun Pony
Perhaps you have been persuaded by previous paragraphs to save the world by building your own solar EV. Congratulations and thanks! Here’s how I did it.
1. Acquire a Worksman Side-by-Side “Team Dual” Tandem Trike. Worksman makes big heavy over-built steel frame pedal-powered vehicles. They are not elegant machines. It is difficult to ride them up even a small hill by pedal power alone since they are intended mainly for recreational use on level bicycle paths. But augmented with small electric motors they become much more useful as transportation. And they provide a great solid base for a solar EV. Cost is $1899 new. I got mine used for $900.
2. Add motors and batteries. There are several possible places to install a motor on a worksman trike: adding a front wheel hub motor, adding a motor connected to the rear axle with a chain, or adding crank drives to the bottom brackets. Adding a front hub motor is the easiest solution and in fact Worksman sells a kit for that. I know from experience however that front hub motors alone have traction issues and they can add a lot of strain to front fork dropouts.
Adding a motor to the rear axle would require manufacturing a way to mount the motor and to tension the chain (which the Beyond Art Collective did for our Sparky the Rideable Unicorn art car). Not impossible but engineering intensive. The last option, adding crank drives, would normally be difficult for two reasons: the Worksman trike uses back-pedaling to brake which most crank drive motors can’t do, and the Worksman has ashtabula one-piece cranks which have a larger bottom bracket shell than most crank drive ebike motors will fit within. Happily, it turns out both of these problems can now be solved! The back-pedal issue can be solved by using the TSDZ2 mid-drive motor, available from Electrify Bike, that has a clutch for back pedal braking. And happily, Electrify also sells an adapter for their motors to fit an ashtabula bottom bracket. At 750 watts max the TSDZ2 is only half as powerful as the BBSHD mid-drive motor, my go-to ebike motor, but we actually don’t want the Sun Pony to go faster than 15 mph for stability reasons. So the TSDZ2 was a perfect choice. Buy two at $525 each.
Lastly, buy two 52v “shark packs” from a reputable source such as em3ev, Grin or Electrify. Cost is around $500 each. Mount the shark packs on the Worksman trike using Grin’s triple bob battery mount.
3. Add solar panels and charge controllers. The cost of solar panels keeps falling, and there are now many portable panels available. You should be able to get a 200 watt panel for less than $200. There are only a few charge controllers available for charging 52v lithium batteries. I went with the more expensive but rugged $210 Genasun 52v lithium battery charge controller available from Grin.
To attach the solar panel I first welded a frame out of lightweight 1”x1” steel tubing. I then mounted this frame on top of a 1.5" square tubing mast that I welded to the Worksman trike between the seats. I attached the frame in such a way that it can be tilted forward when the Sun Pony is parked and then tilted level when the Sun Pony is in motion.
If you don’t have access to a TIG welder you may be able to rig something up with steel or aluminum tubing bolted together.
4. Total cost about $5,000. Ride around and impress your friends!
I plan to add a second 200 watt tilting solar panel to the front end of the trike to give the Sun Pony a total of 400 watts of charging power.
I plan to add a clear vinyl canopy mounted below the solar panel for better rain protection.
I plan to add a front hub motor for more power but also to provide regenerative braking and a physical disc brake. (The Worksman trike comes with a front wheel drum brake and two coaster brakes that all get pretty hot on Ithaca's long steep descents.) I chose the Grin All-Axle motor because of its torque arm for taking strain off of the front fork dropouts, and for the full-programmable regen features provided by Grin’s Phaserunner controller and their Cycle Analyst display.
I plan to park the Sun Pony outside my kitchen window where I have a solar charging station mounted to the window frame. The charging station powers a 12v electrical system in my house that I use for supplemental lighting and recharging electronics. I plan to eventually use ebike batteries to take my house off the grid.
Judy and I are planning to test drive the Sun Pony on a week-long camping trip later this month. We’ll keep you posted!