Saturday, May 30, 2009

Solar Bike FAQ

What is the solar panel for?

Would you believe it's for charging my iPod? Mostly it's charging a battery that runs a motor. Think human-electric hybrid. On long trips, I only use it for extra help up hills. On short trips, I use it to boost my speed and reduce pedaling effort. Imagine commuting 10 miles without breaking a sweat. Imagine riding a bike which pulls its own weight up hills so that it feels weightless.

Do you really have to pedal?

While it's possible to ride shorter distances on flat ground without pedaling, I wouldn't want to. I started this project because I like cycling but I don't like climbing steep hills. This is still a bicycle. If I didn't want to pedal, I would have built a solar electric scooter.

Did you build it yourself?

Yes and no. The bike frame is an HP Velotechnik Street Machine GTe touring recumbent. Most of the other components, like the motor kit, are off-the-shelf items. The lightweight, aerodynamic solar electric module is a one of a kind custom job I designed and built.

Can you charge the batteries while pedaling?

I get this one a lot. In theory, it is possible. In reality, it takes a lot of effort to generate a useful amount of electricity. Imagine riding a bike with the brakes on all the time. How fun would that be?

But what about regenerative breaking down hills and in stop-and-go traffic?

Regenerative braking (using the motor as brakes and using the generated energy to charge the batteries) has attained near-mythical status as a source of free, non-polluting energy. It's like the Holy Grail of energy conservation. Regenerative braking makes sense on an electric car because a car is heavy and has a lot of momentum. Because a bicycle is so much lighter, regenerative braking would only add 2-3% to the battery's range.

The added cost and weight simply aren't justified. In my case, I'm using a mid-drive motor with a freewheel on it which allows me to pedal without using the motor or motor without pedaling or do both at the same time. It's a very efficient, safe set-up and has very little motor drag when pedaling. However, the wheels cannot turn the motor. To add regenerative braking I would have to change to a completely different drive system where the motor is integrated into the wheel hub.

BionX makes an electric bike conversion kit with a regenerative braking option. It's easier to implement this on a hub motor rather than the mid-drive motor I'm using. For the technically-minded, here's a great article with lots of numbers for a more comprehensive analysis: Regenerative braking and electric bicycles (PDF) .

What's with the funny looking bike?

Oh, the recumbent? In the earliest days of this design, I envisioned a large, flat solar panel with the rider sitting in a hole in the middle. Here's a sketch of that idea. I though I would need a low, stable three-wheeled platform to carry such a large panel. I figured the panel would need to be that big because I read that a cyclist uses 100 to 200 watts of energy while pedaling and I imagined being able to cruise all day without getting tired. I have since figured out that I don't need a 200 watt panel but that I do need a battery. The panel placement and design have undergone a least a hundred changes since the start of this project. Eventually, I may build a custom bike using carbon fiber composite construction to make it lighter.

How fast can it go?

  • 52 mph (84 km/h) top speed coasting downhill
  • 15-30 mph (24-48 km/h) pedaling with power assist on flat ground
  • 20 mph (32 km/h) batteries driving motor, flat ground, no pedaling (this is the legal limit in California)
  • 8 mph (13 km/h) projected top speed on solar power alone in full sun, no batteries, no pedaling

What's the range?

  • 34 miles (55 km) on a full charge using just the batteries
  • 20-25 miles (30-40 km) a day on solar power with my current solar module (cloudless day in Northern California in May)
  • 40-60 miles (65-95 km) a day on solar power after I finish my next module
  • Up to 150 miles (240 km) a day starting with full batteries, given ideal sun conditions all day between June and August with my current 40 watt module in the rear and a second 60 watt module in the front (under construction). All of these numbers assume mostly flat terrain. Hill climbing can cut all of these numbers in half.

Are you an engineer?

Nope. Would you believe first semester engineering school drop-out? Basically, I'm just stubborn. I refuse to believe it couldn't be done.

How much did it cost?

About US$ 0.25/mile, assuming it lasts 20,000 miles. I have put 3,100 miles on it so far. Put another way, I've spent enough on research and development to buy two or three really nice carbon fiber road bikes.

Don't see your question here? Drop me a note in the comments.


Anonymous said...

Did you consider a hub motor ?

Mark said...

I really wanted a hub motor. They're quieter and the idea of tucking the motor into the wheel seemed like such an elegant solution.

Then I started comparing weight and efficiency and the mid drive motor won hands down. My 500 watt motor (750W peak) weighs 6.5 lbs and gets 12.8 Wh/mile on flat ground without pedaling, 8-12 Wh/mile with pedaling over all kinds of very steep hills.

Another advantage of the mid-drive is that my motor sees all 8 rear gears so I have great torque for starting up hills in low gear and I can cruise along with the motor assist at higher speeds in higher gears, always running the motor at an efficient speed.

Anybody out there with a hub motor care to share their numbers? I would be particularly interested in Wh/mile if you happen to have that figure.

Anonymous said...

Hi again Mark, I posted the remarks about carbon fibre earlier.

Just a quick question, why is it that the solar panels are averse to any shaded areas? that is why the loss of input for a "few" shaded panels? I guess I could look it up but figured you knew this area quite well.

I am interested in the solar cells as my wife and I are building a 40ft catamaran that is essentially along the "hybrid" lines, insofar as it employs solar, diesel electric, regenerative, wind etc power collection.

I guess my question is, why one cannot create an "intelligent" panel, one that can reroute or bypass shaded segments. As you can imagine there are shade problems with sailing vessels, mast, sail etc.

You may be interested to know that I am designing a small shipboard wave (Oscillating Water Column) power system for our boat, it seems kinda silly to let all that energy go to waste.

I'm building a testbed small scale wells turbine at the moment, and we will see if it can be implemented in a practical fashion, I hope it can.



Mark said...

Hey Craig. Good to hear from you again. Upon reading your comment I immediately thought of the "Sustainable Sailing" cover article in the current issue of Home Power magazine (subscription required). It's about a couple with a 37-foot ocean-going sloop with two 80W solar panels and a wind turbine. Lots of great details about their setup. I would urge you to buy a copy.

The shading problem with silicon PV panels is that a shaded cell behaves like a resistor. In informal tests on my first bike panel, shading one half of one cell out of 36 cut the whole panel's output in half. Shading one whole cell cut power output by 80-90%. The problem can be partly mitigated by using bypass diodes. A typical 12 volt panel with 36 cells may have 2 bypass diodes (each connected to 18 cells) so if a few cells are shaded, you still get some power but at only half the voltage. Depending on your setup (charge controller's minimum voltage, number of panels in your array, etc), this may or may not be helpful. Look for panels that are marketed as "shade tolerant" and consider using 2 or 4 smaller panels instead of 1 big one. You may also be able to minimize the power loss by orienting the panels so that your primary obstructions, such as the mast, cast shadows across columns of cells that share the same bypass diode as opposed to rows of cells spanning several bypass diodes.

Not sure if this is clear enough. It's late and I'm getting sleepy. Shoot me an email ( and I'll try to send a less muddled explanation in a few days when I'm more rested.

Oscillating Water Column sounds cool. Maybe your project can be the subject of a future Home Power article?

Anonymous said...

What mid drive system do you use? I have a ecospeed system on my recumbent. I am in the Northwest, so sunny days are limited to May through October.

Anonymous said...

I get 6-9 wh per km out of my mid drive system. 1000 w motor with a 42 v 20 Ah LiFePo4 battery. I am using an Ecospeed system.

Mark said...

I'm using the E-4 Kit. 500W motor (750W peak). Depending on terrain, riding style and tire pressure, I get 8-17 Wh/mi (5-11 Wh/km) while pedaling. I've abandoned the tadpole trike and I'm currently converting an HP Velotechnik Street Machine GTe to solar. I've looked in the EcoSpeed kits and they looks great but I'm heavily invested in 24V batteries, charge controllers, etc. so it's hard to justify the upgrade. What kind of bike are you using? Any pictures?

samsonlovesyou said...

Hi Mark,

Inspired idea first off. I've found your blog most useful thus far.

Mechanically (and HPV) speaking, I'm completely illiterate, and so far you seem to have a better idea than anyone else on the net, so I hope you don't mind me asking a couple of questions.

I'm planning to embark upon a self-sufficient, eco friendly tour of Europe later in the year, so the solar power bike caught my eye. Obviously, I have carrying issues to be concerned with - tents, rucksacks and possibly cooking equipment etc.

I noted your recumbent tadpole trike idea and it got me thinking - what if you were to build a roof on the trike? Even just built on a couple of strong, sturdy metal stands (attached to wheels or panniers perhaps. Maybe even to the frame.)

That way, you wouldn't have to worry about weight distribution. It'd be centred, stable on 3 wheels and instead of spending a long time building solar panels yourself (I can't even begin to imagine how hard that must have been!), you could just buy 80w panel and attatch it to the roof.

Think it would work? If so, think I could work with it on the tour?

Also, I noticed you asked about hub motors and found this....

Attatch it to the rear wheel of a tadpole?

Feel free to contact me on if that's easier for you.

Thanks Mark!

samsonlovesyou said...

The link I posted doesn't seem to be working, but you can bring up plenty of similar ones by searching for:

"1000w kit bike"

on Ebay.

I'd give you the details to you myself, but most of it's Greek to me...sorry!

Mark said...

Hi Samson,

Glad to hear you got something useful from my blog. Good luck with your tour.

I did a 2000 mile bike trek across Italy a couple of years ago and it was a great experience. No solar and no electric assist but I did lug a tent, sleeping bag and cooking gear up a lot of hills on my Surly Long Haul Trucker (upright road bike). From that experience, I developed an obsession with keeping weight down and that's what drove me to build my own panel.

Keep in mind that an 80W panel designed for rooftop use weighs 8-10 kg (16-20 lb). It will take very sturdy supports and some engineering to protect the panel from shocks and vibrations. I was particularly concerned with raising the center of gravity of the whole bike too high because I enjoy going fast and aggressive cornering.

Another challenge with electric assist on long distance tours is balancing weight and range. If your assist only last 50 miles and you want to go 100 miles in a day, you will have to work very hard to haul all that extra panel, motor and battery weight for the last 50 miles. I'm still working on finding this balance. The most I've done on my setup is a 90 mile day trip and commuting to work 20 miles a day on solar power.

My advice: start now and plan on having the bike ready a couple of months before you head out on the road so you have time to work out the bugs and learn to adopt to the benefits and disadvantages of an electric bike.

Here are a couple of photos and one video of canopy/roof mounted solar panels on bikes that I've found in my travels on the internet:


Kapil Nirmal said...

I am a final year engineering graduate in India. In my final year project we are working on solar powered bicycle.
I want to know how to calculate the required solar panel power for my bicycle.
I am using a 24V, 250 Watt BLDC- hub motor, which is powered by 24V, 15Ah Baterries.
Please suggest me how to calculate the solar panel power.

Mark said...

Hello Kapil,

I'm excited to hear about your project and wish you luck in your endeavors.

Here's my recommendation for figuring out the required solar panel size.

1) First, you will need to determine your bike's energy efficiency in Wh/mile (or Wh/km). Mine is about 8-20 Wh/mile but you may get anything from 5-30 Wh/mile (8-48 Wh/km). I recommend determining this number from actual experiments - riding the bike with a watt-hour meter attached rather than relying on theoretical calculations. Many factors affect this figure including tire pressure, rider and bike weight, riding style (slow/fast, lots of stops and hard acceleration or even pace, etc.), terrain (hilly or flat?) and amount of pedaling effort.

2) Determine how far you want the bike to be able to go in one day under the conditions you tested in part 1 above. 20 miles? 50 miles? 200 miles? This will tell you how watt-hours you need per day.

3) Starting with a fully charged 24V 15Ah battery pack, I would expect about 250 Wh of usable energy if the battery is lead-acid chemistry and maybe 325 Wh if it's LiFePO4. The rest of the energy you need will have to come from the solar panel.

4) You will need to know how many sun-hours are available in your location for the current month. Note that this is not the number of daylight hours but the equivalent of full sun during the course of the day. Here in Northern California, we get a year-round average of 5.5 sun-hours a day for a south-facing fixed-tilt panel. During the peak of summer, a dual-axis tracking panel will see over 11 sun-hours a day.

Assuming the sun is high in the sky when you are charging the bike, the best panel orientation is facing straight up and the best time is right around noon. If you will be charging the bike during parts of the day or parts of the year when the sun is lower in the sky, you will want to have the ability to tilt the panel so it is perpendicular to the sun's rays. If you are building the bike for a race that follows a mostly North-South route, you will probably want to put the panel(s) on the front and back of your bike. If it is an East-West route, you will want the panel(s) on the sides.

Assuming ideal solar conditions, you can expect somewhere around 70-80% of the panel's rated output to be converted to usable energy (charge controller losses, battery charging/discharging inefficiency and other design factor such as less-than-ideal panel tilt all add up).

Hope some of this is useful for you project.


Bill Owen said...

This project is amazing and exactly what we need. Some economists are predicting $8 a litre gasoline when the economy recovers. The day of the personal IC vehicle is almost over. HPV's are the future.

Have you thought about trying to get some gubbmint money? Maybe if you offered to create some jobs in Detroit?

bhanu255 said...

hey mark i want to buy a solar bike for myself. suggest me which is a good india.

bhanu255 said...

hey mark, this is sunil i am planning to buy a solar bike for myself. please suggest me. i stay in india.

Mark said...

Hello Sunil. I'm not aware of anyone selling solar powered bicycles anywhere in the world. The closest thing I've found in my internet travels is something called The Hauler. The website lists a price but also indicates that it's "Out of Stock". If you find another solar bike for sale please let me know so I can share the info with others. -Mark

Mads Lindstrøm said...

Hi Mark,

You write:

Mine is about 8-20 Wh/mile but you may get anything from 5-30 Wh/mile (8-48 Wh/km).

Have you not used multiplication where you should have used division (or the other way around). I mean it cannot be right that it takes more energy 8-48 Wh to go a kilometer, than it takes to go a mile (5-30 Wh).

But fantastic bike you have made.


Mark said...

Right you are. I guess I'm used to converting miles to kilometers and getting a bigger number but in this case it should be smaller. I would also revise the upper part of the range I gave earlier so the new numbers should read: may get anything from 5-50 Wh/mile (3-30 Wh/km).

Mads Llindstrøm said...

Hi Mark,

A bit off topic. I can see you have a wind-screen (front-fairing) on your bicycle, and I was wondering what your experience is with a wind-screen. Do it give you more speed? Or is it primarily a whether proofing thing?

I ask, as I own a recumbent myself and was considering buying the wind-screen from HP Velotechnik (see ).


Mads Lindstrøm

Mark said...

Hi Mads,

Good question. My real motivation for getting the front fairing was to use it as an attachment point for a solar front fairing I'm planning to add to the bike. You can see a rendering of such a design here.

Although I have not attempted to quantify the aerodynamic benefits of the front fairing (such as by doing coast-down tests with and without the fairing), my impression is that it does very little to reduce drag. Based on what I have read on recumbent racing sites, a well-designed rear fairing (tailbox) can do much more for increasing speed.

My current front fairing was very nice this winter for keeping my toes warm and dry. I live in the San Francisco Bay Area and it rains here in the winter though temperatures never go below freezing.


Mads Lindstrøm said...

Hi Mark,

Have you considered doing like this guy: (the Discovery video). He is putting the solar panels in the wheels. But you properly need panels which are highly shade resistant - or maybe a few panels places, electrically, in parallel.

Mark said...

I've posted a detailed response here.

Unknown said...

Hey Mark,

I'm a senior at Thomas Jefferson High School for Science and Technology and am beginning my year long research project. I'd like to build a solar/pedal hybrid recumbent and you seem to have a lot of experience. Would you be willing to give my groupmembers and me some advice about motors, panels/cells and batteries?

Shoot me an email if you're willing-

Thanks a ton,

alan said...

This is great. I have a street machine GTE. Do you have anymore details, photos, notes! ...etc ..:)
p.s. I'm in the UK.

Mark said...

Love the GTe. I put 4000 miles on it in 10 months. Finally killed my mid-drive motor after 7000 miles so now I'm changing it over to a BMC 600W geared hub motor. It's quieter, has more torque and speed and it's more efficient, much to my surprise. What kind of notes are you looking for? The only photo of the Street Machine are in this album.

alan said...

I'm just looking for someone to copy! ... I hope your going to blog your BMC hub build ... otherwise I'm gonna be lost! ... Are you gonna put this bad boy on the front? ..

alan said...

Have you got any photos showing the mounting of the E-4 kit onto your Steet Machine? Was it a nice clean install?

alan said...

Just had a email from HPVelo. They have sent me a data sheet for a BIONX (pedelec electric assist) ... email me if you like and I will forward it to you for interest! .. (btw I dont make kitchens. I make music!) .. :)

Anonymous said...

Hi Mark, your solarbike website is very instructive. I’m jealous about your skills.

I’m also making a solarbike. The base is an upright Koga light touring bike (Terraliner). Instead of the common ebikes, which are heavy, de solarbike should be lightweight. It may not cost substantially more energy to drive the solarbike (not powered) than a naked bike. I need the solarbike to cycle longer distances and hills with less musclepower.

Limitations by law in the Netherlands
The maximum width is 75 cm, maximum speed 15,6 mile/h (25 km/h), maximum power 250 W.

The goal is a solarbike, including solar panel, motor etc. of about 33 pound (15 kg).

50 W musclepower should be enough for pedaling 11 mile/h (18 km/h). 50 W motorpower means doubling the power.

The panel will be about 24 x 32 inch (60 x 80 cm). The maximum power is 50 W which is actually insufficient but I haven’t better cells yet. The solarcells are string ribbon polycrystalline from Evergreen. Efficiency 13 %, 145 Wp/m2. I’m looking for better cells (Sunpower, efficiency 22%). The panel can be made of a honeycomb sandwich.

Here are some lightweight hubmotors:
2,45 kg, front wheel geared hub motor with freewheel, Model V-mini
1,6 kg, front wheel geared hub motor with freewheel, Model Q-F-85SX

First I will look how the solarbike will perform without a battery. Because the solarbike is lightweight it is not dramatically if there is temporarily no sun. Besides, I cycled 40 years without solar power.

First I will look how the solarbike performs without or with simple electronics. I can add things like a maximum power point tracker later. All electronics should be lightweight and have high efficiency.

Schwalbe Marathon Racer 40-622 has a low rolling resistance and is only 430 gram. Also very durable. I use them on several bikes.

There have raised many questions after reading your website:
Building a solarpanel which is light and stiff isn’t easy.
How did you build the flat rear panel:
What are the size, weight, maximum power, real power and efficiency?
Is it a sandwich construction?
Where have you bought the panel materials?
What type of solarcells do you use?
Can you show me how it is mount to the bike with photos.
How does it perform vibrations and wind?

avandalen said...

The post was from avandalen

Mark said...

Hello, avandalen. Thank you for your kind comments. I'm glad to hear that you were able to benefit from my experiments and mistakes. Having tried quite a number of unsuccessful ways to build a solar bike, I like to think of myself as an authority on how NOT to build a solar bike. Remember, success means trying one more time than you have failed.

I'll try to address your comments in order...

I think you'll find that building an electric assist bike that does not weigh significantly more than an unassisted bike is a challenge. The small 250W hub motor is a good start. The goal for my own project has been extended range and I've found over time that weight is not a critical design factor. Adding a second battery pack may add 10 kg but if it extends range by 60 km do I really care about the weight?

50W muscle power is not enough to maintain 18 km/h. Even on flat ground with skinny, high-pressure tires you're going to need 100-150W to maintain that speed.

50W is a probably the biggest size panel you would want to attach to an upright bicycle. However, I would caution that a panel rated at "50W" only puts out that much power under laboratory test conditions. Typically, this means "standard test conditions = STC" or 1000w/sq m irradiance and 25 C cell temperature. That level of irradiance only happens on a very clear day, close to noon and the panel must be pointed directly at the sun. Since the cells are dark and heat up in the sun, this would require an ambient air temperature of around 5-10 C. In warmer weather, the voltage goes down. In reality, you will typically see something like 35-40 watts from a 50 watt panel.

Now for the questions...

How did you build the flat rear panel?

Dual junction GaAs off-spec satellite cells from eBay, laminated with Tedlar back sheet, room temp vulcanizing optical sillicone above and under the cells and polycarbonate top layer. The next panel I build will use vacuum bagging to improve the power to weight ratio.

What are the size, weight, maximum power, real power and efficiency?

Panel size is about 44 x 70 cm, about 1.9 kg, 40 watts coming out of the charge controller on a hot day (probably would be rated at 55W STC?), individual cell efficiency is somewhere in the 20-25% range. I don't have sophisticated test equipment to measure individual cells under STC.

Is it a sandwich construction?

Yes, using fiberglass skins and baltec mat inner layer. Next version will use Carbon fiber skins with Nomex honeycomb contruction.

Where have you bought the panel materials?

Fiberglass and epoxy tools and materials from a local store. Everything else is too specialized to find locally. Much of it came from eBay, the rest came from various internet sites. Some were industrial samples requested directly from the manufacturer.

Can you show me how it is mount to the bike with photos?

Here's the only photo I could find. There's an aluminum tube connected to the bike and the panel had a matched tube made of fiberglass. A quick-release clamp allowed for locking the panel in a rotated position.

How does it perform vibrations and wind?

On the trike, it did bounce around quite a bit but I never noticed it while riding (only when I watched someone else ride it) and it didn't seem to harm the panel. Wind wasn't an issue because I usually locked it in the horizontal position while riding. said...
This comment has been removed by a blog administrator.
Unknown said...

Hi. I thought the solar bike idea was really cool, and I want to make my own, but I was confused about something. I was thinking of using a 24volt motor to move the bike, but if I can acquire enough energy from the solar panels themselves, why not just use the solar panels alone to power the motor?

I could use either 6 of these panels in unison, or I could use 2 of these panels . Wouldn't something along those lines work?

Unknown said...

Sorry. My links didn't work. but the first example was of 6 panels of output of 4volts each, and the second was 2 panels of 12volts each.

P.S. Sorry if this sounds like a stupid question. It just sounds like that makes sense to me.

Mark said...

Hi Lee,

I spent the first six months trying to figure out how to power the bike with just solar panels and no batteries so I completely understand your intention. It seems so compelling - no complicated charge controllers or heavy batteries, just a couple of solar panels and you're riding on sunshine, right?

If that's your vision, you should pursue it and disregard anything else I tell you.

My own attempts to achieve that goal have resulted in three different bike conversions and over 10,000 miles travelled in 3 years. You should consider that if the motor is getting less than about 150 watts of power, you will hardly be able to tell that it's working. For hill climbing, I would recommend a minimum of 300 watts. In order to get 150 watts, you will need solar panels totaling at least 200 watts because the nameplate rating of a solar panel is based on completely unrealistic temperature and irradiance conditions (25 C cell temp and 1000 w/sq m irradiance). This might happen on a very cold, sunny day for a couple of hours around noon but most of the time you will see much less because a warm solar panel produces much less power and a panel that isn't directly facing the sun is getting less than 1000 w/sq m of sun.

I'm currently working on the fourth version of my solar bike. My goal is to build a touring bike that can travel 100-150 miles per day with a camping gear and be powered entirely by a combination of sun and pedal power without plugging into the utility grid for additional charging. Such a scenario requires batteries to store the sun's energy when I'm not moving. For less ambitious projects, I would recommend starting with a simpler battery-powered electric assist conversion and consider adding a small solar panel to help extend the range a little bit.


Unknown said...

Okay. I had the idea for a solar charged battery as well, because it would be useful for cloudy days or night riding, but for the moment I want to stick with no batteries to see what results I can get from sun only. Although I don't know much about electrical physics, because I'm 18 and only ever took one physics class and didn't pay attention (now I realize that I should have), and I don't know about how to find a solar panels wattage, because all the ones I look at online talk about amps and volts only. Also how do you convert watts to kinetic energy to pre-calculate the potential speed of the bike?

Mark said...

I didn't know anything about solar when I started this project. I learned by reading everything I could get my hands on and through trial and error. I would be suspicious of anyone selling solar panels without advertising the wattage rating of the panel they are selling. You can calculate the wattage by multiplying Vmp x Imp. Be careful not to use Voc x Isc. Also, see the post I wrote about selecting solar panels for a bicycle.

Wikipedia has some numbers on energy efficiency of bicycles. Your actual results will be greatly affected by bicycle and rider weight, hills, tire pressure, headwind, motor efficiency, etc. I currently use a 600 watt BMC hub motor and typically ride at 25 mph on flat ground using 600 watts of motor power plus pedaling. This is on a relatively heavy recumbent.

Unknown said...

Thanks so much for the help. I might not be able to do this right away, because I'm going to college in a few weeks, and I need to keep my cash, but I will keep your site bookmarked, and I will continue researching this topic. Maybe after college I can do it. Although by then the solar panels might be cheaper and more efficient anyway.

Albert said...

Mark, I will invite you to my new website, where you can view my solar powered bike. In the summer of 2011 the bike should be ready, I hope.

Albert said...
This comment has been removed by a blog administrator.
Unknown said...

Hi Mark,
I can arrange VC for you,Can you please send your email

SunandFun said...

Reference regenerative braking systems-- How about a mechanical spring system that discharges is 20 or 30 seconds at start up just to get you going. Recharges itself only when you brake.

Anonymous said...

Hi, I work for a East Africa Destination Magazine and we are doing a story on solar powered gadgets. We would love to refer people to your blog, if that's all right, and would love if you had any high resolution photos available for publication. Please send them to
Thanks so much,

jjj said...


We are a couple that would like to go around the world by solar bikes to promote the solar powered bike.

If you are interested, please contact us. Thank you.

Unknown said...

Goodness me so much to learn. Even posting a comment here. Hello Mark, I'm sure this site will become a friend I reference often, but at the moment please forgive me if what I'm doing is against any protocols.
Ok I bought an old e-bike at a garage sale for $10 24v 200w chain driven motor and 2 dead sla batteries which i replaced.
got it going and just love it. I then found a bike trailer, very light, for putting kids in. Apparently can take a load of 50kg plus. I'm in Queensland Aus a very sunny place. Just about to buy a 250 w solar panel at about a dollar a watt, weight 15kg which i intend putting on the trailer and am hoping for performance about the same as I get from the present set-up. Initially I was going to get some lifepo4's but realised that solar would work well with the lead acids and would be more fun too!Tilting the panel in any direction on the trailer would be very easy to accomplish. The 200 w rating for the motor is only possible when the batteries are fully charged. With a 24v bench supply powering the bike it only sinks about 6 amps with the brakes nearly stalling the motor so i thought that even if the panels rating of 250w is a bit generous, I might have enough up my sleeve especially considering the almost overhead summer sun here. Any thoughts? Am i expecting too much?
cheers Clive. (veteran e-biker)

Mark said...

Hey Clive. Sounds like a great project. Couple of thoughts here. Don't trick yourself into thinking that a trailer eliminates the weight difference between SLAa and LiFePO4s. The SLAs are economical but at twice the charge at half the weight, LiFePO4s pack a lot more punch and you don't have to haul all that weight around. Main thing is to size your battery pack for your target range that you wish to travel on a charge.

Size your solar panel based on how long you're willing to wait to recharge your batteries. Do some research on what the "250W" on a solar panel really means. Even in Australia, a "250W" panel will only output about 200W under the sunniest conditions and much less at all other times. Hint: PV power output is a function of cell temperature and irradiance, not just irradiance. Don't rely on solar to run your motor. Use solar to charge your batteries.

Put a lot of thought into how you're going to mount this heavy, fragile, expensive solar panel to your trailer or bike. The panel is not designed for the kind of vibrations you're going to be subjecting it to so you'll need to isolate it from all the bumps. Good luck!

Anonymous said...

Hi Mark!

Very interesting project! I might add a solar panel to my etrike one day to extend the range and/or charge when no wall plug is in sight.

If you don't know them already, here are some pretty usefull links to determine speed and range of an ebike.

-Bicycle Speed and Power Calculator:
-Hub Motor and Ebike Simulator:
-Electric bike trip simulator:


Sunil said...

I have an electric bike, i wish to transfer it as a solar & electric combo application. The bike has 3 batteries of 12 volts which are charged by 230 V / 5 Amp AC supply

Albert said...

Dear Mark Havran,

Thank you for your nice photos from Italy, professional quality!

One post from me is in conflict with something else, can you please remove this post:

Best regards,

Albert van Dalen

63alfred said...

I have been looking at this blog for a long time wanting to convert my electric bike to a solar powered one. I have this fantasy about doing a cross country ride on my electric-assist bike. I have been riding and refining my electric-assist bike for 3 years now. The current configuration can be seen at:
My bike, now equipped with a Cycle Analyst from Grin Technologies of Vancouver, BC, get between 11 and 9.6 Wh/mi when peddling the 12 mile round trip to work here in hilly Seattle. I assume that I could get more on the flats.
An electric-assist bike make biking so much more enjoyable.
Do you have any additional sources for the components to make my bike solar? I assume that all I would need is to buy or fabricate the panels then wire them to my battery via a 12v to 36v charge controller.
Any suggestions you would have would be greatly appreciated.


Unknown said...

Hi Mark,

I envisioned a long bike using a solar panel (flexible and aerodynamic) to keep your legs dry and increasing cycling power a bit. As I read in your post 40 watts are probably the most you can get in sunny weather. On the other hand, when the machine is out all day, it may be a lot more since you are charging the batteries the greenest way.

When adding 40 watts, speed would probably go from 30k/h to 33k/h. When adding 200 watts you may drive around 40 k/h !

What did you use to make your solar panel?

Cheers, Hubert

Mark said...

I've got some older posts here about my attempts to create a lightweight high-efficiency solar panel for use on an electric assist bike. In hindsight, while these attempts were instructive in that I learned a great deal about what works and what doesn't work, in the end they were largely futile.

The relatively recent availability of flexible solar panels made with SunPower cells at around US$2/watt makes all attempts to build your own panels from scratch obsolete. Unless you're building a solar race car as part of a university team, your best option today is to go to and search of "flexible sunpower". That's what I'm doing for my next solar bike project.

Good luck with your project!

Unknown said...

What was the material of front transparent panel you used?

Mark said...

It's a polycarbonate fairing sold by TerraCycle.