Sunflyer intro
To promote solar energy, I develop a solar-powered bicycle. The solar bike is meant as a challenge to get, on sunny summer days, the most pedal assistance as possible out of 1m2 solar panel. This bike is unique; there are hardly any similar projects worldwide.
Unlike most ebikes, which are heavy, the solar bike must be lightweight and sportive. It may not cost substantially more energy to drive the solarbike, when not powered, than a normal bicycle. When there is no sunlight or the batteries are empty the bike should still be light running. The panels on the image are models from Styrofoam and the model has no motor and battery. The project is started in 2010. I hope the solar-bike will be ready in the summer of 2013.
Because I always come across items that I want to improve, I roll from one project to another. Things that I have developed in that way are the lightweight ebike battery charger and the solar cell curve tracer.
The advantage of the Sunflyer solar bike
Ebikes need large and heavy batteries to allow riding long distances, because the battery is charged only once at home. The solar bike approach is different. The PV panels have enough power and give the bycicle an infinite range. The battery is small, and saves weight. Without sun however, the battery can be fast charged en route in about 15 minutes because LiFePO4 batteries allow fast charging. Although, we need a location, for instance a café, that allow use to use the mains.
What it is not
The purpose of the solar bike is not energy saving. A bike is very energy efficient. The cost of the electrical energy that would be needed to cycle a whole day is no more than 50 cents. In terms of energy savings, this is negligible.
The sun's power
Global CO2 emissions have to be drastically reduced within the next few years in order to prevent a disastrous climate change. This is where DESERTEC offers a solution which can be implemented worldwide: Sufficient clean power can be generated in the world's deserts to supply mankind with enough electricity on a sustainable basis.
The total solar collectors surface (for concentrating solar thermal power) needed to provide the electricity for the humankind is just 300x300 km², see here:
Solar bike weight
The first stage is building the World's lightest full-size touring bicycle. This ebike will be complemented with the solar panels and the electronics. The following tables show the parts with their weights.
Lightweight e-bike
| Parts |
weight [kg] |
| Bicycle |
9.2 |
| Brushless DC motor |
1.8 |
| Battery |
1.7 |
| Electronics |
0.3 |
| Fixations , cables, etc. |
0.2 |
| Total |
13.2 |
Solar panels with electronics
| Parts |
weight [kg] |
| 2 Solar panels |
2.5 |
| 2 Solar panel arms |
0.3 |
| Electronics |
0.2 |
| Total |
3.0 |
Total solar bike weight
The total solar bike weight is about 17 kg. To fast charge the battery en route, I have developed an additional lightweight ebike battery charger of 800g.
E-bikes don’t have to be heavy, this is the World's lightest full size racing bicycle:
Critical parts
Many people who know about solar power say that the bicycle is not feasible. But the calculations I have done are positive. The size of the panels is limited and can not be increased further. As with the cars that take part in the World Solar Challenge, perhaps even more, there is a necessity of using high-tech materials. Building a solarbike can only succeed if all these things are fulfilled:
- Using high efficiency solarcells
- The bicycle should be lightweight and sportive
- The rolling resistance of the tires should be low
- The air drag should be low by riding in a aerodynamic posture
- The use of maximum power point tracking (MPPT) for the solarpanels
- Using a high efficient hub motor
- Using high efficient electronics
- A small battery delivers the energy in case of lack of sunlight
- The motor should only be powered at a speed and power where the motor efficiency is high
Lightweight touring bike
The base will be this light touring bicycle of 9.9kg:
This bike has a carbon fork. Although there exist ebikes with hub motors in carbon forks it is not certain whether the fork of this bike is strong enough. But it is so that the maximum torque on the fork caused by braking is always much higher than the torque a hub motor can deliver.
Solar bike versus velomobile en recumbent bicycle
Another approach to cycle with less power are velomobiles and recumbent bicycles. The solution is based on lowering the aerodynamic resistance. At climbing hills however, velomobiles and recumbent bicycles do not have advantages. Also the view around is hindered because of the low seating position.
Solar bike versus solar cars
To get an idea of the solar bike possibilities, we can make a comparison with solar cars. Solar cars participating in the World Solar Challenge may have a maximum solar panel area of 6 square meters. The solar bike has about 1m2, with solar cells of equal efficiency. The solar cars have an average speed of 90km/h. The solar bike speed is only about 20km/h. So, I don't expect a disappointing experience with my solar bike.
Solarcells
It was hard to get high efficiency solar cells with an efficiency of about 22%. When the solar bike prototype is ready and functioning well, I'm considering to let make solar panels by Gochermann Solar Technology.
Electronics
The electronics consists of three main parts
- MPPT. The efficiency of solar cells is maximal at a certain point of its current / voltage graph. To use the cells constantly at maximum efficiency, a maximum power point tracking (MPPT) is mandatory.
- BMS. LFP batteries don't withstand over-charging and over-discharging. Here we need a BMS (battery management system).
- Motor controller. The motor controller has two tasks. First, because we use a brushless motor, it provides the motor commutation. Secondly it regulates the motor power by a switching power regulator.
Also I made a portable lightweight 360W LiFePO4 ebike battery charger to use during a trip.
