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1. Sunflyer intro

To promote solar energy, I develop a solar-powered bicycle. On sunny summer days, the solar bike should drive entirely on solar energy. When there is no sunlight or the batteries are empty, it may not cost substantially more energy to drive the solar bike than a normal bicycle. So, unlike most ebikes, which are heavy, the solar bike must be lightweight and sportive.

Soon became clear that the solar bike is a major challenge, only with expensive high tech materials, such a bike can be built. Therefore I use the best components that are available worldwide.

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, solar cell curve tracer and the lightweight bicycle rear rack.

This is the bike without the solar panels, a lightweight 12.5kg e-bike:

2. Solar bike timeframe

• 2009 The solar bike project started in November 2009.
• 2012 The first stage is building a lightweight full-size touring e-bike.
• 2013 ... 2014 Development of the solar panels. I hope the solar-bike will be ready in the summer of 2013

3. How it started

In 2003 I bought a motorcycle from a colleague, an old Yamaha Virago 535. Many years I have driven through the Belgian Ardennes with great pleasure. Although I was not driving fast, it became too dangerous for me and I sold the motorcycle. But, I began to miss the Ardennes. A bicycle was no option; cycling hills up and down in these mountains is not my hobby. An electric bicycle could replace the motorcycle, but the action radius is too small. Than, I got an idea about building a solar bike...

4. 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.

5. 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.

6. 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 300x300 km², see here:

7. Solar bike weight

The total solar bike weight is about 18kg. To fast charge the battery en route, I have developed an 400W additional lightweight ebike battery charger of 800g.

8. 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

9. 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.

10. 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.

11. 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.