Solar panels electrically

The power from the solar panel depends on:

Solar cell efficiency. The power of the highest efficiency solar cells is 240W/m2 at standard test conditions (STC).These conditions are: irradiance 1000W/m2, air mass 1.5 and cell temperature 25 °C.Panel angle. The angle that the sun hits the panels changes the amount of exposure. Because the solar panels are flat mounted and not faced to the sun, the power is always lower than rated. However, the fact that the sunlight is diffuse, limits this effect.Solar cell reflection. The power will be reduced by the solar cell reflection. The protective top layer should have a low reflection coefficientFull overcast clouds and veil clouds limit the sun radiation a lot, but it has been found out that at half cloudy days the solar bike performs well.Shadow. To understand the power loss effects of shadow, see the article about bypass diodes.

Shadow

In practice the PV panel shadow isn't really so bad. The cyclist is sitting somewhat hunched over on the bike, it isn't an up-right bike. I've taken pictures of the shadow at different sun angles. In most cases there is no shade or just a little bit. With a proper design of the PV panel, with bypass diodes, the power loss due to the shade is no serious problem.

Soldering solar cells

Soldering solar cells requires a soldering tip with a flat surface:

Wind aspects of concern

The air drag is low for a flat plate that is horizontal to the apparent wind. But when the panels are pitched by just a degree or two, this leads to a significant increase in force. In essence we have two inefficient aircraft wings that will generate some lift. This lift will act at a vector that is perpendicular to the apparent wind, not perpendicular to the surface of the solar panels, so will act to unbalance the bike. It will also create induced drag that is proportional to the lift generated, adding to the form drag we have from the projected frontal area of the panels.

Cross winds are the problem here, or more specifically, the vector sum of the side wind and the apparent wind caused by the motion of the bike. The force needed to unbalance a bike, by taking it outside the range of corrective moments that the rider can provide by shifting body weight is pretty small. The lift force vector will change direction extremely rapidly as the bike rolls, going from a maximum positive to a maximum negative value in a short time interval as the panels go from a positive to negative angle of attack relative to any side wind component. A known issue at racing bicycles, is the severe impairment of the steering that comes from using a disk wheel in a crosswind.

To avoid serious problems, the panels may not exceed a certain size and the wind force may not be too large. Although, the area of the PV panels is not much larger than the cyclist frontal area (0.5m2). So I don't suspect much wind problems anyway.

Further weight reduction

The battery charger runs at a frequency of 28kHz. By increasing the frequency, maybe a smaller transformer T2 and inductor L2 can be used which reduces the weight significantly. 

It has to found out if a lighter battery charger, for instance the 180W version, can be tuned from 3A to 8A. The weight can so be reduced to about 500g. Here we can change among other D15 by a Schottky diode and Q1 and Q2 by power mosfets. A smaller housing is the Hammond 1591-DGY, 150 x 80 x 50 mm, weight 128g.

By using high switching frequencies, a power-to-weight ratio of 3kW/kg can be achieved; so a 36V / 10A charger only needs to weigh about 250g.

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.

weight [kg]

Take action against obvious hardware and software patents

One could do on large scale requests to Microsoft to use their brilliant 'IsNot' idea in license. This has yet to be worked out. If you want to help me with this initiative please contact me.

Low rolling resistance tires

Normally, low rolling resistance is achieved by using thin racing tires under high pressure. But the disadvantage is that it exposes the bicycle and its rider with strong vibrations. The solar bike with its many extra components must be protected against vibrations. We can use a feathered bike. But the feathering cost energy and makes the bike unnecessary complicated and heavy. Another approach is the use of thick tires. This is a lightweight and simple solution that gives sufficient damping of vibrations.

My experience is that the Schwalbe Marathon Racer 40-622 tire has a low rolling resistance and is very durable. The weight is only 430 gram. I use this tire on several bikes and I have almost never a flat tire.

Weight for one PV panel

Practical limitations

Note that we need optimum circumstances to ride on solar power, there are many limitations:

• The solar bike is a bike, not a moped. Normally, we have to pedal and the motor give only assistance.
• The bicycle is definitely not a bicycle with impressive performance. The power is small compared with the 500W ebikes used in other countries.
• We require full sun in summertime else the solar bike is not useful. In the Netherlands the solar bike can be used maybe 20 days a year.
• Time of day. Because of the sun angle we can only get sufficient power from the solar panels between about 11:00 am to 4:00 pm.
• Time of year. From October to April the sunlight is not strong enough anymore to deliver energy to de bike.
• Wind is a critical factor. Beaufort 3 (12–19 km/h or 8–12 mph) is already problematic.
• For uphill cycling support, solar energy must first be stored in the battery. This is only possible if we have cycled considerable time without support in advance.

Zonne-energie in Nederland

Zonne-energie in Nederland om elektriciteit op te wekken heeft niet zoveel zin. De opbrengst in Nederland is veel te laag in vergelijking met de kosten van de zonnepanelen. Het is symboolpolitiek, en meer een kwestie van uitdelen van subsidie dan werkelijk een oplossing zoeken voor het energieprobleem. Het geld kan beter worden geïnvesteerd in projecten als Desertec, die zonne-energiecentrales bouwt in de Sahara.

LX2400

To promote solar energy, I develop a solar powered bicycle. This bike is unique; there are hardly any similar projects worldwide.

The use of high-tech components, such as low loss bypass diodes for solar cells, is crucial to successfully finish the project. The bypass diode with the lowest voltage drop is the LX2400, so I will use this one. Read more about the LX2400 HERE.

I would be very grateful if someone can help me to get LX2400 bypass diodes.

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

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.