How to choose solar panels?
What are the differences in energy performance of panels from different manufacturers?
Can the technical specifications indicated on the panels be trusted?
So many questions that solar bike designers ask themselves.
As we will see below: the specifications mentioned on a label do not always hold true. The purpose of this article is to inform on this point of vigilance because on a bike, the weight and the surface of panels are limited. However, this article will not mention any sign brands for the sake of commercial neutrality.
Test protocol
We made the charge measurements of a battery previously discharged to 50%, exposing each panel in turn on a very sunny day in June.
The same charge controller was used for each panel. The table below shows the power measured under these conditions for each panel. Panels 1, 2 and 4 have the same dimensions and consist of 30 cells. Set 3 includes 2 panels of 50 Wc, consisting of 16 cells each.
Results table
| Format | sign | Specified power (manufacturer) | Measured power | Ratio Measured Power / Power Panel C | Price |
 | Panel 1– cell manufacturer: not specified – cell grade: not specified but visible defects: cracks, broken corners… | 100 Wp | 43.6 W | 51,8% | 135 € |
 | Panels 2– cell manufacturer: not specified – cell grade: not specified | 2×50 wc =100 wc | 44.7 W | 53,1% | 285 € |
| Panel 3– cells: Sunpower™ Maxeon – cell grade: B | 100 Wp | 84.2 W | 100% | 175 € |
| Panel 4– cells: Sunpower™ Maxeon – cell grade: A | 110 Wp | 89.7 W | 106,5% | 340 € |
Comments
- The power specification mentioned by the manufacturer is sometimes very far from the measured reality (panels 1 and 2).
- A high price is not always an indicator of panel quality (panel 2).
- Some panel manufacturers mention the manufacturer of the cells (panels 3 and 4). This is an important element to know.
- Very few manufacturers mention the grade of the cells used, even though it is a determining factor.
Reflection
One might have thought that the difference in production from one panel to another would be small (10%) but we realize that it can be very important: up to 50% in this example. For a solar cyclist, it is a shame to equip yourself with panels that produce half as much energy. We could compensate by increasing the number of panels but we would increase the weight of the bike (panels + support structure). This would have a negative impact on the vehicle's energy consumption, maneuverability etc …
Conclusion
It's a good idea to look for reliable and independent sources of information before deciding on a purchase.