On a house roof, shade is predictable. On a bike, it is everywhere: trees, buildings, your own body, a handlebar bag. Partial shading is the biggest hidden loss in mobile solar – and it is often far bigger than people expect.
Why a little shade costs a lot
The cells in a panel are connected in series. Like links in a chain, the weakest cell limits the current of all the others. Shade a small part of a panel and its output can drop out of all proportion to the shaded area.
What bypass diodes do
Most panels contain bypass diodes that let current flow around a shaded group of cells. They prevent the worst losses and protect cells from overheating – but the shaded section still produces nothing. How many diodes a panel has makes a real difference; check the datasheet as described in reading a datasheet.
Several panels make it worse – or better
Panels wired in series share the shade problem: one shaded panel slows the whole string. In parallel, each panel works on its own. A good MPPT controller also matters, because shade can confuse simpler tracking.
And the angle?
A panel facing the sun directly produces much more than one lying flat, especially in the morning, evening and outside summer. Curved flexible panels never face the sun with all cells at once.
Simple habits that help
- Park in the sun and turn the bike towards it at breaks.
- Keep bags, jackets and cables off the panel.
- Keep the surface clean – dust and pollen add up.
See how much this matters in practice with the riders of the Sun Trip.
