“How big does my solar panel need to be?” is the first question every new solar rider asks. The answer depends on how far you ride, where and when – but one simple formula gets you surprisingly close.
The formula
Energy per day = panel watts × peak sun hours × efficiency factor
Peak sun hours are the hours of “full” sunshine a day adds up to – in central Europe roughly 5 in summer and about 1 in winter. The efficiency factor covers heat, cable and controller losses and, above all, the angle: a panel lying flat on a moving bike reaches far less than one tilted towards the sun.
One example
200 W of flat-mounted panels on a summer day: 200 W × 5 h × 0.6 = 600 Wh. A pedelec uses roughly 10 Wh per kilometre, so that is about 60 km of assisted riding – from sunshine alone. In spring, autumn and winter the numbers look very different.
Rules of thumb
- Panels rarely deliver their label power – plan with less.
- On a bike, available area is usually the real limit, not budget.
- Every extra watt adds weight, and weight costs range.
Consumption depends on terrain, load and assist level – see calculating solar e-bike range and Wh, Ah and volts. If you ride mostly from home, a plug-in balcony system may be all you need. Real numbers from the road: the Sun Trip riders and our solar e-bikes.
