During a typical bicycle ride (30 km in a hilly region), about 200 watt-hours are used by the battery of an electric bike. In order to fully re-charge two bicycles (this is usually the case for caravan owners), the on-board battery has to supply a charge of about 50 Ah for these two batteries.
If you take a typical on-board battery with a nominal capacity of 80 to 90 Ah, considering that the actually available capacity is generally 50 to 70 Ah, depending on the state of the charge, you will quickly realise that, after charging two bicycle batteries, the on-board battery will be nearly or fully exhausted.
This is made worse by the fact that charging the bicycle batteries takes place in the evening or in the night, with the consequence that there is little or no support from a solar generator. A fuel cell is a good solution to compensate for the performance deficit of the on-board battery.
