How to understand how long it takes a solar panel to recharge the powerbank?
A 20W panel has an amperage of 1.28A (=1280mA).
If our battery has 20 000 mAh
20000 / 1280 = 15.6 (hours)
Long time right? Keep in mind, however, that a day on the road is easily made up of 10 hours, and therefore you will have those hours of sun exposure (in summer). It won’t charge you all the way, but you’ll make it to the next charge point.
Cost: various. From Decathlon, it costs around €40. The most popular is that of Anker, PowerPort Solar, which costs €70.
Sure, but what if it rains? Or if it’s cloudy? The charging time via the solar panel will increase because fewer Watts will come from the sun.
The hub dynamo doesn’t have these problems because it creates electricity from the movement of your front wheel. So even if you just don’t see the sun for 4 days, you’ll still have electricity. The dynamo is most often used for lights, but it can be used, with a power converter, to generate electricity for use elsewhere – like recharging a power bank.
Let’s redo our calculation:
More or less all dynamos require a minimum of about 2W to start recharging, and we can estimate that you have to pedal at about 13-14 km/h to start it.
The dynamo must then be connected to a small transformer which outputs a power of about 5V at 500mA therefore:
20,000 (the capacity of the power bank) /500= 40 hours
As you can see it will take you a while, but the efficiency of the dynamo lies in the fact that at higher speeds, the amperage increases and, therefore, reduces the time it takes to recharge your powerbank. The obvious advantage is that you’re still producing energy, even if it’s cloudy.
In terms of friction and drag, many studies have been done, and the slowdown caused by the hub dynamo is minimal.
Costs: The dynamo system + power converter will cost you around €400-500.