Originally Posted by
Trevtassie
Just so you know, pretty well everything you've said here is not well informed.
The efficiency of conversion for most dynamo to USB chargers is now in the mid to high 90s percentage wise. So even if you did want to extract 20W it's not going to take 30-35W watts at the crank.
But 10W is what you'll get from a dyno hub at touring speeds, that's 2A. Over a days riding, if you have that going into a battery it's plenty to keep a phone going and have spare for other things. Over a 6 hour day of riding you'll get around 45-50WH into a battery and/or device. I can't imagine why you'd need 120WH a day when you're travelling.
Solar panels are pretty well useless touring unless you're in a desert or Antarctica because you're often in shade or not riding in the right orientation. Having once carried a fairly decent sized one it was ineffective for the room it took up. Also, the guys who we watched getting their panel, battery and gear stolen when they had to put it in a sunny spot slightly away from their campsite ( because you know, trees) probably don't think solar is such a good idea any more. By the time they jumped up to chase the homeless dude running off with their gear, he had way too much of a head start.
For you to be correct, then manufacturers must be de-rating their specs by giant margins. That’s not a bet I’d make for the cost of a dynamo.
I don’t intend on cycling 6 hours a day for starters. I also have power needs that would put 50WH at the very bottom of acceptable for me. So, a dynamo simply won’t work even if we presume the optimistic power conversion efficiency, output and riding time that you claim is correct.
I also agree that I wouldn’t use a solar panel unless I wanted to be only off grid. But, newer solar panels are more highly efficient and the efficiency is going up fairly quickly. I have a 20W panel that cost $75 and I’m going to be fully testing that next week and then when the sun is higher later in the year.
Otherwise, with the appropriate battery and charger (USB-C PD charger with one of the newer batteries that charges at a high USB-C PD input), you can charge that much or more in a very short time. I have a battery that charges at 30W and is, for example, 34Wh in capacity. Newer batteries are coming out that charge yet faster and the the newer GaN chargers are tiny and light for the power output.
My strategy is to look for outlets and charge the appropriate size battery with a small high power USB-C charger since I’ll be in settled areas. The dynamo set up is expensive and marginal in it’s power output (even using your numbers) and won’t work for either the power needs or the tours I’m planning.