A few years ago, I lived off-grid in Washington state. We had a small solar system that struggled to provide enough power in the dark days of winter. To help with the problem, I got myself a bicycle generator thingy - it was essentially a stationary bike stand that generated power as you pedal. We wired it to our battery and used it to provide electricity in times that the sun wasn’t enough. It came in really handy when somebody needed a shower on a dark, cloudy morning, or if I was in a hurry to get a tool charged up, or anything like that. It also doubled as a regular old stationary bike when I wanted to get some exercise.
Just saying… it was a cool way to supplement our tiny photo-voltaic system. I’d highly recommend it to somebody struggling to rely on the sun for electricity through a gloomy winter.
We were able to generate 200-250 watts with a medium pedal speed. I’d typically ride it only for the duration of whatever we were charging - ten minutes while my partner showered, maybe a half hour if I was trying to charge up a drill battery, etc. The bike we used was a 21 speed, so we could shift gears to adjust the amount of resistance.
For anything else, given the time and calories a bike generator requires, I think it might be more efficient to figure out how to do the job without electricity.
Depends on both the task and the person. I have strong legs but bad shoulders. There are a lot of tasks I wish I could convert to pedal power. Some could, theoretically, be run off the bike directly, with the right adapters. But if you don't have the adapters, using the bike to charge a battery might be a workable second-best.