Yeah, good point. The OP said he'd like to avoid charging batteries. In that case, I would recommend a dyno system. You can read about my system, and you can buy from Peter White or one of the vendors I mention in my article.

Jogalite's reflective products are excellent. They reflect well, and they last a very long time. I have some of their stuff from 32 years ago. I'm not kidding. And yes, I have used them a lot over the years. I recently bought this triangle and wear it on my back. It's comfortable enough that I barely feel it. A vest might be a good idea because it's visible from the front and hopefully the sides.