I have used them to power lights and nothing else...yet. The drag will vary with the load and the quality of the hub. However even on the less expensive hubs on the market now the drag is not that noticeable. IMHO a dyno hub is going to be a better choice than solar, it will put out power as long as it is moving. With solar you have to have a certain angle and no clouds to get maximum output. The other option is to use the rechargeable battery packs. I know a couple of people that have used these with good results. They only have to recharge them once a week or so.

Aaron