I've got a dual dynamo/drum-brake hub, the Sturmey Archer X-FDD. It works quite well-- but only at normal biking speeds. Below 10mph it's flickery and annoying.

I've got a dual dynamo/drum-brake hub, the Sturmey Archer X-FDD. It works quite well-- but only at normal biking speeds. Below 10mph it's flickery and annoying. If a horse isn't in a hurry, it usually travels at a walk, which is something like 5mph. So bicycle dynamos won't work well for a buggy.