Interesting discussion about the pros and cons of a dyno hub. I’m sure Steve has put a lot of thinking in this.
On weight terms, I’d argue that the case for battery lights is not easy to make. The differences are minor, as the following comparison shows. I exclude rear lights, which for convenience reasons may be battery lights anyway.
A Tune MIG 45 road front hub – one of the lightest available on the market - weights 45 gram. A Hope Vision one weights 110g without batteries. Assuming Steve carries a set of spare batteries per lamp, batteries add 216 gram (one Eneloop weights 27 gramm, the Vision one uses 4 batteries). Assuming he is carrying two Vision One, total weight of headlights and batteries is 652 grams. The 45 grams for the hub brings this to 697 grams,
A SON deluxe weights 392 grams, the Edelux II weights 85 grams. Throw in 20 grams for cabling and the mounting bracket, and the total weight is 500 grams. Carrying one Hope Vision One with one set of batteries as a backup (218 grams) lifts the total weight to 715 grams.
The point that a damaged dyno hub front wheel may be harder to replace is not too compelling either. In emergencies, Steve could always switch back to battery lights. Moreover, a spare dynamo hub wheel does not cost the earth, relative to the overall costs attached to the whole project.
The drag may be an issue – according to Schmidt’s website, the SON deluxe consumes about 5.5 watt at 25kpm when the lights are running (first graph:
http://www.nabendynamo.de/produkte/SONdelux.html). That may be 3 to 5 percent of Steve’s total energy. When the lights are off, however, it consumes less than 1 watt.
According to Schmidt’s, the difference to a high quality front hub without a dynamo is very small (lower green line in 1st graph in link labeled “hochwertige Vorderradnabe”). According to the chart, a non-dynamo hub consumes about 0.5 watt.
From my point of view, the big advantage of a hub dynamo is that its one less issue you have to think about. It’s basically “fit and forget”. Throw in that Steve seems to have issues with battery lights playing up in the wet, and the case for a hub dynamo becomes even stronger, at least for the time of year with limited hours of day light.