"Philosophical issues"? How about common sense.

Any reservations I have on this one are more physiological/performance oriented than "philosophical".

I could really care less what others do to their kayaks or how they use them from any emotional or ideological standpoint. My interest is more technical/practical. To that end, it's all good fun. I really like seeing these sorts of experiments.

Still, this one is not really very new/novel in function or technology. A trip to the boat (maybe hardware/auto) store and Radio Shack and most of us could do same or better.

Bottom line:

Using this rig on a kayak LIMITS the use of the kayak, preventing a user from doing much of what kayaks are DESIGNED (not romanticized) to do. Many don't use their kayaks as designed - using them more as floating lawn chairs - but that's their choice of use, not what a kayak is optimized for (call that philosophizing if you wish, but it ain't). More importantly...

Using this rig on a kayak LIMITS the users to a kayaker's seating position and gear stowage options - both of which make NO sense for the types of uses this sort of system would be good for.

A canoe make more sense, for purely functional considerations. If you insist on this being about some emotional/traditional context or agenda - I could point you to centuries of outrigger canoe development/design/use/culture. However, as magical and mystical as some South Sea voyage in such craft might seem to us here and now - they, like kayaks, were developed for very functional reasons to do very real jobs.

I'm an Industrial Design by trade, not a Philosopher, and my paddlesports interests and opinions tend to reflect similar proclivities/perspectives. My apologies if I may have inadvertently offended any Philosophy majors who might actually be seeing this stuff from a more dogmatic/romantic perspective - but I rarely see evidence of that sort of thing here (or elsewhere). What I see going on is more of a design critique.

If making a solar/electric power a kayak myself - I would consider placing the motor internally - using a duct/impeller setup like a jet ski (but simpler as a normal rudder would suffice instead of vectoring thrust) - distribute the battery load along the keel line- and incorporate the solar panels into the deck/hatch covers (totally sealed/salt water proof/rescue toughened). This way the main penalties are the added weight, reduced storage capacity and some drag from the intake and exhaust (intake should close and be flush when not in use). Kayak could be paddled normally with or without the motor, in rough water, rolled, etc. For me, as I paddle, that would be fun - but I still have no need for one. If you don't need it to be to that level, but could use some cruise assist, just do this:

http://www.kayak-excursions.com/kayakmotor.html

For a bit more DIY:

http://www.kingfisherelectricboats.com/

A gas version would likely be more popular - but not a big seller and nothing more than a side note/oddity. Proof is that one already exists, though more of a rec boat on steroids than what I was talking about above:

http://www.mokai.com/

For the criminally insane:

http://www.jetkayak.co.uk/splash.htm

Want kayak outriggers?:

http://www.easyriderkayaks.com/outrigger.htm

http://www.kayrak.ca/

http://www.sailboatstogo.com/v_page.php?content=Kayak_Stabilizers

http://www.castlecraft.com/stabilizers.htm

Etc., etc., etc....

Lot's of offerings - and something many could do themselves - yet how often seen on the water? Do you really think the barrier here is emotional?

Back to the one that started the thread:

http://www.solarpoweredkayak.com/

My free professional advice to them, as a Product Designer and paddler would be to develop and offer brackets for canoes too - and expand their market considerably (from infinitessimal to miniscule). Seems like a no-brainer, so I'd like to give them the benefit of the doubt and assume it's in the works if not already done...