Is it technically feasible to make a solar hang glider?
I think you've got your terminology crossed here (but it's not your fault - your sources don't seem to clear on it either).

A hang glider is by definition a solar vehicle: They're non-motorized, and the pilot keeps them aloft by seeking thermal lift (created by the sun shining on the ground and heating it up) or ridge lift (created by wind striking the side of a mountain/hill (ridge) and being deflected up.
Both of these rely on the sun (either directly heating the local ground, or unevenly heating various parts of the Earth's surface, ultimately creating wind).

What you're referring to would be a solar-powered ultralight aircraft -- basically a hang glider with a motor strapped to it, or possibly an electric powered paraglider.  



One could conceivably create a solar-powered ultralight using flexible solar cells on the wing  - in fact a little Googling reveals that it has apparently been done with an electric paramotor (a type of powered parachute) (A little more Googling reveals this wasn't as cool as I previously thought - they seem to have been using a support vehicle to recharge their battery packs (with solar cells).

As far as I'm aware no such vehicle is commercially available at this time (May 2014), but the materials and technology to construct such a vehicle are certainly available (the folks over at the Experimental Aircraft Association could probably provide guidance on building something like this), and it wouldn't surprise me if commercial or kit-build solar ultralights become available at some point in the future.