By the way, are super capacitors still a promising technology? What's the hold up on getting those commercialized?
(2) Today's supercapacitors have very poor energy density even compared to batteries. What they do have is good power density, meaning they can deliver their limited energy very fast.
(3) Boosting the energy density of supercapacitors will happen but requires many years of great strides in nanotech. Research like this, involving 3D nanostructures with enormous surface area: http://phys.org/news/2012-10-sponge-like-graphene-supercapac...
1/2 * c * v^2
Where c is the capacitance in farads, and v is the voltage. That will produce a value of joules. Note that the capacitor is rated for a given voltage, so that goes in as v.
Converting watt hours to joules goes like this: A watt is one joule per second, so a watt hour is 3600 joules.
Very good explanation on the general math and physics of capacitors, current, heat and energy storage, plus awesome demonstrations at the same time :)