http://ihpva.org/rules.htm is a useful read. (And, similar language exists in older revisions of the rules.)
And, here's the relevant rules:
3.1.1 Power: Vehicles must be driven solely by human power. Non-human power sources (batteries, solar cells, etc.) are permitted only for powering sensors, displays, communication equipment and lights. Control devices, cooling fans, powered aerodynamic devices, etc., may not be powered from non-human sources.
3.1.2 Energy Storage: No device which stores energy over more than one input power cycle (e.g., one leg stroke), or which releases energy under control of the operator, may be used in any event except the road race, or speed events longer than one mile. Energy storage devices are permitted in these events provided no energy is stored before the start of the event (this means absolutely no chemical, electrical, kinetic, potential, or other form of energy storage at the start.)
I'd argue that solar power is treated identically to a pre-charged battery by the regulations. Dermal conduction is power generated by the human, however (unless someone slathers additives to the skin to increase the energy in that cell, then it becomes a pre-charged battery again)...
I think part of the controversy was that the "sensors" and "displays" language was intended for cycle computers running off of coin cells, that were helpful but not strictly necessary, not cameras and big backlit color displays running off of a Li-Ion, that were critical to piloting the vehicle.
In any case, there's been at least two rules revisions since that debate happened, and I think the consensus was that as long as the wheels are propelled solely by human power, the vehicle is steered solely by human power, and any aerodynamic effect changes during the run are made solely by human power, it's good. (This is why the language about cooling fans needing to be human-powered exists - and Australian International Pedal Prix actually revised their rules for this year to ban cooling fans, to avoid cheating by using a cooling fan to propel the vehicle.)