Space Shuttle Endeavor?

Before this mission, shuttles had no way of transfering power from the station to the shuttle for use on the shuttle, the shuttle always had it's own supply of oxygen, and electricity and such, so it always had to come down within a specified period of time

this mission is the first mission that the shuttle has used a station to shuttle power transfer system (SSPTS) as a testing system. which will (possibly) allow an orbiter to stay docked to the station for an extra three or four days.

The ISS uses solar photovoltaic panels to generate electricity.

The ISS and the space shuttle both use electricity to power controls and instruments, pumps, lights, fans, and all other equipment.

So the answer is electric, but it is generated by solar panels.

Space station has large solar panels that shuttle doesnt have.

Panels always face sun constant energy in space no clouds