Whether or not they get their electricity from solar panels, satellites still need fuel to keep themselves from eventually crashing back to Earth in an apocalyptic fireball that might, but probably won't, land right on your head. The only way to extend their lifespan is with in-flight refueling, and a new gas station on the ISS might make that possible.
Satellites launch with all the fuel for their entire mission onboard, and when the fuel is gone, the satellite becomes space junk whether or not the rest of it (i.e. the useful and expensive part) is still working. This doesn't just waste gigantic piles of money, it also creates gigantic piles of shiny new deadly space junk. At the same time, sending up more fuel would just make the problem worse, since the refueling spacecraft would just add to the money and mess.
What's needed are orbital gas stations where satellites can come to refuel, and that's exactly what Atlantis is dropping off at the ISS on its final mission. The Robotic Refueling Mission experiment is designed to test the feasibility of having satellites swing by the ISS to get topped off by the station's friendly robot, Dextre. In addition to pumping gas (in this case, ethanol so as not to pollute the atmosphere), Dextre will also be able to perform minor repairs such as replacing insulating thermal blankets, adjusting valves and checking tire pressures and brake lights.
The gas station is scheduled to be tested for the first time in May of 2013, when a weather satellite up for decommissioning will have some fuzzy new magic juice pumped into it courtesy of the friendliest robotic gas station attendant this side of Alpha Centauri.