I'm not sure of the specifics, but the missions principal scientist was my professor in college and he specifically said that they tried some of your exact ideas for the next rover (which was actually a cancelled 2003 mission). They tried a windshield-wiper type deal, layers of plastic film that would roll off every few days (think like a doctor's office, how they tear off that butcher paper and roll a new cover over for each new patient). He didn't delve too much into specifics, but he definately said that they simply didn't get any of these ideas to work. Actually, there was a brief period of time when they were actually close to getting RTGs to power the rovers (plutonium, like the ones used in the Viking landers that allowed them to operate for 5 years), but the Greens stopped that :(
Q: Why can't a brush or wiper be used to clean off the panels and keep the mission going?
A: The solar arrays are fairly large and, subsequently, the brushes or wipers would also have to be large. A brush or wiper system would require too much mass and probably wouldn't do a very good job of getting rid of Martian dust. The particles are only about 1-2 micrometers in size.
Szerintem meg egyszerûen nem volt rá szükség. A járgányok a tudományos küldetésük 95%-át elvégezték az elsõ 90 napban, a hozadék azóta viszonylag kevés, bár persze szép képeket csinálnak, a PR értékük még mindig nagy (de ez nem érdekli a kutatókat). Így azt mondták a NASA-nál, hogy ha választani kell aközött, hogy legyen még egy mûszer és a robot mûködjön 90 napig, vagy legyen egy mûszerrel kevesebb és menjen két évig, akkor inkább az elsõt.