[Bogey78O]

What's happening is the Rover's are benefiting from a martian environment which is keeping their batteries stable and their solar panels clear and receptive. The power loss as a result is far lower than expected.

[ProudVet77]

One of the rovers, I think it was Opportunity, actually had a boost in solar cell output a few months ago. The best they can figure is that while it was in a tilted position going up and down the crater, more of the solar cell array was exposed to the Martian wind and it actually blew some dust off of it.

[Andrewksu]

I would imagine that they had calculated for all of the martian conditions and were expecting a problem with dust on the solar cells and batteries suffering from the cold. It seems unusual that these guys would massively underestimate a vehicle's abilities. I know they over engineer, but they still know what to expect.

I would imagine that the power requirements are pretty high compared to the size of the solar cells, so it seems it would be cutting it close anyway.

It's not unfathomable, but it seems a little odd.