Is that a solar panel in your pants, or are you just happy to see . . . oh. It is a solar panel. Why do you need one?
It's a good question. Solar panels are generally used to heat, electrify, or move something. Pants are best if they don't run off on their own. In the cold, a warm lower body might be nice, but usually there isn't too much sun in cold weather. And no one wants to electrify their pants.
Nevertheless, pants with solar panels in the pockets are available from Silvr Lining. They are listed as 'cargo pants' but look more like pajama bottoms with pockets. The solar panels are installed on each of the pockets, which are big and extremely roomy. The size of the pockets not only accomodates the panels, but helps to carry some of the many gadgets that most people walk around with at all times. When the gadgets run low after a long day of wearing orange bright enough to blend in with a highway trash removal crew, the wearer can simply plug their phone into their pocket.
While many, or all, aspects of these pants can be considered ridiculous - including the thousand dollar price tag - it's nice that Silvr Lining is trying to alleviate the environmental impact of personal technology. Might I recommend for the future something in a sturdy shoe? There are already sidewalks and dance floors that use the impact of people's stomping feet to generate power. Shoes would be useful in all weather, and could be used even indoors by chronic foot-tappers. Overall, they're more reliable and less consipicuous than walking around in pajamas and presenting one's thighs to the sun.