When fossil fuels are burned for power, toxic gases are released into the air. Those toxic gases build up as pollution (yuk!) and contribute to climate changes such as global warming. Also, some fuels such as coal and oil require mining, drilling, and fracking, which can leave the land stripped of plants and trees along with a whole other list of major issues that are harmful.
On the other hand, the sun is a natural power source and solar panels are able to easily capture clean sunlight that can be turned into useable power. No burning or toxic gases needed!
The more people switch their homes and businesses to run on solar power, the less fossil fuels are needed. Which is good since eventually the supply will run out, whereas solar and other renewable sources will be there when we need them.