Its always good to have limiting factors for a character. Especially in a show. I suggest too much solar radiation can have negative effects of the body, like too much stress on muscles and heart from over powering, "roid rages",
But I assuming by your examples, solar manipulation refers to the character body undergoing some photosynthesis that gives him strength. So yes. Biologically yes those could happen. But don't make him like superman.
hmm i gave one of my art redesigns that power lately, basically they absorb sunlight and can use it in different ways, for my character it was pyrokinesis, super strength, super speed, or flight, but i made it so using more then two powers at a time would make her get over tired, also i made her more powerful in the daytime than say night, she can use her powers but only for limited time due to her sun reserves not being replenished in the night.
I suppose you could go about it by explaining that his body converts solar energy into increased strength/agility etc., because, you know... comic science. But I wouldn't go overboard with it... I'm personally thinking along the lines of, perhaps, Spider-Man strong, rather than Superman or Hulk strong.