Hmmm, from what I gathered in these scans is Supes only started getting his powers when he was 16 or so, so all the time he spent under Earths Sun before really doesn't matter (perhaps at that age his body started storing and changing the solor rays). It's his upbringing that makes him hold back unlike Kara but if he did ever let lose he would be more powerful than her.
But this brings up some interesting points, if Kryptonians only develop their powers under a yellow sun at around age 16. Then Kara only absorbed yellow rays from age 16 to however old she is now. So Supes should be stronger due to longer exposeur ( from 16 to...just how old is Supes in the comics anyway), but if those solar panels somehow gave concentrated solar rays then she might be more powerful.
Shouldn't anytime either of them lost their powers from exposure to a red sun reset the 'yellow sun' counter? Anyways, this explaination seems pretty silly to me. If superman has been constantly and continually absorbing more and more energy without hitting a 'high level mark' then shouldn't he be growing constantly more and more powerful by the minute?
What's with Sundipping? Can sups lower his 'sun ray count' by overextending himself?
It seems silly to me. I'd always assumed sups had a certain level of energy he could hold. More was bled off unless he did something like a sun dip. Seems to make sense.