Power plant lakes aren't necessarily more productive in the winter but they are more popular because you get such a jump start on the spawn. It's funny that a lot of people think the fish don't bite during the summer on pp lakes....they don't hibernate...they have to eat. I have had some very productive trips during the dog days of summer. Just like any other lake the morning bite is typically best. The fish will find a spot in the lake where they are most comfortable and the bait fish are handy....finding that area of the lake is the trick.
Yeah, you can find spawners as early as December some times but you will also find a full parking lot. Last year a buddy and I had an awesome day out on Welsh when we fished the discharge and it was 105 degree water temp. But I've also noticed that the grass has grown way thicker this year.