I'm working on an outside place for my yellow bellied slider and the best location would not get direct sunlight.
It's outdoors, facing south (in Europe), but it's covered by an overhang and has some trees in front of it, so the sun never directly shines on it.
I don't know if this setup would be healthy enough for my turtle.
the sun never directly shines on it
. Are you willing to invest in a big mirror, to make the sun shine indirectly? :) Joke aside, you could create a big mirror from some big aluminum foil - you van find them as rolls relatively cheap, being used (layered with some foam) for insulation purposes.