Heat will be a problem in tank like that if sun hits it for extended period of time. My Reef tank only gets hit in the last two hrs of sunset which doesn't do much.
I've had a 75g FW tank in direct light purposely to grow algae, but that i was keeping tropheus, never saw a speck of algae, the bastards.
But would take quite a long time to heat 75g's. Especially when room is kept in the high 60's. With a 55g, as long as it isn't in direct light should be ok but as reefneck pointed out, algae. You prolly will get a buildup of diatom algae unless have a excellent clean up crew which in FW is kinda harder to do then SW.
It is a forum open to discussion, its how get multiple points of view, my neighbor had a 55g, though i never talked to him, he had it directly in the window got grody fast and he moved it, but as mine i showed off especially at nite was a beauty and rub it in his face
I think, if comes to a problem with the light, not that hard nor expensive to add blinds.