"A perfect place for suntanning"
—SlimepediaFree to use
The Solar room is used to turn puddle slimes into Rainbow slimes.Also you can use it to give yourself a tan. Keeping slimes in there will evaporate them.
It cannot make a tarr evaporate,sadly. if you try you get the achievement "It isn't working?"
Unfortunately, you can not evaporate Gold Tarrs because they are 100 percent gold. And in this universe gold does not melt.