Do I really need to put bottle in the sun for "sun tea," or can it just steep overnight in the fridge?
I've never done it, but it can't hurt your wallet too much to try it. After all, if it works for coffee (takes the bitter edge off it), it could work for tea.
It will work in the fridge, though you might not need to leave it as long as overnight. It will be safer. I found this quote from Colorado State extention:
Using the natural rays of the sun to make tea is fun and popular in the summer. However, using such a method to make tea is highly discouraged. Sun tea is the perfect medium for bacteria to grow. If the sun tea has a thick or syrupy appearance, it may be due to the presence of a ropy bacteria called Alcaligenes viscolactis. Ropy bacteria are commonly found in soil and water.”
And check this link: http://www.ext.colostate.edu/safefood/newsltr/v3n2s06.html
I've done it on the counter, not in fridge or in sun, for many years. Never a problem and it works perfectly.