Thanks, both of you, but I am not sure if this refers to my X5.

The First set of instructions would make it appear that its a stretch belt.
However, when I look at my belt I have a tensioner roller that you put manual tension on (as in not a hydraulic tensioner or not a spring loaded one.

Here is the link to the V-belt and belt tensioner:
2008 BMW X Series (E53,E70,E71,E83) X5 4.8i Belt Drive Climate Compressor