Why 3 fan belts?

I was driving up from Harrisburg yesterday (with a lottery winner) when we saw a small car lot that had a few Porsches for sale. We stopped and they showed us a '92 C2 that had a total of 3 belts. One was for the A/C, but the other two ran from the crank pulley to the fan pulley.
My '85 3.2 has only one belt between the crank and the fan... why are there two fan belts between the crank and the fan on the C2 model? Couldn't figure it out by looking at it. Thanks.
regards,
jlex.

The second belt runs the alternator. There is a coaxial inner shaft from the outer pulley.

Bob
90 C4