imsmooth, generally the strategy is to look how many panels fit in a string while staying below the maximum voltage of the inverter. With that done, the MPPT voltage of that string under normal conditions is much lower, and more often than not is within the range for the inverter. Keep in mind that Vmp goes down as panels get warmer, and the number in the spec sheet is at 25C. Panels outside in the sun are 20C above ambient (at the least), so generally they are far warmer than 25C and consequently Vmp is quite a bit lower.
A little calculation showing how it's done may be helpful (for anyone doing string sizing): For your Yingli 160W modules Voc is 29.0V @ 25C. Their temperature coefficient for Voc is -0.37% per degree C.
If you live in the same climate as me, the absolute minimum temperature measured in winter is -35C. To account for colder-than-usual weather, cold spots, radiative cooling etc., I like to have another 5C margin, so I use -40C for our area (there are various opinions on how cold one needs to go for inverter safety, but let's go with this). So, we have a temperature difference of 25 - (-40) = 65C.
This works out to a voltage change of 65 * 0.37 = 24.05%. In other words, on the coldest day the panel's voltage could go up to 1.24 * 29.0 = 36.0 Volt!
The maximum voltage for the inverter is 200V, so that makes for a maximum string size of 200 / 36.0 = 5.5 panels. They don't make half panels, so your maximum string size is 5 panels if your climate is similar to ours.
With 5 panels in series, Vmp for the string @ 25C works out to 5 * 23.0 = 115 Volt. As you can see, that's barely above the lower cut-off of 100V, and actually so close I would probably not use this inverter in our climate since the string MPPT voltage will drop even lower on a hot summer day.
To show the latter, Vmp moves at about the same rate as Voc, so -0.37% per degree C (not quite the same rate, but close enough for government work). On a hot summer day here it gets to be 35C, and the panels on a roof will be around 60C. That means the voltage changes (60 - 25) * 0.37 = 13% lower, or 0.87 * 115 = 100 Volt. Right at the cut-off for the inverter...
In short, for our climate here the shortest string that can be used is 5 panels (to stay within the MPPT voltage range of the inverter). The longest string is also 5 panels (to stay within the maximum inverter voltage).
Hope this helps!
-Rob-