How many SunEye skylines are needed in PV Designer?

It depends on the nature of the obstructions. In general, we recommend that there be readings at the four corners of the array area (or the array plane). In addition skylines should be taken at the points on the array plane closest to obstructions. Also skylines should probably be taken every 20 feet or so. More skylines will generally increase the accuracy of PV Designer calculations, although this may also cause the calculations to slow down.