Two questions:
1)
I have been told that Solar Pannels voltage degrades by a percent or so per year.

Is this accurate? Is it for Voc, Vmp, Nominal Voltage or all three?

2)
IF my inverter operates from say 110VDC to 350 VDC. How do optimize the string voltage?

Given the geometry of my roof, Using say the sharp 80W pannels, I can get a nominal string voltage of 196V, with the 142W I get a nominal string voltage of 112V, and with the 170W moduals, it is 144V.
The Vmp for these are: 276 ,180 ,208

I need some overhead to allow for voltage degradation. Should I use the nominal voltage, or Vmp when calculated string voltage? Looking at the power curves, it seems like I might want to use something inbetween, and then make sure I have enough over head for the voltage to stay above the inverter minimum for 25 years or so. Is my thinking correct?

Thanks,
Greg

For Silcon (poly and mono), its close to unmeasurable the degrading effects. One will get 10X the losses from enviormental issues like dirt and roof mounted arrays usally rarely get attention to keep clean compared to the slow degraing output over a say 50 years

Manufactures are betting is less than 0.5% a year, they all have 25 year warrantys for 80% of rated performance.

For strings, its easest to just use an online configuration tools

This is a good one
http://www.xantrex.com/support/gtsizing/index.asp