Peter's solos are all like arpeggio sort of stuff, quite classical sounding. Something I noticed is you tend to hear Peter's pick hitting the strings a bit harder than Mike's; so that's how I unofficially know when he's soloing.
for me it is quite obvious when Peter's soloing because he uses mostly pentaton notes and no really mad rhythms. On the contrary you can realize Mike's ones by his impossible rhythms. I think Peter's soloing in Wreath, Deliverance 1st solo, A Fair judgement heavy solo 2nd part, When heavy solo, etc. I guess he has no solos on Ghost Reveries at all.
I was glad he only got the one solo on Ghost Reveries. His solo at the end of Beneath the Mire is one of the lowest points on the album for me. It's been my strong belief that his solos never came to the level of Mike's throughout the whole span of the band. I was excited to hear what sort of lead sounds the new guy would add but was pretty disappointed by the solo on Heir Apparent, at least the way it's played on the live video. Who knows, maybe its strength is in layers of harmony which can't be reproduced live *prays*.
not all songs are in open-D tuning, for exemple GrandC, Hours of Wealth is dropped-D for sure Mikael wrote on the official Opeth homepage that Peter did not do so much for the co-writing as earlier, this may shows that he was kinda about to leave for a couple of years, don't you guys think?