If your evil cleric is daring and can get close -
Use a Blasphemy spell, and beat the thing's SR
No will save for Solar
Wizards or clerics:
Use Banishment while presenting an evil holy symbol and unholy water. (for a certain +2 to SR and a +4 to save DC)
possible additional modifiers:
- Casting from "desecrated or unhallowed ground" (power components I would hope)
- use of the "curse" mode to hinder opposing alignment (good) as per "bestow curse" (save forefit as you chose to enter the area)
20th level caster needs 11+ on the d 20 to beat the SR.
This presumes only the holy symbol and the unholy water (and not even power components at that)
- this is a "recalculated base" Save DC of 20 to 21 + modifier; and your upper level wizard or cleric usually has a modifier of +6 to +10 (maybe more depending on how maxed out the score) before feats or other modifiers In this - your modifier is going to have to be greater than the solar's possible roll.
IMC If you want an effective "no real save no Sr" on the solar - this is what you could use;
Cleric or wizard; 20th caster level(effective or actual):
Things that modify SR roll
+ 2 Power unholy symbol/Divine Focus
+ 2 Unholy water (IMC - there is a power version)
+ 2 Unhallowed ground (as power component)
+ 2 Wearing A Talisman of ultimate evil
(minor artifact - but hey we ARE talking a solar)
+ 2 Spell Penetration
+ 4 "Greater Spell Penetration"
(If you have it the feat "overlaps" Spell penetration)
+ 1 The caster himself is a consecrated evil priest/blackguard
+2 If the caster were a Demon, undead lich (or the like)
As for making the save DC a 40+ (so solar can't save safely)
+4 Power Holy symbol
+4 Power Unholy water
+4 Unhallowed Ground
+4 Wearing a Talisman of Ultimate Evil
+4 If Caster is a Demon, Lich, or the like
+2 If caster is a consecrated evil priest/blackguard
+2 Spell focus
+4 Greater spell focus (overlaps - does not stack W spell focus)
+ 4 "Curse mode" of Unhallow hindering good aligned creatures as per Bestow Curse's secondary -4 to all saves effect (this is actually (actually a penatly to the solar)
Two powerful "hypothetical combinations"
Wizard/lich - 20th level; using power unholy symbol; power unholy water; with Greater Spell Penetration, intelligence modifier +8(or greater)
Needs a 2 on a d20 to beat the SR - save DC 40 for the solar
Lich/Cleric - 20th level using power unholy symbol; power unholy water; on unhallowed ground, spell penetration feat and wisdom modifier of at least +8
Needs a 1 on a d20 roll to beat the SR (sure thing) - save DC 40