If the game is winner take all, a solo gets you all the d points and v points wagered.
If the game is points per supply centre, a solo gets you (and any other survivors) n% of the d points (where n is the percentage of total centres you own), while v points are distributed on a similar basis (namely, you lose points to anyone who did better than you, inversely related to how much better than you they were expected to fare). Naturally, if you win, you get a larger share of the points than anyone who lost but managed to survive.
So, yes, 18 centres on classic under PPSC is still a solo, but no, you don't win the entire pool with that solo.