The 30-year-old England batsman, who has a benefit in 2007, led the side to promotion in both county campaigns.
This year's playing squad will all remain at the club for next year, with Daryl Mitchell, who scored his maiden ton in 2006, agreeing a two-year deal.
Will Gifford and Ed Foster remain on summer contracts whilst they complete courses at university.
Solanki played the final two matches of the 5-0 series defeat against Sri Lanka earlier this summer and was named in the provisional 30 for the Champions Trophy, but failed to make the final 14.
Domestically, aside from leading the side to second place in both the Championship and Pro40 second divisions, he scored four centuries and four fifties at an average of 46, including a career-best 222 against Gloucestershire at Bristol in June.