The solution architect outlines the solution, leads the detailed design, implementation and delivery (to testing) of incremental releases.
The solution architect writes the solution architecture document. Ideally, basing it on my recommended template, your solution architect has read and loves all the books in my recommended reading list.
Your solution architect was once a developer, and while working full-time in this role rarely permits taking actively part in coding, your ideal candidate still finds time to keep up with the developers.