The right-back, 22, scooped the prize for the second successive season, edging out skipper Johnnie Jackson with striker Yann Kermorgant third.
Solly has missed just one league match this term and also scored a goal-of-the-season contender away at Blackpool in October.
He wrote on Twitter: "Very proud and a very happy man tonight!! Appreciate everything!!!"
Midfielder Jackson, who scored 12 goals this season, was named Players' Player of the Year and winger Callum Harriott Young Player of the Year.
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- Yann Kermorgant