Yes, SOLIDS is a Scrabble word!

Letter values in Scrabble US: S 1, O 1, L 1, I 1, D 2, S 1.

Is it a valid word?

SOLIDS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

matter that is solid at room temperature and pressure
the state in which a substance has no tendency to flow under moderate stress; resists forces (such as compression) that tend to deform it; and retains a definite size and shape
a three-dimensional shape

Also: solid state.