Actually, if you just want to see the volumes/mount points that are currently in use by this sql instance, you don't need powershell.

I use this query across all my sql instances using powershell to collect and centralise the data. Is very useful for capacity planning.

;WITH FileIds

AS

( SELECT DISTINCT database_id, file_id

FROM MASTER.SYS.master_files AS mf

)

SELECT DISTINCT

volume_mount_point ,

logical_volume_name,

(total_bytes / 1073741824) SizeGB ,

(available_bytes / 1073741824) FreeSpaceGB,

(available_bytes / 1073741824.0)/ (total_bytes / 1073741824.0)*100 PercentFree

FROM FileIds f

CROSS APPLY sys.dm_os_volume_stats (f.database_id, f.file_id)