Watts (KWHr) are the same, irregardless of voltage and amperage.
THere may be a savings if the demand (KW) is reduced by the new drive.
There are also some savings if you have a new high efficiency type motor. The basic calc for watts (KW) times time, will give you the base answer. As to the efficiency, the code letters, and the nameplate info should give you the data for that.