Is there an easy way of deleting Departments which does not exist in the current year?

Did you really want to delete the department or simply make it inactive? Deleting departments is not really fiscal-year specific and if you deleted a department, it would affect all existing fiscal years.

If you really want to delete a department code, this is stright-forward enough from the Edit Departments function. If the department exists for accounts, you can also choose to delete all related accounts - unless any have balances or posted details, in which case deleting is prevented.

The next release of Ledger 90B will allow setting a department and all related accounts as inactive.