In Qld we have the same scheme - rebate $8000 - my cost was $1900 (2 storey house) - have had my first rebate credited on power bill $30 for 3 mths - -----
It depends upon how much power one uses during the day - for me probably heaps ---- pool - washing machine - two fridges etc. etc. and 3 people. Average power bill $450 a qtr - so hey any rebate is OK