The average Melbourne house produces 12 tonnes CO2 every year, through its use of fossil fuels to supply its energy. Passive solar design can cut this by about 3-4 tonnes. (The slice in the picture above.) Efficient appliance selection, (including heating, and hot water) can cut another 3-4 tonnes. (Another slice. Yum.)
The last piece of the puzzle to creating a Positive House, is to use PV's (Photovoltaic panels) to generate enough electricity to supply the remainer - essentially eating that last piece of the pie!
From experience we have found that for a small family in a sustainably designed home, a 3-4kW panel system is all that is required to break even, or perhaps produce more than you use over year - becoming Carbon Positive. That's a good feeling.
With PV systems becoming cheaper and battery technology coming along quickly, we may be able to disconnect from the electrical company directly, as we become our own producer of energy.
The concept of community power is also a strong movement in recent years, where we can on sell our excess power to our neighbour, for a more equitable price, than to the oliogopolistic power company. Definitely another space to watch!