How much energy in kilowatt hours is theoretically available from
sunlight in Canberra Australia per square meter per year. The answer I am
really after is how many solar cells at what efficiency do I need to
install on my house roof so that I can generate enough energy to meet
my energy needs. I can find the kilowatt hours I consume from my
electricity bill. Another way of putting it are solar cells on
rooftops capable of meeting domestic energy needs and so theoretically
are they a way of reducing our carbon emissions.

It would be easier if you could just state: 

I need this many xxxx kwh of energy through solar panels.  Please
provide solutions including size of grid and cost for home use.

So how much energy do you use?

Here is a little info on Australian solar powered homes

http://www.greenhouse.gov.au/renewable/home/index.html

http://www.greenhouse.gov.au/renewable/power/raps-cs1.html

http://www.greenhouse.gov.au/renewable/power/raps-cs2.html


Why not just buy GreenPower and have someone else run the grid for you...
Households can call the customer service number on their electricity
bill and ask to join up to an accredited Green Power product. Remember
each energy supplier will have their own name for the accredited Green
Power product they sell, such as ?GreenLiving? or ?GreenEarth?, and
have different options for the levels of Green Power you can purchase.

http://www.greenpower.gov.au/pages/

BTW...

According to NOVA 400 joules of energy per metre/second hit Austrailia

400 joules is equiv to 400 watts if perfect conversion existed...for
solar cells you can count on perhaps 25 percent or as low as 13!.

Therefore you will get between 50 and 100 watts per square metre of solar cells.

Here is  a good article I found:
http://socialwork.arts.unsw.edu.au/tsw/D48CanSolarSources.html





http://www.science.org.au/nova/005/005act02.htm

Lets assume the 400 watts, average, per square meter is correct for
December from 8 am to 6 pm, and you buy 20% solar cells that respond
well to low angles of incidence. Sorry to make this complicated, but
the 25% cells only work well if you keep turning them to face the sun
as they usually have built in magnifing lens. So an average of 80
watts for 10 hours = 800 watt-hours per day. That will keep a large
bank (million cubic centimeters = one cubic meter) of new batteries
fully charged if you use little or none of the power. You need perhaps
ten square meters = an array 2 meters by 5 meters to keep slightly
aged and abused batteries charged in June and provide some power you
can use each month except June and part of July. This assumes you have
ten square meters of steep roof 45 degrees or steeper which faces
North and that this portion is rarely or never shaded by nearby trees
or other structures. It also assumes cloudy days are rare. Less roof
tilt is ok in December, but even 10 square meters may not keep your
batteries fully charged in late June each year, with less roof tilt.
The steep roof tilt is less important in Northern Austraila than in
Tasmainia. After you find the price of 10 square meters of solar
panels, you likely will not want to think more square meters. I
suggest you start out small, until you understand the details, and
think of your system mostly as back up power, when your electric
utility is out for a few days. You can use 10,000 cubic centimeters of
battery, but your charge controller will often shut down your system
to avoid over charging your puny battery, which will then be damaged
by excessive discharge if you use even one kilowatt hour from the
battery during a utility black out.  Neil

You will notice, I did not mention volts nor amp-hours as this
complicates the discussion. For a small system 12 volts is logical as
12 volt inverters are avaiable cheap, but not legal to connect to you
utility grid. Cover your best eye if you attempt to use these cheap
inverters on the power grid, as they may fail every 100th time they go
on line, perhaps much oftener. 120 volts seems logical as some devices
designed for 60 hertz ac wok well on dc. For reasons unknown to me 120
v dc is not popular. Big systems use many solar panels in series to
produce several hundred volts. This allows smaller wire sizes, but I
have seen copper wire up to one centimeter in diameter recomended,
making the wire a major budget item.   Neil

I know you are hopeing the 80 watts per square meter is pesimistic,
but my friend who has operated a one square meter system for 3 years
charging 12 volt batteries, all but convinced me that 60 watts per
square meter is about all you can expect even in the sunniest
locations. Clearly you can produce enough green energy from solar
panels for about double the cost your utility charges, with uncommon
skill or luck and a very favorable roof. The cost is at least tripple
if you figure your time at minimum wage. ie you will replace your
batteries perhaps 15 times in the 30 years you can optimisticly expect
your solar panels to be significantly useful, if you fail to guard
your batteries from both over charge and excessive discharge. I have
not used a charge controller, but I suspect they undercharge batteries
that are near the end of their useful life. If you move, you likely
will not be able to convince the buyer of your house, that your
expensive system adds value to the house.
The power grid systems typically do not have batteries, so you cannot
even get emergency power during sunlight hours when the utility is
down. These on the grid systems are more costly, but the government
incentitives may off set the extra cost over a bare bones emergency
power system, which may not be elegible for the incentitives. If you
do your own work, electrical burns and shock are a serious hazzard on
the a 40 kilowatt system and a minor hazzard on some 4 kilowatt
systems.  Neil