I am taking on board Benny's information that petrol as fuel yeilds 10kWh/litre.
My arithmetic is unreliable, so correct me if I have it wrong.

My calculation stands, up to my fuel cost being $7/hour at 50 km/hr.
Then I assumed my petrol cost about the same as my grid power: 33 cents/kWh (all inclusive).
Since a litre of petrol costs me $1.40, and yeilds 10kWh, I must be paying only 14 cents/kWh for energy as petrol. I am surprised that energy from petrol is cheaper than from the electric grid. Is this a well-known fact?

The effect on my final calculation is to change the estimate of the power I use while driving from 21 kW to 50 kW.

well if you can work out how much CO2 ever person uses then the government can put a carbon tax on indivdual people as well. That person uses 15% more energy so they should be a seperate tax to cover their wasteful energy output <img src="http://www.ata.org.au/forums/my-plugins/bb-smilies/default/icon_smile.gif" title=":)" class="bb_smilies" />

FYI Catsopilia and to make your calculations more consistent, petrol contains about 35MJ/l or about 10kWh/l

Saul Griffith's site is
http://www1.wattzon.com

Very good but US specific.

I agree its a very useful discussion, especially when tied to the CO2 emissions metric.

I discussed my 250 kg per capita p.a. model in my post "My 250kg CO2.."

The mitigation efforts have so far been quite successful, lowering energy use and emissions from 4800kg (2400 per capita) to 1800kg (900 per capita)

All sources - historical
       Type            source      CO2 g/kwh Amount     Emissions
                                     rate     p.day       p.a.
-----------------------------------------------------   ---------
Electricity       grid hydro            230     36.6        3073
Electricity       PV solar               50        0           0
Solar Thermal     Evacuated tubes         5        0           0
Solar Thermal     Solar air heater      0.5        0           0
Gas               barbecue              450      0.1          16
Petrol/diesel     car                   250       19        1750 (actually more km per day)

      total                                                 4839kg

Current Situation after adding Evacuated tubes and 1.52Kwp PV solar 

Significant sources
       Type            source      CO2 g/kwh Amount     Emissions
                                     rate     p.day       p.a.
-----------------------------------------------------   ---------
Electricity       grid                  230      9.2         772
Electricity       PV solar               50      5.8         106
Petrol/diesel     car                   130       19         910

      total                                                 1788Kg

The current electricity use is 15kwh per day or 7.5kwh per person.(of which 5.8 provided by PV)
The reduction program I outlined included retrofitting Enerlogic 70 low e film to windows but the release of this product has been delayed for 2 more months.(December?)

The most significant item which would drop the emissions to under 250kg per person is an efficient electric car. Since we only average 19km per day, we would seem to be ideal candidates for using an electric car. I noticed Mitsubishi has released the imiev for private buyers, so I'll have to investigate the feasibility of that. Interestingly, with an elctric car we could still achieve the target with electricity rated at 900g/Kwh CO2 emissions, provided the Enerlogic gives the anticipated Kwh reductions as well.
This is how it hopefully looks after the program is completed (with 900g/Kwh power);

Significant sources - sensitivity to 900g CO2/Kwh grid
   add second string 1.5kwp solar PV
   Insulate single glazed windows with Enerlogic lamination
   exchange cars for 10km/kwh (i.e.90g/km)imiev or similar

       Type             source       CO2 g/kwh Amount     Emissions
                                       rate     p.day       p.a.
-------------------------------------------------------   ---------
 Electricity        grid                  900      3.4 kwh    1117
 Electricity        PV solar               50     11.6 kwh     212
 Petrol/diesel      car                   130        0 km        0
 Electric Vehicle   achieves 10km/kwh      90       19 km      630 (only 7000km/yr)
 Insulate windows   Enerlogic             900       -5 kwh   -1643

      total                                                    316Kg

I think this is a very useful discussion to have. Another way is to simply divide our nation's energy consumption by its population (but that doesn't account for the goods and services transferred off-shore).

Private and commercial transport, construction and manufacturing account for a large proportion of energy use. Transport infrastructure including roads and bridges which we take for granted but consume a lot of materials and energy.

The equation should also include where we buy our food, the things we purchase and import and the places we want to go.

Are you aware of Saul Griffith's energy based approach? He has a good TED video and presentation on the topic. There was also a website set up a couple of years ago which allowed users to pick and mix consumer items and activities to build up their own energy profile. I signed up but I can't remember the name of it.

A quick google pulled up this reference but it isn't his actual website:
http://itc.conversationsnetwork.org/shows/detail3771.html

In the "developed" or "modern" world each of us uses a lot of energy. How much do we use? How much do we need to use?

I just jotted down a few ideas.

House energy
To run my house (sole occupant, 150 square metres) I use 8 kWh/day, which I think is not extravagant. In a 24-hour day, that is an average power (rate of energy use) of 333 Watts. This is just a very small part of the actual house cost, of course. The energy invested in building it and in supplied town services could also be expressed as power use.

Food
I must eat. Wikipedia tells me the recommended (male) daily energy intake is 10MJ/day.
http://en.wikipedia.org/wiki/Food_energy
Since 1kWh is 3.6MJ, that is 2.78 kWh/day which, divided by 24, is 116 watts. Since my food mainly comes from the supermarket, the energy for producing, processing and moving that food must be used at a much higher rate, probably in the kilowatts.

Driving.
Although my car engine power is 112kW, that is not a useful figure. The fuel consumption is given as 10 litres per hundred kilometres, and a litre costs me $1.40, so the energy cost is $14/100km. At 50km/hr that is $7/hr.
I am going to make the reasonable assumption that energy from petrol costs much the same as energy from the electrical grid: about 33 cents/kWh. If so, my driving uses 21kW, as opposed to walking, which uses about 0.05kW (I think).

Total rate of energy use
Like everyone else, I spend all my income on energy in one form or another. Taking that figure of 33cents/kWh, I am using energy at an average rate of 11.5kW. If shipwrecked on a desert island, I could survive at 116W, according to the nutritionists. I am using energy at 100 times the rate that I need.