Today I decided to bend my rules a little bit and write a factual daylog.

It occurs to me that all the energy I use in a day can be easily converted to Joules, the basic SI unit of energy. I use electricity, gasoline, and food to power just about everything I do, and there are very few things that I can't keep track of directly. Now a great deal of energy is wasted in efficiency losses here (especially in lighting and driving), but I'm not figuring how much energy I'm applying here, I'm figuring how much energy usage I'm responsible for, which includes efficiency loss. Besides, if we start considering efficiency losses, the definition of efficiency comes into play. One might consider the energy that is wasted heating a car's engine as an efficiency loss, unless one is driving in the winter when this heat proves very useful in warming the driver.

I eat somewhat less than 2,000 food calories a day. Electricity is metered and I get billed for it every month. I fill up my car's gas tank weekly from a metered pump. Heat and water are included with my rent, however, so I can't keep track of those very easily. If I consider a typical summer day I can exclude heat, but I'll have to ignore the energy involved in pumping water into my apartment unfortunately, as I have no good way to estimate that with any degree of accuracy. Likewise, I'll ignore the energy I am responsible for at work, because my share of the total is negligible and would make little difference if I wasn't there.

I eat roughly 2,000 food calories per day. 1 food calorie = 4.184E3 Joules, so this works out to a daily total of about 8E6 Joules.

My electric bill averages out to about 200 kiloWatt-hours per month. 1 kWh = 3.6110E06 Joules, so this works out to a total of 720E6 Joules per month, or 24E6 Joules per day.

I fill up my car with roughly 8 gallons of gas in a normal week (I have a half-hour freeway commute to work). Of course this is highly variable depending on how many errands I have to run that week, or if I'm driving to visit my parents, but a normal week is typically about 8 gallons (1.14 per day). A gallon of gas contains about 100E6 Joules, so my daily gasoline usage is about 110E6 Joules.

So to compare:

Food            Electricity     Gasoline        Total Daily Energy Use
2,000kCal       5,700kCal       26,000kCal      34,000kCal
2kWh            6.7kWh          30kWh           39kWh
8MJ             24MJ            110MJ           140MJ
0.01 gal/gas    0.25 gal/gas    1.1 gal/gas     1.4 gal/gas
6% of total     17% of total    77% of total

This is about 50 GigaJoules per year, or 500 gallons of gas, which is roughly the energy you can get from the nuclear fusion of half a gallon of deuterium fuel.

For more fun with energy, see: