12 Steps: the cascading maths

The maths starts with the US consumption of 118 billion gallons of oil a year for travel in cars and light trucks.

Step 1: Stay Home 5 percent. Fuel reduction = 5 percent.

Step 2: Walking 5 percent. Cumulative fuel reduction = 10 percent.

Step 3. Cycling 15 percent. Cumulative fuel reduction = 25 percent.

Step 4. Ride-Sharing 5 percent. Cumulative fuel reduction = 30 percent.

Step 5. Transit, LRT, Trains, 20 percent. Cumulative fuel reduction = 50 percent.

Step 6. Shift to car sharing for 50 percent of vehicle owners. No fuel impact, since this is an ownership method change, not a fuel change.

Step 7. Electric Vehicles (EV) for 50 percent of the remaining trips. Cumulative liquid fuel reduction = 75 percent.

Step 8. Hybrid EV cars for half the remaining trips (12.5 percent of the total), with 85 percent improved efficiency. Cumulative liquid fuel reduction (75 + 10.625) = 85.625 percent.

Step 9. Smart Cars for the remaining non-EV trips (12.5 percent of the total), with 90 percent improved efficiency. Cumulative liquid fuel reduction (85.625 + 11.25) = 96.875 percent.

Total fuel needed = 3.125 percent of 118 billion gallons = 3.7 billion gallons a year.

Existing buses use 2.1 billion gallons a year, which could be halved to 1.05 billion gallons with hybrid drives. Add fuel for the many new bus trips: each bus carries 20 people, replacing 15 cars, and does 20 mpg, resulting in a 95 percent reduction in fuel needed for those trips = 1 percent addition = 1.18 billion gallons. Taken together, this produces a need for 2.23 billion gallons.

Existing trucks use 38 billion gallons a year. By switching to hybrid drives, we cut the fuel use by half to 19 billion gallons, then subtract 20 percent for more local production = 15.2 billion gallons.

Existing flying uses 21 billion gallons. Subtract 40 percent for travel by rail (using electricity), and a further 40 percent for more sustainable living = 7.56 billion gallons.

Total liquid fuel needed for all travel: 28.69 billion gallons; call it 30 billion.

Step 10. Total biofuel potentials, per year.
Cellulosic ethanol from grass crops and agricultural wastes:10-20 billion gallons
Biodiesel from vegetable oils and animal fats: 4.6 billion gallons
Biodiesel from harvested algae per 20,000 hectares: 10 billion gallons
Oil from thermally depolymerized agricultural wastes: 143 billion gallons
Compost gas from nation-wide composting: 0.9 billion gallons.
(1 tonne yields 70 litres; 1 ton yields 16.8 gallons. Halifax, a Canadian city of 350,000 people, yields 61,000 tons of compostables through their green box system. 1 person yields 0.174 tons a year = 12.18 litres = 3.2 gallons (8 gallons per household). USA: 293 million people could theoretically yield 937 million gallons)

Step 11: Renewable electricity. A typical car that is converted into an EV uses around 300 watt hours per mile. An EV-1 that was tested in 1966 used 164 watt-hours per mile. If a smart-EV used 100 watt hours per mile, those 1,000 billion miles would require 100,000 billion watt hours (100,000 gigawatt hours) of electricity a year. At 100 watt-hours per mile, a year's driving of 10,000 miles will need 1,000 kWh. At the current market price of 10 cents/kWh, this would cost $100.

Wind: North Dakota has 1.2 million gigawatt-hours of available wind power potential, 12 times more than we need. At the current price of 5 cents kWh for wind energy, 10,000 miles would cost $50.

Solar: With 3 hours of sunshine a day, a house in Seattle with a 1 kilowatt PV system on a south-facing roof will generate 1095 kilowatt hours of electricity a year, enough to power a 2-seater smart EV for 10,950 miles; call it 10,000 miles. With an installation cost of $8,000 for a life of 20 years, and a 5 percent 20 year solar mortgage adding $4,500, that's $625.

Gasoline:  At $2 per gallon, those 10,000 miles will cost you $800 a year. At $10 per gallon, as the oil begins to run out, they'll cost $4,000.

Guy Dauncey, July 2004. www.earthfuture.com.