Sunday, January 5, 2014

Gas Math


Climate crisis gas math

In the climate crisis, we all need to grasp our gas math to help us keep breathing.

The bottom line is the main hypothesis of this blog:  electric cars running on renewable energy can help us meet California's goal of reducing greenhouse gases 80% below 1990 levels by 2050.  Actually, 2050 is too late; we need to cut greenhouse gases ASAP.

California's goal is to cut greenhouse gases to less than 100 MMT (million metric tonnes) of CO2 per year by 2050.  That would be about 2 MT (metric tonnes)per person (assuming 50 million people in California in 2050).  Half of California's CO2 currently comes from petroleum, so the goal is 1 metric ton per person from petroleum, i.e. driving.

Can we do this with internal combustion engine (ICE) vehicles?

One metric ton weighs 2200 lbs.  One gallon of gas creates 25 lbs of CO2 (counting extraction and refining).  Therefore, we should burn no more than 2200/25 = 88 gallons of gas per year.  If we drive an average of 12,000 miles per year, that would mean we need to average 136 miles per gallon (12,000/88), for an ICE vehicle.  This does not include the CO2 created in producing the vehicle.  Counting these emissions, the average car (25 mpg) emits about 1.1 lb per mile (500 g/mile), or 13,200 pounds per year = 6 metric tons.    So we really need cars that get 13,200 / 88 = 150 mpg.

Side note to re-state calculation above:   the average car consumes 12000 miles / 25 mpg = 480 gallons of gas per year.  480 gallons x 25 lbs/gallon = 12,000 pounds of gasoline plus 1,200 pounds CO2 to account for manufacture of the car = 13,200 pounds.
 New EPA standards call for 54.5 mpg by 2025.  This would cut the CO2 by more than 1/2—down to about 3 tons per car per year, but still not close to 1 ton.  Reaching 1 ton may be possible for an ICE car, but a lot of new technology would still be required. 

Alternatively, assuming an average of 50 mpg, the one ton goal could be reached by reducing vehicle miles traveled (VMT) by 2/3.  The trips could be replaced  with transit and bicycles and walking. But, because transit, bikes, and walking only operate effectively in a high density environment, this would require rebuilding all of California's cities to higher transit-friendly density, with the exception of already-dense locations such as downtown San Francisco.  Alternatively, perhaps Skype and similar technologies will reduce the number of trips.  Indeed the rapid increase of vehicle miles traveled that has occurred over the 20th Century has stopped in recent years (see graph below).  Whether there will be an actual drop in VMT remains to be seen.  Certainly tele-commuting and more transactions handled online, higher density land use, improved transit, improved bicycle facilities, and improved pedestrian facilities are all important to helping reduce the miles driven.  But it is highly unlikely that such massive changes can occur fast enough to stop climate catastrophe.
Total Vehicle Miles Traveled
Vehicle miles traveled (in millions) has declined slightly since 2005.  Source: http://www.ssti.us/2013/02/per-capita-vmt-ticks-down-for-eighth-straight-year/

 Electric cars to the rescue?

For an electric car powered by solar or other renewable energy, the technology is mostly here already to reach the equivalent of 150 mpg, 1 tonne of CO2 per year.  An EV powered by solar power creates about 119 g/mile  for manufacture of the car, the batteries, and the solar panels.  This is  119 g/mile ÷ 454 g/lb = .26 lbs / mile.  For 12000 miles that would be 12000 x .26 = 3,120 lbs = 1.4 metric tons.  So instead of needing to reduce CO2 from 6 tons per year, or even 3 tons, to one ton, an EV running on renewable energy needs to reduce CO2 from 1.4 tons to 1 ton.

To get to 1 ton per person it would be necessary to reduce the 119 g/mile produced in manufacturing the car, the batteries, and the solar panels, or reduce the miles driven per person.  Each of these is a realistic possibility. 

 If the car only goes 8,500 miles per year, the total emissions would be 1 ton. If two people share the car, and it goes 12,000 miles, it would emit 0.7 tons per person, well below the goal.

If the emissions were reduced to 80 g/mile, the emissions for 12,000 miles would be 80/454 x 12,000 = 2,115 lbs., i.e. below the 1 metric ton goal.  This could be accomplished by more efficiency in the production process, use of lighter materials, more recycling of materials. . . Or it could be accomplished by extending the life of the batteries and vehicle.  The 119 g/mile number assumes a vehicle/battery life of 120,000 miles.  If the car and batteries last 240,000 miles, the g/mile would be reduced by 1/2, i.e. 60 g/mile.  Also, wind turbines have a lower carbon footprint than solar panels, so this would also reduce the emissions from electric vehicles.

Reduction of miles driven can be accomplished by a fee on miles driven over a certain amount, say 10,000.  All of the items listed previously relating to ICE vehicles--tele-commuting and more transactions handled online, higher density land use, improved transit, improved bicycle facilities, and improved pedestrian facilities—can also help keep the transportation-related CO2 under one ton per person.  Since electric vehicles powered by renewable energy already bring us close to 1 ton per person, the reductions in vehicle miles traveled based on these land use and planning changes are more feasible than in the case of ICE vehicles.

All in all, getting to 1 ton of CO2 per person is quite achievable if the State moves away from ICE vehicles, or those ICE vehicles are much more efficient than current technologies.  In either case the total gasoline consumed in California would drop drastically.  In the case of electric vehicles, there would be practically no need for gasoline.  If ICE vehicles become efficient enough to meet California's CO2 reduction goals, gas consumption would fall by 80%.  This would be sufficient to close most of California's 18 refineries unless they are allowed to export oil without any cap (which AB32, California's Global Warming cap and trade law allows.)

This raises the question of what happens to those displaced workers (estimated 4,000 but needs checking)  The answer is that installing solar panels, building wind turbines, updating electrical systems, and these types of jobs will far surpass the refineries in job creation.  Refinery workers should be given training in the new fields of work and given priority in hiring.

One technical issue facing electric vehicles is the need for quick charging stations for interstate trips and long trips within California.  Current EV ranges of 80 or so miles are clearly inadequate for most travelers, even with fast charging.  The Tesla range of 300 miles is much more reasonable for long trips, and Tesla's fast charging network may provide the answer here.  Trailers with extra batteries that can be swapped easily at drop-off/pick-up locations is another solution to this problem.

The cost of EVs is commonly cited as an obstacle, but EV prices are dropping steadily.  With tax credits the Chevy Spark price is now $17,450, i.e. about the same as an ICE car but far superior in handling, acceleration, and gas savings.  Another  financial obstacle is lack of 240 volt wiring and outlets in many older homes and in apartments.  This is a case where subsidies and low cost loans would be highly cost effective and beneficial.
 Per Capita Vehicle Miles Traveled
Note:  per capita vehicle miles traveled has dropped more than total VMT due to increases in population.

3 comments:

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