The Ergosphere
Thursday, August 19, 2004
 

You find you get what you need

It is often asserted that oil is essential to the US economy because "we cannot get the energy we need any other way."  Another reason put forth is that oil is uniquely suited to the purpose of transportation, and we have nothing else which will serve at a price we can afford.  These claims have enormous technical, economic and political implications.  Anything of such importance should be examined very closely, because the consequences of being wrong are so great.

The transport sector of the US runs almost entirely on oil.  The US Department of Energy posts figures detailing US consumption from 1949 through the latest year presently available, which is 2002 2004.

Anything that accounts for less than 500,000 bbl/day is insignificant, so I'll ignore it.  What remains are jet fuel, distillate fuel oil (diesel) and motor gasoline.  It's doubtful that anything will substitute easily for jet fuel so that's out.  This leaves diesel and gasoline, which together account for 58% of all US consumption of petroleum products.

In that year, gasoline consumption averaged 8.665 million bbl/day, and diesel another 2.445 million bbl/day.  A barrel is 44 US gallons.  The energy content of gasoline is about 115,000 BTU/gallon while diesel is around 145,000.  Over the road diesel engines hit maximum efficiencies around 40%, while gasoline engines run quite a bit less than that in normal use, especially with automatic transmissions; assume 20%.  By the time that energy gets to the wheels it's quite a bit less than the raw fuel consumption would suggest. What does it amount to, total?  What's the average power?

 Fuel  mmbbl/day  TBTU/day  Efficiency  Output, TBTU/day  Output, GW 
 Gasoline  8.665  43.8  20%  8.77  107.0 
 Diesel  2.455  15.7  40%  6.27  76.5 
 Total  11.120  59.5   15.04  183.5 

An average power of 183.5 GW isn't huge compared to other energy usage.  The summer electric generation capacity of the USA in 2002 was over 900 gigawatts, roughly 5 times as much as the average output of all gasoline and diesel powered transport.

If we define our transport energy needs as what we actually use (without including losses in conversion, and ignoring potential improvements in efficiency) it appears that they are rather modest.  An average power of 183.5 GW is less than 700 watts per capita.  If it could all be supplied from electricity without transmission losses it would only increase US consumption by about 40%.  That's a lot of energy, but if it was sent during off-peak hours it wouldn't even make the grid break a sweat.

This should make you think.  If a person's transport energy needs are small enough that a single 14-gauge extension cord could supply them with capacity left over, the problem of changing from oil to another energy source might easier to tackle than is commonly supposed.  We don't have to look far for motivation, either; we have a host of reasons to want to do this, including

(Notice that I didn't mention the #1 controversial reason for such a move.)

The required energy supply is within reason.  The problem which remains to be solved is to find a safe, efficient and cheap method of getting energy (whether from coal, nuclear, or renewables) from the grid to wheels.  If we can package what we need, it's certain that we can get it.

One possibility for that is in the queue of future posts.  Stay tuned.

 
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