Re: Mileage and Watts
- From: Tim Keating <NotForJunkEmail@xxxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 18 Jul 2005 16:30:21 -0400
On Mon, 18 Jul 2005 11:57:57 -0400, Front Office
<yourmother@xxxxxxxxx> wrote:
>
>I can hold an average speed of 12.5 mph around
>town on my Trek mountain bike. The hilly terrain
>here accounts for the low average speed. (On
>flat roads I can hold steady at 17-18 mph for
>30 minutes or more, easily.)
>
>I estimate (guess, actually) that I'm getting
>100 watts to the rear wheel, average, on hilly
>terrain or on flat terrain. I estimate, too,
>that my body is metabolizing solar energy at a
>rate of about 400 watts total to get 100 watts
>to the rear wheel.
>
>If I had a small engine on my bike (i.e., a
>gasoline engine, rather than my solar-powered
>body) that could operate at 25 percent efficiency,
>then it should be to burn a gallon of gasoline
>(31,000 calories) at 400 watts of total fuel
>input energy rate for 90 hours. That much time,
>at 12.5 mph, would move me and my bike, or any
>like-sized vehicle, through a distance of
>1,125 miles. I.e., I could get ~1,100 mpg.
>
> From this I conclude that speed and the
>cross-sectional area of a vehicle determine the
>maximum distance you can go on a given amount of
>energy. I.e., the faster you go, and the larger
>your vehicle, the less distance you can go on
>a given amount of energy.
>
>I also conclude that any mid-sized car, whether
>it uses gasoline or batteries or fuel cells, or
>any combination thereof, will use the same amount
>of energy to cover a given distance at a given
>speed, and any benefit that comes from batteries
>or fuel-cells would come from the slightly greater
>conversion efficiency of central power plants,
>compared to piston engines.
First item, automobile internal combustion engines very
inefficient. Most of your fuel's energy ends up as waste heat.
(~85%-90%).. Hybrids are bit better since they have a tendency to
run a smaller ICE in a more efficient power range.
Second item, then add in that your fuel source (gasoline) is
requiring ever higher energy inputs(losses) before it get to your
tank. (As time progresses oil requires more exotic oil recovery
methods, ever higher refining, and distribution overhead.) Combined
with first item, one would be lucky to get 5 to 10% useful work out
of each gallon of crude oil.
Third item is that you're dependant on a commodity in high demand
and limited supply. Thus in the foreseeable future you can expect to
pay a price premium for additional supplies of gasoline.
Four item current price of gasoline/imported oil is heavily
subsidized by our DOD protecting the sea lanes and the occasional
overthrowing a sovereign government. Fully loaded cost of oil is
around $100 per barrel of Oil. (Gasoline really should be priced
around 5$ a gallon just to cover direct expenditures.)
Then there is the environmental impact/costs to consider.
>Please criticize this line of thinking.
You need to consider the entire cost cycle of a fuel before you can
make accurate comparison.
.
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