|
|
BobG wrote:
A msg on this newsgroup couple weeks back said you could get 700
gallons of soybean oil from an acre of soybeans, and running a tractor
up and down an acre a couple of times took less than 10% of that amt of
fuel. The Dept of energy says we use 24 quadrillion BTUs in
transportaion fuels... assuming that gal of biodiesel weighs about 7lbs
and produces about 15,000 BTU per lb, you can compute how many gallons
and acres it takes to produce that number of BTUs. I did it and it was
about 10 or 15% the area of the US., so complete conversion to
biodiesel looks feasible to this engineer.
I've done this calculation several times, in different ways, and
come up with various answers. Here is one way to look at it.
Assume 1000~W of sunlight power falls on each m2 of land in the US,
which means 1,000~W * 1,000,000~m2 = 1000~MW/km2. Assume the
sunlight falls on the earth for 10 hours a day, then there are
10,000~MWh/da-km2. A year is 365 days; thus 10,000~MWh/da-km2 * 365
da/yr = 3,650,000~MWh/km2-yr.
The US land area in the 48 states is 8,588,712 sq km--See:
wonderclub.com/Atlas/usland.htm
Thus, 8.589~Mkm2 * 3,650,000~MWh/km2-yr =
31,350,000,000,000,000,000~Wh/yr, which is about 31,350 Quadrillion
Watt-hours (QWh).
Assume growing soybeans for oil uses 1% of the energy from the Sun,
then 31,350~QWh/yr * 0.01 = 313.5~QWh/yr.
Assume 20% of the US land area can grow soybeans, then 313.5~QWh/yr
* 20% = 62.7~QWh/yr.
24~quad/yr = 7~QWh/yr (Quadrillion Watt hours per year), which
means that about 11% of the land area could grow enough soybeans to
supply oil for 24 quad.
This estimate is based on the best figures I can find on the net.
However, I think it is too optimistic.
--
Humbly--Ed
"If the man doesn't believe as we do,
we say he is a crank, and that settles it.
I mean, it does nowadays, because now we
can't burn him." (Mark Twain)
|
|