[ExI] Dollar a gallon gasoline

[hkhenson]

Dollar gas

With enough investment, engineers can do just 
about anything not forbidden by physical laws.

Gasoline is just a form of stored chemical 
energy.  It is compact because 65% of the mass of 
the reaction products (CO2 and water) comes from 
oxygen in the air.  Gasoline or equal chemical 
energy sources can be synthesized from air and 
water at reasonable cost if you have a source of really inexpensive energy.

How inexpensive?  As a rough estimate, the cost 
of electrical energy will have to be 10-20% of 
the cost of the product.  The energy in gallon of 
gasoline is about 40 kWh or at 5 cents a kWh 
about two dollars, implying that we could make 
gasoline from electricity today at some $10-20 a 
gallon.  The cost of energy to run a synthetic 
fuel plant would have to fall to the sub cent per 
kWh range to expect liquid fuels at a dollar a gallon.

Is that possible?  Assuming solar, i.e., no cost 
for fuel, the cost is mostly due to capital 
costs.  There are about 8,000 hours in a 
year.  Taking a 4 year payback, that’s 32,000 
hours, which means (selling the power for a 
cent/kWh) the installed cost of a kW has to be $320 or less.

Is *this* possible?  At extremely high levels of 
production, costs approach the cost of materials 
and energy.  The parts of a solar power satellite 
consist of supporting wings, solar cells, 
transmitter and ground station.  A kW is 2-4 
square meters of wing surface.  The estimated 
mass, including the transmitter is 2kg/kW, half 
of which will probable be Invar.  Because of the 
35% nickel content of Invar, the material cost of 
the support structure will be in the range of $10 
an installed kW.  The cost of solar cells in the 
extreme case is mostly due to the energy required 
to reduce sand (zero cost) and purify the 
silicon.  In very high volume, this would be 
about 40kWh/kg or $4 down to 40 cents at the 
target energy cost.  The space elevator energy 
cost is about a Gw-day to lift a Gw of capacity, 
so an installed kW would take 24 kWh, 24 cents at 
the target energy price.  In the limiting case, 
it seems possible that an installed kW in space 
could be done for under $200 a kW.

There will be some low cost structural mass in 
the rectennas because it takes 4 square meters to 
collect a kW.  It should take in the order of 100 
microwave diodes, but those are already in the 
sub cent range.  Diodes, antenna support, and 
DC/AC power conversion (based on the cost of PC 
power supplies) might be in the $100/kW 
range.  (For a sanity check, 1/3kW PC power 
supplies cost no more than $30 to make.)  Land is 
assumed at zero cost because rectennas can be installed over farmland.

So while initial power sat energy would be sold 
into the market a 5-10 cents a kWh, there are no 
barriers I can see to the cost of bus bar energy 
to synthetic fuel plants falling over time into 
the sub cent per kWh­implying that dollar a 
gallon (or even less) fuels are within physical reality.

Of course, the lower you want to drive cost, the 
higher the initial investment.  Even making use 
of surplus items such as the Enterprise for the 
surface anchor, the cost of the space elevator 
project may be the most expense project ever under taken.

It just depends on how much people want dollar gasoline.

Keith Henson

PS  This sort of material really should go on a 
wiki.  Anyone have a wiki site available?