| You can pick these up on the net for about $30 (google
"KILL-A-WATT"). It displays an impressive array of all kinds of
electrical data, but most importantly it will tell you how many
watt-hours of electricity it took to accomplish a fill. You can see in
the picture above that the PHILL is pulling 830 watts, which is
comparable to a midsize microwave oven or a 1HP motor. I did notice that
power consumption increased as the fill progressed, with the PHILL
drawing in excess of 900 watts towards the end of the cycle. Again, not
really surprising. Too bad the KILL A WATT doesn't have a pulse output
or this thing would really be the bomb! OK, so you
probably want to know what the bottom line is. In order to figure out
what it's costing me to fill up my car we have to do a little bit of
math. As consumers, we are programmed to think in terms of gasoline
usage when it comes to the economics of alternative fuels. Naturally, we
want to compare how much we pay to fill up our car with the price per
gallon on the sign at the gas station. Because of this, the amount of
CNG fuel dispensed or stored in a vehicle is usually specified in GGE,
or gallons of gas equivalent. 1 GGE would be roughly equivalent to the
amount of energy delivered by 1 gallon of regular unleaded gasoline. The
exact value varies because the energy content of both natural gas and
gasoline vary by region and time of year, but a widely accepted
approximation is that one GGE is equivalent to 127 cubic feet of natural
gas.
That being said, I can now correlate the amount of gas registered on
my gas submeter to GGE. According to the owner's manual, my Honda Civic
GX holds 8 GGE at 3600 PSI. So using the conversion factor of 127 cu.
ft. per GGE, I would expect to use roughly 1000 cu. ft. of gas to fill 'er
up from empty. Of course, nobody in their right mind would run a NGV to
empty.
The other part of the equation is how much you pay for the gas piped
into your house. This varies greatly depending on where you live and
what time of year it is. I live in SE Wisconsin, and my current rate for
gas (August 2005) is $0.9352 per therm. What the heck is a therm you may
ask? Well, here comes the science: a therm is a term (of course of
course) used by the gas industry to bill for your gas usage based on
its' energy content. Technically, a therm is the volume of gas required
to deliver 100,000 BTU of heat energy. A good approximation to use is
96.7 cu. ft. of gas per therm. With that in mind, it takes about 1.3
therms of gas to make 1 GGE of CNG. That adds up to $1.215 per GGE. Not
bad, considering that gas is running close to $2.50 per gallon around
here.
That would be all we needed to know if it wasn't for the electricity.
Since the PHILL can only pump 0.4 GGE per hour, it would take 2.5 hours
of run time to compress one GGE of gas. With an average draw of, say,
875 Watts of electricity it would take about 2.2 KWH (kilowatt-hours)
per GGE. Again, the cost of electricity varies by location and time of
year (sometimes even time of day). I currently pay about $0.10 per KWH
(August 2005) so we would have to add $0.22 per GGE to the cost of the
gas.
That brings the price up to about $1.43 per GGE. If we could stop
there, this price would be comparable to the current price at the pump,
which is about $1.45 at my nearest fill station. Unfortunately for
me, the local government still wants their tax dollars despite all the
economic and environmental benefits using a clean burning fuel like CNG
brings to the party. Currently the state of Wisconsin has no incentives
for using alternative fuels, and they levy a $0.24 per gallon tax on all
alternative fuels as well. Shame on you, Wisconsin! Anyways, that brings
my cost per GGE to $1.67. It's still a deal compared to gasoline, plus
I'm not funding the evil oil empire anymore. Take that, Exxon! Sorry
"Shrub". <insert your own smug epithet HERE>.
|
