This is a rather interesting question...
There is, of course, no exact answer to this question. Trying to use
a Ford Expedition engine vs a Honda motorcycle engine will undoubtedly
yield different results. This is due to things like engine
efficiency, compression ratios, and the like.
In a power plant, the fuel is used solely to heat water. The water
becomes steam, and you know the rest. Basically every power plant out
there is a glorified steam engine. We can say that almost all the
heat generated from burning fuel gets used to heat the water. Thus, a
typical power plant is very efficient. Because of this relatively
high efficiency, you would expect power to be cheap. Also, power
plants use fuels like coal and nuclear energy, neither of which can
currently be used in modern cars. Coal is very cheap by industry
standards.
Of course, then there is the fact that the consumer's cost of
electricity includes all the power lines, maintenance, workers, union
fees, CEO's vacation home, etc all of which drive up the cost
somewhat. So in reality, your electricity price includes the cost of
electricity, plus the electric company's costs, plus their profits.
One final point to consider is that utilities are often subsidized by
the government, which drops the price somewhat.
In the case of an automobile, the fuel is used effectively as an
explosive. The fuel explosed inside a cylinder which causes the
piston to move, which causes a driveshaft to rotate. If you connect
an electrical generator to the driveshaft, then you get electricity.
A typical automobile engine is about 25-35% efficient, in the sense
that 25-35% of the energy from fuel is converted to work. Now,
attaching a generator to the driveshaft reduces this figure somewhat.
A good typical electrical generator is about 85% efficient, resulting
in about 20 - 30% total efficiency. This means that about 20-30% of
your total fuel's chemical energy is converted to electricity. The
remainder is converted to useless heat.
In terms of costs, you pay for gasoline and only for gasoline. Of
course, if you want to get picky, you need to include all the
maintenance, depreciation of the car, insurance, oil changes, and so
on. These will be in addition to the gasoline cost. In the case of
the electic company, though, all these "extra fees" are already
included as part of your basic service.
Now that we've gotten that boring introduction out of the way, here's
the answer to your question:
Gasoline has a heat of combustion of approximately 43MJ/kg. One
gallon of liquid gasoline weighs approximately 2.76 kg, so 1 gallon of
gasoline has 118.8kJ of energy.
Assuming an efficiency of 22%, we get approximately 26kJ of
electricity per 1 gallon of gasoline. Subtract the electricity
required to keep the engine running, for things like fans,
alternators, spark plugs, computers, etc, and you get about 24kJ of
electricity output. This is equal to approximately 6.6 kWh.
At $2.00 per gallon for gasoline, you're talking 30.3 cents per kWh.
Interestingly, the Honda EG2500 gasoline powered generator generates
2300W for 2.9 hours on one gallon of gas. This amounts to 6.7kWh or
30 cents per kWh, meaning you get about the same results with a gas
powered generator as you do with a gas powered car engine. No
surprise there. |
