The Peak Oil theory does not
maintain that we are running out of
oil, but rather that oil discoveries and production are already going
into a
permanent decline, with ever increasing production costs and ever
decreasing reserves.
Professor
Gigabyte
"Understanding
depletion is simple. Think of an Irish pub. The glass starts full and
ends empty. There are only so many more drinks to closing time. It is
the same with oil. We have to find the bar before we can drink what is
in it."
Colin Campbell
What
peaking does mean, in energy terms, is that once you've peaked, further
growth in supply, is over. Peaking is generally, also, a
relatively quick transition to a relatively serious decline at least on
a basin by basin basis. And the issue then, is the world's
biggest serious question.
An important element in comparing
fossil fuels with other forms of energy generation goes by the
unfortunately unmemorable acronym of EROEI – "energy returned on energy
invested". An alternative version of this is the EPR – Energy Profit
Ratio. To produce any energy, whether it is pumping oil out of the
ground, or building and operating a wind turbine, you need to use some
energy in the process. If the energy returned is less than the energy
you produce, it is generally not worth producing it (but see below).
As a simple example, imagine a (very
small) car whose fuel tank holds 1 liter of petrol. The car's
fuel efficiency is 20 km per liter. If the nearest petrol station is 5
km away, fine – you wait until the tank is quarter full then drive
there to refill (positive EROEI). If it is 10 km away, you have gained
nothing (and lost money) – by the time you have refuelled and driven
home, you only have enough fuel left to return to the station to fill
up again. And if the station is 15 km away, once you have filled up and
reached home, you would not have enough left to get back to refuel
again. You would be better off staying at home and simply using up the
existing petrol for other journeys (negative EROEI).
This example is mainly about fuel
consumption rather than EROEI but the analogy holds: if you think of
taking petrol from the station as extracting oil from a well, and the
petrol used to drive to and from the station as the combined energy
used to extract oil (manufacturing materials, building roads and
pipelines, operating the well), you can see the principle.
The EROEI is calculated by taking the
energy content of your energy (in whatever units you wish) and
subtracting the energy used in producing the energy. The result will be
a number either negative, positive or zero. The higher the number, the
better.
The EPR is similar but the energy
content is divided by the energy to produce: the answer will be a ratio
where 1 is equal to the zero if EROEI, and less than 1 is equal to a
negative.
As an example, if it takes the
equivalent of 1 MJ of energy to extract oil which, when burnt, can
produce 10 MJ, then the EROEI is 10–1 = +9 and the EPR is 10/1 = 10. If
it took 15 MJ of energy to extract the oil, the answers would be –5 and
0.7.
The only time when negative
EROEI can be worthwhile is if the energy produced is in a more useful
form than the energy used. For example, oil can be used not only for
energy generation but to make petrochemicals whereas wind-generated
electricity cannot. So it could be more worthwhile using some
wind-electricity to pump oil-energy out, even if the EROEI is negative.
Using the car analogy above, if the journey to the 15 km petrol station
was also used to deliver some goods to sell, you would gain elsewhere
even if you lost out on the petrol. But negative EROEI is only
acceptable if you have ample supplies of the one form and it looks
likely in the future that we will be struggling for all.
