I'm Jonathan Tomkin from the University of Illinois.
We've just been talking about oil and about how consumption of oil has moved
from conventional to unconventional reserves.
These unconventional reserves prove, prove not just technological challenges, they
also require more effort. The early oil sources sometimes gushed out
of the ground, whereas today, much more effort is needed to extract that oil.
In the early days, you would need to use about one oil barrel's worth of energy to
get 100 oil barrels extracted. This number has been declining in recent
years. Modern efforts, for example, offshore
drilling requires maybe ten times as much effort.
So we would only get ten oil barrels worth of energy back for that oil barrel of
energy invested. This is a increasing problem in fossil
fuel extraction in, in the world today. This concept is known as energy returned
on energy invested. Its the ratio of how much energy we get
back on a given effort. You might think of it as similar to
financial return on an investment. If you invest $1,000 and returned $2,000,
then you would have a factor of two, you have doubled your money.
So, we would say, you would have an EROEI of two To make a renewable energy example,
if we use 200 megawatt-hours to construct a wind turbine it reproduces about 200
mega watts per year, and has a life span of around twenty years, we might say it
has EROEI of twenty. Those figures are roughly right, so we can
see that when we construct a wind turbine, we get a net energy return.
We get twenty times as much energy back as we put in.
Here's a list of those sorts of energy returns.
As you can see, different methods of energy extraction have different energy
returns on energy invested. And there has been changes over time.
What's interesting of course is that everything requires some energy investment
in the beginning. If we're going to build a wind farm, for
example, we have to manufacture the steel or aluminum and build the structures and
that requires energy. So we need to invest some energy in the
beginning to get that return. The problem is that things are getting
worse. Oil and gas in the 1970's return, had an
energy return of about 30 and then more recently, we're seeing numbers like
fourteen, even ten, and the oil sources of the future, things like tar sands and
shale are even worse with energy returns of around five.
So we're only getting five barrels of oil back for every barrel of oil we burn to
extract it. Hydro power is very good.
We get very high energy return. I remember we have to build dams and build
turbines and so there is an energy investment, but we have a very high energy
return for those systems, but most renewables aren't nearly as good.
Whan we build the PV array or wind power farm, we have to put a lot of energy into
creating, manufacturing those devices. Similarly, another popular renewable
energy source, bio-fuels, has a very low energy return.
This varies from country to country but in the United States, most estimates of the
energy return of bio-diesel from soy or ethanol from corn has a value of 1.3.
So in other words, for every barrel of oil that we invest in producing that resource,
we get about 1.3 back. So a very low energy return.