EROEI

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From the course by University of Illinois at Urbana-Champaign

Introduction to Sustainability

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University of Illinois at Urbana-Champaign

Introduction to Sustainability

500 ratings

This course introduces the academic approach of Sustainability and explores how today’s human societies can endure in the face of global change, ecosystem degradation and resource limitations. The course focuses on key knowledge areas of sustainability theory and practice, including population, ecosystems, global change, energy, agriculture, water, environmental economics and policy, ethics, and cultural history. This subject is of vital importance, seeking as it does to uncover the principles of the long-term welfare of all the peoples of the planet. As sustainability is a cross-disciplinary field of study, this foundation requires intellectual breadth: as I describe it in the class text, understanding our motivations requires the humanities, measuring the challenges of sustainability requires knowledge of the sciences (both natural and social), and building solutions requires technical insight into systems (such as provided by engineering, planning, and management).

From the lesson

Energy

In this module, we will look at energy use. We will also consider what the trend of energy use means for the planet, and how we might transition to a more sustainable pattern of use.

Meet the Instructors

Dr. Jonathan Tomkin
Associate Director
School of Earth, Society and Environment

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.

What happens if we there was an energy return of one.

Just think about this for a moment. It's not worth the effort.

We get just as much energy back as we put in.

What happens if the energy return goes below one?

Well, that's senseless. We're getting less energy back then we're

putting in. That's a little bit like investing $ten

and getting $five back. That would be an energy return of .5.

Clearly, that is not worth our time or our effort.

So in general, fossil fuels have seen a decline on that energy return of

investment. Coal and natural gas still look pretty

good though. Are those sources gonna be available in

the future? That's what we'll look at in the next

lecture. >> Produced by OCE, Atlas Digital Media,

at the University of Illinois, Urbana-Champaign.

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