On embodied energy and eROI
Dr. Lars Schernikau: Energy Economist, Commodity Trader, Author
Details including the full Blog The energy nobody counts: embodied energy, the first step in understanding eROI
are available at www.unpopular-truth.com
We spend a great deal of time discussing how much energy our electricity systems can “produce” but far less attention is given to a different question of how much energy does it take to build them in the first place?
Every power plant begins long before the first unit of electricity reaches the grid. Raw materials are extracted and processed, components are manufactured, equipment is transported, infrastructure is constructed and the entire system is assembled.
Energy is consumed at every step and the energy investment is largely invisible once the finished power plant begins operating, but it has not disappeared from the equation.
This is embodied energy, and understanding it is essential if we want to estimate how much energy an energy system truly returns to society.
When we talk about an energy technology, we tend to focus on what happens once it is operating:
- how much electricity it generates
- how much it costs to operate
- its emissions during operation
- its natural capacity factor driven by nature
- its operational utilization or curtailment and
- realistically how long it is expected to last
Figure 1: The Embodied Energy Cycle … of Electricity Generating Equipment
But a power plant does not begin its life at the moment it produces its first kilowatt-hour, as long before this moment, energy has already been consumed. (Figure1)
Raw materials must be mined, ores must be processed and refined, steel, aluminium, copper, silicon, cement and countless other materials must be manufactured. Components must be produced, transported and assembled. Roads, foundations, transmission connections and other infrastructure may need to be constructed.
All of this requires energy – embodied energy which is the energy invested in creating the system that will subsequently produce energy for us.
And once we begin looking at energy systems through this lens, an interesting question emerges:
How much energy do we have to invest before we get energy back? As we all understand that energy is not created from nothing.
For example, let’s consider a solar installation.
Sunlight itself may arrive without a fuel bill, but converting that sunlight into enough, usable electricity requires a substantial physical system.
Quartz and other raw materials must be extracted, silicon refined and processed. Glass, aluminium, copper and steel all materials used for the production of solar cells, modules, inverters and electrical equipment. Everything must then be transported to the project site and installed and after some years, dismantled and disposed.
The same principle applies to every energy technology. Wind turbines require steel, concrete, copper, composites and extensive manufacturing. Nuclear power plants require enormous quantities of specialised materials and construction. Coal and gas require mines or wells, processing, transportation and generating infrastructure.
The question, therefore, is not whether an energy technology requires energy to exist. They all do. The more useful question is how much.
From embodied energy to energy return
This is where the concept of Energy Return on Investment, or eROI, becomes very interesting. At its simplest, eROI asks us to compare the energy an energy system delivers with the energy required to make that energy available.
The principle is quite intuitive. If we invest one unit of energy and receive only slightly more than one unit back, very little surplus remains. If the same energy investment produces a much larger energy return, the situation looks very different.
This makes eROI fundamentally different from a purely financial measure.
Money can change value as commodity prices fluctuate, interest rates move, subsidies, taxes and regulation can all change project economics considerably.
Energy, however, remains physical.
A ton of steel consumed energy during production, regardless of how its financial cost was allocated, and that makes the energy invested into our energy infrastructure worth understanding.
But where do we draw the line on embedded energy?
This is where the apparently simple idea becomes considerably more complicated.
What exactly should count as embodied energy?
Should we include only the energy required to manufacture the principal equipment? Or should we include:
- mining and refining the raw materials?
- transportation?
- construction?
- supporting infrastructure?
- grid connections?
- replacement components?
- decommissioning?
The answer to this question is an important one, because changing the boundary changes the result.
Another very important variable in this equation is asset lifetime.
A system operating for 20 years will produce a different lifetime energy return from one operating for 30 or 40 years.
Natural capacity factor also matters hugely, because installed capacity tells us how much a system could generate at a given moment and not how much electricity it actually “produces” over its lifetime.
Even seemingly small assumptions can therefore have surprisingly large consequences.
This is why a headline comparisons of different energy technologies should be considered carefully. Two studies can appear to analyse the same technology and arrive at very different conclusions without either necessarily being wrong. They may simply be making different assumptions, using different lifetimes and natural capacity factors and utilization assumptions.
What happens when we apply this to a real project?
The theory becomes much more interesting when applied to something that actually exists. In my latest analysis, I use the Al Dhafra Solar PV project in the United Arab Emirates as an illustrative case.
It is one of the world’s largest solar photovoltaic projects and provides a good opportunity to ask a deceptively straightforward question.
How much energy had to be invested before this project could begin producing electricity, and how should we account for it?
Answering that means moving backwards through the physical system…
- panels become silicon, glass, aluminium and other materials
- mounting structures become steel
- electrical systems require copper and additional components
- leading us further upstream into mining, refining, manufacturing and transportation…
Suddenly, the finished solar farm that we see above ground becomes the final stage of a much larger industrial and energy chain and the precisely where embodied energy becomes useful.
It forces us to look beyond the visible generating asset and to consider that the numbers are only as good as the assumptions made.
Estimating embodied energy for a project of this scale is not a matter of finding one number in a database.
Material quantities need to be estimated, energy intensities must be assigned, manufacturing and transport assumptions need to be considered and system boundaries must be identified.
Figure 2: Embodied energy and price correlate [based on Gutwoski et al 3]
Then the energy invested must eventually be compared with the energy the project can realistically be expected to generate.
And here we have another important distinction to consider – Installed capacity is not useful electricity generation.
A gigawatt of installed capacity does not “produce” one gigawatt continuously throughout the year. Actual generation depends on the resource, location, operating conditions, natural capacity factors, utilization, curtailments, system losses and other factors. The expected lifetime then determines how long that annual output continues.
Change those assumptions and the resulting energy return changes with them.
That does not make the exercise useless… but quite the opposite.
It reveals exactly which variables we need to understand before making sweeping claims about the performance of an energy technology.
The first step
Embodied energy alone does not tell us whether solar, wind, coal, gas, hydro or nuclear is “good” or “bad”. Nor should eROI be treated as the only metric by which an energy system is judged.
Energy systems have to satisfy many requirements simultaneously: reliability, affordability, environmental impact, resource requirements, infrastructure needs and their ability to deliver energy when and where society requires it. But before comparing the energy return of different technologies, we first need to understand what we are counting.
That begins with the energy invested
And that is why embodied energy is not the conclusion of the eROI discussion.
It is only the beginning
In “The Energy Nobody Counts – Embodied energy: The first step in understanding eROI”, I go considerably further, breaking down what embodied energy entails, examining the methodological boundaries, and applying the concept to the Al Dhafra solar project to see what the numbers could look like.
The calculations and what they imply for the next step in understanding eROI, makes the story a particularly interesting one.
Take a moment to read my blog: “The Energy Nobody Counts – Embodied energy: The first step in understanding eROI
