How to continue economic growth in a context of energy transition? Prof. Hervé Jeanmart1 and PhD student Elise Dupont2 try to answer this question by studying the return on renewable energy investment and its impact on society.
‘We must aim for 100% renewable energy!’ We’ve all heard this kind of confident statement. Today, however, in most developed countries, so-called ‘modern’ renewable energy sources such as wind and solar are still in their infancy. Faced with this need to move towards 100% renewable energy, Prof. Hervé Jeanmart and PhD student Elise Dupont ask: What is the real potential of renewable energy (wind and solar)? What is its capacity to replace fossil fuels while satisfying the growing needs of societies driven by economic and demographic growth?
Return on energy investment
To answer these questions, Prof. Jeanmart has been working for several years on return on energy investment. ‘We all know about return on financial investment’, he says. ‘Return on energy investment is a similar concept, but focused on energy production.’ To build energy-generating facilities (e.g. a wind turbine), materials must be assembled, moved, installed, maintained, dismantled, recycled, and so on. All these actions consume energy. On the other side, as soon as the wind blows, the wind turbine produces energy. Energy return on investment is the ratio between what a facility produces over its lifetime, and what is required to build and maintain that same facility.
A word model
For four years, Elise Dupont, a PhD student at the UCLouvain Institute of Mechanics, Materials and Civil Engineering (IMMC), has worked under the supervision of Prof. Jeanmart, especially on wind and solar energy. She addresses how much energy such facilities produce. Her main source is global weather data, coupled with land use databases. Using a grid drawn on a map of the world, she first identified areas where we can’t install solar panels or wind turbines (city centres, unpopulated areas, mountains, etc.). She then estimated one facility’s output and solved an optimisation problem that concerns wind turbines in particular: if we put a lot of wind turbines in the same area, they influence each other and their yield is lower. She then analysed the potential of each area and sorted the data by quality according to their energy return. In addition, she focused on facility life cycle analysis: what energy mobilisation is needed to build and maintain a wind turbine or solar panel? The result is a ratio, the so-called energy return rate, which will fuel other studies on the consequences of our societies’ energy transition.
Diminishing energy returns over time
In our current energy system, energy sources with very different ratios coexist. For example, oil has a very high energy ratio (from 60 to 100 to one) because, at least originally, it took little energy to draw it out. At the other extreme, biofuel has a fairly low energy return (from two or three to one). Our researchers noted that any given ratio decreased over time. Take the example of oil, which, originally, sprang naturally under pressure. Over time, more expensive equipment had to be used to extract it. Its energy return has dropped, and perhaps one day oil will be too expensive in terms of energy return to extract. For wind and solar, the ratio also decreases, in accordance with their expansion, the best sites being exploited first. One thing is certain: the ratio of renewable energies is currently lower than that of historical oil. That raises a question: Can we maintain society as we know it with a renewable energy source that has a lower energy return?
Preventing economic collapse
If UCLouvain researchers are interested in this issue, it’s because economists are also thinking about the trajectory that society could follow in the event of an energy transition. However, they already say that below a certain ratio, our societies are collapsing, especially because the energy sector takes up too much of our economic activity. Studying energy return on investment makes it possible to anticipate the right paths to take and determine the conditions and parameters that would make possible a transition to a renewable world, thereby preventing collapse and preserving our societies. Renewable energy ratio decrease rates are a function of renewable energy expansion and will fuel the work of economists but also other researchers who think globally about the consequences of the energy transition on our societies.
Toward significant solar energy development
At this stage, some conclusions can already be drawn from the analyses by Ms Dupont and Prof. Jeanmart. ‘It’s confirmed that at a global scale, the potential of wind and solar is very great’, Prof. Jeanmart says. ‘This potential is even far above our current needs. On the other hand, for Europe, current consumption is of the same order of magnitude as the potential.’ Next, concerning wind, the main finding is that there are many good sites around the world to install turbines, but wind’s energy return rapidly decreases as it expands. Solar panels don’t influence each other. Their ratio, although lower than that of wind, decreases less rapidly as their use expands. ‘Solar will still develop significantly’, Prof. Jeanmart says. It will do so in one of two ways:
panels will be more efficient and more expensive;
panels will be less efficient and less expensive and easier to install en masse.
Thus, according to UCLouvain researchers, the planet’s energy future will involve development of solar and wind while changing our consumption patterns in accordance with lower returns on energy investment.
Now that most of the figures have been collected, the UCLouvain team plans to do the same work for biomass, which will be more complex analytically given the sector’s diversity. Next, the objective will be to introduce data in economic models that predict possible trajectories for our societies during energy transition. This would be the starting point for a study linking energy and economics. In a few years, the study of the physical constraints of renewable energy installations will be completed. Other researchers will be able to seize these numbers and see how to continue to develop our societies in a harmonious way.
(1) Professor at the Louvain School of Engineering (EPL) and member of the UCLouvain Institute of Mechanics, Materials and Civil Engineering (IMMC). (2) PhD student at the UCLouvain Institute of Mechanics, Materials and Civil Engineering (IMMC).
A glance at Hervé Jeanmart's bio
Hervé Jeanmart has been a UCLouvain civil engineer since 1996. In 2004, after his PhD studies and thesis on fluid mechanics (defended in 2002), he became a professor at UCLouvain. He is a member of the Institute of Mechanics, Materials and Civil Engineering (IMMC). Active in the field of thermal machines and alternative fuels, he also studies links between energy and economic activity.