By: Ryan Cashen
When I decided to pursue a graduate education, I knew that I wanted to perform research that would make contributions towards a sustainable energy future. The ability to “generate” and supply energy on demand seems to be a vital aspect of modern life, but the methods that have let us achieve this energy supply have devastated the water, air, plant and animal life that create our global environment. So, what if we didn’t have to choose between our environment and the existence of complex technologies, transportation, products, and social systems? This question is at the heart of a large amount of research in environmental and energy issues. This question is what led me to join the Gebbie Research Group!
To answer questions about how to separate the demand for energy and production from environmental impacts, our group has been working on a few different things. One goal we have is to understand how to control chemical production pathways in ways that save energy and open new doors for the chemical industry (stay tuned for our next ISEE article!). Another goal we have is to explore molecular-level aspects of sustainable energy storage devices and materials. I’ll address a few of the research directions relating to energy efficiency and sustainable energy production soon. First we need to address the following questions: what is energy, how do we generate it, and how do we use it? Let’s dive in!
What is Energy?
Energy—it’s a phrase that we are all familiar with, but the concept can be quite abstract. Nearly all of the classes that I took in my entire undergraduate education are based on understanding the different forms and applications of energy to the world around us. In my experience, the engineering classes that aren’t related to energy were the math classes, which later primarily served to help us model systems related to energy anyway. At one point, I recall renaming my studies as “Chemical Energy-neering”. How can a topic be so broad that it requires so many classes to learn about it and so many researchers to study it? The short answer is that there are many categories and forms of energy. Before we go further, it is important to establish that energy isn’t created or destroyed. However, one type of energy can be turned into another type of energy. Answering the question, “what is energy?” is simplified by first answering the question, “what forms of energy are there?”
The many types of energy are often broken down into broader categories. For example, we often distinguish between kinetic energy and potential energy. Kinetic energy describes how much of an object’s energy comes from the speed that it is moving. For example, a car driving on the highway will have much more kinetic energy than a bike. Potential energy tells us how much energy an object “stores” at one point in time due to the forces that it feels in its environment (which also often depend on the distances between things). For example, a book on the top of a bookshelf has more gravitational potential energy (it is given this name since gravity is the force we consider here) than it does when it is on the floor. But if energy can’t be created or destroyed, and the potential energy is lower with the book on the floor, where did the rest of the energy go? Some of the potential energy was transformed into kinetic energy, which we can see from the object speeding up as it falls. Then, when it hits the floor, that kinetic energy is transferred into various forms, such as sound (acoustic waves in the air), and very small movements in the floor that it hit, which dissipate the energy to a much larger area so we don’t really see much else happen.
Figure 1 – Illustration of a book sitting on the bookshelf with potential energy before it falls off the shelf, transferring potential energy to kinetic energy. When the book lands, the kinetic energy is transferred to the floor and the air (sound). The difference in height before/after the book fell determines how much potential energy was transferred. Illustration by Ryan Cashen.
In some sense, we can think of potential energy as a scale that lets us know how much energy is transferred when an object moves from one place to another. This is useful, since we usually care about how much energy we can get out of devices, not how much energy the object has. These ideas apply to molecules in energy storage devices as well, but the source of the forces is a bit different than in the case of gravity. We often lump together the microscopic forms of energy (microscopic kinetic and potential energy) into one category, called “internal energy”. Changes in internal energy determine how much the temperature of an object will change. If you want to read more about this topic, check out some of the “Learn More!” links below. For energy storage devices, the energy that we are often concerned about is the difference in potential energy that arises from ions (charged atoms or molecules) being on one side of the device compared with the other side. This is a large factor in determining how much energy the device can supply!
Part of the reason that energy is such an abstract concept is that humans have little intuition about it. We can see when objects are moving fast. We can heat or cool our house to a certain temperature, but the amount of energy that it takes to get to that temperature (and hold it there) depends on so many factors. We can tell when things feel ‘warm’ or ‘cold’, but we cannot see or feel energy itself. At best, our senses of taste, sight, touch, smell, and sound are all indirect indications of when energy is transferring from one object to another. It is often still hard to get intuition to tell how much energy is transferred, since different forms of energy are associated with dramatically different amounts of change in things that we sense. The next example may shine some light on why this intuition is hard to develop.
Imagine we heat up one cup of water from room temperature to boiling temperature to make some tea. That would take about 80 kilojoules (a unit of energy), but that number doesn’t really mean that much without more context. More useful is the question of “what else could we do with that much energy?” Pretend that we could take all of that energy and instead put it into the macroscopic kinetic energy of the water (speed!). If we also pretend that the air wouldn’t slow down the cup of water as it flies through the air, then the speed of the object would be more than 1800 miles per hour! This illustrates how powerful (no pun intended) it is to be able to conveniently transform energy into different forms and minimize any inefficiencies. If you are curious about how to calculate some of these values, check out this website (https://www.physicsclassroom.com/class/energy).
Figure 2 – Dramatic illustration of a cup of water flying through the air at 1800 miles per hour (faster than an airplane). In reality, drag forces due to the presence of air would restrict the speed of such objects significantly, illustrating how much of the kinetic energy would get transferred to the air instead. This is why planes don’t go as fast as we wish they did. Flames added for dramatic effect. Illustration adapted by Ryan Cashen.
The importance of energy is hopefully highlighted in these examples. Everything from driving a car, to powering a cell phone, growing a plant, going for a run, and even just thinking, takes energy that has to come from somewhere. Energy is valuable because the transfer of energy in different forms is what makes everything happen.
How do we “generate” energy?
Energy generation is a bit of a misleading term, remembering that we can’t really create energy. Rather, we mean to ask, “how do we transform one form of energy into another form that we can use?” As we mentioned before, the amount of energy that an energy storage device stores really just refers to how much energy we can get out of it. One form of supplying energy is electricity. We’re all familiar with electricity, but where does the current come from? One example is a battery. Ions move across a battery to a lower energy state, and electrons simultaneously move through external wires (whatever device the battery is connected to) allowing us to extract some of that potential energy as electricity to power our phones, laptops, electric vehicles, and more. Another example is a water turbine, which is put in dams to convert kinetic energy from falling water into electricity by rotating a large turbine connected to a generator . The most common form of energy generation is the combustion of fuels. In this process, a fuel is burned, releasing large amounts of heat and carbon dioxide. The heat is transferred to huge baths of water, which then boil to make steam. From here, the steam passes through a turbine, again transforming mechanical energy into electrical energy. For transportation purposes, fuel-based energy is burned, but instead of boiling water to pass steam through a turbine, the combustion of fuel generates large pressures in the vehicles engine, where the piston in the engine then rotates a series of rods leading to the tires of the vehicle.
Figure 3 – Image of a two-cell battery. Ions move across the bridge in the middle to maintain charge balance, and electrons move through the external wire, powering the connected device. Image source: Wikipedia
So what are the sources of energy that we use? Figure 4 shows the sources of energy production worldwide, and how it has changed after nearly 50 years. We see that the largest energy sources are still natural gas, coal, and petroleum, all of which are forms of combustible fuels which release large amounts of amount of carbon dioxide. However, it looks like a larger fraction of the supply switched from oil to natural gas, with Nuclear Energy (this form of energy production would need a whole separate article!) and “Other renewables” slightly increasing.
Figure 4 – Primary energy supply by the type of fuel, worldwide . Image source: International Energy Agency
Researchers from Lawrence Livermore National Laboratory have put out similar information about energy sources in the United States each year, including where the energy is used (Figure 3).
Figure 5 – Sources of energy generation and consumption in the United States during 2019. Information courtesy of the Lawrence Livermore National Laboratory and the Department of Energy. Image source: Lawrence Livermore National Laboratory and the Department of Energy
It looks like “retail electricity” (which does not account for electricity generation on-site at homes or at industrial/commercial sites) is also only about a third of the energy that was used in the United States in 2019.
There are many places where the researchers in sustainable energy and environmental sustainability come into this picture. I’ll take the liberty to divide the research between topics that address issues on supplying energy (generation methods), topics that address issues with delivery of energy, and topics about optimization and control in energy systems. Note: there are many areas of energy research that are actively studied; I’ll only mention a few kinds. Check out this resource if you would like a more comprehensive summary (https://www.nrel.gov/research/learning.html).
Energy Generation Issues and Research
Notice in Figure 5 that only about one third of the energy that is produced actually ends up being useful. The rest of the “rejected energy” is a result of inefficient technologies which make it difficult to avoid things like heat loss when generating electricity with methods that involve high temperatures that result from burning fuels (any “warmth” that you feel is a result of lost energy; a perfect car engine wouldn’t warm up). Keep in mind, making energy production more efficient means that we would have to generate less energy in the first place, resulting in a reduction of harmful emissions associated with fuel combustion processes. One interesting field of research is the study of thermoelectric devices. That is, solid devices with no moving parts that use differences in temperature to move electrons and produce electricity. Could these thermoelectric materials help make energy generation more efficient? It’s a work in progress! Even after the electricity is generated, running the electricity through wires has its own losses; about 5% of the total electrical energy produced is lost in transmission .
Figure 6 – A thermoelectric Seebeck module, which is often used for the opposite purpose of energy generation. Instead of capturing lost heat, it is often powered by a current to generate a temperature gradient (one side gets hot, the other gets cold). Image source: Wikipedia
Many other generation technologies are being studied as well, but we’ll spare you the pages of details and aim for a brief summary instead. Geo-thermal energy often utilizes heat stored under the surface of the earth in geographically appropriate regions to generate electricity via turbines . Current hydroelectric power (recall our dam example) studies include cost/benefit analysis of developing hydropower facilities in various locations . Studies of solar energy generation are under way, seeking ways to increase the amount of energy that is recovered by each photon (each ”particle” of sunlight) that hits the solar panel. If any of these topics are interesting to you, check out the links in “Learn More!” below for a variety of sources about active research in solar energy!
Figure 7 – Geothermal Power Station in Nesjavellir, Iceland. The plume of “smoke” isn’t actually smoke. It is steam generated from the electricity generation process. Image source: Wikipedia
Another field of research related to the sustainability of energy supply is the development of better strategies for capturing pollutants that come from fuel-combustion sources of energy. The idea here is that if we capture much more of the harmful products of burning fuels, then the environment will not be negatively impacted, and we may be able to use the captured materials for something useful! The common name for this research is “carbon capture”. Some of the research in this field is performed by the companies that burn the fuels in the first place, since the source of the pollutant is in their chemical plant . The goal is to continuously reuse materials that conveniently “soak up” carbon dioxide (fun fact: some Ionic liquids can do that!) and other species, and then pass that material into another piece of equipment where the carbon dioxide is stored. There are a variety of other options for sustainable energy generation that involve specialized equipment at the energy generation site, but we’ll save that discussion for another time.
Energy Delivery Research
Consider all the actions that you take each day, and how they change the amount of electricity that you use. Before you wake up, the chances are that you aren’t using as much energy. When you wake up, turn on lights, cook a meal, turn on heating or air conditioners, or take a warm shower, you are changing the amount of energy that energy systems must deliver. Multiply this much variation in energy demand by the millions of people that energy systems might have to provide for, and you’re in for a logistical nightmare. To make matters worse, renewable energy sources, like solar energy, only come at certain times of the day! The early morning and the evening are the times of the day where energy demand starts to increase, which is the same time that the sun either is still rising or is starting to set !
Figure 8 – Image of the rising sun, when solar energy is limited, but the demand for power rises as well. Image source: Needpix.com.
If the energy producers at any point don’t meet the total demand, then some locations may experience dimmed lights, lower power, or no power at all. Imagine if a hospital were to lose power; that’s a disastrous scenario. Luckily, many essential services have backup generators . The ability to store excess energy on-site is a great backup plan, but let’s discuss how energy storage technologies could potentially help smooth the demand for energy to make delivering energy a more consistent job, therefore reducing the likelihood that energy demand isn’t met in the first place.
The idea behind peak shifting is to store the leftover energy that is produced from renewable resources when the demand is low and use it when the demand is high. On top of providing more energy from renewables, this has the added benefit of smoothing out the amount of electricity that providers need to supply . However, this method requires there to be a device or system where energy can be conveniently stored and drawn. The popular choice for this method at the moment is Pumped Hydroelectric Storage, which was estimated to comprise about 96% of the world’s energy storage capacity . The idea here is to pump water uphill when energy is produced in excess and flow it back downhill to generate electricity when it is needed. There are many active investigations that explore the applicability of various forms of batteries, such as lithium ion, lead-acid, redox flow, and molten salt batteries, for grid-scale energy storage .
The study of batteries and other ion-based electrical energy storage devices has significant promise for increasing the safety of electronic devices and vehicles. While hydro-power is great for storing energy on the large scale, we unfortunately can’t really use a waterfall to power our electric vehicle. Hydrogen fuel cells have been mentioned as a possibility, however, hydrogen is flammable and poses a serious safety risk when stored in large enough amounts that would make commercial transportation feasible. Fuel cells are super exciting devices, however, and you should check them out if you get the chance!
As the shift towards electric vehicle production gains steam, the demand for fast-charging, large capacity, and inherently safe ion-based energy storage devices increases. This field of research is part of what the Gebbie research group is working on! If the way that ions move in energy storage devices is better understood, then materials can be selected to allow the device to be charged very rapidly. If the interactions between ions and the various portions of the energy storage devices are better understood, then the device can be designed to be stable at many different conditions (thus avoiding the recent case-studies of flammable cell phones and electric vehicles). These improvements would facilitate a smoother transition away from combustion-based transportation and make your next electric vehicle road trip much more enjoyable!
Figure 9 – Cartoon representation of an ionic system where the movements of ions can be studied. Aspects that may be important are the symmetry, the attractive/repulsive forces, sizes of the ions, and the “electric field” imposed on the system. Image provided by the Gebbie Lab
Optimization and Control Strategies for Energy Systems
Some areas of energy research span both the supply and the delivery of energy. Design and optimization of models for energy systems allow researchers to make decisions about many factors that influence the overall efficiency of energy systems. For example, Dr. Victor Zavala’s group here at UW-Madison performs optimization on energy systems to address challenges such as intermittent renewable energy, and resulting price uncertainty (link to website: http://zavalab.engr.wisc.edu/projects/batteries). Since power demand changes throughout the day, the pricing often does as well, adding further complexity to managing energy systems. Optimization techniques can help energy systems utilize the tools they currently have to ensure power demand is met. Bottlenecks and shortcomings can be identified to motivate modifications to current infrastructure as well. Researchers in this field can account for economic, policy, and technology factors that can provide information to legislators and energy producers to develop a more robust and efficient energy market. For example, a robust analysis could identify the costs/benefits associated with installing renewable infrastructure. Such tools and analyses are important for understanding the complexity of large-scale systems which include many constraints on how much, how often, and where energy can be produced or demanded.
Figure 10 – Cartoon of power plant distribution, indicating the many logistic concerns that come into play for supplying power. Image source: Wikipekia
It is fascinating how energy can be so convoluted, yet so instrumental in everyday life. With our world demanding more and more energy to support so many aspects of our society and culture, researchers expand the search for solutions to achieve this demand without harming our environment (including ourselves!). It is exciting to be a part of the field of researchers who are working to understand sources of sustainable energy sources and develop technologies to meet current needs. We are excited to see how the field progresses and share our learning with the broader community.
- There is a large amount of publicly available information across many fields at the National Renewable Energy Laboratory website https://www.nrel.gov/research/data-tools.html
- Khan Academy is an excellent online resource for learning a variety of topics! Here is a link to their discussion on some different types of energy. https://www.khanacademy.org/science/biology/energy-and-enzymes/the-laws-of-thermodynamics/a/types-of-energy
- An introduction to energy calculations https://www.physicsclassroom.com/class/energy
- Information about hydroelectric powerhttps://www.instituteforenergyresearch.org/?encyclopedia=hydroelectric&gclid=Cj0KCQjwu8r4BRCzARIsAA21i_BE65bUl4Kh1jiVKch9bZ4GBb6R3kgVT_5BGMLANzlWyyar4wj7bFkaAmD-EALw_wcB
- More information on how generators transform mechanical energy into electricity https://www.eia.gov/energyexplained/electricity/how-electricity-is-generated.php
- The MIT Energy Initiative has a large amount of information about modern research initiatives related to sustainable energy. They also have a podcast, so feel free to check that out! http://energy.mit.edu/
- Check out this website for some active research being performed in the field of solar energy: https://www.energy.gov/eere/solar/solar-energy-evolution-and-diffusion-studies-seeds
- An excellent source from NREL about the various types of renewable energy https://www.nrel.gov/research/learning.html
- A general summary of grid storage techniques that exist in the United States, and some quantitative measures of how much each technique contributes http://css.umich.edu/factsheets/us-grid-energy-storage-factsheet
- Our own previous ISEE article about ionic liquids and some of their interesting applications https://interfaces.che.wisc.edu/what-are-ionic-liquids/
- Excellent source on many frequently asked questions regarding grid-scale battery energy storage https://www.nrel.gov/docs/fy19osti/74426.pdf
|||iea.org, “Total primary energy supply by fuel, 1971 and 2017,” 26 November 2019. [Online]. Available: https://www.iea.org/data-and-statistics/charts/total-primary-energy-supply-by-fuel-1971-and-2017.|
|||U. E. I. Administration, “How much electricity is lost in electricity transmission and distribution in the United States?,” 31 Dec. 2019. [Online]. Available: https://www.eia.gov/tools/faqs/faq.php?id=105&t=3.|
|||IRENA, “Geothermal Energy,” International Renewable Energy Agency, 2020. [Online]. Available: https://www.irena.org/geothermal. [Accessed 16 July 2020].|
|||O. o. E. E. a. R. Energy, “Hydropower Research & Development,” Energy.gov, 2020. [Online]. Available: https://www.energy.gov/eere/water/hydropower-research-development. [Accessed 18 July 2020].|
|||ExxonMobil, “Carbon Capture and Storage,” ExxonMobil, 2020. [Online]. Available: https://corporate.exxonmobil.com/Research-and-innovation/Carbon-capture-and-storage?utm_source=google&utm_medium=cpc&utm_campaign=XOM+%7C+Corp+%7C+ELH+%7C+Traffic+%7C+Non+Brand+%7C+Technology+%7C+Carbon+Capture+%7C+Exact&utm_content=Non+Brand+%7C+Carbon+%. [Accessed 18 July 2020].|
|||U. E. I. Administration, “Demand for electricity changes through the day,” Independent Statistics & Analysis, 6 April 2011. [Online]. Available: https://www.eia.gov/todayinenergy/detail.php?id=830. [Accessed 18 July 2020].|
|||APNews, “Backup generators keep hospital operating in power outages,” AP , 21 Mar. 2019. [Online]. Available: https://apnews.com/051daafc9f7348649f34eac94cc5d818. [Accessed 18 July 2020].|
|||C. S. Engineer, “Implementing energy storage for peak-load shifting,” CSEmag, 12 Dec 2014. [Online]. Available: https://www.csemag.com/articles/implementing-energy-storage-for-peak-load-shifting/. [Accessed 05 07 2020].|
|||T. M. Gür, “Review of electrical energy storage technologies, materials and systems: challenges and prospects for large-scale grid storage,” Energy & Environmental Science, vol. 11, no. 10, pp. 2696-2767, 2018.|
|||T. Bowen, “Grid-Scale Battery Storage,” Sep. 2019. [Online]. Available: https://www.nrel.gov/docs/fy19osti/74426.pdf. [Accessed 19 Jul. 2020].|
|||V. U. o. Technology, “New material breaks world record for turning heat into electricity,” 14 Nov. 2019. [Online]. Available: https://phys.org/news/2019-11-material-world-electricity.html.|