Before my memories grow even dimmer I should write down some thoughts about the class I taught Spring term: The Physics of Solar and Renewable Energies. Like its companion course, The Physics of Energy and the Environment, which I taught the quarter before and wrote about here, it’s a course for non-science-major undergraduates at the University of Oregon (UO). Again I taught online, using Zoom, during our third and hopefully last quarter of Covid-induced remote education. The course syllabus is here.
The goals of the course are to convey an understanding of how alternative energy sources (alternatives to fossil fuels) work, and what determines their abundance and accessibility. The Energy and the Environment class isn’t a prerequisite, so we very briefly sketch the background of how much energy we use and why we should care about alternative energy.
A major theme of the class is the importance of being quantitative about energy. Popular media, and popular opinion, are filled with absurdly innumerate treatments of energy issues, most often in the form of silly “let’s use X for green energy!” articles. (See here for example.) Our power consumption in the industrialized world is enormous — each of us have the equivalent of a hundred 100-Watt light bulbs constantly running — and over 80% of our energy is supplied by burning fossil fuels. I try to convey that it’s important, and easier than people realize, to make simple, powerful estimates of energy use and abundance.
Mini-projects: hydro, wind, and solar abundance
The course has a variety of assignments and assessments. Among them were three “mini-projects” in which students assessed roughly how much power is available and how much is currently being used from water, wind, and sunlight, considering particular U.S. states and some global regions. By “available” I mean available in a fundamental sense, set by the physics underlying these energy sources, which we explored in the classes preceding each exercise.
Hydroelectric power, for example, is set by the rate at which water collects and descends from higher to lower ground, determined by the total rainfall in a region and the elevation difference between that region’s high and low points. A flat, dry state has less hydroelectric potential than a hilly, wet one. It’s entertaining to sketch a cartoon of each state as a flat block, with elevation and rainfall being things one can look up, and ask what power the state would get if it captured, for example, 10% of the maximum power allowed by simple physical laws related to gravitational potential energy. Here’s me sketching (not during class, but in a video I made separately):
The students each evaluated this for several states, looking up their annual rainfall and mean elevation to estimate the upperbounds on hydropower. (Here’s the assignment.)
What one finds is that there are already several states, including Oregon and Washington, that are generating this much hydroelectric power — in other words, there’s little room for improvement. The same conclusion follows from more detailed assessments (such as this, from the Dept. of Energy) and from other people’s rough estimates, such as this from a wonderful book by Tom Murphy at UCSD that inspired this exercise and that I’ll comment on more below. One could at best expand hydropower by a factor of 2 or 3 in the U.S., but not more than this. (And note that in the Northwest, we’re dismantling dams to facilitate fish migration; it’s hard to imagine changing course to build more dams instead.) Currently, the U.S. gets about 2.5% of our energy from hydroelectric sources. Globally, the potential for increasing hydropower is a bit larger than it is in the U.S., but not by a lot.
For wind, we can think about the rate at which kinetic energy is carried by moving air, which sets the upperbound on how much power something that captures that kinetic energy (like a wind turbine) can generate. For this, wind speed is crucial. This isn’t surprising, but the scaling with wind speed is — as we deduce in class, power scales as wind speed to the third power, so a region with twice as fast winds will have eight times the power available. (Hence the appeal of turbines in blustery off-shore spots.) There’s a wonderful interactive online resource of wind speeds all over the globe, the Global Wind Atlas:
One can select or draw regions and learn the average windspeed, and even the distribution of speeds. Using this to calculate the power that’s potentially available leads to the conclusion that expanding wind power by 10x or more is feasible, again a similar conclusion to what’s reached by more exact methods. Given that wind currently supplies about 2.6% of our energy in the U.S., one can expect wind to be able to be a sizeable, but not dominant, source of power. (There are challenges to achieving this, of course, most notably storage.) The assignment is here.
The final mini-project is on solar power. Again, there’s a great resource, the Global Solar Atlas.
Again, one can draw or select regions, and assess how much solar power potential there is. I had the students graphically indicate the amount of ground coverage necessary to supply reasonable amounts of power; one finds that it’s not much land — there’s a lot of power available in sunlight, more than enough to supply us. Of course there are significant challenges — cost, storage, and more — but abundance isn’t an issue. The assignment is here.
All of these estimates are almost comically simple, but are remarkably accurate in terms of “orders-of-magnitude” assessments of renewable energy futures. I claim that every journalist who writes about energy or climate should be able to do analyses like this, a state were not even remotely close to.
I would have liked to do more with nuclear power. We covered it briefly. I’ll just copy what I wrote about last term, since it still applies: “It’s hard to cover nuclear power without being dismayed by our low use of it — it’s clean, well-understood, abundant, and extremely safe. This link gives an excellent graph of death rates per energy extracted, even including disasters like Chernobyl, kills far fewer people than fossil fuel pollution, and doesn’t produce CO2 emissions.” Issues of waste are not difficult to deal with, especially in comparison to issues of carbon dioxide emissions from fossil fuels. Unfortunately, I don’t think we’re actually serious about tackling climate change if we’re not open to nuclear power.
I thought the projects went well — students found them interesting, I found them interesting, and they gave some practice in looking up data, analyzing data, and thinking a bit. Of all the components of the course — exams, reading quizzes, post-class notes, and more, similar to what I wrote about last term — the projects had the highest correlation with the overall grade: r = 0.75.
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Books, etc.
There’s no textbook for the course, though I assign a lot of readings / videos that are a mix of current articles (especially from The Economist) and recordings of me explaining things. About halfway through the term I discovered the new, excellent Energy and Human Ambitions on a Finite Planet, by Tom Murphy, which was “written to support a general education college course on energy and the environment” at UCSD. It’s clear, quantitative, through, and well-written — a great read for anyone interested in energy and the environment. It’s also free as an e-book! (I bought a paper copy.) If I had found it earlier I would have made more use of it. It reminds me a lot of David MacKay’s wonderful Sustainable Energy – without the hot air, which is also available free; Murphy’s book is longer and more physics-focused, and also structured as a textbook.
Engagement, evaluations, and Zoom
A lot of my thoughts about this class are the same as the preceding one, so I’ll be brief in commenting here. Just like last term, I found remote teaching, via Zoom, to be more tiring and less pleasant than teaching in person. Also like last term, things like writing in real time and asking a lot of poll questions helped. About a quarter of the class seemed very engaged and enthusiastic; at least a quarter had zero engagement. Very few students (about 10%) turned on their video during classes.
Last term, only 5 of 63 students submitted end-of-course evaluations — pretty typical for online courses. This term I begged people to write, and got 19 of 69. The comments included a lot of very positive statements (“This has been an absolutely incredible class”) and complaints that there was too much work, though the average amount of time students reported working on coursework (not counting class sessions) was 6.5 hours/week. I’m not sure what to conclude from all this — every term it seems ever clearer that there are wonderful students who want to push themselves and learn things, and a large and growing fraction who have no real reason for being at a university, other than that society expects it for ill-defined reasons. The latter group doesn’t have much interest in coursework; they’re fine people (I assume), and it’s unfortunate and wasteful that we waste so much of everyone’s time and money processing them, factory-like, at modern U.S. universities.
Overall, the term went as well as I could have expected, and I was again reminded of what fascinating topics energy and the ways we use it are, and it was great to see quite a few students agree! I’ve taught this course before, but not since 2016. Some things are unchanged but still amazing to think about, like the physics of how a solar panel works, turning light into electricity thanks to the magic of semiconductors. Some things are remarkable in their progress in just a few years, like the cost per Watt of solar panels, which has plummeted. I think I’m scheduled to teach this again in 2022 — we’ll see what the world is like then!
Today’s illustration.
A few attempts at copying, in watercolor, one of the cupcakes in Wayne Thiebaud’s Four Cupcakes. Thiebaud’s paintings are brilliant. My copies are not, though I think they became less bad as I progressed (bottom to top). The process made me even more impressed by Thiebaud’s art.
— Raghuveer Parthasarathy; August 21, 2021
