An Exergy Crisis
In last week’s Archdruid Report post, I discussed the difference between energy and exergy, or in slightly less jargon-laden terms, between the quantity of energy and the concentration of energy. It’s hard to think of a more critical difference to keep in mind if you’re trying to make sense of the predicament of modern industrial civilization, but it’s even harder to think of a point more often missed in the rising spiral of debates about that predicament.
The basic principle is simple enough, and bears repeating here: the amount of work you get out of a given energy source depends, not on the quantity of energy in the source, but on the difference in energy concentration between the energy source and the environment. That’s basic thermodynamics, of the sort that every high school student used to learn in physics class back in those far-off days when American high school students took physics classes worth the name. Put that principle to work, though, and the results are often highly counterintuitive; this probably has more than a little to do with the way that even professional scientists miss them, and fumble predictions as a result.
The current brouhaha over anthropogenic climate change offers a good example. There’s been a great deal of high-grade fertilizer heaped over the issues by propaganda factories on all sides of that debate, but beneath it all is the tolerably well documented fact that we’re in the middle of a significant shift in global climate, focused on the north polar region. The causes of that shift are by no means entirely settled, but it seems a little silly to insist, as some people do, that the mass dumping of greenhouse gases into the atmosphere by humanity can’t have anything to do with it – or, for that matter, that it’s a good idea to keep on dumping those gases into an atmospheric system that may already be dangerously unstable for reasons of its own.
Still, for the next decade or more, that bad idea is very likely to remain standard practice around the world, and one reason for that is that climate change activists have shot themselves in the foot. No, I’m not talking about the recent flurry of revelations that some IPCC scientists diddled the facts to make a good but undramatic case more mediagenic. Nor am I talking about the awkward detail that the IPCC scenarios assume, in the teeth of all geological evidence, that the world can keep increasing the amount of fossil fuels it extracts and burns straight through to 2100. The problem goes deeper than that, down to the decision to define the crisis as “global warming.” That seems sensible enough – after all, we’re talking about an increase in the total quantity of heat in the Earth’s atmosphere – but here as elsewhere, the fixation on quantity misses the crucial point at issue.
I’m not generally a fan of Thomas Friedman, but he scored a bullseye in his book Hot, Flat, and Crowded when he pointed out that what we’re facing isn’t global warming but “global weirding:” not a simple increase in temperature, but an increase in unexpected and disruptive weather events. As the atmosphere heats up, the most important effect of that shift isn’t the raw increase in temperature; rather, it’s the increase in the difference in energy concentration between the atmosphere and the oceans. The thermal properties of water make the seas warm up much more slowly than the air and the Earth’s land surface, and so even a fairly modest change in the quantity of heat causes a much more significant change in exergy. Again, it’s exergy rather than energy that determines how much work a system can do, and the work that the Earth’s atmosphere does is called “weather.” Thus the most visible result of a relatively rapid rise in the heat concentration of the atmosphere isn’t a generalized warming. Rather, it’s an increase in extreme weather conditions on both ends of the temperature scale.
This isn’t a new point. It has been made repeatedly by a number of scientists and, interestingly enough, by large insurance companies as well. Munich Re, for example, pointed out a few years back that at the current rate of increase, the annual cost of natural disasters caused by global climate change would equal the gross domestic product of the world well before the end of the 21st century. Had climate advocates taken that as their central theme, this winter’s abnormally harsh storms in the eastern half of the US would have provided plenty of grist for their mills; even hardcore skeptics, as they shoveled snow off their driveways for the fourth or fifth time in a row, might have started to wonder if there was something to the claim that greenhouse-gas dumping was causing the weather to go wild. Instead, seduced by our culture’s fixation on quantity, climate advocates defined the problem purely as a future of too much heat, and those same skeptics, shoveling those same driveways, are rolling their eyes and wishing that a little of that global warming would show up to help them out.
It’s probably too late for climate change activists to switch their talking points from global warming to global weirding and be believed by anybody who isn’t already convinced, and so we’ll likely have to wait until the first really major global climate disaster before any significant steps get taken. (Given the latest reports from the Greenland ice cap, that may not be too many decades in the future, and any of my readers who live within fifty feet or so of sea level might find it advisable to relocate to higher ground.) Still, the same confusion between energy and exergy impacts the crisis of our time in other ways, and some of those are central to the themes this blog has been exploring in recent months.
One of the common ways to avoid thinking about our predicament, as I mentioned last week, is to cite the quantity of energy that arrives on Earth by way of sunlight every day, and note that it’s vastly greater than the quantity of energy our civilization uses in a year. That’s true enough, but it misses the point, which is that the energy in that sunlight has very modest amounts of exergy by the time it crosses 93 million miles of space to get to us, and it can therefore do only modest amounts of work. Strictly speaking, we don’t face an energy crisis as fossil fuels run short; what we face is an exergy crisis – a serious shortage of energy in highly concentrated forms. That’s a problem, because nearly every detail of daily life in a modern industrial society depends on using highly concentrated energy sources.
Longtime readers of this blog will recall that calling something a problem has certain definite implications. A problem, at least potentially, has a solution; that’s what differentiates it from a predicament, which cannot be solved and simply has to be lived with. The depletion and eventual exhaustion of fossil fuels, and the absence of any sign of an abundant high-exergy replacement for them in this small corner of the cosmos, is a predicament. The dependence on these fuels of most of the activities of daily life in the industrial world is a problem, because a great many of those activities don’t actually need anything like the amount of exergy we put into them.
Here’s an example. Nearly every home in the industrial world has hot water on tap. That’s by no means a pointless luxury; the contemporary habit of washing dishes, clothes, and bodies with ample amounts of hot water and soap has eliminated whole categories of illnesses that plagued our ancestors not that long ago. A very large fraction of those homes get that hot water by burning fossil fuels, either right there at the hot water heater, or at a power plant that uses the heat to generate the electricity that does the heating. A society that has ample supplies of high-exergy fossil fuels can afford to do that; a society running out of exergy is likely to face increasing troubles doing so.
There’s a crucial point not often recognized, though, which is that it doesn’t take that much exergy to heat a tank full of water from ambient temperature to 120° or so. The same thing can be done very effectively by energy sources that aren’t very concentrated, such as sunlight.
Enter the solar hot water heater.
This is arguably the most mature and successful solar technology we’ve got right now. The process is simple: one of several different kinds of collectors gather heat from the sun and transmit it either to water, in places that don’t get freezing temperatures, or to an antifreeze solution in places that do. In a water system, the hot water goes from the collector to an insulated tank, and eventually to the hot water faucet; in an antifreeze system, the antifreeze circulates through a heat exchanger that passes the heat to water, which then goes into an insulated tank to wait for its moment of glory. In most parts of the United States, a well-designed solar hot water system will cut a home’s energy use to heat water by 70%; in the Sun Belt, it’s not at all uncommon for a system of this sort to render any other hot water heater unnecessary.
Now it will doubtless already have occurred to my readers that installing a solar hot water system in their homes will not save the world. What it will do, on the other hand, is take part of the work now done by highly concentrated energy sources – most of which are rapidly depleting, and can be expected to become more expensive in real terms over the decades to come – and hand it over to a readily available energy source of lower concentration that, among other things, happens to be free. That’s an obvious practical gain for the residents of the house, and it’s also a collective gain for the community and society, since remaining supplies of high-exergy fossil fuels can be freed up for more necessary uses or, just possibly, left in the ground where they arguably belong.
It’s curious, to use no stronger word, that so eminently practical a step as installing solar hot water systems has received so little attention in the peak oil and climate change communities. It’s all the more curious because the US government, which so often seems incapable of encountering a problem without doing its level best to make it worse, has actually done something helpful for a change: there are very substantial federal income tax benefits for installing a residential solar hot water system. Why, then, haven’t solar hot water heaters blossomed like daisies atop homes across the country? Why haven’t activists made a push to define this proven technology as one part of a meaningful response to the crisis of our time?
It’s an interesting question to which I don’t have a definite answer. Partly, I think it ties into the weird disconnect between belief and action that pervades the apocalyptic end of contemporary culture. Of the sizeable number of people in today’s America who say they believe that the world is coming to an end in 2012, for example, how many have stopped putting money into their retirement accounts? To judge by what little evidence I’ve been able to gather, not very many. In the same way, of the people who say they recognize that today’s extravagant habits of energy use are only possible because of a glut of cheap abundant fossil fuels, and will go away as fossil fuels deplete, those who are taking even basic steps to prepare themselves for a future of scarcity and socioeconomic disruption make up an uncomfortably small fraction. It’s hard to imagine passengers on a sinking ship glancing over the side to see the water rising, and going back to their game of shuffleboard on the deck, but a similar behavior pattern is far from rare these days.
Still, I think part of the issue is the same fixation on quantity I’ve discussed already. Solar hot water heaters don’t produce, or save, a great quantity of energy. Water heating uses around 15 per cent of an average home’s energy bill, and so a solar hot water system that replaces 70% of that will account for a bit more than 10% of home energy use. (This is still enough to pay for most professionally installed solar hot water systems in 3 to 7 years, mind you.) If every home in America put a solar hot water heater on its roof, the impact on our total national energy consumption would be noticeable, but in terms of raw quantity, it wouldn’t be huge.
Still, this misses at least three important points. First, of course, installing a solar hot water system can very easily be one piece of a broader program of energy conservation with a much larger impact. Knock 10% off household energy use with a solar hot water system, another 10% by insulating, weatherstripping, and the like, another 10% with an assortment of other simple energy-saving technologies (any halfway decent book on energy conservation from the Seventies has plenty of suggestions), and another 20% with lifestyle changes, and your home will be getting by with half the concentrated energy it uses right now. If even a large minority of homes in America took these steps, or others with similar effects, the effect on national exergy use would be very substantial indeed.
Second, there’s a very large and underappreciated difference between essential and nonessential energy uses, and it’s one that many of us will learn to recognize in the challenging years ahead. A great deal of energy use in America today is nonessential – think for a moment of all the energy currently devoted to the tourism industry, which is a very sizable sector of the US economy these days, and could be shut down tomorrow without impacting much of anything but the unemployment rolls – and a very large amount of that will go away as America slides down the curve of energy descent toward its near-future status as a Third World country. Whether or not hot water is strictly essential, its direct practical benefits in terms of health and comfort put it a good deal closer to the core, and that makes finding low-exergy ways to provide it particularly important.
Third, as I’ve already suggested, we face an exergy shortage rather than an energy shortage. That doesn’t make our predicament any less severe, mind you. A strong case can be made that available exergy places a hard upper limit on the human population of the planet, and as our supplies of exergy diminish, so will the human population, and at this point it’s all too likely that most of that reduction will happen in the traditional manner, via those four unwelcome guys on horseback. It does mean, though, that individuals, families, and communities that take steps to meet as many of their energy needs as possible using relatively low-exergy energy sources can have a disproportionate impact on the way that the future unfolds.
I’ve argued elsewhere that Jevons’ Paradox – the rule that gains in the efficiency with which a resource is used tend to increase the use of the resource – only applies when cost is the only restriction to the use of the resource. When use of a resource is declining due to factors external to the economy, such as geological limits, gains in efficiency lessen the economic and social impact of shortages and buy time for a more gradual decline. Solar water heating is one example of a technology that can help our communities and societies make constructive use of that effect, and it’s also a technology that can be put to use by individuals right now. I’ll be discussing other options of the same kind in the next few posts.
What do you think? Leave a comment below.
Sign up for regular Resilience bulletins direct to your email.
This is a community site and the discussion is moderated. The rules in brief: no personal abuse and no climate denial. Complete Guidelines.