The Tarpaper Shack Principle (2011)

Was it just me, or were last Friday’s New Year celebrations a bit short on enthusiasm? The chance to give the smoking wreckage of 2010 a decent burial might have inspired some cheer, except that 2011 seems unlikely to bring anything better. With the price of oil lurching around the $90-something a barrel range, a so-called economic recovery that has been almost entirely confined to press releases, and the electorate slowly waking up to the fact that the only change they can believe in that’s coming from the Obama administration is the kind Rudy Vallee sang about in “Brother, Can You Spare A Dime?” – well, let’s just say that none of this adds up to optimism for the year ahead.

Thus the New Year’s Eve blog post from Chuck Burr at Southern Oregon Permaculture was timely. At a time when plenty of people are still insisting that the whole world can adopt a middle-class lifestyle powered by renewable energy resources, Burr cited hard numbers from a representative case study – his own solar-powered home – to show why high-tech renewables are at most a way station partway down the Long Descent. His argument will be familiar to readers of this blog: the photovoltaic system that powers his home won’t generate enough electricity in its lifetime to both account for the power that goes into making and maintaining it, and provide enough electricity to maintain a modern lifestyle for its end user. Burr went on to suggest, reasonably enough, that using high-tech renewables is still a good idea for now, since it will help cushion the future in which green plants may well turn out to be the most efficient source of primary energy around.

He’s likely right, but there are challenges in the way of even so modest a project. The obvious issue – the fact that the very large number of people closing in on their 99th and last week of unemployment benefits, and the even larger number caught in the stagflationary vise of dwindling wages and soaring bills, aren’t going to be in any position to buy and install expensive photovoltaic systems – is symptomatic of a far more profound and pervasive difficulty.

That difficulty, interestingly enough, was sketched out well in advance in the pages of The Limits to Growth, still the best – and thus, inevitably, the most reviled – map of the future toward which the industrial world is hurtling, eyes closed and pedal to the metal. It’s always fascinated me that in a society that claims to make most of its decisions on the basis of economics, so few people grasped the essentially economic argument at the core of the Limits to Growth analysis. That study did not claim, as so many people still insist it claimed, that the resources on which industrial society depends are going to up and run out one of these days. It proposed, rather, that the real costs of extracting resources and dealing with the consequences of environmental pollution, both of which are driven by economic growth, necessarily increase faster than the rate of economic growth itself, and sooner or later will force industrial civilization to its knees.

Perhaps the most visible signpost along the way to that destination is the point at which a society can no longer provide for its future and pay its current expenses out of existing resources. You know that point has arrived when a society begins neglecting its infrastructure, slashing basic services, discarding those economic sectors that cost too much to maintain, and abandoning those people who lack the political clout to make good a claim on slices of the dwindling pie. Readers here in America who don’t find this description oddly familiar are encouraged to take a good hard look out the nearest window.

The consequences of that logic pose an immense challenge to the more optimistic proposals for dodging the resource crunch at the end of the age of cheap petroleum – the nuclear power plants, high-speed rail networks, immense solar installations in assorted desert countries, and the rest of it. All these would require huge inputs of real wealth – not currency, which can be manufactured at will by central banks, but energy, materials, knowledge, and labor – real wealth – which are a good deal harder to conjure up out of twinkle dust. The Limits to Growth model suggests that underneath the smoke and mirrors of the financial economy lies the awkward fact of a shortfall in real wealth, caused by the need to divert a growing fraction of real wealth to meet the direct and indirect costs of extracting resources, on the one hand, and coping with the impacts of environmental pollution on the other. If that’s what’s going on – and I think a good case could be made for that thesis – then trying to scrape together enough real wealth to cover the cost of these projects simply piles another burden onto an already overloaded economic structure, and if pursued with enough misplaced enthusiasm, could conceivably become the trigger that brings the whole thing crashing down.

Now of course there’s another way to go about preparing for a future of scarce expensive energy, and it’s one of the key strategies of the "green wizardry" I’ve been discussing here iover the last six months or so. The central concept of that strategy might as well be called the Tarpaper Shack Principle: you don’t actually have a resilient energy technology unless you can build it from readily available materials, and put it to work for some useful purpose, while living in the kind of tarpaper shack the last Great Depression made famous. You may well end up living in something like that, you know; a great many people did the last time the industrial economy came unglued, and we are arguably in a much worse position today than in 1930, so looking up some renewable energy technologies that could have been made and used in a 1930s Hooverville may be more than a thought exercise just now.

Finding such technologies may seem like a tall order. It isn’t; there are scores of proven, mature technologies that can be tacked together from scrap, powered by renewable energy sources that cost little or nothing, and contribute mightily to getting the basic tasks of living done more easily, safely, and cheaply. The fireless cooker, the topic of last week’s post here, is one of them, and so is the technology I’d like to introduce this week, the solar box cooker.

It’s hard to think of anything as cheap that accomplishes as much. You can make one out of cardboard, glue, used newspaper, aluminum foil, and a piece of discarded window glass. Placed in direct sunlight, it will easily get up to oven temperatures and cook your meals for free. It can also be used to purify tainted water, sterilize bandages, or do anything else that 300° to 400° F of even heat will do for you.

The solar box cooker also has the not inconsiderable advantage of teaching three of the basic rules of working with solar energy in a way most people grasp intuitively at once. Rule #1 is the greenhouse effect: energy from sunlight that passes through glass and is absorbed by something inside the glass tends to get trapped there, because glass is transparent to visible light but opaque to the infrared wavelengths that radiate out from warm objects. Rule #2 is the thermal mass effect: some materials absorb heat better than others, and if you put something with a high capacity for heat absorption in the presence of a heat source – say, a pot of beef stew in direct sunlight – it will soak up heat that can then be put to work. Rule #3 is the insulation effect: some materials resist the flow of heat better than others, and if you surround your thermal mass with a bunch of insulation, the heat absorbed by the thermal mass will stick around longer and do more work. (Keep these three rules in mind and most of what we’ll be covering in the months just ahead will be a lot easier to follow.)

There are several standard designs of solar box cooker. The simplest looks exactly like what the term suggests, a square or rectangular box – or, more precisely, a box within a box, with insulation between them to form a heat barrier – with a pane of glass on top. A hinged lid covers the glass when the box cooker isn’t in use; it has tinfoil on the underside, so that when you’re ready to use the box, the lid can be propped up at an angle to reflect more sunlight into the box. Yes, you can make one out of cardboard and newspaper in about an hour, and yes, you can then set it out in the sun and cook your dinner with it.

The more complex designs put the glass pane at an angle, to increase the amount of sunlight that gets in, and have more reflecting surfaces for the same reason; the fanciest look like metal flowers or props from 1970s science fiction movies, and you don’t want to make them out of cardboard because they can get hot enough inside to set the cardboard on fire. I’ve seen some very impressive solar box cookers on the fancy end of things, with mirrors that would do justice to a telescope and elegant arrangements to track the sun; they arguably go well beyond anything you’d be able to put together while living in a tarpaper shack, but there’s always the possibility that you might get lucky while combing through the ruins of an abandoned suburban housing development.

Two other developments off the same basic approach are also worth mentioning. The first was invented by one of the patron saints of green wizardry, the redoubtable 19th-century French solar energy pioneer Augustin Mouchot. Tasked by the French government with coming up with solar technologies for the French colony in Algeria – which has a surplus of sun and, at least in Mouchot’s time, a shortage of most other energy sources – Mouchot invented, among other things, a solar cooker for units of the French Foreign Legion stationed there. The device was simplicity itself – a cone of metal, reflective on the inside; a cylindrical steel cooking chamber that went up the centerline of the cone; and a tripod stand. Mouchot’s solar cooker was collapsible, weighed less than forty pounds, and cooked a pot roast to a nice medium rare in under half an hour. It remained standard issue for French troops in North Africa for decades; I have no idea if any examples survive, but it’s 19th century technology, and an enterprising metalworker ought to be able to knock one together fairly easily – even in a tarpaper shack.

The other device I have in mind comes from the other end of the solar cooking spectrum, but it’s as elegant as the Mouchot cooker and even more portable. The Umbroiler was invented by American solar pioneer George Löf and marketed for a while in the 1960s and 1970s. It’s exactly what the name suggests: a sturdy umbrella frame with silver metallized cloth in place of the usual fabric, a grill in place of the handle, and a tripod on what’s normally the top of an umbrella and is the underside of the Umbroiler. It folds up like any other umbrella, but when you open it and point it toward the sun, you can cook anything from fried eggs to hot coffee on the grill. The original version was too expensive to be commercially viable, due mostly to the high cost of metallized fabric back in the 1960s; these days, that has changed, and since any patents have long since expired, a revival of the Umbroiler could make somebody with a sewing machine and some metalworking skills a very functional small business.

By now, I suspect, some of my more skeptical readers will doubtless be jumping up and down, eager to point out that solar cookers aren’t viable everywhere, and only work when the sun’s shining. This is of course true, but it’s also beside the point. Nothing in the appropriate technology toolkit is suited to every context – that’s one of the implications of that word "appropriate," after all – and nothing ever again in human history will provide our species with the kind of instant, context-free torrent of energy we now get from fossil fuels. Once those are gone, the entire approach to technology that’s built on the assumption of abundant, highly concentrated, highly portable energy supplies goes whistling down the wind, and the approaches – in the plural – that will replace it are going to be less convenient, less portable, and less capable of ignoring the rest of the cosmos than what we’re used to.

What that means in practical terms is that the well-equipped kitchen in the tarpaper shack that’s waiting for you a few years down the line will have a solar box cooker, which you can use on sunny days, and a small, efficient stove and fireless cooker, which you can use on cloudy days. It really isn’t that complicated, once you grasp the crucial point that a technology that relies on diffuse renewable energy sources doesn’t work the same way as a technology that relies on concentrated fossil fuels. That’s one of the lessons of the Tarpaper Shack Principle, and it’s also one of the gifts that the solar box cooker in particular has to offer.


The solar box cooker is one of the few creations of the old appropriate tech movement that hasn’t been allowed to languish in obscurity, largely because of its huge advantages in the Third World. The photocopied pamphlets I got back in the day from Solar Box Cookers Northwest, one of the pioneering organizations in the field, have long since been superseded by websites brimfull of practical information. The best of the lot just now is -- click on the link marked "build a solar cooker" and you’ll soon be wallowing in plans I would gladly have given my eye teeth to get hold of thirty years ago.

There are also several very good books on the subject. Beth Halacy and Dan Halacy’s Cooking with the Sun is a little out of date but remains well worth having, not least because of its detailed recipes and cooking instructions. Joseph Radabaugh’s Heaven’s Flame covers many of the newer developments and provides an excellent guide to designing and building your own inexpensive solar cookers. Another durable classic, Ken Butti and John Perlin’s A Golden Thread, covers the early history of solar cooking and has a good illustration of Mouchot’s solar cooker.