Case Studies in Ecodesign: DIY Solar Oven
July 15, 2007
By Adam Brock
The phrase “sustainable design” is often associated with things like bioplastic, solar-powered flashlights, or cradle-to-cradle office furniture. While these and other innovations continue to push the green design envelope, even the most forward-thinking ecoproducts can’t honestly be called sustainable quite yet: they’re still nowhere close to eliminating their negative impact on the planet.
The good news, though, is that actual sustainable design is entirely possible. The trick is in redefining our notion of what “design” is: just like electricity generation and food production, the most sensible approach to design from an ecological standpoint is to decentralize. Contrary to what corporations would have you believe, there’s no reason we need to rely on mass-produced stuff to meet our needs. It might take a little more work, but putting design into our own hands is cheaper and more rewarding than getting something from a store. It can often be more effective, too; after all, nobody knows the clients better than the clients themselves.
With these values in mind, me and my fellow volunteers at ROSE decided to undertake the design challenge of cooking food completely sustainably: using only recyled materials and the power of the sun. No fossil fuels, no embodied energy, no money. It was a high benchmark, and from the beginning, we knew we probably wouldn’t meet all the constraints on the first try. But we were just as interested in the process of designing and building the cooker as we were in the final product.
We based the oven’s design on one described in Aric McBay’s Peak Oil Survival: Life After Gridcrash (a great resource guide to becoming more self-sufficient, even if you don’t subscribe to the apocalyptic predictions of the peak oilers). Basically, the design consisted of an insulated wooden box with metal lining on the insides, and a glass top tilted at 30 degrees for maximum solar exposure. Around the top was a sheetmetal funnel designed to channel more of the sun’s rays into the box. Food was to be inserted through the back, which folded down like an oven door.
We sized the cooker around a sheet of old window glass that Jeevan had lying around, which we had trimmed in the Kanda market. The box itself was constructed out of sheets of used concrete formwood, and we employed ash, collected graciously by Jeevan’s wife from around the village, as an insulator. So far, so good – we had almost all the materials we needed, and still hadn’t spent a rupee (or a kilowatt hour). But we couldn’t source any used metal sheeting, which was an essential component of both the inside lining and the funnel on top. In the end, we caved and got it new at the market. It was an unfortunate compromise – metal is one of the most energy-intensive materials to produce and transport – but a necessary one nevertheless.
Constructing the oven proved to be at least as challenging as designing it. I hadn’t picked up a saw since 7th-grade stagecraft class, and the tools we had to work with weren’t exactly top quality. As is always the case, there were plenty of unexpected challenges we had to solve on the fly as the design came together: the nails kept bending, some of the boards split, the metal wouldn’t blacken in the fire, and the ash kept leaking out of the seams in the wood. But, little by little, the challenges were met, the oven took shape, and after a solid three days of sawing, cutting, nailing, trimming, grouting, and adjusting, we had a pretty decent-looking solar cooker in front of us.
To put the oven to the test, we decided to see if we could bake some challah. After collecting all the ingredients and kneading and braiding the dough (a design challenge in itself), we put the loaf in the oven on a hot afternoon and waited. After a couple hours, we opened the oven door and cautiously felt around. It was hot, alright… but not hot enough, probably only 200 degrees or so.
What went wrong? After some examination, we decided that the box hadn’t been made airtight enough – we could feel several places where the hot air was leaking out. Fixing it would’ve required temporarily dismantling the metal funnel and finding a better sealant than the cement we’d been using – certainly possible, but not in the two days we had left at Kanda.
In the end, then, our sustainable solar oven wasn’t quite sustainable, and it wasn’t much of an oven, either. But was it a failure? I don’t think so. For me, the learning process alone was enough to justify the financial and ecological costs of the project. And it’s entirely possible that another ROSE volunteer will improve the cooker in the months to come, making the design fulfill its intended purpose. For now, then, I’ll see it as a collaborative work in progress – and a valuable lesson in forest green design.