A Solar Oven for Cloudy Days
Every Boy Scout or Girl Guide probably had the experience of building a simple solar oven: an insulated box, some aluminum foil, and plastic wrap, and voila! On warm, sunny, summer days, you can bake. On cloudy days, well, you need another plan. The redoubtable [Kris De Decker] and [Marie Verdeil] provide one, with this solar-electric oven over on LowTechMagazine.
Now, you might be wondering: what’s special here? Can’t I just plug a full electric range-oven into the inverter hooked to my Powerwall? Well, yes, Moneybags, you could — if you had a large enough solar setup to offset the storage and inverter losses, that is. But if you only have a few panels, you need to make every watt count. Indeed, this build was inspired by [Kris]’ earlier attempt to power his apartment with solar panels on his balcony. His electric oven is one of the things that stymied him at that time. (Not because cooking took too much energy, but because it took too much power for his tiny battery to supply at once.)
That’s why this oven’s element is DC, driven directly from the panel: there are no batteries, no inverter, and no unnecessary losses. The element is hand-made to match the solar setup, avoid an unnecessary electronic thermostat, and is sized to keep the oven from getting too hot. The oven itself is tiny, only large enough for a single casserole pan, but it does cover 90% of their cooking. A smaller oven is obviously going to need less power to heat up, but it also makes it practical to wrap it in oodles of insulation to reduce losses even further.
Indeed, between the 5 cm of insulation and thermal mass from the mortar-and-tile interior, when preheated by the specified 100 W panel, this oven can retain its cooking temperature well after sunset. Instead of needing a battery, the oven is the battery. It’s really quite elegant. That does require a certain mental adjustment as well: “cooking temperature” here is only 120°C (248°F), about a hundred F less than most recipes in our cookbooks. This hack is almost like a solar-powered cross between an oven and a slow cooker.
It’s undeniably efficient, but we can only imagine it would take some getting used to. Of course, so does running a solar-powered website, and LowTechMagazine has kept that going since 2018.