One-day project: Build a hot-box solar oven

Illustration by Vic Kulihin
Date:29 July 2011

No power? No problem. Bake off the grid with a sun-fuelled oven hot enough to raise some dough.

1 Find parts
On a cool day, our solar oven got hot enough to bake a killer batch of scones – and in the summer, it can whip up brownies during load shedding. The project makes use of scraps (or full 1,2 m x 2,4 m sheets) of 20 mm and 12 mm plywood. It also requires 4d trim nails, a 2-metre length of 40 mm-wide flat wood trim, 90 cm of 6 mm-square moulding, a half-sheet of 12 mm rigid foam insulation, a half-sheet of 12 mm drywall, two white ceramic knobs, eight 75 mm mending plates, construction adhesive, high-temperature flat black spray paint, heavy-duty aluminium foil, No. 8 bolts, washers and nuts and a piece of 6 mm plate glass cut to 330 mm x 370 mm, with the edges sanded smooth.

2 Build the box

Construct an open-top box using 20 mm plywood for a 355 x 395 mm bottom. Use 12 mm plywood to make four 180 mm-tall sides. With a vice and pliers, bend the mending plates to 135-degree angles. Fasten two plates to each box side with 25 mm No. 8 bolts, washers and nuts. Cut pieces of rigid foam insulation to line the box interior. Glue the foam to the plywood using construction adhesive. Cut and glue drywall panels to fi t on top of the foam. Paint the interior black.

3 Prep the top

Nail wood trim over the edges of the foam and drywall. Cut the moulding into four 230 mm lengths. Centre the glass pane over the opening. Put the mouldings around the glass perimeter. Nail them down to steady the pane. Glue the knobs to the glass.

4 Make reflectors

Cut rigid foam to four 300 mm x 600 mm panels. Wrap the foam in aluminium foil. Bolt the panels to the plates.

5 Bake it up

Prep food in a black enamel pot with a lid; set the pot in the box. Replace the glass. Prop up the oven at an angle so the sun and refl ectors shine directly on it. Use an oven thermometer to gauge heat. Note: this oven does not bake as quickly as a regular one (but our scones, with butter and berry jam, were still delicious). Wear oven mitts to handle the ceramic knobs – they get hot!

More to do in August

Get snipping

After a long, bare winter, you want your garden to be bursting with life in spring. To ensure a good show of blooms when the temperatures start rising, don’t forget that mid-July to early August is the time to prune your roses.

Make a move

Irritated by that shrub that always gets in the way? Worried about bushes that don’t get enough sun? Potplants growing too big for their boots? With plants in a state of retarded growth, and less likely to be attacked by pests or disease, now’s the time to transplant.

Paint those walls

We’re not joking: paint in winter. Depending on where you live, naturally: for instance, the highveld’s dry winters are a perfect time to get your home into shape.

Web: For more one-day DIY projects, visit