Solar Cooking 101

Namibia is blessed by bountiful sunshine virtually the entire year. Therefore, it makes sense to make every effort possible to utilize this renewable, environmentally-friendly, free source of energy. Especially when you consider that the alternatives are firewood (which entails walking 5-10 km to collect, and then cooking over a smoky open fire) or gas/electric (increasingly expensive and key contributors to greenhouse gases).

At NaDEET, solar panels provide nearly all our power (complemented by a small wind turbine, and a generator for special occasions). It’s stored in batteries to provide electricity at night, and it manages to heat our water, run our lights, fridge and freezer, not to mention assorted computer equipment.

Of course, one of the biggest ways that we utilize solar power—at the Centre and at Base—is through solar cooking! The time has come to reveal the underlying science behind these gadgets. Grab your lab goggles and prepare for…SOLAR COOKING 101.

First, here are mini-experiments to experience the basic principles of how we can harness the sun’s energy (we do these with NaDEET participants during our “Powers of the Sun” rotation).

Absorption

Close your eyes, resting one hand on a large piece of cardboard painted black and the other on one painted white. The black one is noticeably hotter, as it absorbs the sun’s heat energy. Try to trick your partner by switching around the cardboard placement.

Reflection

Using a small mirror, try to reflect sunlight onto a cardboard target that another member of your group is holding. See how the light gets more intense as more and more people have their mirrors reflect onto the same point. Get distracted for a bit shining light into group members’ eyes, and then back to business. See if you can bounce light from one mirror to another mirror and then to the target.

Greenhouse Effect

Close a thermometer inside a glass bottle, and leave another out. Notice that the trapped one reads several degrees hotter. This is like the earth’s atmosphere trapping in heat and gases.

Bundling

When light passes through a magnifying glass, it is possible to “bundle” it—that is, concentrate all the energy into a small point. And then you can burn newspaper! Wow – the powers of the sun! I particularly like this experiment because it taps right into what kids love to do when given a magnifying glass. I remember this one EE class with the 1st/2nd graders in Costa Rica, where we were trying to observe insects in the garden.

Number of kids who used magnifying glass to closer examine insects: ~2

Number of kids who used magnifying glass to burn something: ~16

Conduction/Insulation

See lengthy hula post.

Now, onto the equipment:
Pictured below are two pieces of equipment that we use to solar cook with groups at NaDEET. Usually, the kids have never seen them before and they're really impressed. By the time they leave (if we have our way), they're won over to the possibility of solar energy and they want to convince their family/school to buy a solar oven! The solar oven is on the right, and the parabolic solar cooker (which makes a mean lentil soup) is on the left (featuring said kettle of lentils).

1. Parabolic Solar Cooker (left)

When the sun hits the sides of the cooker, the angles of the shiny metal walls reflect all the light toward the center. Concentrated, bundled, the sun’s energy is enough to boil a pot of water in no time! The cooker needs to be readjusted every 10 minutes, as the sun moves in the sky (but I am lazy and usually do it every 40 minutes or so…)

2. Solar Oven (right)

The sunlight hits the mirror and is reflected into the oven. The inner walls are painted black to absorb heat energy. The top is glass to create a greenhouse effect. The walls are wood, stuffed with foam, to provide insulation and keep the heat trapped within.

3. Hot box (sorry, not pictured)

Since prime sunlight is during the middle of the day, you have to be savvy and cook your dinner at this time too. But, oh no! Won’t it get cold before you eat it? Not if you put it in a hot box! A hot box is a wooden box crammed with newspapers to keep the hot pot nice and insulated during the afternoon hours. None of that energy is flowing out!

Basically, solar cooking has been my latest obsession.

It's pretty perfect for me: it's a challenge, it's environmentally friendly, and I can stick something in there and forget about it without the possibility of burning down the house. The latter has come astonishingly close to occurring in both Palo Alto AND Williamstown, with the crises being only narrowly avoided thanks to vigilant cohabitants.

One thing that I love about NaDEET is this idea of 'practice what you teach.' It means that down at NaDEET Base (1.5 kilometers away from the Centre, this is where the office is; it's where we live when groups are not in session), we also try to solar cook as much as possible. I've been trying to solar cook exclusively, with the only exception of hot water in the early morning (to put in a thermos for my sunrise dune walks!).

One big difference between solar cooking and regular cooking is the necessity of planning everything in advance. The sun is only shining in cookable force from 9:00 a.m. to 3 p.m., so if you want to solar cook your dinner, you have to start preparing it at lunch time (and then you put in in the insulated "Hot Box" to keep it warm).

Basically, I've been cooking up a storm...but with delightful consequences.