I recall articles in kids' magazines in the mid-80's about how to build solar cookers. Apparently, they are already in widespread use today, with many different designs:

http://solarcooking.org/plans/

Does anyone know what makes this new design special?

Most "solar cookers" try to focus sunlight directly on the object to be heated. This new design is almost exactly like a traditional oven in that the main goal is to heat air, and not the food directly.

The ones you link to look significantly more difficult to build. This one is two boxes and a piece of plastic (from what I understand).

I guess this is neat, because I remember building a similar device when I was a kid, but it couldn't boil water or do any useful cooking. It was sort of able to warm up a hot dog...

You mean, like the first box cooker on the page?:

http://solarcooking.wikia.com/wiki/Minimum_Solar_Box_Cooker

Like the cooker in the article, it is a foil-lined cardboard box, with a black-painted cardboard box inside. And it recommends a plastic bag instead of a plexiglass cover, so it might be considered even more basic than the one in the article.

> The ones you link to look significantly more difficult to build. This one is two boxes and a piece of plastic (from what I understand).

Seems to be the case, and looks like a significant difference. There's also a plexiglass cover, which likely helps insulate the heat inside. Simple yet ingenious, like the hipporoller ( http://www.hipporoller.org/ ). Absolutely fantastic.

For a more high-end design you can attach a heat sensor and make it electric-hybrid. Or gas-hybrid... or crankshaft-hybrid!!

Not to criticize your creativity, but I propose changing the title, because I was expecting something about food, which it isn't entirely. But it is full of awesome and based in Nairobi!

I've made one of these before... along with the rest of my third grade class. I guess someone should have called CNN back then.

An estimated time to boil a liter of room temperature water and cook a sunny side up egg would have been helpful.

Good catch. Some optimistic back-of-the-envelope says it could be around 5 min for the liter of water. (The egg should go faster, if I remember my WWII-in-North-Africa frying-eggs-on-tanks movie scenes right ;-)

Assumptions: 1 square meter blackbody collector for 1 kW/m2 solar radiation, plus dt of 80C (which, for 1l water, needs 80 kcal = 80 x 1.162 Wh) -> 335 seconds.

I'd say a one square meter (~10 sq.feet) box is about equivalent to a standard 700W microwave - between 10 am and 3 pm on sunny days ...

Just for the record: a couple of days later, a local newspaper had this story; their short piece said the box would boil 10 liters in 2 hours.

That's about double my optimistic estimate, which did not take into account any losses by conduction or convection. From the pics, the box doesn't seem to be as big as 1 meter square either.

Could also be used to distill/desalinate water when it's not in use for other purposes.

Solve the simplest problem that tons of people have. Excellent invention in my opinion.