You forget the real limits that these people will face : the human body. And, as neighboring Rwanda has demonstrated, those limits are quite unforgiving.

Everything else was done by hand, using ZERO energy.

Does the human body use "zero" energy ? Well let's take a look at the efficiency. Let's estimate that plant production from sunlight is less than 2% efficient. Let's disregard that meat production from plants is less than 0.02% efficient. Let's forget that our own systems are only about 2% efficient (and that's only if you count every action, including sleep, getting sick and masturbating as "useful work", otherwise you don't even want to think about the efficiency of the human body).

How much energy does it require to keep a human body merely alive ? The main "cost" of a human body is the fact that we're warmblooded, that we can never, ever, lower the rate of energy consumption in our organs more than a few tenths of percents. Staying alive on the North Pole therefore requires much, much more than staying alive on the equator. Kenya is a benefactor of this effect, and fortunate in this regard.

http://en.wikipedia.org/wiki/Basal_metabolic_rate#Animal_BMR

The energy requirement of the human body is 16 kilocalories per day per pound. I'm about 135 pounds, so that means 2160 kilocalories per day. (yes the wikipedia article is wrong, wikipedia's always at best inaccurate). That means I'm, at total rest, am about 2 incandescent light bulbs.

But that's not the amount of sunlight energy it takes to keep me alive. Let's measure this against total amount of incoming sunlight. Arable land is about 10% of all land, which is about 1/3rd of the planet. Meaning we can actually use 3% of incoming sunlight. I eat about 1/10th meat and 9/10th plants. That means 216 kcal / 0.02% / 2% / 3% + 9/10 * 2160 kcal / 2% / 3%. This number does NOT include transport, so it is only valid for subsistence farmers, who do not use any fertilizer, machines or anything. Let's assume getting food to your average urban dweller is 10% efficient, and producing it using industrial agriculture is another times 10% efficient.

So how much sunlight does this "ZERO" energy usage require ? 87 323 566.7 watts per subsistence farmer. 8.7 billion watts per city dweller. Every single person on this site, JUST TO KEEP EM BREATHING requires 8.7 BILLION watts of sunlight to be sent to earth. I'm sure getting anyone of them to build a house makes 9 billion out of it. Btw : this is just breathing, nothing more. Not tv, no computer, and certainly no internet or cell phones.

That's only zero energy expenditure if your middle name is Hussein, spending other people's energy.

I think Ndege's article is seriously over-optimistic. As is Gail's concluding scenarios page. And Eric's comment here.

Human groups rarely handle contraction at all well. The world's supposed elites are already doing a pretty abysmal job of handling merely the end of growth, let alone the downslope to come. The probability of "developed" societies getting down that unfamiliar icy slope without slipping into catastrophe I would rate as negligible.

Others above here have rightly identified one difference from Kenya - that we in the "developed" world have become severely impoverished in the most basic skills for survival and low-energy happiness.

Eric's notion that there's no problem because we do not need to invent is also seriously misconceived. Just because there are a few books in libraries and a possible handful of people have some of the skills and tools does not mean that that basic expertise can be suddenly scaled up once the corporate system collapses (even if slowly).

Documentation of the techniques of the 1700s-1900s? Show me a single cobbler alive in the UK. How does one promptly extract such skill from "documentation" (wherever that may be)? I am talking about a most basic human requirement, for wearable shoes once we have to get everywhere by foot and shoes no are longer shipped over from China. The cobbler of Nuremberg was already moaning about the complaints of his uncomfortable customers back then (in Die Meistersinger von Nurnberg, 1867), so look forward to some whopping corns in the bright future folks.