Just thought I'd do some calculations specifically about the Gobi desert.
[The tone of this post has changed slightly from "wow china has a lot of people" to "wow there's lots of space in the Gobi, we can power the world from up there"; to "wow it's bitingly cold up there".... :)]
The Gobi is Northerly, high up and is dry in Summer. It's cold and snow-laden in winter however. It has an area of around 500,000 square miles (1,300,000 square km). [Source: http://tinyurl.com/d2t37m ]
[ http://en.wikipedia.org/wiki/Gobi_desert ]
Can we do Solar here? The temperature in winter seems to be cold. Around -15 to -25 Celsius. There might be a problem with water pipes involved in Concentrated Solar Power freezing. Even the mean annual temperature seems to be quite low - around zero e.g. at Sivantse (-2.5C) or Ulaanbaatar (3C).
So it's not clear that we can do CSP on the Gobi plateau. Maybe we should ask a (Chinese) engineer? You could try using anti-freeze as a coolant but mirrors and pipes are probably going to be unpleasant and expensive to erect in biting -20C to -30C temperatures and strong Siberian winds.
Using (hopefully cold-resistant) photovoltaics might be a better plan.
[ http://www.withouthotair.com ]
Let's say (generously) they achieve 5W/m2 [Similar to Bavarian Solar Park]
Let's say that 1million square km can be used. Then the Gobi can provide 5,000GW. That's about one third of total world energy consumption and 5kW for 1 billion people.
But it's still a bit chilly up there. And PV is likely to be expensive, (remember you've got to pay for the systems integration, not just the panels).
What about wind? 2W/m2, (assume only 0.5 million square km - if it's mountainous or even hilly then the valleys are less useful), 1000GW = 1kW per person for a billion people. Maybe not the whole story, but a significant input to China's energy consumption. It's high up in UlanBator and very windy.
Surely therefore wind (cheap; can be done now) is the one to go for? Wind is notoriously intermittent but my guess is that the Gobi is big enough and continental wind currents reliable enough to give some assurity.
My conclusion from this post is:
a) If renewables are reasonably feasible on the Gobi then they could power a large fraction (wind) or all (solar) of China's energy consumption.
b) However, the economic costs and engineering difficulties in the Gobi should not be underestimated, specifically the Siberian conditions (freezing temperatures, biting winds, windchill in the -40s permafrost?).
c) Wind seems the best option (can deal with mountainous terrain without huge costs), and (by carpetting every hill and plateau in the Gobi) could make a contribution of about 1000GW to China's energy needs
d) If Solar is possible up there, then Solar can power all of China, but I'm sceptical about the total systems costs of doing so at present,