Re: solar power will be the limiting factor on what humans can do in the long run
Bollocks! A small fraction of the Sahara desert alone could generate more electricity than the human race currently uses.
The Solar radiation flux onto Earth's surface is about a kilowatt per square meter. Allowing 10% for harvesting efficiency and a factor of two for dark night-times. you need 20 m^2 per kW power-station output. A large power station is a Gigawatt: a million kilowatts, or 20 square kilometers of desert covered in solar panels.
10% for harvesting efficiency is a nonsense. I refer you to Wikipedia:
Solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 40.7% with multiple-junction research lab cells and 44.4% with multiple dies assembled into a hybrid package. Solar cell energy conversion efficiencies for commercially available multicrystalline Si solar cells are around 14-19%. The highest efficiency cells have not always been the most economical — for example a 30% efficient multijunction cell based on exotic materials such as gallium arsenide or indium selenide and produced in low volume might well cost one hundred times as much as an 8% efficient amorphous silicon cell in mass production, while only delivering about four times the electrical power.
However, there is a way to "boost" solar power. By increasing the light intensity, typically photogenerated carriers are increased, resulting in increased efficiency by up to 15%. These so-called "concentrator systems" have only begun to become cost-competitive as a result of the development of high efficiency GaAs cells. The increase in intensity is typically accomplished by using concentrating optics. A typical concentrator system may use a light intensity 6-400 times the sun, and increase the efficiency of a one sun GaAs cell from 31% at AM 1.5 to 35%.
You're looking at a 20% conversion efficiency probably, so you need to increase your area by a factor of five. So that's 100km² / GW. The area of the Sahara is 9.4 million km². That gives you a total power output of 94,000 GW, or 823.4 PWh per annum. Planetary energy consumption in 2008 was approx. 144 PWh. So the Sahara, assuming you could cover it ENTIRELY with solar panels, keep them clean, and with an exact 50/50 split of day/night, and that each panel was generating it's maximum possible theoretical output the entire time it was in sunlight, would provide about half of the planetary energy requirements. Realistically, probably more like a quarter or less.
And then, on top of all that, you've got transmission losses to take into account. You'd lose another 10% or so in that. Again, from Wikipedia:
As of 1980, the longest cost-effective distance for Direct Current transmission was determined to be 7,000 km (4,300 mi). For Alternating Current it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter than this.
Can anyone spot any problems with this plan? Answers on a postcard...