Even so, an average-sized residential roof will generate quite a lot of power relative to what the inhabitants use on all but apartment towers - and those are usually surrounded by enough parking, on which we can build sunshades with solar panels, to compensate.
"Got rice?" Not here in Asia, where most people live.
Even so, an average-sized residential roof will generate quite a lot of power relative to what the inhabitants use on all but apartment towers - and those are usually surrounded by enough parking, on which we can build sunshades with solar panels, to compensate.
The developing world is rapidly urbanizing and moving in to - you guessed it - apartment towers. The world at large is also moving away from cars.
What is your idea of an 'average sized' residential roof, anyway? Perhaps you are aware that US houses have the largest floorspace per capita of anywhere in the world, except Australia?
No offence but it looks like you have a very North American (chiefly US) perspective.
Show me a city in Asia, and I will show you land 100-200km (often 25-50km) away that is barely used, having been given over to scrub or wilderness or low-value agriculture. Only in the centers of the most dense cities do land prices even eclipse solar panel prices when considering this power generation method. This has to be the case, for transportation reasons: a city can only grow where it has access to significant amounts of land to feed itself. The amount of land required to feed a person tends to vastly overshadow the amount of land required to power that person's share of the generation infrastructure.
200kg of rice staple a year per person (estimate from Burma of strict rice consumption diet) / 4 tons rice per hectare (world average) = 500 square meters per person, for a no-protein diet. Replace rice with wheat, and add some meat + dairy, and you increase that figure by several times.
...
Napkin Math (Guaranteed to one order of magnitude):
China uses about 500 watts per person.
Beijing's region gets about 5kwh/m^2/d of insolation
At 10% efficiency that's 500wh/m^2/d
That means 1 person needs 24m^2 of land given over to solar panels
Beijing has 20M people
That's 480 km^2 (a square plot of land 20km x 24km) that Beijing would have to find to place solar panels; Compare with, for example, the size of Beijing.
...
The Chinese province of Inner Mongolia has sufficient unused desert scrubland to power the entire world several times over, if:
A) The solar panel price problem is solved
B) The energy storage problem is solved
C) Electrical distribution infrastructure is approached in a systematic manner
Thanks for the admission of poor premise. I'm just not clear what "the rest" was.
You continue to talk about "unused" land near major population centers, then combine rice-yield statistics from tropical, water-rich environments with an example of Beijing, an arid climate with relatively extreme temperature fluctuation making it a very poor yielding area for rice (though it is grown, you get only one instead of two and often three crops per year in tropical/subtropical zones).
I admire your optimism with regards to solar and share your concerns around world energy usage and the need to actively consider alternative energy generation, but I think the sad reality is that cities are a lot less space-rich than you assume and that solar yields in places like Beijing are too space inefficient to give the types of returns you are looking for.
You will have, of course, noticed that right next to Beijing (>21 million) are also the cities of Chengde (173km; ~4 million), Datong (265km; ~3.5 million), Tianjian (112km; >13 million), Shijiazhuang (267km; >10 million), Tangshan (157km; ~8 million), Zhangjiakou (160km; ~4.5 million)?
Despite this density, Chinese are well fed, a fact which derives from very high efficiency land use with strong government support for agricultural research and technology. Huge projects such as the Grand Canal[1] have supported these populations for millenia.
It's great to discuss these things, but the reality on the ground is very different to napkin-world. In short, I'm sorry but you're probably more than one magnitude out... "guaranteed".