According to some blogger with a solar observatory, last Sunday June 22nd (see how I like to keep things timely?) was International SUNday, a day devoted to appreciating our life-giving sun through observation (with proper equipment of course) and education  . I came across the holiday after a friend had posted it on Facebook with a list of sun-related facts. I had intended to include the bit of trivia about how how the sun could provide some so-many-thousand times more energy than we consume each year, but I couldn't remember it and looked up the numbers behind it. I instead got distracted and decided that perhaps I should follow up with a blog post about it, which you're currently being subjected to.
Factoring in panel efficiency (~20%) and land cover (~30%), the energy that could be captured from the sun is 420-times our total annual energy consumption . This means that covering 1/420th of land area (0.2%) in panels would be able to meet all of our transportation- and stationary-energy needs. This comes to 110,000 sq. miles, which is about the area of Nevada . This seems like a lot, and it is, mostly because we use A LOT of energy. It seems a bit hopeless to try and tile all of Nevada in panels, but that doesn't take into account is that we humans have gotten really good at building things over large areas already, and not just simple things: cities. I looked up the population density of the largest cities and found that they're in the 10,000 people/sq. mile ballpark  . We know half the world's population lives in cities now, so that makes 335,000 sq. miles, or 0.6% of land area.
1) I actually think it's pretty amazing that in 200 years of modernization and urbanization, we've only covered 0.6% of land area; the world is BIG. That said, even having only covered that 0.6%, we've managed to screw up a lot of natural processes. Humans are MESSY.
2) This means that if we cover 1/3 of city area in panels, we'd be able to meet all our energy needs via solar power. Based on my years of playing SimCity, that's roughly what roads typically take up (NOT an endorsement for "solar freakin' roadways," we know that's a silly idea; just serving as a comparison).
Now, real talk:
This is a quick analysis that is based on averages. Solar power isn't available everywhere all the time and there are locations where it wouldn't make a lot of sense. It was meant to provide context: yes we can build enough panels to cover that area because we've built more of more complicated things, but no it isn't going to be easy. Here's where it gets interesting though. Urbanization is a very strong force; most of the growth in population is going to be in newly urbanized areas in developing regions of China, India, and Africa . In other words, the way we as a civilization will grow in the next 30 years is going to be by building new densely populated areas, not by making current population centers denser. 2/3rds of the new people expected by 2030 will live in buildings that don't currently exist yet in regions that are characterized by high solar insolation . This is a HUGE opportunity. Those new urban areas need to be extremely efficient and reliant on local renewable energy, primarily solar.
Want to change the world? Become a contractor specializing in building low-cost, low-energy apartments in developing countries, or a local policy expert pushing for low-energy new building codes. That will mean the difference between a future of much of the same (that is to say, getting worse), and a future with an inflection point.