There has been a lot of debate over the last decade over what types of energy production should be used to replace fossil fuels as our primary source. From my perspective, the entire conversation is utterly pedantic, and I will attempt to explain why. Math is included.
The Earth presents a 127 million square kilometer profile to the sun. For those that don't know, a profile is the 2 dimensional area that is orthogonal (perpendicular in every direction) to the sun's radiation. Every meter of the profile gets approximately 1 kilowatt of sunlight. That's a rate, not a quantity, 1 kilowatt is 1 kilojoule per second, 1 kilowatt-hour is 3600 kilojoules. Now, even considering that most solar panels only convert 15% of that into electrical energy, and that only 30% of the planet is land and only 3% of that is urbanized, if we laid out solar panels covering an area equal to the urbanized area, it would generate (127,000,000 [km^2] * .03(.3) * .15 * 1000000 [m^2/km^2]) 171.45 Terawatts of power. That might not seem like much, especially when you consider that we consume over 100,000 Terawatt-hours per year (whole planet), but remember, it's a rate, Joules per second. In fact, at that rate we would produce (171.45*60*60*7.639*365) 1,720,954,406 terajoules of energy per year, or (9011412000/3600) 478042 terawatt-hours of energy. That is almost five times what we use right now. No massive desert solar farms, no environmental impact, just rooftops and parking lots. We don't need any source other than solar to power our civilization.
Below is explanations of things I think might confuse.
Notes: Why 15% efficiency isn't "bad". Solar panels get 15% of 1 kilowatt. That's a constant 150 watts, all day, every day. It's effectively infinite, although the panel will wear out after a couple decades. Gas motors range from 20% to 40%, though gas power plants can get up to 60-70% with cogeneration. This is finite, however, since it requires fuel, and the processes of extracting the fuel from the ground require energy, all of which are subject to their own losses from efficiency. TLDR: 15% of infinity > 70% of any finite value.
The 7.639 number is the equivalent time a panel is exposed to sunlight in a day if it were exposed to constant maximum sunlight. Basically it accounts for the decrease in sunlight early and late in the day and converts the 12 hours of often marginal sunlight into 7.639 of constant maximum in order to make the math easier. If I didn't do that, and you don't know how integrating with trigonometric functions worked, you wouldn't be able to follow what I was doing.
1 watt = 1 joule per second = 1 ampere * 1 volt
1 kilowatt = 1000 watts
1 kilowatt-hour = 1000 watts for 1 hour or 3600 seconds, so 3600 kilojoules
1 Terawatt = 1,000,000,000,000 watts
1 kilometer = 1000 meters, therefore 1 square kilometer = 1000 squared, or 1000000 square meters