The energy needs of the world’s economy seem to be easy to model. Energy consumption is measured in a variety of different ways including kilowatt hours, barrels of oil equivalent, British thermal units, kilocalories and joules. Two types of energy are equivalent if they produce the same number of units of energy, right?
For example, xkcd’s modeler Randall Munroe explains the benefit of renewable energy in the video below. He tells us that based on his model, solar, if scaled up to ridiculous levels, can provide enough renewable energy for ourselves and a half-dozen of our neighbors. Wind, if scaled up to absurd levels, can provide enough renewable energy for ourselves and a dozen of our neighbors.
There is a major catch to this analysis, however. The kinds of energy produced by wind and solar are not the kinds of energy that the economy needs. Wind and solar produce intermittent electricity available only at specific times and places. What the world economy needs is a variety of different energy types that match the energy requirements of the many devices in place in the world today. This energy needs to be transported to the right place and saved for the right time of day and the right time of year. There may even be a need to store this energy from year to year, because of possible droughts.
I think of the situation as being analogous to researchers deciding that it would be helpful or more efficient if humans could change their diets to 100% grass in the next 20 years. Grass is a form of energy product, but it is not the energy product that humans normally consume. It doesn’t seem to be toxic to humans in small quantities. It seems to grow quite well. Switching to the use of grass for food would seem to be beneficial from a CO2 perspective. The fact that humans have not evolved to eat grass is similar to the fact that the manufacturing and transport sectors of today’s economy have not developed around the use of intermittent electricity from wind and solar.