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Transformity and transitioning to renewable energy

A while back I wrote an article which I called Equalling the Sun. I demonstrated that with a mere 2.5% growth in demand for energy each year we would demand as much radiant energy as the sun provides the surface of this planet in about 400 years. I've reposted the important parts of the essay in a companion post. (Warning: contains a lot of arithmetic.)

At the time, I thought this was a revelation. I thought I'd stumbled upon irrefutable logic that we needed to start curbing our energy use and to start doing it very soon. Surprisingly, this is not the reaction I got. While it was true that many people found the figure of 400 years to be smaller than they thought it would be, especially at such a modest growth rate, they reasoned that 400 years was a long way off so that we were in no danger right now.

With the knowledge I had at the time, this figure was the best upper bound I could come up with. I was aware that the best solar cells are only 30% efficient and that we couldn't cover the entire surface of the planet with solar cells, because most of it is water. But when I took these facts into account and introduced them into my calculations we still had more than 200 years before mankind's thirst for energy would run up against the limits (at the aforementioned growth rate of 2.5%).

But that was before I knew about transformity, a concept introduced by Howard T. Odum. Transformity is a useful measure of the embodied energy of things. What makes it different to other measures of the same concept, such as the nutritional information on the back of a can of spinach, is that it measures it with respect to solar energy. The sun may imbue an object with energy in one step or in many steps. For instance, the sun may heat air, thus turning it into wind. Or the sun may be captured by green plants which are then eaten by a creature followed by another creature until finally that creature lands on our plates as food. In each step of the process energy is lost. For instance, it takes roughly 1500 joules of solar energy to produce 1 joule of wind energy. Transformity measures the ratio between these values. Thus, the transformity of wind is 1500. It's a unit-less value. Think of it as a multiplier that you can use to equate different forms of energy. e.g. 10 joules of wind energy = 15,000 joules of solar energy.

Transformities increase as you add more conversion steps. The wind, which was formerly heated by the sun, may then go on to drive a turbine which produces electrical energy. We may find that it takes, say, 6 joules of wind energy to produce 1 joule of electrical energy. The transformity of the electrical energy is thus 9000. We get this value by multiplying the transformities at each conversion together. You can see from this simple example that depending on how energy is produced its transformity can be different.

One of the most fascinating tables in Odum's book, A Prosperous Way Down, lists the transformities of various things. It's often a lot larger than you think. For instance, the transformity of grain is about 86000. This seemed far too large to me at first glance. Was Odum really telling me that it required 86 kJ of sunlight to produce a single joule of grain energy? But it seems roughly correct when you do the maths. When you take into account that the sun provides 1300 joules per second to each square metre of the Earth and, further, that a crop may take 90 days or so to mature you find that the sun has provided an awful lot of energy. And in return a single square metre of that crop may only return on the order of 100,000 joules of energy that a human being can digest.

This is where we must pause for a moment and examine the concept of energy quality. Although energy is lost in each conversion the quality of the energy is often improved. For instance, liquid fuels, such as petrol, have a very high energy density on the order of several million joules per litre. Such liquid fuels are easily transported and are non-perishable. Energy in this form is much more useful to us than an equivalent amount of sunlight.

After "sanity checking" the value given by Odum for the transformity of grain I'm inclined to believe the figure that says the transformity of fossil fuels is approximately 50,000. Here's where things get interesting. In my essay I showed that the sun beat down about 13,000 times more energy than we derived from burning fossil fuels in the year 2005. The figures were taken from a spread sheet on world energy markets that I downloaded from the BP website. (Interestingly, I had these figures confirmed for me at a coal industry presentation that I attended and a talk by the German Greens MP Hans-Josef Fell.)

The fact that the sun provides 13,000 times more energy than we used in 2005 leads most people to heave a sigh relief. What an abundance of energy! Even Hans-Josef Fell tried to convince the audience of his talk with this logic. But if all of this energy were turned into fossil fuels through natural processes (which takes millions of years) we would actually have a short-fall of energy. Why? Because the transformity is 50,000, a figure much larger than 13,000.

Maybe human ingenuity can do better. Perhaps we can create energy sources that have the quality of fossil fuels but with a transformity better than 50,000. But we shouldn't bet on it. You often hear that it will be possible to make an easy transition from our current fossil fuel based economy to one based on renewable energy. Calculations like the one I've just performed show that this is a little more difficult than it first sounds. I'm not saying that there isn't a way to produce fuels with transformities better than 50,000, but I hope I've highlighted the importance of this concept in any discussion on transition to alternative energy sources.