smilenergy EnergyAnCivilizationNotes
Model of Energy Flow
what you need is a latticework of mental models in your head. And you hang your actual experience and your vicarious experience that you get from reading and so forth on this latticework of powerful models. And with that system, things gradually get to fit together in a way that enhances cognition. - Charlie Munger
The information in Smil’s work is all very interesting and in my opinion an engaging read. In saying that,I’ve always found I needed some sort of lattice work on which to put the information and data he details. The hope is to define an informal model of energy flows in out biosphere to understand the possible change it could undergo.
What kind of models of energy can we take from Smil?
In the field of ecology there is the idea of an energy pyramid. It’s graphical representation of the available energy in an ecosystem. Each level aims to represent a trophic level. The primitives of this system are producers, consumers and decomposers. Below is my rough diagram of this system.
Each primitive in the system has a metabolism and performs respiration for work. Lots of engines that convert chemical energy into kinetic, electrical and other forms of energy.
A consumer performs some work with the consumable biomass from the layer it depends on. For most consumers this is everything that keeps them alive like finding food, maintaining body temperature, rebuilding tissue and cells. Its evident that a consumer that uses all its metabolism to sustain itself has no way to change the system its in. If you’re a cow, this work is the form of staying alive and eating more plant matter, maintaining some population determined by the amount of embedded energy in plant matter. Humans are different. The outcome of their metabolic work can affect the energy balance of the system itself.
In this system there is a fixed amount of energy. What technology enables us to do is utilise more of this energy. The harness allows us to take advantage of the energy from the horse. The irrigation technology allows us to utilise more energy from the sun. In saying this, there is an implicit calculus that takes place. The energy required to irrigate a hectare of land might not be ‘worth it’.
What does ‘worth it’ mean in the energy context?
It means that the energy benefit from this irrigated land is not worth the effort. If we were to analyse a population of settled people. We might be able to determine what they will do by this energy calculus. That is, their optimisation function would be energy return. Where can they channel their energy to get the highest energy return. This is complex because theres unbounded ways to do this (knowledge creation). We could focus on the intensification of agriculture. Smil highlights 3 changes that were required here. Lets focus on irrigation and fertilization.
Ok, so a portion of the energy required to sustain an agent now goes toward some future payoff. Mysteriously, they’re spreading shit on their fields. What weirdos! But wait, after 6 months, rather than a year, they have a harvest. Their population grows. They keep doing this, growing more until they hit a new maintenance yield.
Abstractly, what does technology do?
It creates a net energy return. Any applied science improves the amount of energy return for a given input. This is how you model an agent in this system.
The Model
What is the data I’m looking for? We need inputs to outputs and also a sense of how we get our initial population. How the initial population is calculated based on available resources.
Variables of interest
Power Density
GPP, Gross Primary Product is a rate of conversion of the suns energy into biomass. Net primary productivity subtracts the energy used for maintenance and cellular respiration. Smil uses a term called Power Density for this rate of energy flow per unit land area.
It’s more intuitive to think of the yield of crops in terms of each harvest in a year. What power density does is just reduce the granularity of this to the second.
Power
Power describes the rate of consumption of the energy flows. Smil uses 670 → 940 kJ/h breaks down to 186→~260W. Evaluating on a per second basis would just be convention.
Energy as a flow (Power Density)
Energy is a flow because it must be replenished. This is due to the fact that it becomes unusable, not that it is destroyed. Mass, in the form of molecules are conserved.
Plants ‘capture’ or utilise a small portion of the light energy incident on them. Roughly 1-2%. On top of this, only about 40% of this is net product biomass.
Population density
The dependent variable is population density. Crudely, the goal of a given population is to increase its surviving offspring. This is also a representation of how much population you ‘could’ support.
Net Primary Productivity
Gross primary productivity (GPP) is the total of new plant mass photosynthesised during a given period of time, usually one year. A large part of it (typically 50%) is rapidly re-oxidised during autotrophic respiration (RA) that energises synthesis of complex carbohydrates, proteins and lipids require for plant growth and maintenance. Whatever remains is the net primary productivity (NPP)… [human appropriation of NPP] mean of several major studies is 25% https://vaclavsmil.com/wp-content/uploads/TWFR-JanFeb2016-Harvesting-the-Biosphere.pdf
This is a measure of biomass for consumption by humans.
Walk through some Smil calculations and identify these variables.
Layering on The Carbon cycle
There is a fixed amount of matter in our planet between the atmosphere and bioshpere. Carbon, Hydrogen, Nitrogen, Oxygen, Phosphurus and Sulphur are the key nutrients for maintaining life. Each nutrient has an associated cycle that is ‘driven’ by energy from the sun. There is a reservoir and then a cycling into the environment and then back to that reservoir.
For example, the reservoir for water (which would offer hydrogen and oxygen) are the oceans (How did the oceans develop?). The sun causes evaporation and eventual precipitation allows humans and plants to consume this water before giving it back to the reservoir (now Earth and inevitably the ocean).
For Nitrogen, fixation from the atmosphere (70% of which is Nitrogen) is done by bacteria. Decomposition is the returning of nitrogen to the atmosphere.
Operating within this system again, fertilizer improves the gross primary production (not the net). Increasing the nitrogen cycles efficiency. Something like irrigation would also contribute to this.
Creating our own engines
We can branch everything humans have ever done under expending heat with their metabolism. Normally, this just involved hunting, foraging, generally just staying a live and meeting evolutionary requirements. Smil introduces the idea of a lever and this is what technology is in this regime. Our metabolic processes developed ways to change the system it operated within.
As an engine, the metabolic process is good but we start to leverage other engines, like domesticated animals to do work. We gain leverage on the amount of work we can do. We also compete for the primary producer with other consumers.
Bypassing the land constraint
I think Smil sees land as a crucial constraint on developments. He uses a power per unit land metric most of the time, which
You can see that something like a solar panel bypasses the energy constraint, or efficiency constraints of plants. As a civilization we initally operated within this system. The first inanimate prime movers took advantage of other forms of energy like gravity over decades (water power). And the suns energy is a more implicit form through the wind.
Net energy return.
This is a concept Smil uses.
Limits of Traditional Farming
What is the natural limit in a system like that shown above? There is a certain net primary product that is constrained by the natural nutrient cycle.
p.82 Traditional farming replaced nitrogen in 3 ways:
- Directly recycling unwanted crop residue, like straw which were not going to be used for feed or fuel or anything else.
- Using organic waste (animal and other).
- Cultivating legumes to enhance nitrogen soil content for other crops.
Smil gives a sense of the rates in our above diagram.
If we take our system as some amount of land and the consumable biomass as wheat, A good late Qing dynasty winter wheat harvest of about :
- 1.5 t/ha
- required just over 300 hours of human and about 250 hours of animal labor.
- Fertilization took, respectively, 17% and 40% of these totals.
- Fertilization hours are 51 and 100 hours.
- 10 t/ha of fertilizer which contains 0.5% nitrogen.
- Due to leaching only half that nitrogen becomes available.
- 25 kg/ha nitrogen for crops.
- Each kg will add 10kg of grain. So 25*10 = 250kg of extra grain.
- 3% used then as animal feed.
- I think what Smil is saying is that you get 200kg of flour (2.8GJ) for 51 hours of extra work (40MJ) of energy.
The harness, redirecting flows of energy for our needs.
A horse has work capacity. The goal is to use this work capacity for work we want to do. Using our brains, we channel the work the horse is able to do to our needs through technology. In an abstract sense, the energy of the horse is now ‘usable’ by us.