Sustainability & The Second Law of Thermodynamics

6 min readJan 25, 2022

Julian Godding, Senior Data Scientist, Gardin

Image: Julian Godding


At Gardin, sustainability and science are at the heart of what we do. As engineers with backgrounds in fields ranging from optoelectronics, condensed matter, robotics and, of course, plants, we often discuss our favourite areas of research and argue over their respective merits. However, if there is one area of science that we all look upon with awe, it is the Laws of Thermodynamics.

Comprised of three distinct laws, these axioms are the most foundational in our understanding of the universe and, according to Einstein, are such that “within the framework of the applicability of its basic concepts, will never be overthrown.”

You have already heard from us on the First Law of Thermodynamics, so this write-up will explore the Second Law and how in our minds, it provides an interesting lens to understand the need to develop a sustainable future for our planet.

The Second law is the hardest of the three laws to understand because it deals with the concept of entropy — a term most people do not come across very often.

The Second Law states that an irreversible, spontaneous process takes place when the Gibbs Free Energy decreases and the total entropy, S, of a system and its surroundings increases.

There is a bit to unpack here but let us start with entropy. Entropy is technically defined as the number of possible unique ordered states in a system, this leads many to understand it as the ‘amount of disorder.’ For example, there are many more ways of arranging molecules in a gas than in a solid where each particle is held in a fixed position. However, one of the problems with this understanding is that we all know the modern world is full of order — so how did these processes happen if the second law holds true?


For a process to occur, classical physics tells us work is done using energy, but not all work is useful. Work can be fully converted to heat but not all heat can be converted to useful work. This gives rise to the concepts of enthalpy, H, which describes the ‘quantity’ of energy (explored in our blog on the first law) and exergy, E, which reflects its corresponding ‘quality.’ Exergy describes how much energy obtained from the carrier can be turned into useful work and for physical states is defined by; E = (H — Ho) — To(S — So), the ‘o’ indicates a reference standard temperature and pressure (298 K, 1 atm). Using this equation, we see that entropy defines the amount of useful work from a quantity of primary energy. Exergy relates to Gibbs Free energy, G = H — TS, as the maximum work that is available from a system and is usually considered as the change in free energy during a process. The two equations are equivalent when T=To. In summary, the ability for processes to occur arises from an associated increase in entropy, with larger entropy increases yielding more useful work that can be done.

Before industrialization, the agrarian economy could rely on windmills for grinding flour, bulls for ploughing fields and logs for heating. However, industrialization and the invention of the combustion engine led to an enormous demand for exergy (and entropy) that could not be fulfilled with traditional sources. Instead, this need was met with fossil fuels — large, controllable sources of entropy through their combustion into gaseous CO₂ and water. The neoclassical model of economics postulates an isolated circular flow of money from businesses to consumers via products and services. However, we are now starkly aware that this flow is in fact dependent on the irreversible extraction of natural resources and their subsequent disposal as waste.

Our entropic waste is filling the atmosphere like a balloon, a system which is too small to contain it.

The idea of economic externality was recently popularized in the book Donut Economics but has been an area of study since the 1970s. The theory was pioneered by the bio-economist, Georgescu-Roegen, who was the first to regard the throughput of the economy as an entropic flow, subject to the same constraints of physical processes bound by the Second Law. He saw the Second Law as the ‘taproot’ of economic scarcity, and it is for this reason that we believe the law provides an interesting lens to view the sustainable transition.


The clean energy transition is not just about averting a climate crisis, it is also an opportunity to create a society that is more prosperous, equitable and beautiful. Today, we are bound to a status quo where the supply of energy is controlled by a cartel of authoritarian regimes with atrocious human rights records; that alone should be enough to make anyone think change would be a smart idea.

Scarcity arises because our entropic system is limited to the planet and society’s demand for fossil fuel energy is putting the system severely out of balance. However, there is an alternative; a limitless source of entropy that could enable unparalleled economic progress. The Sun.

A source of so much entropy that if we can expand our entropic system to encompass it, scarcity no longer becomes relevant. To put this in perspective, each hour the sun delivers enough energy to the Earth’s surface to satisfy global energy consumption for an entire year. We simply need to expand our balloon of entropy to the solar system and the second law still holds.

The methods of expanding our entropic system to the sun are well known; harnessing the power of solar rays, wind currents and the water cycle, just as our agrarian ancestors did but using modern technology to fulfil the massive energy requirements of society today. What is more, this method of energy harvesting is hugely more efficient than fossil fuels and the reason again lies in the second law. Fossil fuels result in the destruction of up to one-third of their own useful energy through heat transfer, ending up as random thermal fluctuations of surrounding molecules, requiring us to extract multiple times more primary energy than what we can usefully harness. In other words, we are releasing enormous amounts of CO₂ without even getting any value from it. Although solar and wind power are limited in their power conversion efficiency, they do not use heat transfer to deliver useful secondary energy in the form of electricity. This means that in a clean energy system, our total primary energy consumption would in fact decrease significantly.


The future energy system is needed not just to avert catastrophic climate change but to fundamentally transform the modern economy to improve the prosperity of those who were previously so limited by access to energy. Unlike fossil fuels, renewable energy production creates no waste and has zero-marginal cost. As with the zero-marginal cost of information that has come out of the age of computing, the age of sustainability will initiate an extraordinary excess of electrons. This will act as a powerful driver of growth for disruptive business models such as desalination, carbon capture and of particular interest to Gardin — vertical farming.

The goal will be to produce as much as physically possible with no thought of the cost of input or waste because there will not be any. Gardin is working with farmers to show them that their largest cost, energy, can become a revenue source without any loss to product quality when used in combination with our technology.

Although the need for a clean energy system is well known to all, by viewing society through the lens of thermodynamics, we come to appreciate the enormous potential that such a transition holds. This first-principles approach makes it clear that the end of fossil fuels is inevitable, purely on the grounds of thermodynamic efficiency. Our Sun is the most magnificent gift and harnessing its entropy can bring prosperity for all. It is up to us to decide how quickly change happens.

Julain Godding, Senior Data Scientist at Gardin

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