Interview: the skeptic's view on Thermodynamics, entropy & complexity — what would change their mind

The global economy operates at approximately 11% aggregate exergy efficiency, meaning that nearly 89% of all primary energy inputs are dissipated as waste heat or irreversible losses before delivering useful work. This sobering figure, derived from comprehensive thermodynamic analyses of industrial systems, represents the fundamental challenge that skeptics raise when evaluating sustainability claims: no matter how sophisticated our technologies become, the second law of thermodynamics imposes non-negotiable boundaries on efficiency gains. In synthesizing conversations with physicists, industrial ecologists, and complexity scientists, a coherent skeptical perspective emerges—one that demands rigorous thermodynamic accounting before celebrating any green transition narrative. These experts are not opposed to sustainability; rather, they insist that meaningful progress requires confronting entropy head-on rather than obscuring it with optimistic assumptions.

Why It Matters

Thermodynamic constraints represent the ultimate physical limits within which all sustainability efforts must operate. While policy discussions often focus on carbon accounting and renewable energy deployment, skeptics argue that without understanding exergy destruction and entropy generation, we risk pursuing strategies that merely shift environmental burdens rather than reducing them.

The connection between thermodynamics and climate solutions is direct: every energy transformation involves some irreversible loss. When a coal plant operates at 33% thermal efficiency, it means two-thirds of the chemical energy in the fuel becomes waste heat. Modern combined-cycle gas turbines achieve 60% efficiency—a remarkable improvement—but still face fundamental Carnot limits dictated by temperature differentials. Solar photovoltaics convert roughly 20-25% of incident radiation to electricity under real-world conditions, constrained by the Shockley-Queisser limit and practical losses.

Exergy analysis provides a more rigorous framework than simple energy accounting. Exergy measures the maximum useful work obtainable from a system relative to its environment—the "quality" of energy rather than mere quantity. A rigorous exergy audit of the global economy reveals that the largest destruction occurs in combustion processes, heat transfer across temperature gradients, and mixing of streams at different compositions. Understanding these destruction points enables targeted interventions rather than diffuse efforts.

Energy Return on Investment (EROI) offers another critical lens. Fossil fuels historically delivered EROI ratios of 30:1 to 100:1—enormous surpluses that powered industrial civilization. Current renewable technologies typically achieve EROI ratios between 10:1 and 25:1, sufficient for viability but representing a different energy paradigm. Skeptics emphasize that net energy analysis must account for the full system boundary, including manufacturing, installation, grid integration, and end-of-life processing.

Key Concepts

Entropy and Sustainability

The second law of thermodynamics states that entropy—a measure of disorder or unavailable energy—must increase in any spontaneous process. For sustainability, this means that maintaining ordered structures (cities, ecosystems, industrial systems) requires continuous energy throughput. The economist Nicholas Georgescu-Roegen argued that economic processes are fundamentally entropic, converting low-entropy resources into high-entropy waste. While his specific formulations remain debated, the core insight persists: sustainability is not about stopping entropy production but about matching dissipation rates to renewable energy inputs.

Exergy Analysis

Exergy analysis partitions energy flows into their useful (exergy) and unavailable (anergy) components. A factory receiving 100 MW of natural gas chemical exergy might deliver only 40 MW of useful shaft work, with 60 MW destroyed through combustion irreversibilities, heat exchanger losses, and friction. Identifying where exergy destruction occurs guides process optimization. Industrial facilities applying rigorous exergy analysis have achieved 15-30% reductions in primary energy consumption by targeting high-destruction nodes.

EROI Fundamentals

Energy Return on Investment quantifies the energy delivered by a system relative to the energy invested in building and operating it. An EROI of 10:1 means that for every unit of energy invested, ten units are returned. Below a threshold of approximately 5:1, systems struggle to sustain complex civilization because the energy surplus required for non-energy activities (food, healthcare, education) diminishes. Wind energy typically achieves EROI of 18-25:1, utility-scale solar reaches 10-20:1, and nuclear ranges from 10-75:1 depending on methodology and boundary definitions.

Thermodynamic Limits to Efficiency

Carnot efficiency establishes the theoretical maximum for heat engines: η = 1 - (T_cold / T_hot). A steam turbine operating between 600°C (873K) and 30°C (303K) faces a Carnot limit of 65%—and practical limitations reduce this further. Similar fundamental limits exist for photovoltaics (Shockley-Queisser at 33% for single-junction silicon), fuel cells (limited by Gibbs free energy changes), and refrigeration systems (Coefficient of Performance bounded by temperature ratios).

Complex Systems Thinking

Complexity science contributes the insight that systems with many interacting components exhibit emergent behaviors not predictable from component properties alone. Energy systems, economic networks, and ecosystems all demonstrate non-linear responses, threshold effects, and path dependencies. The skeptic's concern is that linear extrapolations of efficiency improvements or technology deployment may miss systemic feedbacks that undermine projected gains.

Thermodynamic and System Efficiency KPIs

Metric	Description	Typical Range	Best Practice Target
Exergy Efficiency	Useful exergy output / exergy input	5-40%	>50% for industrial processes
EROI	Energy returned / energy invested	5:1 - 30:1	>15:1 for grid viability
Carnot Utilization	Actual efficiency / Carnot limit	40-70%	>75%
Primary Energy Factor	Primary energy / delivered service	1.5-3.0	<1.5
Entropy Generation Rate	Irreversibility per unit output	Variable	Minimize absolute value
System COP	Useful output / total system input	0.3-4.0	Context-dependent optimization

What's Working

Industrial Ecology Approaches

Industrial symbiosis networks, where waste streams from one facility become inputs for another, demonstrate practical entropy management. The Kalundborg Eco-Industrial Park in Denmark has operated since the 1970s, exchanging steam, gypsum, fly ash, and other materials among participating companies. Quantitative studies show 30% reductions in water consumption and significant decreases in virgin material requirements compared to isolated operations.

Life cycle assessment (LCA) methodologies, while imperfect, have matured considerably. ISO 14040/14044 standards provide frameworks for tracking environmental burdens across product lifetimes. When combined with exergy analysis—creating "exergoenvironmental" assessments—these tools reveal optimization opportunities invisible to simpler metrics.

Exergy-Based Optimization

Process industries increasingly apply pinch analysis and exergy methods to reduce energy consumption. The chemical sector has achieved documented efficiency improvements of 20-40% in new plant designs using systematic thermodynamic optimization. Heat integration, cogeneration, and cascade utilization of temperature gradients all follow from exergy principles.

Advanced manufacturing facilities now incorporate real-time exergy monitoring. Sensors tracking temperature, pressure, and composition enable continuous calculation of destruction rates, allowing operators to identify and address inefficiencies as they develop rather than discovering them in annual energy audits.

What's Not Working

Rebound Effects

The Jevons paradox—where efficiency improvements increase rather than decrease total consumption—remains inadequately addressed. Historical data consistently show that energy efficiency gains at the device level translate to smaller-than-expected reductions in aggregate consumption. A 50% improvement in automobile fuel economy, for instance, may yield only 20-30% reduction in fleet fuel consumption as lower operating costs encourage more driving.

Skeptics argue that sustainability analyses systematically underestimate rebound magnitudes. Economy-wide models suggest rebound effects of 50-80% for many efficiency interventions, meaning that direct energy savings are largely offset by induced consumption elsewhere in the economy. Without explicit policies constraining total throughput, efficiency gains may simply accelerate resource depletion.

Complexity Blindness

Many sustainability projections assume linear scalability: if one solar panel works, a million will work proportionally. Complex systems research suggests otherwise. Grid integration challenges, supply chain bottlenecks, rare material constraints, and land-use conflicts introduce non-linearities that degrade performance at scale. The learning curves that drove dramatic cost reductions in early deployment may flatten as easy gains are exhausted.

Interdependencies between systems create vulnerabilities. Electrification strategies assume reliable grids; grid reliability assumes predictable supply; predictable supply assumes stable climate; stable climate is precisely what we're trying to achieve. These circular dependencies mean that transition pathways face more uncertainties than straightforward engineering calculations suggest.

Theoretical vs. Practical Limits

Academic analyses sometimes conflate theoretical potential with achievable performance. Laboratory solar cells reaching 47% efficiency tell us little about field performance of 22% modules degrading 0.5% annually. The gap between thermodynamic limits and practical constraints—materials availability, manufacturing tolerances, environmental exposure, maintenance requirements—often spans factors of two or more.

Skeptics point to systematic optimism bias in technology assessments. Cost projections for nuclear power, carbon capture, and hydrogen production have repeatedly underestimated real-world expenses. Thermodynamic analysis can establish absolute bounds, but translating those bounds into deployable systems involves sociotechnical complexities that pure physics cannot predict.

Key Players

Santa Fe Institute

The Santa Fe Institute has pioneered complex systems approaches to sustainability challenges. Their research on scaling laws, network dynamics, and evolutionary economics provides theoretical foundations for understanding energy system transitions. Work by researchers like Geoffrey West on metabolic scaling reveals deep connections between energy throughput and system organization.

Systems Innovation

Systems Innovation offers educational resources and analytical frameworks for understanding interconnected sustainability challenges. Their materials on circular economy, regenerative design, and complex adaptive systems help practitioners move beyond linear thinking toward holistic approaches aligned with thermodynamic constraints.

MIT Energy Initiative

The MIT Energy Initiative combines fundamental research with practical deployment analysis. Their studies on EROI, grid integration, and technology assessment maintain rigorous standards while engaging real-world complexity. The Low-Carbon Energy Centers address specific technology pathways with attention to both theoretical limits and implementation barriers.

International Institute for Applied Systems Analysis (IIASA)

IIASA conducts integrated assessments of energy-environment-economy interactions at global scales. Their models incorporate thermodynamic constraints alongside economic and policy factors, providing scenarios that respect physical limits while exploring feasible transition pathways.

Academic Programs

University programs in industrial ecology (Yale, TU Delft), ecological economics (Vermont, Leeds), and energy systems engineering (ETH Zurich, Stanford) train researchers and practitioners in thermodynamically-grounded sustainability analysis.

Examples

Example 1: Exergy Optimization at BASF Ludwigshafen

BASF's Ludwigshafen Verbund site exemplifies industrial exergy optimization at scale. The integrated chemical complex links over 200 production plants through shared material and energy streams. Steam at multiple pressure levels cascades through processes according to temperature requirements. Waste heat from exothermic reactions drives endothermic processes elsewhere. Comprehensive exergy analysis identified opportunities that reduced site-wide primary energy consumption by 18% between 2005 and 2020, despite increased production volumes. The investment payback periods averaged under three years, demonstrating that thermodynamic optimization often aligns with economic optimization.

Example 2: Denmark's District Heating Network

Denmark's district heating network, supplying over 60% of households, demonstrates system-level exergy thinking. By distributing heat from power plants, waste incineration, and industrial processes at moderate temperatures matching end-use requirements, the system achieves exergy efficiencies far exceeding individual building heating systems. Combined heat and power (CHP) plants operating in this mode achieve effective utilization rates above 85%. The network's gradual transition to lower supply temperatures (from 90°C toward 55°C) further reduces distribution losses and enables integration of lower-grade heat sources including data center waste heat and solar thermal collectors.

Example 3: Rocky Mountain Institute's Whole-System Design

Rocky Mountain Institute's methodology for whole-system design applies thermodynamic principles to building and industrial systems. Their work on the Empire State Building retrofit demonstrated that by reducing cooling loads through efficient lighting and daylighting (addressing the low-exergy waste heat problem), the building could downsize mechanical systems and achieve 38% energy reduction with three-year payback. The approach inverts conventional practice: instead of sizing systems for peak loads, it minimizes loads first and right-sizes equipment accordingly, reducing both capital costs and operating energy.

Action Checklist

• Conduct a comprehensive exergy audit of your facility or system, identifying the five largest destruction points and quantifying their magnitudes in consistent units
• Calculate EROI for energy investments using consistent system boundaries that include manufacturing, installation, grid integration, and decommissioning phases
• Implement real-time efficiency monitoring with dashboards displaying both first-law (energy) and second-law (exergy) metrics to identify degradation and optimization opportunities
• Evaluate rebound effects explicitly in project proposals by modeling behavioral responses to efficiency improvements and incorporating demand-side measures
• Engage with industrial symbiosis networks or initiate material/energy exchange discussions with neighboring facilities to capture waste stream value
• Apply pinch analysis to thermal systems, identifying minimum utility requirements and designing heat exchanger networks that approach these limits

FAQ

Q: Doesn't improving efficiency always help sustainability, regardless of thermodynamic details?

A: Not necessarily. Efficiency improvements that reduce costs can stimulate increased consumption through rebound effects, potentially increasing total environmental impact. Thermodynamic analysis helps identify which interventions deliver absolute reductions versus those that merely shift burdens. Additionally, efficiency measures with low EROI may consume more energy in implementation than they save over their lifetime. A complete thermodynamic accounting reveals whether interventions produce genuine net benefits.

Q: How can renewable energy sources overcome the EROI challenge compared to fossil fuels?

A: Renewable EROI ratios, while lower than historical fossil fuel values, remain well above viability thresholds. Wind and hydro achieve EROI comparable to current fossil fuel extraction (which has declined from historical highs as easy reserves deplete). The transition requires societal adaptation to different energy surplus magnitudes—potentially less total throughput but sustainably maintained. Improvements in renewable manufacturing efficiency continue to increase EROI as learning curves progress.

Q: Why should engineers care about entropy when designing systems?

A: Entropy generation directly corresponds to exergy destruction—the loss of potential to do useful work. Minimizing entropy generation means minimizing fuel consumption, emissions, and operating costs simultaneously. Engineers who ignore entropy may achieve good first-law efficiency while destroying exergy through poor temperature matching, unnecessary mixing, or friction losses. Second-law analysis reveals optimization opportunities invisible to first-law metrics alone.

Q: Can complex systems thinking actually improve practical sustainability outcomes?

A: Yes, by revealing non-linear dynamics that linear projections miss. Complex systems approaches have identified tipping points in energy transitions, lock-in effects from infrastructure investments, and feedback loops that amplify or dampen interventions. This understanding helps avoid investments that appear beneficial in isolation but fail systemically. It also reveals leverage points where small interventions produce disproportionate effects.

Q: What would change skeptics' minds about current sustainability approaches?

A: Skeptics would become more supportive upon seeing: (1) transparent exergy accounting in climate policies and corporate sustainability reports; (2) explicit modeling and measurement of rebound effects with policies addressing them; (3) EROI calculations using consistent, auditable methodologies across technologies; (4) acknowledgment of complexity and uncertainty in long-term projections; and (5) demonstrated absolute reductions in material throughput and entropy generation rather than efficiency improvements alone. Evidence that these considerations are genuinely integrated into decision-making would address the core skeptical concern that current approaches optimize the wrong metrics.

Sources

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• International Energy Agency. (2023). World Energy Outlook. IEA Publications. Comprehensive data on global energy flows and efficiency metrics.

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• Valero, A., & Valero, A. (2014). Thanatia: The Destiny of the Earth's Mineral Resources. World Scientific. Comprehensive exergy analysis of mineral resource depletion.