12.4 Life Cycle Assessment and Sustainability Metrics

Life cycle assessment (LCA) is a powerful tool for evaluating the environmental impacts of energy systems. It considers all stages, from raw material extraction to end-of-life disposal, helping identify hotspots and improvement opportunities.

Sustainability metrics quantify environmental, economic, and social aspects of energy systems. Multi-criteria analysis balances conflicting objectives, while strategies like increasing renewable energy use and implementing energy-efficient technologies can improve overall sustainability.

Life Cycle Assessment (LCA) Methodology

Life cycle assessment for energy systems

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• Systematic approach evaluates environmental impacts of product or system throughout entire life cycle
  • Raw material extraction, manufacturing, transportation, use, end-of-life disposal or recycling
• Four main stages of LCA:
  1. Goal and scope definition: Purpose, system boundaries, functional unit, assumptions
  2. Life cycle inventory (LCI): Quantifies inputs and outputs of materials, energy, emissions for each stage
  3. Life cycle impact assessment (LCIA): Evaluates potential environmental impacts based on LCI data
     • Impact categories: Global warming potential, acidification, eutrophication, resource depletion
  4. Interpretation: Identifies significant issues, evaluates results, draws conclusions
• Identifies environmental hotspots and improvement opportunities in energy systems and products
• Results compare environmental performance of alternatives and support decision-making

Sustainability Metrics and Analysis

Sustainability metrics and applications

• Quantify environmental, economic, social aspects of energy systems and products
• Carbon footprint measures total greenhouse gas emissions associated with product or system
  • Expressed in carbon dioxide equivalent (CO2e)
  • Includes direct and indirect emissions from all life cycle stages
• Water footprint assesses total volume of freshwater used and polluted by product or system
  • Blue water (surface and groundwater), green water (rainwater), grey water (water required to dilute pollutants)
• Energy return on investment (EROI): Ratio of energy delivered by system to energy required to produce and deliver that energy
  • $[EROI](https://www.fiveableKeyTerm:eroi) = \frac{Energy\ output}{Energy\ input}$
  • Higher EROI indicates better energy efficiency and sustainability
• Other metrics: Ecological footprint, material intensity, social indicators (job creation, community impact)

Multi-criteria analysis of energy systems

• Multi-criteria decision analysis (MCDA): Structured approach evaluates and compares alternatives based on multiple criteria
• MCDA tools balance conflicting objectives and stakeholder preferences
• Common MCDA methods:
  1. Weighted sum method: Assigns weights to each criterion, calculates overall score for each alternative
  2. Analytic hierarchy process (AHP): Pairwise comparison of criteria and alternatives to derive priority weights
  3. Outranking methods (ELECTRE, PROMETHEE): Compares alternatives based on outranking relationships
• Analyzes trade-offs between economic (cost, profitability), environmental (emissions, resource use), social (health, equity) aspects of energy systems
• Sensitivity analysis assesses robustness of MCDA results to changes in weights and input data

Strategies for energy system sustainability

• LCA and sustainability metrics provide insights into environmental, economic, social performance of energy systems and products
• Strategies for improving sustainability:
  1. Identify most significant environmental impacts and root causes
  2. Evaluate alternative materials, technologies, processes that reduce impacts
  3. Optimize system design and operation to improve efficiency and minimize waste
  4. Engage stakeholders to understand needs and preferences
• Examples of sustainability improvement strategies:
  • Increase use of renewable energy sources (solar, wind, hydropower)
  • Implement energy-efficient technologies and practices (LED lighting, insulation)
  • Design products for recyclability and easy disassembly
  • Promote sustainable consumption and end-of-life management (recycling programs)
  • Collaborate with suppliers and customers to reduce impacts across value chain
• Monitor and report progress using sustainability metrics to track effectiveness of improvement strategies and communicate achievements to stakeholders