Integrating Specific Exergy and Development Feasibility for Sustainable Geothermal Site Assessment in Japan: A Quantitative Matrix Framework

Geothermal resource quality alone does not determine whether a project can be developed under favorable local and institutional conditions. This study integrates thermodynamic resource quality with site-level development feasibility for 18 Japanese geothermal sites included in a published Specific Exergy Index (SExI) dataset. Development feasibility is represented by a weighted score based on four criteria: hot-spring conflict risk, environmental and zoning constraints, consensus-building and regional acceptance, and infrastructure accessibility. SExI and development feasibility show a positive but statistically non-significant association (Pearson r = 0.430, p = 0.075). Using thresholds of 0.5 on both axes, 5 sites are classified as high SExI/high feasibility, 1 as high SExI/low feasibility, 6 as low SExI/high feasibility, and 6 as low SExI/low feasibility. Alternative weighting scenarios preserve the baseline quadrant membership, although sites near the feasibility threshold remain more sensitive to scoring assumptions. These results show that thermodynamic quality and development feasibility are related but distinct dimensions. The proposed matrix provides an exploratory screening framework for identifying whether geothermal development is primarily limited by resource quality or by site-specific socio-institutional conditions.