Where would you site an offshore wind farm? Comparing an objective, constraints analysis approach with a subjective, all-stakeholder perspective approach using a multi-criteria decision support tool for offshore NW Ireland

Detailed methodologies for a Geographic Information System (GIS)-based multi-criteria decision support tool based on 186 spatial datasets spanning geological, oceanographic, meteorological, biological, social, and economic parameters for an offshore floating wind farm developed in NW Ireland are presented. These are aggregated into six Combined Data Layers weighted by expert input. Two modelling approaches were applied: (1) an soft constraint analysis which is an objective approach with the 50% suitability threshold replicating the Irish government's Designated Marine Area Plan (DMAP) methodology; and (2) a stakeholder-weighted GIS-based multi-criteria decision analysis using the Analytic Hierarchy Process (AHP). Both approaches produced broadly consistent spatial outputs, with increasing suitability further offshore. Stakeholders rated some areas as more suitable than the objective model, indicating greater tolerance than is strictly necessary. The highest levels of stakeholder disagreement occurred in areas with the lowest suitability, highlighting the least suitable sites are more controversial among stakeholder groups, signifying zones of potential conflict. Conversely, areas with high suitability showed strong cross-group consensus, suggesting widespread support. This methodology provides a replicable framework for integrating technical constraints and stakeholder values in marine spatial planning. By identifying zones of alignment and contention, it offers a powerful tool to improve site selection, reduce conflict, and accelerate offshore wind development through enhanced social acceptance.