Comparative techno-economic assessment of centralized and decentralized apartment PV systems in Australia and the United Kingdom

Apartment photovoltaic (PV) systems are constrained by limited roof area, internal distribution, multi-user allocation, and partial utilization of generated energy, meaning installed capacity alone does not reflect system performance. This study develops a deterministic, scenario-based techno-economic framework to evaluate how alternative apartment PV architectures convert available generation into realised user-level energy. Two configurations are examined: centralized shared systems and decentralized unit-level systems. These are evaluated across three building archetypes (10, 30, and 60 dwellings) under selected Australian and UK regional PV-yield conditions, producing 12 comparative scenarios. System performance is assessed using the Energy Access Ratio (EAR), alongside accessible energy, self-consumption, share of benefiting dwellings, and economic indicators. The economic component is implemented as a screening-level assessment, providing indicative annual bill savings and basic investment metrics (payback period and net present value) rather than a full techno-economic feasibility analysis. Cross-country differences arise from assumed regional yield, tariff, and institutional parameters within the scenario framework. Results show that centralized systems consistently outperform decentralized configurations in building-level energy utilization and benefit delivery efficiency. EAR values range from 0.66 to 0.81 for centralized systems, compared with 0.31 to 0.47 for decentralized systems, with up to 115% higher accessible energy in large-building scenarios. Although accessible energy per dwelling declines with increasing building scale due to roof-space constraints, centralized systems remain more effective through aggregation and coordinated allocation. Sensitivity analysis identifies participation rate and infrastructure capacity as key performance drivers. The findings demonstrate that system architecture strongly influences how available generation is translated into realised user-side benefit, and that higher generation does not necessarily improve building-level performance. Therefore, enhancing allocation mechanisms and system integration is critical for improving both performance and inclusiveness in apartment-based distributed energy systems.