Rapid decarbonization and decentralization of power systems are driving the integration of renewable generation, energy storage and digital technologies into unified energy ecosystems. In this context, photovoltaic (PV) systems combined with battery and hydrogen storage and blockchain-based platforms represent a promising pathway toward sustainable and transparent energy management. This study evaluates the techno-economic performance and operational feasibility of integrated PV systems combining battery and hydrogen storage with a blockchain-based peer-to-peer (P2P) energy trading platform. A simulation framework was developed for two representative consumer profiles: a scientific–educational institution and a residential household. Technical, economic and environmental indicators were assessed for PV systems integrated with battery and hydrogen storage. The results indicate substantial reductions in grid electricity demand and CO₂ emissions for both profiles, with hydrogen integration providing additional peak-load stabilization under current cost constraints. Blockchain functionality was validated through smart contracts and a decentralized application, confirming the feasibility of P2P energy exchange without central intermediaries. Grid electricity consumption is reduced by up to approximately 45–50% for residential users and 35–40% for institutional buildings, accompanied by CO₂ emission reductions of up to 70% and 38%, respectively, while hydrogen integration enables significant peak-load reduction. Overall, the results demonstrate the synergistic potential of integrating PV generation, battery and hydrogen storage and blockchain-based trading to enhance energy independence, reduce emissions and improve system resilience, providing a comprehensive basis for future pilot implementations and market optimization strategies.

Building heating energy demand is influenced by indoor temperature, air exchange, and climatic conditions. This study examines the individual and combined effects of these parameters on a district-heated multi-apartment residential building in Osijek, Croatia. A TRNSYS model was evaluated using measured space-heating consumption for the analysed period from October 2024 to April 2025 and representative TMYx weather data. In the model, air exchange was represented by an effective air-change rate accounting for both uncontrolled air infiltration through the building envelope and natural ventilation associated with occupant window opening. The measured seasonal consumption was 666.16 MWh, while the model predicted 670.61 MWh, resulting in a deviation of 0.67%. The model was then used for a full-factorial analysis including nine indoor temperatures from 18 to 26 °C, nine effective air-change rates from 0.30 to 0.70 h⁻¹, and six Croatian locations, giving 486 simulation scenarios. Under reference conditions, heating demand in Zadar and Split was 44.05% and 50.93% lower than in Osijek/Čepin. Increasing the indoor temperature from 18 to 26 °C increased seasonal demand by 432.63–525.32 MWh, while increasing the effective air-change rate from 0.30 to 0.70 h⁻¹ increased it by 182.67–296.55 MWh. The analysis also showed a positive interaction between indoor temperature and effective air-change rate. For the analysed building, the results can support more sustainable energy use by informing energy-efficient building operation and district-heating demand planning, while the reported numerical sensitivities remain specific to the case-study building.