Photovoltaic (PV) systems offer significant potential for net-zero emission targets, due to their flexibility and high exploitation capacity. However, effective carbon monitoring, reporting, and verification (MRV) methods are crucial for their life cycle. The present study introduces a novel blockchain-based carbon auditing tool aimed at supporting the life cycle assessment of PV systems in Hong Kong's building sector. Consequently, all relevant information throughout the PV system's life cycle is uploaded and securely recorded within the blockchain system. The decentralized network structure, distributed consensus, and cryptographic methods employed by blockchain technology ensure the traceability, immutability, and transparency of the recorded information. Furthermore, this study provides an analysis of the installation potential and life cycle environmental benefits of PV systems in Hong Kong's building sector. Finally, the feasibility of the proposed framework is demonstrated through case studies conducted in Hong Kong. These findings underline the reliability of the proposed blockchain-based tool as a technological foundation for carbon MRV in the Hong Kong building PV sector.