In 2011, MassCEC began implementation of a multi-year performance monitoring campaign of 54 residential and commercial-scale solar hot water systems across the state in order to understand how well the equipment performed, how performance compared to expectations, and to identify performance issues of systems. The results of this analysis are presented in two reports. The Commonwealth Solar Hot Water Program Residential Performance Monitoring Interim Report provides an overview of project monitoring and an initial assessment of contractor performance estimates collected under MassCEC’s Commonwealth Solar Hot Water pilot program, which ran from February 2011 through June 30, 2012. The Commonwealth Solar Hot Water Program Performance Monitoring Final Report provides a detailed assessment of the performance data collected across all system and compares performance of monitored systems to both standardized and contractor performance estimates.