Experimental optimization of the performance and reliability of stand-alone photovoltaic systems

Stand-alone photovoltaic systems are deceptively complex. Optimizing the performance and reliability of these systems requires a complete understanding of their behavior as a function of site-dependent environmental conditions. Individual component specifications provide useful design information. However, to fully understand the interactions between components, it is necessary to simultaneously characterize the performance of the system and its separate components under actual operating conditions. This paper describes how a new 30-day outdoor testing procedure was coupled with array performance modeling to accomplish this objective. The procedure measures battery capacity, determines appropriate set-points for charging, and based on daily intervals quantifies DC-energy available from the array, charge-controller efficiency, battery efficiency, inverter efficiency, overall system efficiency, days of autonomy, and AC-energy available by month.