Methods for Assessing Longitudinal Variations of Energy Production by PV Systems

Energy efficiency programs, such as Better Building Initiative, assume that our knowledge is adequate to understand and assess energy savings and productions, in order to guide investment decisions so that energy savings goals are achieved. However, energy savings and productions following the implementation of energy improvements, such as Photovoltaic (PV) systems, are subject to significant short- and long-term variations over time. Understanding the longitudinal variations of energy savings and productions is critical to achieve energy savings goals. The objective of this paper is to identify and characterize main properties of longitudinal energy productions following the implementation of photovoltaic (PV) systems. Graphical and statistical time series methods are used to directly extract knowledge from the actual longitudinal energy productions. The data about longitudinal energy productions of forty five PV systems were used in this study. The data were provided by Florida Solar Energy Center. The identified properties of longitudinal energy productions are outliers, level shifts, seasonalities, long-term trends, and short-term variations. It is expected that the knowledge about longitudinal variations of energy productions improve maintenance, design and investment analysis of PV systems in order to achieve energy productions goals. It is also anticipated that the proposed methods can be used for identifying and characterizing longitudinal energy productions following the implementation of other energy improvements.