Reliability and availability analysis of a fielded photovoltaic system

Abstract

System level reliability and availability estimates are required to facilitate cost tradeoff studies associated with competing photovoltaic systems. Estimates of reliability are necessary in developing maintenance cost projections over the system lifetime. Availability estimates provide an input into annual energy generation projections. This paper describes a comprehensive approach to developing reliability and availability estimates for a large photovoltaic system. System reliability and availability were defined based on the operator's expectations and a Reliability Block Diagram (RBD) was developed to model system behavior. The RBD developed is a hierarchical reliability model. Larger functional elements are decomposed into smaller functional elements. The granularity of the model is determined by the level that failure data are collected. Field data, failure times and repair times, were collected and analyzed for a five year time period from a 4.6 MWdc photovoltaic system operated by Tucson Electric Power (TEP) at Springerville, Arizona. Failure and repair distributions were fitted to these field data. These results were then used to populate the RBD and produce system level estimates of reliability and availability. The results of these analyses are: 1. a summary of failures for each main component of the system, 2. a summary of failure distributions/rates and repair times for each main component, 3. system reliability and availability versus time projections, and 4. an estimate of the number of failures for each main component over the system's life.