RESEARCH ARTICLE Multi-pronged analysis of degradation rates of photovoltaic modules and arrays deployed in Florida K. O. Davis 1 * , S. R. Kurtz 2 , D. C. Jordan 2 , J. H. Wohlgemuth 2 and N. Sorloaica-Hickman 1 * 1 Florida Solar Energy Center, University of Central Florida, 1679 Clearlake Rd., Cocoa, FL 32922–5703, USA 2 National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401–3305, USA ABSTRACT The long-term performance and reliability of photovoltaic (PV) modules and systems are critical metrics for the economic viability of PV as a power source. In this study, the power degradation rates of two identical PV systems deployed in Florida are quantified using the Performance Ratio analytical technique and the translation of power output to an alternative reporting condition of 1000 W m 2 irradiance and cell temperature of 50  C. We introduce a multi-pronged strategy for quantifying the degradation rates of PV modules and arrays using archived data. This multi-pronged approach utilizes nearby weather stations to validate and, if needed, correct suspect environmental data that can be a problem when sensor calibrations may have drifted. Recent field measurements, including I-V curve measurements of the arrays, visual inspection, and infrared imaging, are then used to further investigate the performance of these systems. Finally, the degradation rates and calculated uncertainties are reported for both systems using the methods described previously. Copyright © 2012 John Wiley & Sons, Ltd. KEYWORDS degradation rate; energy yield; archived data; Performance Ratio *Correspondence Kristopher Davis, Nicoleta Sorloaica-Hickman, Florida Solar Energy Center, 1679 Clearlake Rd., Cocoa, FL 32922–5703, USA. E-mail: kdavis@fsec.ucf.edu; nhickman@fsec.ucf.edu Received 24 June 2011; Revised 27 November 2011; Accepted 30 November 2011 1. INTRODUCTION Field testing has played a vital part in determining photo- voltaic (PV) performance and lifetime. Dating back to 1983, the Florida Solar Energy Center (FSEC) has performed outdoor performance measurements on various kinds of PV modules at different locations in Florida, as shown in Figure 1. With over 150 systems listed in the FSEC PV system database, 70 of which have performance data, there is clearly a rich history of archived data that can be used to better understand and quantify the long-term performance of PV modules and systems. DC operating current, DC operating voltage, and AC power were recorded for extended periods of time (greater than 3 years), along with environmental conditions such as plane-of-array (POA) irradiance, module temperature, and ambient temperature. For many of these systems, the initial data monitoring served some function other than determining long-term performance degradation. Some of the systems were used to better understand the role of PV in the development of zero-energy buildings [1,2]. Other PV systems, installed on schools in Florida, were monitored to educate students on PV technology and also gather statistical information regarding life-cycle costs [3]. Recent efforts have sought to relate the long-term performance of these systems to life-cycle costs and economic payback time [4]. Long-term performance of PV systems is an area of critical importance from the perspective of both manu- facturers and end users. End users want to harvest the maximum amount of energy per rated watt throughout the expected 20+ year operational lifetime. To stay competitive, module manufacturers guarantee minimal degradation throughout the lifetime of the product. Standard warranties typically guarantee a power output after 20 years of 80% of Standard Test Conditions (STC) nameplate. Clearly, if a large number of a man- ufacturer’s modules have higher degradation rates than expected, then the company’s financial security can be significantly compromised by the cost of replacing these defective products. There is also potential damage to a PROGRESS IN PHOTOVOLTAICS: RESEARCH AND APPLICATIONS Prog. Photovolt: Res. Appl. (2012) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/pip.2154 Copyright © 2012 John Wiley & Sons, Ltd.