Performance loss rates of floating photovoltaic installations in the tropics

Abstract

Floating photovoltaics (FPV) is a relatively new concept for the PV community. The operating environment of FPV systems is different from that of conventional PV systems and offers the potential advantage of higher energy yield. Consequently, there is a rapid increase recently in both the installed and planned capacity of FPV systems worldwide. However, there exists a lack of knowledge and data about the performance stability of FPV systems. This paper presents, for the first time, a detailed analysis of the performance stability of FPV systems from one of the largest FPV testbeds worldwide, located on the Tengeh Reservoir in Singapore (tropical rainforest climate). The study is based on data gathered during the operation period of April 2017 to March 2020. Three commonly-used statistical methods are deployed to calculate performance loss rates (PLRs) — ordinary least squares (OLS), seasonal and trend decomposition using locally weighted scatterplot smoothing (STL) and year-on-year (YoY) methods. The mean PLRs of eight monitored FPV strings (all deploying crystalline silicon modules) based on OLS, STL and YoY are −0.7, −0.5 and −0.5%/year, respectively; the median annual PLRs (in the same order) are −0.6, −0.5 and −0.5%/year, respectively. These values are in line with the performance warranty from PV module manufacturers. Furthermore, a comparison is also made to two monitored PV strings (both deploying crystalline silicon modules) from a nearby rooftop reference system. Overall, there is no significant difference in the performance stability between the rooftop and the FPV installations in the testbed during the first three years of operation.