Efficiency of maximum power point tracking in photovoltaic system under variable solar irradiance

Abstract

Field conditions decrease the energy output of photovoltaic (PV) systems, mainly due to excessive temperatures. However, in regions with moderate ambient temperatures, as in Poland, solar energy is commonly delivered with highly fluctuating irradiance. This introduces yet another source of energy losses due to the non-ideal tracking of actual position of Maximum Power Point (MPP). Majority of PV-systems are equipped with DC/AC and grid-connected inverter. Since the solar energy flux is variable, an adequate MPP-tracking algorithm is required to handle a wide range of load levels and face rapid changes of input power. Along with the essential DC/AC conversion, the quality of MPP-tracking must also be taken into account in evaluation of inverter efficiency. The tracking in dynamic conditions has been addressed only recently. Several algorithms has been studied theoretically, experimentally or in laboratory conditions by applying artificial input test-patterns. This work takes the opposite approach by applying the recorded real-life solar irradiance and simulating the tracking behavior to study the problem for true field conditions in Poland. The simulation uses the unique high-quality irradiance data collected with 200 ms time resolution. The calculation of both static and dynamic MPP-tracking efficiency has been performed for representative variable-cloudy day, applying commonly used Perturb&Observe tracking algorithm.