Novel mathematical modeling, performance analysis, and design charts for the typical hybrid photovoltaic/phase-change material (PV/PCM) system

Abstract

As a type of hybrid PV/T solar collector, the PV/PCM system is typically used to produce and store both electrical and thermal energy in a variety of applications. Specialized computational-fluid-dynamic (CFD) models such as Ansys FLUENT and COMSOL are currently used to simulate the operation of these systems. However, the relatively long computation time of these models, which can range from a few hours to a few days for even simple system variables, poses a challenge. Therefore, the effort in this study has been devoted to developing an alternative mathematical model for PV/PCM systems that is sufficiently accurate, fast to compute, and simple to use. The proposed model is based on an exact five-parameter photovoltaic model coupled with a well-established photovoltaic/thermal network. The overall heat transfer coefficient of the thermal component (PCM) within the system's network is determined using two novel formulas in relation to the PCM's average temperature across its solid, melting, and liquid phases. The proposed model was implemented in MATLAB as a code that utilizes straightforward numerical functions without the use of mesh patterns. The model was then validated via both CFD and experimental verification. The results indicated that the model is reasonably accurate in terms of percentage errors and correlation coefficients. The model's computation time for system temperatures and PV power is less than 14 s, with a total simulation time of 2.2 h at a time step of 2.5 min, compared to 16 h for CFD. Thus, the developed model can substantially help in conducting comprehensive investigations of PV/PCM performance characteristics, parametric analyses, and design charts using a diverse range of system variables. Two performance indexes for the PV/PCM system were introduced: the PCM melting time interval and thermal efficiency. It was found that the PCM performs better in its upper layer, and this layer, which accounts for only about 5%–6% of the total PCM thickness, primarily governs the aforementioned performance indexes as well as the overall heat transfer coefficients. The melting time interval was found to increase linearly with PCM thickness, whereas the thermal efficiency increases logarithmically with incident solar radiation, with greater rates at lower solar radiation levels. However, over the three phases, the PV efficiency varies within a narrow range of 15.5–17.3%. The parametric analyses showed that thermal efficiency increases approximately fivefold as ambient temperature increases from 0 to 35 °C, but decreases by 55% as wind speed increases from 0 to 4 m/s.