Photovoltaic Thermal systems (PVT) combine photovoltaic and solar thermal technologies to produce electricity and heat concurrently from one system. These systems usually include solar panels that capture sunlight and convert it into electricity. They also use the panels’ heat to produce hot water or space heating. Through integrating these two technologies, PVT systems provide enhanced energy efficiency and maximise the utilisation of solar resources. This makes them a highly appealing choice for generating renewable energy in residential and commercial settings. With the integration of photovoltaic and thermal capabilities, the energy output of solar energy systems is maximised, resulting in improved overall performance.

This project is a paper validation study in which a photovoltaic thermal system is simulated using DO radiation model. The reference paper, “Coupled thermal-optical numerical modeling of PV/T module – Combining CFD approach and two-band radiation DO model [1] ” is selected. In the following, a schematic of a PV/T system is shown.

• Reference [1]: Maadi, Seyed Reza, et al. “Coupled thermal-optical numerical modeling of PV/T module–Combining CFD approach and two-band radiation DO model.” Energy conversion and management198 (2019): 111781.

Figure 1- Schematic of PV/T system extracted from the reference article

Simulation Process

As shown in Figure 1, the system consists of different parts, which indicates how much accuracy and endeavour it requires. It is designed using Design Modeler software. Further, because a structured grid is going to be employed, additional operations need to be considered in this step to create several blocks. As a result, it paves the way for the generation of a hexagonal structured grid later on in ANSYS Meshing. Figure 2 illustrates the division of the system and 1738000 created mesh cells.

Figure 2- Structured Mesh grid over the computational domain

Based on the given assumptions, the walls and pc-Si layer are considered to be non-gray diffuse surfaces. It is worth mentioning that the optical properties of a non-gray surface vary with radiation wavelength, whereas they remain constant for a gray surface. It is assumed that the incident solar radiation is perpendicular to the module surface. Moreover, Table 5 in the article shows the correlation used for water properties. Almost all of the thermal properties are temperature-dependent. However, the complex correlation of viscosity led us to write a User-defined function (UDF) for it. Finally, the Discrete Ordinates (DO) radiation model is employed.

Post-Processing

The PVT system’s thermal cascade displays an elegant interaction between conductive and radiative heat transfer mechanisms. After passing through the glass layer, solar radiation reaches the pc-Si layer, which is the place of photovoltaic conversion. The remaining energy is then converted into thermal gain. Peak temperatures are concentrated around the water tubes, and the temperature distribution across the absorber surface follows an unusual pattern. The working fluid undergoes a planned temperature increase from an inlet state of 311K to an output temperature of 316.67K, a 5.67K increment that shows efficient thermal energy capture. This pattern of temperature evolution, represented by the contours, demonstrates how well the direct absorption and secondary heat transfer pathways are captured by the DO radiation model

Figure 3- Temperature distribution over the absorber and tubes

The dual-output aspect of the system is evident in its performance measurements, where a crucial validation criterion is electrical efficiency (η_elec). The PV cell temperature (T_pv), as predicted by the numerical simulation, is 317.74K, which is just 1.57K higher than the reference value of 319.31K. In contrast to the 10.42% electrical efficiency described in the paper, this thermal prediction corresponds to an electrical efficiency of 10.1%. The small efficiency difference of 3.07% confirms the quantitative method as well as the intricate relationship between temperature-dependent material properties and the DO radiation model. notably, the findings verify that the coupled thermal-optical processes are sufficiently captured by the structured mesh resolution of 1.738 million cells, especially at the crucial interfaces where radiation-to-thermal energy conversion takes place.