A group of scientists led by the Chouaïb Doukkali University in Morocco has designed a photovoltaic-thermal solar panel based on a channel-box heat exchanger aimed at improving convective exchange.
They explained that the proposed design offers the advantage that the entire panel surface is in direct contact with the fluid, while sheet and tube PVT modules offer a small contact area between the sheet and the tube. “In addition, this proposal seeks to solve the problem of temperature inequality, which impacts the durability of PV panels,” they added.
The proposed heat exchanger includes three zones for coolant inlet (AZ), heat exchange (ZE), and fluid evacuation (VZ), respectively. It uses water as a cooling fluid, which flows through the heat exchanger to utilize the heat produced by the PV module. “The EZ consists of an alveolar plate, comprising a flat top wall in contact with the rear of the PV module, and a bottom wall,” the group specified. “These walls have a thickness of 0.4 mm, which facilitates the optimum transfer of the heat between the PV module and the circulating cooling fluid within the channels.”
The heat exchanger is divided into two zones – an aluminum solid zone and a fluid zone where water flows inside the solid zone. The PVT panel also includes a photovoltaic module, a Tedlar layer, two transparent layers of ethyl vinyl acetate (EVA), and a glass cover plate.
Using the COMSOL software, the research team conducted a series of simulations to assess the system's performance based on solar irradiance and volumetric flow rate. It assumed it to be in a steady state and with no dust accumulated on its surface. The analysis also took into account parameters such as solar cell temperature, coolant outlet temperature, cell efficiency and yield, as well as thermal energy recovered, thermal efficiency, and overall efficiency.
“In COMSOL, PVT and PV modules are meshed using a physics-controlled meshing sequence,” the academics explained. “This approach results in a progressive increase in the number of grids elements at each limit, enabling precise resolution of heat transfer phenomena and flow fields.”
The simulations showed that the flow rate is a key factor for the panel performance, with every 10 L/h increase in fluid flow reducing solar cell temperature by around 0.885 C, which in turn results in a power yield increase of about 0.798 W. Furthermore, every 10 L/h increase in fluid flow increases the cell efficiency by approximately 0.051%.
The PVT panel was also found to achieve an electrical, thermal, and overall efficiency of approximately 12.11%, 78.59%, and 90.7%, respectively. “When the flow rate and inlet temperature are maintained at 180 L/h and 29 C, respectively, total system efficiency increases from 83.15 to 90.7% as solar irradiance rises from 2 x 102 to 103 W/m2. Consequently, for each increase of 102 W/m2 in solar irradiance, there is a 0.94% improvement in overall efficiency,” the academics emphasized.
The system was introduced in the paper “Numerical study of a water-based photovoltaic-thermal (PVT) hybrid solar collector with a new heat exchanger,” which was recently published in e-Prime – Advances in Electrical Engineering, Electronics and Energy.
“The proposed PVT-C offers good results in terms of temperature inhomogeneity and overall performance,” the scientists concluded. “In this context, it will be worthwhile recommending the realization of this new PVT-C, which is easy to integrate into the building and can be adapted to meet air or water needs according to the seasons and the building's thermal requirements.”
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