Modeling of Energy and Exergy Efficiencies in High Vacuum Flat Plate Photovoltaic Thermal (PV-T) Collectors

Abstract

This work deals with the performance evaluation of novel flat photovoltaic-thermal (PV-T) modules under vacuum. Through a 1D (dimensional) steady-state-energy-balance numerical model developed in MATLAB, two different layouts are studied: the first consisting of a photovoltaic (PV) cell installed just below the glass encapsulating the flat panel, and the second where the PV cell is placed on the selective solar absorber (SSA). In both cases the thermal and electrical efficiencies have been evaluated at different SSA operating temperatures, in the range of 323 K to 423 K. The analysis has been conducted at different energy bandgap (Ebg) of the PV cell and assuming a variable transmittance or emittance of the PV cell, depending on the design. The two systems efficiency comparison has been carried out at the same operating temperature. Overall, this work highlights the importance of high vacuum insulation, which guarantees the reduction of convective thermal losses, and shows that the maximum energy is produced for PV cells with Ebg ≈1.5-1.7 eV, depending on layout and operating temperature, by including the thermal output in the PV-T optimization. The energy and exergy efficiencies obtainable using the proposed PV-T systems are considerably improved compared to the results previously reported in the literature.

High Vacuum Flat Plate Photovoltaic-Thermal (PV-T) Collectors: Efficiency Analysis

“…The goal is year-round heat generation at medium temperatures, where the main technological challenges lie, and efficient power generation. However, in [31] we demonstrated that layout B, rather than layout A, is the one that maximizes the conversion of solar energy to electrical+thermal energy, allowing the entire portion of the solar spectrum not converted to electricity by the PV layer to reach the SSA below (see in particular Figs. 1 and 7 in [31]).…”

“…However, in [31] we demonstrated that layout B, rather than layout A, is the one that maximizes the conversion of solar energy to electrical+thermal energy, allowing the entire portion of the solar spectrum not converted to electricity by the PV layer to reach the SSA below (see in particular Figs. 1 and 7 in [31]). However, the previous model was developed by setting β=-0.2 %/K, limiting the description to a few real solar cells (mainly crystalline silicon cells).…”

“…In a recent article by De Luca et al [31] 1 , the authors proposed two novel layouts of evacuated hybrid PV-T collectors that faithfully reproduce the existing high-vacuum flat plate (HVFP) collector produced by TVP Solar [27]: an evacuated metallic case is covered by a highly transparent glass and is equipped with a selective solar absorber (SSA). Of course, the systems also include a PV layer, which in principle could be placed below the glass cover (layout A) or above the SSA (layout B).…”