Basics of the photovoltaic thermal module - Solar Energy Sciences and Engineering Applications - page 162

Figure 5.3.4 Two-absorber PV/T model.
applies two-absorber geometry. As shown is Figure 5.3.4, this design can lower the
temperature of the PV cells on average, but it is relatively complicated to manufacture.
5.4 TECHNIQUES TO INPROVE PV/T PERFORMANCE
There are numerous methods to enhance the performance of PV/T air collectors such
as the use of fins attached to the PV rear surface, corrugated sheet or wire mesh in
the air channel or providing air circulation on both front and rear surfaces of the PV
module.
Elements of several geometries can be placed between PV module and opposite
channel wall, as well as on the back wall, by which air heat extraction can be effected
more efficiently (Tripanagnostopoulos, 2007). Roughening the opposite channel wall
with ribs or/and using a wall surface of high emissivity, which is a considerably lower
cost air heating improvement, has also been adapted (Figure 5.4.1a). In addition,
a corrugated sheet inside the air channel along the air flow can be attached on the
PV rear surface as well as on the opposite channel wall surface (Figure 5.4.1b). An
alternative modification is to insert lightweight pipes along the air flow in the air
channel, with slight elasticity to ensure satisfactory thermal contact with the PV rear
surface and channel wall (Figure 5.4.1c). These pipes can effectively extract heat from
the PV panel by all three modes of heat transfer (conduction, convection, and radiation)
thereby restricting the opposite channel wall surface temperature being overheated.
Tiwari et al. (2011) presented four types of photovoltaic modules and their applica-
tions. They are crystalline PV modules, thin film PV modules, single and multi-junction
PV modules. Based on their cost analysis results, the BIPVT systems are reported to be
more favorable than the conventional BIPV systems. In extension to the said work, they
have also evaluated the overall performance of four types hybrid PV/T model, which
are unglazed hybrid PV/T with tedlar, unglazed hybrid PV/T without tedlar, glazed
hybrid PV/T with tedlar, and glazed hybrid PV/T without tedlar (Tiwari and Sodha,
2007). Experiments were conducted to validate the thermal model for unglazed PV/T
air heating systems for summer conditions and the study concluded that the glazed
hybrid PV/T without tedlar had the best performance, especially when in operation