Environmental Engineering Reference
In-Depth Information
5.2.1 Liquid PV/T collector
In order to improve the energy performance of the photovoltaic system, much effort
has been spent on research and development of the hybrid PV/T technology. One of the
design modifications is to increase the PV module performance by circulating water to
extract the heat using water as the coolant. These liquid PV/T collectors are similar to
conventional flat-plate liquid collectors; an absorber with a serpentine tube or a series
of parallel risers is applied, onto which PV has been laminated or glued as an adhesive
epoxy joint.
Two common configurations used in PV/T systems are: “Parallel plate config-
uration'', and “Tube-in-plate configuration''. Prakash (1994), Huang et al. (2001),
Tiwari and Sodha (2006) and Tiwari et al. (2006) have worked on the parallel plate
design, while Zondag et al. (2002), Chow (2003), Chow et al. (2006), Kalogirou
(2001), Huang et al. (2001) and Tiwari and Sodha (2006) have carried out an
in-depth study on tube-in-plate design. Within the first works on PV/T water sys-
tem, Bergene and Lovvik (1995) initially conducted a theoretical study on PV/T water
system composed of flat-plate solar collector with solar cells. Their proposed system
is particularly suitable to preheat the domestic hot water.
More recently, Zondag et al. (2003) grouped the design concepts of water-type
PV/T collectors into four main types: sheet and-tube collectors, channel collectors,
free-flow collectors, and two-absorber collectors. These collector types are designed
for pump (forced) circulation (Figure 5.2.1). Based on numerical analysis it has been
suggested that a channel should be provided to effect liquid flow below the transparent
PV module to effect higher collector efficiency (Chow et al., 2006). Nevertheless, from
the viewpoint of good overall performance and structural simplicity, single-glazing
sheet and tube hybrid PV/T collector is regarded as the most promising design.
Dubey and Tiwari (2008) designed an integrated photovoltaic (glass-to-glass) ther-
mal (PV/T) solar water heater system and tested it in outdoor conditions of India.
Similarly, Erdil et al. (2008) constructed and tested a hybrid PV/T system for energy
collection at geographical conditions of Cyprus, where they used water as the cooling
fluid. It was reported that the payback period for their proposed modification was less
than 2 years which made their hybrid system economically attractive. Also, Daghigh
et al. (2011) used water as the working fluid and had presented the advances in liquid
based photovoltaic/thermal (PV/T) collectors. The liquid-based photovoltaic thermal
collector systems are practically more desirable and effective than air-based systems.
Temperature fluctuation in liquid based PV/T is much less than the air-based PV/T
collector. The future direction of water-cooled and refrigerant hybrid photovoltaic
thermal systems was also presented. Their study revealed that the direct expansion
solar-assisted heat pump system could achieve a better cooling effect than the PV/T
collector.
Similar to the above modeling work, Chow et al. (2006) had developed a numerical
model of a photovoltaic-thermosyphon collector system using water as a working fluid
and verified the model's accuracy by comparing with measured data. The energy per-
formance of the collector system was examined, through reduced-temperature analysis
and the study was further extended to analyze the performance of the system in the “hot
summer and cold winter'' climate zone of China. The numerical results were found to
be very encouraging, and according to them the equipment is capable of extending the
Search WWH ::
Custom Search