Exergy analysis of solar energy systems - Solar Energy Sciences and Engineering Applications - page 114

Figure 3.3.12 Effect of increase in solar flux on overall system energy and exergy efficiencies.
3.3.3.3 Results and discussion
In Figure 3.3.12, the study of the effect of solar radiation on the overall energy and
exergy efficiencies has been carried out. It is noticed that the overall energy and exergy
efficiencies decrease when the solar radiation is increased while keeping air inlet tem-
perature, area of the PV/T and time for which solar radiation is available constant
at 25 ◦ C, 10 m 2 , and 12 hr, respectively. The energy and exergy efficiencies drop from
14.44% to 12.13% and 7.33% to 6.15% respectively, as the solar radiation increases.
As the solar radiation increases the power production capacity of PV module increases
and at the same time heat transfer rate also increases. The increase in power means
that more water molecules are broken down to produce hydrogen. On the other hand,
increase in the rate of heat results in a higher amount of heat given to the absorption
system to provide the fixed amount of cooling. This increase in rate of energy fed into
the cooling system results in the degraded performance of the cooling system as the
cooling system rejects more heat through the condenser to achieve the desired cooling.
These degrading performances of the cooling system result in lower energy and exergy
COPs of the system. As the performance of the cooling system degrades the overall
efficiency of the system decreases because more energy is being consumed to acquire
the required outputs.
The increase in area of the PV module results in a higher power output from the PV
module and higher hydrogen production. The solar radiation, operating hours, and air
inlet temperature are kept constant at 608 W/m 2 , 30.8 ◦ C, and 12 hr, respectively. The
power output and hydrogen production increase from 0.28 kW to 0.86 kW and 5.24 kg
to 15.7 kg, respectively as shown in Figure 3.3.13. The power output of the PV module
is directly related to the solar radiation and the area on which it is concentrated. As
the solar radiation increases, the molecules in the PV module vibrate at a higher pace