Exergy analysis of solar energy systems - Solar Energy Sciences and Engineering Applications - page 109

The overall energy and exergy efficiencies of the solar PV/T system are defined as

W so Q so

+

η ov,en = I × A

1000

(3.3.19)

W so

+ Ex PV / T
Ex so

η ov,ex = (3.3.20)

3.3.2.3 Results and discussion

This section highlights the importance of conducting a parametric study to see the
effect of variation in operating conditions such as ambient temperature and solar flux
on energy and exergy efficiencies of the system.
The ambient temperature plays an important role in the performance of any system.
Figure 3.3.7 shows how the energy and exergy efficiency of electrical and thermal
systems vary with a rise in ambient temperature. The electrical energy efficiency is seen
to be a constant at 9.46% whereas electrical exergy efficiency is found to be decreasing
from 9.04% to 7.74%, respectively with an increase in ambient temperature from
280 K to 310 K. The thermal energy and exergy efficiencies are found to be increasing
from 5.89% to 61.65% and 1.28% to 11.6%, respectively with a rise in ambient
temperature. The overall energy and exergy efficiencies are found to be increasing
with a rise in ambient temperature as displayed in Figure 3.3.8. The overall energy and
exergy efficiencies are found to be increasing from 15.36% to 71.11% and 11.22%
to 21.59%, respectively with a rise in ambient temperature. These figures show that
a rise in ambient temperature affects the performance of the system a lot. It is also
observed that having a solar PV/T system is better than having an individual solar PV
or thermal system, as a solar PV/T system has higher energy and exergy efficiencies as

Figure 3.3.7 Effect of rise in ambient temperature on electrical and thermal energy and exergy
efficiencies.