Exergy analysis of solar energy systems - Solar Energy Sciences and Engineering Applications - page 99

authors feel that a thorough understanding of exergy and the insights it can pro-
vide into the efficiency, environmental impact and sustainability of energy systems
are required for the engineer or scientist working in the area of energy systems
and the environment. The need to understand the linkages between exergy and
energy, sustainable development and environmental impact has become increasingly
significant.
The solar PV and PV/T systems are one of the most significant and rapidly devel-
oping renewable-energy technologies, and its potential future uses are notable. During
the last decade, solar PV and PV/T applications have increased in many countries and
are observed throughout the residential, commercial, institutional and industrial sec-
tors. The clean, renewable and in some instances economical features of solar PV and
PV/T systems have attracted attention from political and business decision makers and
individuals. Advances in solar PV and PV/T technology have also driven the trend to
increased usage.
Solar energy resources and technologies have three main benefits which are (a)
they generally cause no or less environmental impact as compared to other energy
sources, (b) they cannot be depleted; in contrast, fossil fuel and uranium resources
are diminished by extraction and consumption, and (c) they favor system decentral-
ization and local solutions that are somewhat independent of the national network,
thus enhancing the flexibility of the system and providing economic benefits to small
isolated populations. Also, the small scale of the equipment often reduces the time
required from initial design to operation, providing greater adaptability in responding
to unpredictable growth and/or changes in energy demand.
Exergy, as a potential tool, has several qualities that make it suitable as a com-
mon quantifier of the sustainability of a process (Dincer and Rosen, 2004; Sciubba,
2001). These qualities are (a) exergy is an extensive property whose value is uniquely
determined by the parameters of both the system and the reference environment, (b)
if a flow undergoes any combination of work, heat and chemical interactions with
other systems, the change in its exergy expresses not only the quantity of the energy
exchanges but also the quality, (c) the value of a product of a process, expressed in
terms of 'resource use consumption,' may be obtained by adding to the exergy of the
original inputs all the contributions due to the different streams that were used in the
process.
The higher performance, lower cost and better reliability demonstrated by today's
solar PV and PV/T systems are leading many potential users to consider the value
of these systems for particular applications. Together, these applications will likely
lead industry to build larger and more cost-effective production facilities, leading to
lower solar PV and PV/T costs. Public demand for environmentally benign sources
of electricity will almost certainly hasten adoption of solar PV and PV/T. The rate of
adoption will be greatly affected by the economic viability of solar PV and PV/T with
respect to competing options. Many analysts and researchers believe that it is no longer
a question of if, but when and in what quantity, solar PV and PV/T systems will see
widespread adoption.
In Table 3.2.1, the general thermodynamic quantities and general energy and
exergy balance equations as well as energy and exergy efficiencies are listed as they
will be employed for system analyses and performance assessment.