Environmental Engineering Reference
In-Depth Information
Low-temperature thermal sources are usually used for direct application such as
providing hot water or heat to the building. Medium temperature thermal sources
are used for either producing cooling with the help of absorption cooling sys-
tems or producing power using Organic Rankine Cycles (ORCs). High temperature
thermal sources are used to produce huge amounts of power by running a steam
cycle.
Integrated solar energy systems provide an attractive way of producing multiple
outputs such as power, heat, hydrogen, cooling etc. in an environmentally benign
manner. As it is expected that future economy will be dominated by hydrogen fuel,
many researchers have studied integrated solar energy systems for hydrogen pro-
duction. Thomas and Nelson (2010) stated that hydrogen fuel can be produced by
using solar electric energy from photovoltaic (PV) modules for the electrolysis of
water without emitting carbon dioxide or requiring fossil fuels. The results of anal-
yses conducted by different researchers such as (Ratlamwala et al., 2011; Koroneos
et al., 2004; Yilanci et al., 2009) related to solar hydrogen production show that
an integrated solar production system is very promising technology as it produces
hydrogen in an environmentally friendly and cost effective manner. Also studies have
shown that using solar for hydrogen production enhances the efficiency of the over-
all system. Solar PV/T systems can also be used for multi-generation purposes as
studied by Ratlamwala et al. (2011) where energy and exergy analyses show that
integrated solar energy systems are suitable for hydrogen and cooling production.
In this chapter, the aim is to discuss energy and exergy related aspects of solar
energy systems, consider various solar energy based systems for analysis, assess-
ment and comparison, and evaluate them for practical applications from the exergy
point of view.
3.2 ENERGY AND EXERGY ASPECTS AND ANALYSES
The relationship between energy and economics was a prime concern in the 1970s.
At that time, the linkage between energy and the environment did not receive much
attention. As environmental concerns, such as acid rain, ozone depletion and global
climate change, became major issues in the 1980s, the link between energy uti-
lization and the environment became more recognized. Since then, there has been
increasing attention for this connection, as it has become more clear that energy pro-
duction, transformation, transport and use all impact the Earth's environment, and
that environmental impacts are associated with the thermal, chemical and nuclear
emissions which are a necessary consequence of the processes that provide benefits to
humanity.
Many suggest that mitigating the environmental impact of energy resource uti-
lization and achieving increased resource utilization efficiency are best addressed
by considering exergy. The exergy of an energy form or a substance is a measure
of its usefulness or quality or potential to cause change. The latter point suggests
that exergy may be, or provide the basis for, an effective measure of the poten-
tial of a substance or energy form to impact the environment. In practice, the
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