Civil Engineering Reference
In-Depth Information
To summarise, the energy and exergy efficiencies are the major performance
evaluation indexes for PV/T systems, whereas the primary-energy-saving effi-
ciency and solar fraction are occasionally used to evaluate the fossil fuel-saving
capacity of the PV/T systems. In reality, different end-users have different energy
demands that would somehow affect the performance of the PV/T systems in use.
Choosing an appropriate evaluation method for a specific PV/T installation would
need to take both energy supply and demand into consideration.
2.3.2 Economical and Environmental Assessments
In terms of economic measures of the PV/T, Tripanagnostopoulos et al. (
2005
)
suggested the LCC assessment method which takes into account the capital cost of
system installation and associated operational and maintenance cost over the
system's life cycle. The time-related issues such as inflation, tax and/or company
discount rates should also be the factors to be considered. A simplified approach
for assessing PV/T's economic value is by using CPT (in year), which ignores the
time-relevant items and maintenance cost and therefore is inaccurate. Table
2
details the cost breakdown/payback issues related to various types of PV/T
installations.
For environmental measures, two payback items, the EPBT and the greenhouse
gas payback time, can be applied. EPBT is the ratio of the embodied energy for the
PV/T and its annual energy output. Embodied energy refers to the quantity of
energy required to produce the PV/T in its production phase. Chow (
2010
) sug-
gested the mathematic expressions of the EPBT and GPBT for the PV/T system as
below:
EPBT
¼
R
pvt
þ
R
bos
R
mtl
E
pv
þ
E
th
þ
E
ac
ð
20
Þ
where R
pvt
;
R
bos
and R
mtl
are the embodied energy of the PV/T system, the balance
of system and the replacing building materials; E
pv
is the annual useful electricity
output; E
th
is the annual useful heat gain (equivalent); and E
ac
is the annual
electricity saving of HVAC system due to thermal load reduction.
GPBT
¼
X
pvt
þ
X
bos
X
mtl
Z
pv
þ
Z
th
þ
Z
ac
ð
21
Þ
where X represents the embodied GHG (or CO
2
equivalent) and Z is the reduction
in annual GHG emission from the local power plant owing to the PV/T operation.
The environmental measures of the selected PV/T installations are given in
Table
3
(Tripanagnostopoulos et al.
2005
).
