Page 237 - Materials Chemistry, Second Edition

226 R. Laleman et al.

The EPT’s presented here were calculated based on the CED’s or EPT’s
mentioned in the cited publications. The results in Fig. 8 are adapted from the
2
original results, in order to be applicable to regions with a low (950 kWh/m /y) or
2
high (1,700 kWh/m /y) irradiation. For reasons of comparability and transparency,
the system’s performance ratio (p) was estimated to be 75 % (Alsema and Nie-
uwlaar 2000) in all cases. In other words, we assume that 25 % of the produced
electricity is lost in the inverter and cables. The Conversion coefficient (C) was set
at 0.35 (Alsema and Nieuwlaar 2000; Gürzenich and Wagner 2004). Keeping all
these parameters constant results in an EPT that is only influenced by the Con-
version efficiency (h) and the CED (see Eq. 2). Not all of these data are specifically
applied to a household PV system, some are LCA’s of large-scale PV systems (Ito
et al. 2010). However, since most of the GHG emissions are related to the pro-
duction of the module, including this data in the overview does not affect the
overall conclusions that can be drawn from this review.
The EPT’s published by Raugei et al. (2007a, b; Raugei et al. 2007a, b) for
CdTe PV systems are much shorter than the EPT’s that were found using the data
in Ecoinvent. The efficiency of a CdTe module mentioned in the Ecoinvent report
n°6 is rather low compared with the recent figures published by Raugei and Frankl
(Raugei and Frankl 2009) (Table 4). In the case of CdTe, an efficiency increase
from 7 % (according to Ecoinvent) to 10 % (Raugei and Frankl 2009) results in a
decrease in the EPT by 30 %. A higher efficiency entails that fewer modules are
needed to obtain a 3 kWp installation. In this case, the total surface needed for a 3
2
2
kWp PV installation would decrease from 43 m to 30 m , resulting in less support
structure and thus a lower CED and EPT. An increase in efficiency can thus partly
explain the low EPT’s published by Raugei. However, in a recent paper by Ito
et al. (2010), the EPT is quite equal for all PV types (EPT = 2–3 y with high
irradiation), not indicating a shorter EPT for CdTe systems (Ito et al. 2010).

4.2 GWP Review

From Fig. 9, we can conclude that the GWP of a 3 kWp PV system is about the
same for all types of PV modules and is situated around 6,000 kg CO 2 -eq. It is
important to mention that the PV systems analyzed by Ito et al. (2010) are not
residential types but large-scale systems installed in the desert, nevertheless their
results are comparable with ours.