Environmental Engineering Reference
In-Depth Information
obtained in both sites with the introduction of the feed-in tariff or any combination
of more than one condition including the feed-in tariff. As in the previous case, it
is worth mentioning the results in the scenario A+B, as this can be considered a
quite possible situation and the values obtained for NPV (equal or higher than the
initial investment) and Payback time (close to or below half the expected lifetime)
would already be quite satisfactory.
6.3.7 Environmental Considerations
To evaluate the three technologies proposed in terms of environmental perform-
ance, several relevant published studies were reviewed (Frankl et al. 2004,
Jungbluth et al. 2008, Ecoinvent 2007). Emissions of air pollutants of PV systems
are due to energy use in the life-cycle stages previous to operation. In the final re-
port of a project called ECLIPSE (Frankl et al. 2004) there is a table comparing
the air emissions (in terms of CO 2 , NMVOC, CH 4 , NOx, Particulates, and SOx)
attributable to the life cycle of four different PV families (mc-Si, pc-Si, a-Si and
CIGS); the last three are the ones assumed for our case study configurations. Ac-
cording to that assessment, the mc-Si rankings are the worst in four of the five
cases (except for Particulates); a-Si and CIGS show almost the same value of CO 2
and NMVOC emissions; CIGS shows a slightly higher value in CH 4 , but ranks
better in Particulates and SOx. So the best choice would be either a-Si or CIGS
depending on what level of importance were set on each emission type (a-Si is
better in terms of greenhouse gases for example).
In a specific comparison of life-cycle carbon emissions, a figure in the same re-
port (Frankl et al. 2004) displays the levels corresponding to the three technolo-
gies used in this case study, under irradiation levels of South Europe (similar to
Brazil's average): these are about 44 gCO 2 eq/kWh for CIS, about 43 gCO 2 eq/kWh
for a-Si, and about 49 gCO 2 eq/kWh for pc-Si. In this case the preference would be
for a-Si, but this is practically equal to CIS. Using these values one can calculate
the savings in terms of CO 2 emissions that the implementation of each of these
technologies in our building would bring about (in the base case), taking as emis-
sions average value for Brazil's electricity mix the one derived from the study of
Coltro et al. (2003), that is 80.5 gCO 2 eq/kWh. Using the values of expected an-
nual electricity generation for each configuration, the results for a 30-year lifetime
are: 37.68 tCO 2 eq for CIS, 31.24 tCO 2 eq for pc-Si, and 40.12 tCO 2 eq for a-Si.
In a recent article by Jungbluth et al. (2008), one of its comparative bar graphs
illustrates the non-renewable CED (Cumulative Energy Demand) estimated for the
manufacturing and installation of slanted-roof PV systems of nine different tech-
nologies, among which are the three considered in this case study. The values
from that publication are: 27.2 MJeq/Wp for CIS, 27.6 MJeq/Wp for pc-Si, and
29.0 MJeq/Wp for a-Si. If one multiplies them with the required installed capacity
determined for each case (i.e. 26.40 kWp of CIS modules, 25.60 kWp of pc-Si
modules, 27.36 kWp of a-Si modules), the resulting total energy requirement is:
7.181*10 5 MJeq for CIS, 7.066*10 5 MJeq for pc-Si, and 7.394*10 5 MJeq for a-Si.
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