Page 431 - A Comprehensive Guide to Solar Energy Systems

Chapter 22 • Life Cycle Analysis of Photovoltaics: Strategic Technology Assessment 441

Table 22.3 The Primary Energy Consumption of the BOS Components for Two Types
of PV Systems, and the EPBT and EROI on a System Level
Rooftop Grount-Mount PV Plant
Module 1 2 3 1 2 3
Structure, cabling/ 225 225 225 645 645 645
MJ m −2
Inverter/MJ m −2 704 675 614 254 243 222
Total/MJ m −2 929 900 839 899 888 867
EPBT/yr 0.9 0.7 0.7 0.8 0.7 0.7
EROI (E out /E in ) 13 15 15 14 16 16

Source: Data are from [2].

over 30 yr by 2025 compared to 15 yr now) and low-cost support structures, cabling and
electrical connections. As Table 22.3 shows the inverter accounts for a considerable share
of the CEd of rooftop systems, and even a modest increase in the inverter lifetime would
therefore significantly decrease the system EPBT. The inverter is less important in the case
of large-scale PV plants, where the support structure dominates the CEd.
Table 22.3 also shows the system EROI values of crystalline silicon PV in 2020 with old
BOS data.

22.8 Conclusion

In this chapter, we summarized life-cycle impacts from (1) current vintage of commercial
PV technologies and (2) future c-Si modules via a prospective LCA of crystalline silicon
PV technologies expected to materialize on or about the year 2020. To do so, we devel-
oped three technological scenarios (two based on monocrystalline silicon and one based
on quasi-monocrystalline silicon), building on various existing roadmaps. To summarize,
increasing the cell efficiency is (after scaling up) the most important lever to reduce en-
ergy demand and costs. By using high quality passivation and BJ higher efficiencies can be
achieved while simultaneously reducing the wafer thickness, which reduces the embodied
energy even further. however, thinner wafers also require novel cell processing and encap-
sulation schemes, which we accounted for. We forecast that the EPBT of crystalline silicon
modules could be reduced to 0.5 yr (0.7 yr when including BOS) provided that planned
technological advances will occur. The EROI of PV modules could increase by a factor two
to three in the coming years, and lie in the same range as electricity from coal-fired power
plants.
This is a prospective LCA, subject to technological improvements taking place, and as
such it carries a considerable degree of uncertainty. To address parameter uncertainty,
results were provided with a 95% confidence interval, but scenario uncertainty remains.
however, since the general tendency of maturing technologies is to become less energy
and material intensive and we have used data that are representative of, at best, the situa-
tion today, these forecasts can be considered conservative.