Page 421 - A Comprehensive Guide to Solar Energy Systems

Chapter 22 • Life Cycle Analysis of Photovoltaics: Strategic Technology Assessment 431

22.2.1 Interpretation and Reporting

The ISO 14040- and 14044-standards provide a framework for LCA. however, this frame-
work leaves the individual practitioner with a range of choices that can affect the validity
of the results of an LCA study. Thus, this author initiated and led an IEA PVPS task (Task
12), which developed guidelines to offer guidance for consistency, balance, and quality
to enhance the credibility of the findings from PVs LCAs [6]. The guidelines represent a
consensus among PV LCA experts in the united States, Europe, and Asia, for assumptions
on PV performance, process input and emissions allocation, methods of analysis, and re-
porting of the results. The latter is of the utmost importance as parameters varying with
geographical zones and system boundary conditions can significantly affect the results;
accordingly, transparency is essential in comparing product life cycles. As pointed out in
the IEA Guidelines, transparency in reporting is of the utmost importance because pa-
rameters vary with geographical zones, and a system’s boundary conditions and modeling
approach can affect the findings significantly. At a minimum, the following parameters
should be reported: (1) On-plane irradiation level and location; (2) module-rated efficien-
cy; (3) system’s PR; (4) time-frame of data; (5) type of system (e.g., roof-top, ground mount
fixed tilt or tracker); (6) expected lifetime and degradation ratio for PV and balance of
system (BOS); (7) system’s boundaries (whether capital goods, installation, maintenance,
disposal, the transportation- and recycling-stages are included for both PV modules and
balance-of-system (frame, mounting, cabling, inverter; for utility applications the trans-
former, site preparation, and maintenance); (8) the place/country/region of production
modeled (e.g., average grid, site specific power use (e.g., hydro, coal), and (9) explicit goal
of the study (e.g., static or prospective LCA, prototype or commercial production, current
performance or expected future development). In addition, a LCA report should identify
the following: The LCA method used, especially if is not process-based; the LCA tool (e.g.,
Simapro, Gabi, etc); databases used [e.g., Ecoinvent, GaBi, Franklin, national Renewable
Energy Laboratory (nREL)]; the EPBT calculation method; commercial representativeness
of the study (required if the data are from a pilot-scale production), and assumptions for
production of major input materials, e.g., solar grade (SoG) silicon, aluminum (primary
and/or secondary production).

22.3 Current Photovoltaic Status
22.3.1 Major Technologies

The PV systems comprise PV panels (also called modules) and BOS (mechanical and elec-
trical components such as support and mounting structures, inverters, transformers and
cables, as well as system installation, operation and maintenance). The currently domi-
nant PV technologies are: sc-Si, mc-Si, CdTe, and CIGS.
Fig. 22.2 shows the respective flow diagrams for the c-Si and thin film PV systems.
After the metallurgical (mG) and SoG Si production stages, mc-Si ingots are cast and
sawn into wafers: sc-Si PV cells additionally require an intermediate Czochralski (Cz)