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448 A COmPREhEnSIVE GuIdE TO SOlAR EnERGy SySTEmS

telluride (CdTe) technology was limited by Te reserves [23]. later, the potential for large-
scale manufacture of PV and its metal requirements were estimated in several studies with
similar conclusions [24–26]. In response to findings of possibilities in material constraints
associated with rapid PV development, Wadia et al. examined extraction costs and supply
constraints for 23 materials relevant to semiconductors, including those relevant to PV, and
found large differences in material extraction costs over space and time [27]. In 2009, Fthe-
nakis raised the issue of secondary ore constraints to thin-film PV production due to limita-
tions in annual production of primary ores [28]. Then in 2011 Candelise et al. examined the
possibility of material constraints, specifically for In and Te in thin-film PV and found that
although there was little evidence that production would necessarily be constrained, cost
reductions would be [29]. By identifying potential PV and material utilization efficiency
improvements in 2012, Fthenakis determined that the Te available from copper refineries
is sufficient for several TWs of production by mid century [30]. In 2013, the Critical materi-
als Institute was founded in the Ames laboratory as part of the uS department of Energy
and identifies Te as a critical material for solar cells to this day [31]. later in 2014, houari
et al. used a systems dynamic model to evaluate Te availability and thin-film PV growth
and found the industry would be less constrained than previously calculated [32]. In 2015
Grandell and hook identified In, Te, Ge, and Ru as potentially critical to thin-film PV devel-
opment in the terawatt range [33]. Finally in 2017, davidsson and hook concluded that
although the scale of the required materials could become problematic for currently com-
mercial technologies, especially thin-film and crystalline silicon (c-Si) PV, the conclusion
cannot be drawn that material availability is likely to act as a constraint on total growth of
PV [34]. There have been recent attempts at calculating reserves without explicit, accurate,
and time sensitive reporting from corporations, however, without any agreement on meth-
ods or definitive values as of yet [35,36]. As can be understood from this reading, the prob-
lem of calculating the possibility of material constraints concerning secondary ores, given
better forecasts of future output or in terms of their respective reserve base, is not settled.

23.3 Material Requirements for PV

There are five different technologies typically discussed in the literature pertaining to
materials relevant to the PV industry: mono-crystalline silicon (mono-Si) and multi or
poly-crystalline silicon (multi-Si or poly-Si), which are both forms of c-Si PV, and amor-
phous silicon (a-Si), CIGS and CdTe, which are all forms of thin-film PV. All five technolo-
gies have different pathways for production and therefore can carry different footprints
based on where they are manufactured [37]; however, the amounts of nonfuel materials
required for each technology is generally the same, although it varies widely based on
technology. Table 23.1 illustrates some of the materials of interest based on PV technology.
Each technology has its advantages and disadvantages as well as different metal con-
tent. C-Si is the most popular and widely deployed PV technology to date. It is most
popular in large-scale and rooftop applications. Thin films are generally less efficient
than c-Si cells, but they are also less energy intensive to produce and can be applied in