Page 445 - A Comprehensive Guide to Solar Energy Systems

Chapter 23 • Materials: Abundance, Purification, and the Energy Cost 457

of a-Si installment [33,48]. In 2016 worldwide production was estimated at 160.5 t [46] and
although the uSGS do not have data on Ge reserves, Frenzel et al. estimate the reserves to
be around 119 kt [49].

23.3.12 Indium

like Ge and Cd, In is a relatively new industrial metal and is derived from Zn production.
Applications for In include fusible alloys, solders and electronics, semiconductors and
thin films for liquid crystal displays—which is its main application today. Typically, the
residues from Zn smelting and roasting are leached and concentrated into a precipitate
that includes precipitation. Process steps for purification include recovery from Zn leach-
ing, roasting, concentration, solvent extraction, back extraction, plate immersion, anode
casting, electrorefinement, vacuum distillation, and zone refinement. The last three steps
can be repeated several times until the metal is of sufficient purity for application in CIGS
technology. Amounts ranging between 4.5 and 83.79 kg of In are consumed per megawatt
of CIGS installed [6,33]. In 2016 worldwide production of Se was estimated at 655 t [46].
The reserves are not calculated by the uSGS although Grendall and hook estimate them
to be 11 kt [33].

23.4 Energy Costs of Materials
This section considers the energy costs of developing the materials necessary to construct
PV systems. Since the PV systems are an energy delivery system, insight into the energy
required to develop the materials, especially as a trend over time, is of concern (see Chap-
ter 26). If the literature on energy requirements for PV systems is small, that for material
constraints is meager, and synthesis for the energy requirements for materials in PV sys-
tems is inadequate. The role of energy in the processes by which materials are obtained
and prepared for industry is rarely mentioned in the past [50–52]. little work is available
on the energy requirements to generate the elements from primary ores and is scarce con-
cerning that for secondary ores important to advanced technologies, such as PV.
The extraction of metals from geological deposits on Earth and their concentration
for modern industrial utility requires a significant amount of energy. In 1986, hall et al.
[53] provided a thorough historic examination into resource materials and their energy
requirements, though unfortunately their data is for the 1970s and previous years. Sub-
sequent data has been comparatively inconsistent, although improving due to life-cycle
Analysis standards, and usually held or withheld by private interests. In 2009, Fthenakis
et al. did give some estimates for the energy use in mining and smelting of minor elements
[26]. later, hall et al.’s work was somewhat updated by Gupta and hall in 2012 [54] where
the authors also raised the issue of rising energy costs as ore grades are degraded and the
impact of such increases on the overall efficiency of PV systems as an energy delivery sys-
tem. That question was further explored in the recent works of Koppelaar and Koppelaar
[55] who evaluate the impact of ore grade and depth on the energy inputs to Cu mining