Page 435 - A Comprehensive Guide to Solar Energy Systems

Chapter 23 • Materials: Abundance, Purification, and the Energy Cost 447

developed for use; however, to determine criticality both are necessary to observe. unfor-
tunately, resources and reserves of critical metals are very difficult to calculate because
they are almost all extracted from mineral deposits as by-products of Zn, Cu, Fe, Au, lead
(Pb), nickel (ni), titanium (Ti), aluminum (Al), platinum (Pt), and tin (Sn) [17]. Therefore,
despite their respective importance to PV technologies, secondary ores such as Te, indium
(In), germanium (Ge), gallium (Ga), and selenium (Se) are typically of significantly lesser
economic value than their primary source ores in a given mining operation. As such, they
are rarely part of a company’s core business and hence are less likely to be extracted or
even have their presence reported [18]. For example, global demand for Te was 200 t in
−1
2009 and at 145 $ kg it can be considered valuable, however, it all came as a by-product of
millions of tons of Cu and Au mining and so is insignificant to the profits of the companies
involved [19]. This makes secondary ores more vulnerable to supply disruptions, which
increases their chances of being critical metals to the PV industry—among other high-tech
industries such as cellphones, computers, and televisions.
Given the interest in material constraints to industries such as PV production, it is no
surprise that recent efforts have been made to quantify future supply disruptions. Sher-
wood et al. modeled resource criticality in modern economies using agent-based dynamics
in 2017 and found that there are vulnerabilities from technological interdependence [20].
Contrary to traditional economic models, their model removed simplifying assumptions
of smooth growth, cost-shares in determining production, economic agents that act with
perfect information and foresight, and included that the economy consists of represen-
tative agents and not a multitude of heterogeneous agents. They modeled technological
growth as a complex adaptive system and applied biophysical constraints on macroeco-
nomic growth. They found that with high levels of technological interdependence, remov-
ing any resource led to a significant decline in production output. Grandell and Thorenz
[21] and Grandell et al. [22] examined the role of critical metals in future markets of renew-
able energy technologies, including PV. After modeling for a number of assumptions in
future energy and economic output and composition, they found that a number of metals
could constrain clean energy development in the future. Specific to solar energy were Ag,
In, Te, and ruthenium (Re). notably, Ag demand was modeled to exceed known resources
by more than 300% and reserves by almost 450% as it is used in virtually all solar energy
technologies and electronics in general, including electric vehicles. In other words, Ag
demand is expected to grow significantly in the future of both energy production and con-
sumption technologies. There is some, but very little, literature already available on the
subject of material constraints specific to the solar energy industry.
unfortunately, information on material constraints to PV is relatively scarce and given
its novelty, there are more questions than answers at this time. This is due mainly to the
uncertainty of the composition of future energy economies, as is today, but was even more
so in the past. As we can make better predictions of what the future may look like, the pos-
sibility of material constraints will become clearer. In the year 2000, Andersson evaluated
the material necessary for large-scale thin-film PV development and found that copper
indium gallium selenide (CIGS) technology was limited by In reserves and that cadmium