Page 443 - A Comprehensive Guide to Solar Energy Systems

Chapter 23 • Materials: Abundance, Purification, and the Energy Cost 455

various uses in the chemical industry and the electronics industry. Relatively small quanti-
ties of Si are processed into high-purity Si for use in the semiconductor industry as chips for
computers and the solar energy industry as photovoltaic cells. Si is typically sourced from
silica in various natural forms, such as quartzite. It is generally produced in submerged-
arc electric furnaces and then further refined by the Siemens, modified Siemens, Fluid-
ized Bed Reactor or Czochralski process. From quartz sand, Si is refined into metallurgical
grade Si and from there it is further refined into electronic grade Si, which is of the highest
purity. historically, electronic grade Si was mostly supplied to the computer industry for
making integrated circuits and other electronic components. Since the purity required for
producing c-Si and a-Si modules is lower than that for integrated circuits, the PV industry
relied on the “off-grade” Si that was not suitable for the electronics industry. Today, the PV
industry has grown to the size that a small proportion of solar-grade Si comes from “off-
grade” sources and most of it now comes from sources specific to PV production. Amounts
−1
in the area of 33.08 kg of Si are consumed per megawatt of p-Si installed, 40.07 kg (mW)
−1
for m-Si and 18.4 kg (mW) for a-Si [6,37]. It is possible that solar grade Si be sourced from
recycled waste in the future, unfortunately the present economics are not in favor of it. The
uSGS reports that an estimated 7.2 mt of Si was produced in 2016; however, that includes
ferrosilicon, which is not a pure Si metal [46]. They provide no reserves or resources data
due to its abundance. despite this abundance in material, glass production capacity is a
concern and Burrows and Fthenakis predict that thousands of new float-glass plants will
have to be built to meet industry needs over the next 20 years [47].

23.3.8 Silver
The history of Ag in human civilization is thousands of years old as it has been used for
utensils, jewellery, and even currency. Ag exhibits high ductility, electrical conductivity,
malleability, and reflectivity. In fact, of all metals, Ag has the whitest color, the high-
est optical reflectivity, and highest thermal and electrical conductivity. Today it can be
found in electronics, coins, jewellery and silverware, photography, antimicrobial ap-
plications, clothing, pharmaceuticals, plastics, batteries, bearings, brazing, soldering,
catalytic converters, electroplating, inks, mirrors, water purification, wood treatment,
and solar photovoltaics. The chemical characteristics of Ag are similar to Cu and it can
even substitute Cu on an atomic level in most minerals formed in the ground. Ag can
be a principle product for a mine, or it can be obtained as a by-product of Pb, Zn, Cu,
and Au mining. Once extracted, Ag containing material is beneficiated and refined by
smelting and leaching. To produce solar-grade Ag, the concentrate also undergoes elec-
trolytic Cu refining. Ag can be found in all forms of PV technology depending upon the
design. It is used in c-Si for metallization of the module and in general for its excellent
electrical conductivity. Cu can substitute for it in some applications. Amounts ranging
from 5.17 to 19.2 kg of Ag are consumed per megawatt of overall PV installations [6,21].
In 2016 an estimated 27 kt of Ag was produced worldwide and reserves were estimated
at 570 kt [46].