Page 442 - A Comprehensive Guide to Solar Energy Systems

454 A COmPREhEnSIVE GuIdE TO SOlAR EnERGy SySTEmS

some degree in every PV technology today, however, it is explicitly important for CIGS
PV. Amounts as low as 16.97 kg of Cu are consumed per megawatt of CIGS installation. If
one assumes a mix of solar technologies consisting of 80% c-Si, 10% a-Si, and 5% CdTe
and CIGS each, then up to 2.19 t of Cu are consumed per megawatt of mix installed [6]. In
2016 worldwide production of Cu was estimated at 19.4 mt with reserves at 720 mt, while
9
known world resources are currently estimated at 2.1 × 10 t (2.1 Gt), plus another esti-
mated undiscovered 3.5 Gt [46]. Cu is also important to PV production as it is the primary
ore for Se and Te.

23.3.5 Selenium

Compared to other materials, Se is relatively new to industry. Growth in consumption was
driven by applications in rubber compounding, steel alloying, and Se rectifiers. By 1970 its
major use was as a photoconductor in paper copiers. Today Se is used to decolorize green
tint in different glasses, in architectural plate glass as an insolating agent, in catalysts to
enhance selective oxidation, plating solutions, blasting caps, corrosion resistance, electro-
lytic production of manganese, and in Cu, Pb and steel alloys to improve machinability. It
is also an essential micronutrient found in fertilizer and used as a dietary supplement for
humans and livestock. Se is recovered from the electrolytic refinement of Cu. It accumulates
in the electrolyte or “anode slimes” after Cu electrolysis has been performed. In general, Se
is concentrated using very strong acids or roasting and leaching, followed by hydrometal-
lurgical processing and precipitation. Se is an integral semiconductor for producing CIGS
modules. Amounts ranging between 0.5 and 84.41 kg of Se are consumed per megawatt
of CIGS installed [6,33]. In 2016 worldwide production of Se was estimated at 2.2 kt with
reserves at 100 kt [46].

23.3.6 Tellurium

Tellurium is also relatively new to industry and also a relatively rare element. It was used in
the chemical industry as a vulcanizing agent and accelerator in the processing of rubber
and a catalyst for synthetic fiber production. Today it used as an alloying additive in steel,
copper, lead, cast iron, and malleable iron. like Se, Te is recovered from Cu anode slimes
but in much lower concentrations. It is also recovered from effluent in the process of refin-
ing Pb. General steps in refining Te include separation, roasting, leaching, cementation,
electrolysis, vacuum distillation, and zone refinement. One of the major uses for high-
grade Te today is as a semiconductor in the development of CdTe thin-film PV modules.
up to 90.38 kg of Te is consumed per megawatt of CdTe installed [6,33]. In 2016 worldwide
production of Te was estimated at 400 t with reserves at 2.5 kt [46].

23.3.7 Silicon
Si is the most abundant element on Earth. Si in the form of silicates constitutes more than
25% of the Earth’s crust. Today the uses of Si include the production of Al and Al alloys,