Not so Green Solar Energy
Otis A. Glazebrook IV
Solar is thought of as clean and green because it isn't used much yet and the associated environmental problems are small enough to paper over. On a large scale, solar will almost certainly be at least as problematic as conventional energy souces.
You think solar electrical generation is going to save you or the Planet? Think again.
While it is true that photovoltaic solar panels do not pollute while they are producing electricity -- what about the manufacturing process? What happens when these panels reach the end of their projected lifecycle in twenty-five years? (This is, by the way, an optimistic view of their useful life.)
Those questions are addressed in a study by the watchdog group Silicon Valley Toxics Coalition.
"Green Power" is being hyped as the "Safe Solution." It is anything but safe -- when all factors are considered.
Here is a partial list (eight of fifty) of chemicals associated with solar photovoltaic (PV) manufacturing and disposal:
Arsenic (As) can be released from the decomposition of discarded GaAs solar PV cells. Inhalation of high levels of arsenic causes throat soreness, lung irritation, increased lung cancer risk, nausea and vomiting, decreased production of red and white blood cells, abnormal heart rhythm, damage to blood vessels, and "pins and needles" sensations in hands and feet. Ingesting or breathing low levels of inorganic arsenic for an extended period causes skin darkening, and small "corns" or "warts" appear on the palms, soles, and torso. Skin contact may cause redness and swelling. Ingestion can increase skin, liver, bladder, and lung cancer risks. Ingesting very high levels can result in death.
Cadmium (Cd) is a by-product of zinc, lead, or copper mining. Workers can be exposed through cadmium smelting and refining or through the air in workplaces that make Cd-based semiconductors. Acute symptoms vary depending on the specific cadmium compound, but can include pulmonary edema, cough, chest tightening, headache, chills, muscle aches, nausea, vomiting, and diarrhea. Cd is chronically toxic to the respiratory system, kidneys, prostate, and blood and can cause prostate and lung cancer. NIOSH considers cadmium dust and vapors as carcinogens. California has also determined (under AB 1807 and Proposition 65) that cadmium and cadmium compounds are carcinogens.
Chromium VI (Cr VI) is used in PV modules for chrome-plated hardware such as screws and frames. High levels of chromium have provoked asthma attacks, and long-term exposure is associated with lung cancer. Handling liquids or solids containing Cr VI can cause skin ulcers. Swallowing large amounts will cause upset stomach, ulcers, convulsions, kidney and liver damage, and even death. The EPA classifies Cr VI as a known human carcinogen.
Hexafluoroethane (C2F6) is used to etch semiconductors. It is an asphyxiant and in high concentrations may cause dizziness, nausea, vomiting, disorientation, confusion, loss of coordination, and narcosis. Very high concentrations may cause suffocation. Liquid hexafluoroethane may cause frostbite. Harmful amounts may be absorbed if skin contact is prolonged or widespread. It is listed as a potent greenhouse gas by the IPCC.
Nitrogen trifluoride (NF3) is used to clean reactors and etch polysilicon semiconductors. It emits toxic fumes when burned or reacted and can cause asphyxiation. The IPCC considers NF3 a significant greenhouse gas, making fugitive emission control very important.
Selenium (Se) is found in CIS/CIGS as an alloy of diselenide. Short-term exposure to high concentrations of selenium may cause nausea, vomiting, and diarrhea. Chronic exposure to high concentrations of selenium compounds can produce a disease called selenosis. Major signs of selenosis are hair loss, nail brittleness, and neurological abnormalities (such as numbness and other odd sensations in the extremities). Brief exposures to high levels of Se can result in respiratory tract irritation, bronchitis, difficulty breathing, and stomach pains.
Silane (SiH4) gas is used to apply silicon thin films and make silicon crystal semiconductors. Major health hazards include respiratory tract, skin, and eye irritation. Silane gas is extremely explosive. At room temperature, silane is pyrophoric-it spontaneously combusts in air without external ignition.
Tetrobromo bisphenol A (TBBPA) is a reactive brominated flame retardant used in the printed wiring boards of more than 90 percent of electrical and electronic products. The main use of TBBPA in solar PV is in inverters. Occupational exposure may occur from contact during production or through dust inhalation. Recent concerns focus on TBBPA as an endocrine disruptor; it is similar to bisphenol A, a known estrogen mimic. TBBPA also bioaccumulates in organisms.
Compare this with the byproducts of Coal combustion from the Coal Utilization Byproduct Research:
Each year, the U.S. electric utility industry generates about 100 million tons of coal combustion byproducts. Just over half of this amount is fly ash (a talcum-like solid in the flue gas from a coal-fired boiler), approximately one-fourth is sludge from wet flue gas scrubbers, another 16 percent is boiler ash (a heavier, coarser solid removed from the bottom of a boiler), and about 7 percent is boiler slag (a hard, glassy material made from boiler ash that has been melted by the heat of the combustor).
Currently only about a third of this coal ash and just over one fourth of the scrubber waste is recycled in commercially beneficial uses. The largest amount is fly ash that is typically used as a Portland cement replacement in concrete and concrete products. The remainder, more than 70 million tons a year, is disposed of in impoundments and landfills.
Many experts believe the coal combustion byproducts represent a vastly underused resource. Combustion byproducts can strengthen construction materials and reduce overall product costs. The gypsum-rich byproducts of flue gas scrubbers can provide plants with nutrients and enhance depleted soils in various agricultural applications. Coal combustion byproducts can be used to immobilize hazardous wastes for safer disposal.
Greater use of coal combustion byproducts can also help reduce concerns over greenhouse gases. Using fly ash for cement making, for example, reduces the need for limestone calcination, a process that requires a large amount of heat typically provided by burning fossil fuels. For every ton of fly ash used in concrete, approximately 0.8 tons of carbon dioxide would be prevented from being released into the atmosphere."
Notice how the "Green Solutions" always seem to create more problems and pollution than they could ever be expected to solve?
americanthinker.com
etoxics.org
....
Although the solar PV boom is still in its early stages,
disturbing global trends are beginning to emerge. For
example, much of the polysilicon feedstock material (the
highly refined silicon used as the basic material for
crystalline silicon PV cells) is produced in countries like
China, where manufacturing costs and environmental
regulatory enforcement are low.6 In March 2008, the
Washington Post reported that at least one plant in China’s
Henan province is regularly dumping extremely toxic silicon
tetrachloride (a corrosive and toxic waste product of
polysilicon manufacturing) on nearby farmland. According to
Li Xiaoping, deputy director of the Shanghai Academy of
Environmental Sciences, “Crops cannot grow on this, and it
is not suitable for people to live nearby.”7 Silicon
tetrachloride makes the soil too acidic for plants, causes
severe irritation to living tissues, and is highly toxic when
ingested or inhaled.
.........
III. Hazardous Materials Used in Solar PV Cell Production
Silicon-based solar PV production involves many of the same materials as the microelectronics industry and therefore
presents many of the same hazards. At the same time, emerging thin-film and nanotech-based cells pose unknown health
and environmental dangers. This section provides an overview of the hazards posed by current and emerging solar PV
production technologies.
A. Crystalline Silicon (c-Si)
As with the production of silicon chips, production of c-Si wafers begins with the mining of silica (SiO2), found in the
environment as sand or quartz.† Silica is refined at high temperatures to remove the O2 and produce metallurgical
grade silicon, which is approximately 99.6 percent pure. However, silicon for semiconductor use must be much purer.
Higher purities are achieved through a chemical process that exposes metallurgical grade silicon to hydrochloric acid
and copper to produce a gas called trichlorosilane (HSiCl3). The trichlorosilane is then distilled to remove remaining
impurities, which typically include chlorinated metals of aluminum, iron, and carbon. It is finally heated or “reduced”
with hydrogen to produce silane (SiH4) gas. The silane gas is either heated again to make molten silicon, used to grow monocrystalline silicon crystals, or used as an input for amorphous silicon (see next section).
The next step is to produce crystals of either monocrystalline or multicrystalline silicon. Monocrystalline silicon rods
are pulled from molten silicon, cooled, and suspended in a reactor at high temperature and high pressure. Silane gas
is then introduced into the reactor to deposit additional silicon onto the rods until they “grow” to a specified diameter.
To produce multicrystalline silicon, molten silicon is poured into crucibles and cooled into blocks or ingots. Both
processes produce silicon crystals that are extremely pure (from 99.99999 to 99.9999999 percent), which is ideal for
microchips, but far more than required by the PV industry. The high temperatures required for c-Si production make it
an extremely energy intensive and expensive process, and also produces large amounts of waste. As much as 80
percent of the initial metallurgical grade silicon is lost in the process.21
Sawing c-Si wafers creates a significant amount of waste silicon dust called kerf, and up to 50 percent of the
material is lost in air and water used to rinse wafers.22 This process may generate silicon particulate matter that will
pose inhalation problems for production workers and those who clean and maintain equipment. The U.S. Occupational Safety and Health Administration (OSHA) has set exposure limits to keep ambient dust levels low and recommends the use of respiratory masks, but it has been suggested that, despite the use of respiratory masks, workers remain overexposed to silicon dust.23
† The mining of metallurgical grade silica can produce silica dust that has been associated with silicosis, a severe lung
disease. Only a fraction of silica goes to the semiconductor industries, with most being mined for the steel industry.
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The use of silane gas is the most significant hazard in the production of c-Si because it is extremely explosive and
presents a potential danger to workers and communities.24 Accidental releases of silane have been known to
spontaneously explode, and the semiconductor industry reports several silane incidents every year.25
Further back in the silicon supply chain, the production of silane and trichlorosilane results in waste silicon
tetrachloride (SiCl4), an extremely toxic substance that reacts violently with water, causes skin burns, and is a
respiratory, skin, and eye irritant.26 Although it is easily recovered and reused as an input for silane production, in
places with little or no environmental regulation, silicon tetrachloride can constitute an extreme environmental hazard.
As the Washington Post reported in March 2008 (see above), polysilicon manufacturing is expanding rapidly in China,
but facilities to recycle silicon tetrachloride and other toxic outputs are not keeping pace.27
The extremely potent greenhouse gas sulfur hexafluoride (SF6) is used to clean the reactors used in silicon
production. The Intergovernmental Panel of Climate Change (IPCC) considers sulfur hexafluoride to be the most
potent greenhouse gas per molecule; one ton of sulfur hexafluoride has a greenhouse effect equivalent to that of
25,000 tons of CO2.28 It can react with silicon to make silicon tetrafluoride (SiF4) and sulfur difluoride (SF2), or be
reduced to tetrafluorosilane (SiF4) and sulfur dioxide (SO2). SO2 releases can cause acid rain, so scrubbers are
required to limit air emissions in facilities that use it.
It is imperative that a replacement for sulfur hexafluoride be found, because accidental or fugitive emissions† will greatly undermine the reductions in greenhouse gas emissions gained by using solar power.
Gee, does that mean we should hold up on solar power development till this problem is solved - FOR ENVIRONMENTAL REASONS?
Other chemicals used in the production of crystalline silicon that require special handling and disposal procedures
include the following:
• Large quantities of sodium hydroxide (NaOH) are used to remove the sawing damage on the silicon wafer surfaces. In some cases, potassium hydroxide (KOH) is used instead. These caustic chemicals are dangerous to the eyes, lungs, and skin.
• Corrosive chemicals like hydrochloric acid, sulfuric acid, nitric acid, and hydrogen fluoride are used to remove
impurities from and clean semiconductor materials.
• Toxic phosphine (PH3) or arsine (AsH3) gas is used in the doping of the semiconductor material. Though these are
used in small quantities, inadequate containment or accidental release poses occupational risks.29 Other chemicals used or produced in the doping process include phosphorous oxychloride, phosphorous trichloride, boron bromide, and boron trichloride.
• Isopropyl alcohol is used to clean c-Si wafers. The surface of the wafer is oxidized to silicon dioxide to protect the
solar cell.
† Fugitive air emissions are air pollutants that are not caught by a capture system. These may be due to equipment leaks,
evaporative processes, and windblown disturbances.
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• Lead is often used in solar PV electronic circuits for wiring, solder-coated copper strips, and some lead-based
printing pastes.
• Small quantities of silver and aluminum are used to make the electrical contacts on the cell.
Chemicals released in fugitive air emissions by known manufacturing facilities include trichloroethane, acetone,
ammonia, and isopropyl alcohol.30
A1. Monocrystalline Silicon Production Hazards
Monocrystalline silicon (mono c-Si) is formed when the one single crystal cools into a cylinder (called a rod or ingot).
Thin wafers are then cut from the cylinder.
Mono c-Si is produced in large quantities for the computer industry. Because the purity of silicon needed for solar PV
is less than that required for silicon chips, the PV industry has historically relied on purchasing (at reduced cost)
silicon wafers and polysilicon feedstock rejected by the chip makers.31 The production of solar grade silicon is growing
as demand in the PV industry is outstripping the available computer industry castoffs.
In addition to the chemicals used by all crystalline silicon cell production (see above), additional chemicals used to
manufacture mono c-Si solar cells include ammonium fluoride, nitrogen, oxygen, phosphorous, phosphorous oxychloride, and tin.32 Like most industrial chemicals, these materials require special handling and operating standards to prevent workplace hazards or exposure to toxics.
For further explanation of the above process diagram refer to Figure 7 in Appendix B, page 39.
Figure 7: Crystalline Silicon Generic Process Diagram
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A2. Multicrystalline Silicon Production Hazards
To make multicrystalline silicon (multi c-Si) wafers, molten silicon is poured into crucibles under an inert atmosphere
of argon gas and slowly cooled to form thin squares. These cells are typically less pure than mono c-Si, particularly
around the edges due to contact with the crucible during crystallization. They are less efficient but are also less
expensive and less energy-intensive to make. Multi c-Si has a significant share of the c-Si market at about 67 percent
in 2004.33 Overall, the lifecycle impacts of mono c-Si and multi c-Si have a similar profile, although the energy used in
production is higher for mono c-Si.34
Other materials used or produced in the manufacturing of multi c-Si that require special handling and operating
procedures include ammonia, copper catalyst, diborane, ethyl acetate, ethyl vinyl acetate, hydrogen, hydrogen
peroxide, ion amine catalyst, nitrogen, silicon trioxide, stannic chloride, tantalum pentoxide, titanium, and
titanium dioxide.35
New production practices are on the c-Si manufacturing horizon, and new technologies are being developed to
significantly reduce energy consumption.36 Efforts are being made to make thinner wafers—microcrystalline Si and
nanocrystalline Si—that use less silicon, but these require manufacturing techniques from nanotechnology that may
pose new kinds of occupational risks.
B. Amorphous Silicon (a-Si) Thin Film
The chemical composition of amorphous silicon (a-Si) allows it to be deposited in a thin layer on materials such as
plastics, glass, and metal. To make a-Si cells, silane or chlorosilane gas is heated and mixed with hydrogen, then
deposited as a thin film of a-Si (an alloy of silicon and hydrogen) on these materials. As mentioned previously, silane
(SiH4) gas is extremely explosive and poses a potential hazard to production workers and nearby communities.37 The
semiconductor industry has a history of silane gas explosions and occupational injuries.38 Chlorosilane gases are also
very toxic and highly flammable.39 However, because the amount of silicon used is much smaller than in crystalline
silicon production, less silane is needed to produce a-Si.
Hydrogen is also an explosive gas, and therefore poses an occupational hazard for workers.40 In addition, methane
gas is often mixed with the waste streams from the deposition process to literally burn off additional hydrogen.
Methane is another highly flammable gas that poses a greenhouse gas threat if released into the atmosphere.
Germane gas, often used to dope a-Si, is also explosive and considered toxic to the blood and kidneys.41
Chemicals used to etch and clean wafers—such as hydrochloric acid, hydrofluoric acid, phosphoric acid, and sodium hydroxide—require special handling to avoid occupational injury. Other dangerous chemicals used in the manufacture of a-Si include acetone, aluminum, chlorosilanes, diborane, phosphine, isopropanol, nitrogen, silicon tetrafluoride, tin, and, where germane is used, germanium and germanium tetrafluoride.42 The
tetrafluoride compounds above can emit toxic fumes if heated.
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Figure 8: Amorphous Silicon (a-Si) Generic Process Diagram
C. Cadmium Telluride (CdTe) Thin Film
Cadmium telluride (CdTe) thin-film solar PV panels use layers of CdTe and cadmium sulfide (CdS). Cadmium (Cd) is
a by-product of zinc mining, and batteries and solar cells are major end uses. The rare metal tellurium (Te) is a byproduct
of copper, lead, and gold mining, and its scarcity may eventually prove to be a bottleneck for CdTe cell
production. This will make the recovery of Te through recycling essential for the success of this rapidly growing
technology.
Cadmium telluride PV cells are produced by a process called electrodeposition, which efficiently applies a thin film of
semiconductor material to glass or plastic, with less raw material waste than amorphous silicon thin-film production.
CdTe thin films are deposited via electrical charge onto a surface using a solution of cadmium sulfate (CdSO4) or
cadmium chloride (CdCl2), mixed with tellurium dioxide (TeO2). Cadmium in wastewater used to rinse CdTe films
presents potential water pollution issues, but it can be reclaimed and reused in the deposition of the cadmium sulfide
(CdS) layer.43
There are several ways of producing the CdS layer. One method deposits the layer by heating the surface and directly
applying a mixture of cadmium sulfate (CdSO4), thiourea (also called thiocarbamide, CS(NH2)2), and ammonia (NH3);
only 1 percent of the cadmium used as an input is disposed of as solid waste.44
Another method uses the same chemicals and dips the surface into a chemical bath, but this method is less efficient
in terms of raw material use. A third method deposits a solid CdS powder directly onto the surface after vaporizing the
chemicals. In each of these methods the cadmium compounds are recycled, albeit not at 100 percent, as some
For further explanation of the above process diagram refer to Figure 8 in Appendix B, page 39.
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material is released in air exhaust and water effluent. For the latter two methods mentioned above, 10 to 30 percent of
cadmium input is disposed of as solid waste.45
The major health and safety hazards associated with the manufacture of CdTe cells relate to the use of cadmium,
cadmium sulfide, cadmium chloride, and thiourea. Cadmium is a known carcinogen46 and is considered
“extremely toxic” by the U.S. Environmental Protection Agency (EPA)47 and Occupational Safety and Health
Administration (OSHA).48 It has the potential to cause kidney, liver, bone, and blood damage from ingestion and lung
cancer from inhalation, and workers may be exposed to cadmium compounds during the manufacturing process. The
European Economic Community (EEC) has prohibited the sale of most products containing cadmium for health and
safety reasons. While the toxicity of cadmium is well known, there is limited information on cadmium telluride (CdTe)
toxicology.49 It is not clear whether or not the EEC will grant CdTe manufacturers the exemptions necessary to allow
sales of these modules in the European Union (E.U.). It is believed to be less toxic than cadmium compounds found in
nickel cadmium (NiCd) batteries.50 The Pesticide Action Network recognizes thiourea as a “Bad Actor Chemical”
because it is a known carcinogen and can be toxic.51
For further explanation of the above process diagram refer to Figure 9 in Appendix B, page 40.
Figure 9: Cadmium Telluride (CdTe) Generic Process Diagram
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The potential for dust and fumes creates potential hazards for workers during the preparation of materials, from scraping and cleaning CdTe products, and from fugitive emissions. Other hazardous inputs in the production of CdTe panels include molybdenum, nickel, sulfur, tellurium, and tin.52
As noted previously, the emerging use of nanoscale CdTe, also known as CdTe quantum dots, raises unknown safety
issues that must be identified and addressed.53 Properties of materials at the nanoscale may differ significantly from
those of larger particles of the same material, including increased toxicity, potential for bioaccumulation, and
nanoparticle mobility in the body.
Another safety concern regarding materials used in CdTe (and also in CIS/CIGS cells, discussed below), is the risk of
toxic releases during fires in residential and commercial structures where these cells are installed. The compounds
that would be released during fires pose a potential risk of toxic exposure, although the short-term nature of fires and
the fact that cadmium vaporizes at temperatures higher than typical household fires, suggest that the risk is minimal.54
However, the release of toxics from commercial buildings and industrial facilities during fires remains a concern, as
fire temperatures can be higher in these kinds of structures.
D. Copper Indium Selenide (CIS) and Copper Indium Gallium Selenide (CIGS)
This rapidly emerging solar PV semiconductor technology has the potential to revolutionize the industry with its ability
to print thin layers of semiconductor material on a wide range of materials. CIS and CIGS are also some of the bestabsorbing
semiconductor materials.
Depositing the CIS/CIGS layers onto a surface requires the mixing of copper and indium (and gallium in CIGS) with
hydrogen selenide and the use of various industrial techniques.55 One new process using nano-sized particles in an
ink suspension is able to utilize 100 percent of gallium and indium inputs, which is important because these are
globally rare metals.56
There is little information available about the toxicity of CIS or CIGS crystals, but numerous chemicals are used in the
production of CIS and CIGS panels, many of them very toxic. These include hydrogen selenide (or selenium hydride, H2Se), which is considered highly toxic and dangerous at concentrations as low as 1 part per million in the
air. It is used as the primary source of selenium and is consumed in the step called selenization, in which hydrogen
selenide is introduced into the atmosphere of a reactor to provide excess selenium to react with the other metals.
Hydrogen selenide will present potential occupational health and safety issues. New processes that avoid using
hydrogen selenide have been developed, but these are more expensive and are not currently used to manufacture
CIS/CIGS.57
Another concern with the use of selenium is the potential formation of selenium dioxide (SeO2) at high temperatures.
Selenium dioxide is a tissue poison like arsenic, and great care must be taken to ensure that workers are not exposed
to this occupational air pollutant.58 Reactions at high temperatures facilitate the uniformity of CIGS and CIS crystals,
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which is important for scaling up solar cell production. Selenium dioxide is vented into a water solution, where it forms elemental selenium. The recovery of selenium in this step is very high, but not 100 percent, and fugitive emissions do occur.59
CIS/CIGS panels often use a layer of cadmium sulfide (CdS). Salts of cadmium are released into the water as CIS
cells are rinsed, which means that the concerns above about cadmium apply. The CdS layer can be replaced with an
alternative material, such as zinc sulfide (ZnS) or indium sulfate (In2SO4), but CdS is more efficient.60
Copper, indium, and selenium are considered to have a mild toxicity, while gallium (only used in CIGS) has a low
toxicity. Dust from copper, indium, gallium, and selenium accumulate in the equipment used for production, presenting
potential inhalation risks to workers.61 Other materials used in CIS and CIGS production include hydrogen sulfide (a
gas used in CIS cell production), molybdenum, and zinc oxide. Molybdenum and zinc oxide are used as the back and front contacts that carry the electricity and are considered non-toxic.62
For further explanation of the above process diagram refer to Figure 10 in Appendix B, page 40 Figure 10: Copper Indium (Gallium) Selenide (CIS/CIGS) Process Diagram
For further explanation of the above process diagram refer to Figure 10 in Appendix B, page 40.
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E. Gallium Arsenide (GaAs) and Multijunction Cells
Gallium arsenide (GaAs) is currently used in multijunction solar PV cells, combined with thin-film materials such as
cadmium telluride (CdTe), amorphous silicon (a-Si), aluminum indium phosphide (AlInP), aluminum gallium indium phosphide (AlGaInP), or gallium indium phosphide (GaInP). GaAs technology is also used in concentrator cells, which focus incoming sunlight to increase its intensity. Because of the high cost of inputs and the manufacturing process, GaAs cell adoption has been limited to communication and military satellite applications.
The production of GaAs crystals starts with gallium and arsenic in pure form. The materials are combined and GaAs
crystals grow on a surface made of germanium or silicon. Newer methods use trimethyl gallium ((CH3)3Ga) and trimethyl arsenic ((CH3)3As) gases. There is a debate in the scientific community about whether trimethyl arsenic detoxifies arsenic or transforms it into a carcinogen.63 These gases are exposed to a heated surface where the GaAs crystals are grown. Different layers of these crystals are doped with different gases to make each layer sensitive to different parts of the solar spectrum.
The limited toxicological data on gallium arsenide suggest that it could have profound effects on lung, liver, immune,
and blood systems if workers are exposed for extensive periods during manufacturing or if chemicals are accidentally
released.64 There is little toxicological data on gallium, but it is widely used as a marker/tag in MRI tests, and believed
to be safe in small doses.
For further explanation of the above process diagram refer to Figure 11 in Appendix B, page 41.
Figure 11: Gallium Arsenide (GaAs) Generic Process Diagram
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Additional toxic materials used to produce GaAs PV cells include the following:
• Arsenic is a metalloid used to produce gallium arsenide crystals. Arsenic is highly toxic and carcinogenic,65 and
extreme caution will be required to avoid occupational hazards as the use of this technology expands.
• Phosphine and arsine are highly toxic gases used to dope GaAs crystals, but they are not found in the final PV
cells. Less toxic alternatives are being developed (including tertiary butyl arsine and tertiary butyl phosphine),66
and researchers are looking into substituting hydrogen with non-explosive (inert) nitrogen.
• Trichloroethylene, a known carcinogen, is a solvent used for cleaning. Other chemicals used or produced in the
manufacturing process include hydrochloric acid, methane, triethyl gallium, and trimethyl gallium, 67
F. Emerging Solar PV Technologies
It is difficult to speculate about the production hazards presented by the next generation of solar PV technology as
most are still in the theoretical or laboratory stages of development. Future applications for solar PV include new
configurations of multijunction cells, as well as the following:
• Dye-sensitized solar cells release electrons from (in one particular case) titanium dioxide covered in a pigment
that effectively absorbs sunlight.
• Organic (living or dead carbon-based) solar cells are made of biodegradable materials. At this point, many of
these organic technologies degrade during operation, making them very unstable and far from commercial
viability.
• Hybrid cells that combine various technologies and therefore present all the production hazards associated with
their constituent semiconductors.
Emerging solar cell technologies are also rapidly incorporating advanced techniques in nanotechnology, such as the deposition of nanocrystals. Nanotechnology applications to solar cell manufacturing include nanoparticles suspended
in ink, quantum dots, nanowires, and silver cells. Nanotech is also being used to produce very stable laminate layers
to protect solar cells. These emerging uses merit considerable attention and the development of proactive labor
standards to safeguard against unknown hazards.
IV. Potential End-of-Life Hazards for Solar PV Products
What will happen to today’s solar panels at the end of their usefulness, which is estimated at 25 years or more? Not only do solar PV products contain many of the same materials as electronic waste (e-waste), but they also contain a growing
number of new and emerging materials that present complex recycling challenges. These challenges include finding ways
to recycle the small amounts of valuable materials on which many of the new solar PV technologies are based.
Much like e-waste, solar panels will leave a toxic legacy if they end up in landfills (where the materials they contain can
leach into groundwater) or incinerators (where burning can release toxic materials into the air).68 To avoid a repeat of the
e-waste crisis, we need to ensure that decommissioned solar PV products are recycled responsibly and do not enter the
waste stream at all. Responsible recycling means that waste is not shipped to developing countries for dismantling or
recycled using U.S. prison labor.
One option could be to recycle solar PV panels that contain toxic metals at existing responsible e-waste recycling facilities† or at facilities that recycle batteries containing lead and cadmium, thereby keeping toxics out of the municipal incinerators and landfills.69 However, the latter hazardous waste recovery facilities are often low-tech and in need of substantial research and development to improve their environmental footprint. For example, most recycling facilities reclaim metals using smelters, which are known to increase the risk of lung cancer from cadmium exposure in recycling workers and residents in nearby communities.70
Extended Producer Responsibility (EPR), such as manufacturer take-back requirements (see sidebar, page 3), will be the
key to ensuring that these complex and diverse solar PV products can be safely recycled. Making manufacturers
responsible for the lifecycle impacts of their products will provide incentives for the development of safe and effective
recycling technologies and for the design of products that are easier to recycle. Plans for recovering and recycling
materials at the end of product life should be standard practice for any product identified as a “renewable” energy source.
A. Solar PV Toxic Waste is Also E-Waste
Because solar PV semiconductor manufacturing processes have roots in the microelectronics industry, many of the
chemicals found in e-waste are also found in solar PV, including lead, brominated flame retardants, cadmium, and
chromium. Each of these is described in more detail below. Many of the toxic materials currently used in the PV sector
are being phased out of electronic products in the E.U., but are still currently used in most of the U.S.
† Recyclers that have signed the landmark “Electronic Recyclers Pledge of True Stewardship.” For additional information, see:
computertakeback.com
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Lead is often used in electronic circuits, including solar PV circuits, for wiring, soldercoated copper strips, and some lead-based printing pastes.71 Lead is highly toxic to the
central nervous system, endocrine system, cardiovascular system, and kidneys.72
Because lead accumulates in landfills, discarded solar PV panels have the potential to leach into drinking water. In one study, solar PV modules using lead solder exceeded by 30
percent the maximum allowable concentrations for lead in the Toxicity Characteristic Leaching Procedure (TCLP)standards set by the U.S. EPA.73 This can be easily resolved by using lead-free solders (such as those containing tin, silver, or copper), but current U.S. regulations do not require lead-free solder in the manufacture of solar panels or any electronic devices.74 The E.U. has been more proactive, restricting the sale of electronics with lead-based solders.
Brominated flame retardants (BFRs), polybrominated biphenyls (PBBs), and polybrominated diphenylethers (PBDEs)
are added to plastics to make them less flammable. They are used in circuit boards and solar panel invertors (which convert DC to usable AC power). BFRs contain bromine atoms, which are released as the plastic heats. Combustion is slowed as the additional bromine in the air interferes with the supply of oxygen needed to sustain fire.
Brominated flame retardants have become ubiquitous in the environment; they are found at high levels in a wide range of
living organisms, from harbor seals in San Francisco Bay, to Arctic polar bears, to the breast milk of humans in the United
States.75 PBDEs bioaccumulate in fatty tissues; they are recognized as toxic and carcinogenic and are described as
endocrine disrupters.76 The E.U. and the states of Washington and California have banned the manufacture, distribution, or
processing of goods with PBDEs.
The Global E-Waste Crisis
The global tide of toxic electronic waste (e-waste) is an
escalating environmental and health disaster, especially for
countries in Asia, West Africa, and Latin America where ewaste
is often shipped for cheap recycling.
According to EPA estimates, in 2005 more than 2.6 million tons
of e-waste were generated in the U.S., and that flood of waste
is expected to increase dramatically with the nationwide switch
from analog to digital TV in February 2009.
In 2005, only 12.5 percent of that 2.6 million tons was collected for recycling. The remainder—more than 87 percent—was
disposed of, largely in U.S. landfills or incinerators. The
hazardous materials in e-waste, which include lead and other
toxic heavy metals like mercury, chromium, and cadmium, can
leach out of the landfills into groundwater and streams, and the burning of plastics can emit dioxins into the air. As of March 2008, at least ten states had passed laws banning disposal of some electronics in landfills.†
Some of that 12.5 percent of e-waste collected for recycling is
recycled responsibly, but an estimated 50 to 80 percent of it is exported to developing countries where it is dismantled or
disposed of using very rudimentary and toxic technologies.††
The imprecision of that estimate reflects the fact that it is almost impossible to track the amount of U.S. e-waste that is shipped overseas. The U.S. is one of only three nations (the others are Afghanistan and Haiti) that have not ratified the Basel Convention, an international treaty designed to stop free trade in hazardous wastes. In addition, a significant amount of U.S. ewaste is recycled using prison labor in this country.†††
† Electronics TakeBack Coalition, “E-Waste: The Exploding Global Electronic Waste Crisis,” October 10, 2008 (Issue briefing book), p. 8, available at computertakeback.com
†† Ibid., p. 4.
††† Ibid., p. 6.
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Hexavalent chromium (Cr(VI)) is used in many solar panels as a coating to absorb solar radiation, and it is also found in screws and circuit board chassis. It is considered carcinogenic.77 Several companies have phased out the
use of hexavalent chromium in solar modules.
Solar PV, like most electronics equipment, contains recoverable metals. Copper wiring, nickel, silver, and aluminum
contacts, and aluminum frames can be recycled like other scrap metals.
The sections below outline the end-of-life recycling challenges for specific solar PV technologies.
B. Crystalline Silicon (c-Si)
End-of-life hazardous waste issues: As outlined above, c-Si circuitry and inverters contain hazardous materials such
as lead, brominated flame retardants, and hexavalent chromium. Toxic materials contained in the actual c-Si
semiconductor materials are below levels regulated by the EPA.
Recycling options: Used silicon wafers can be melted into new silicon ingots and cut into new wafers. It takes far less
energy (estimates range from 30 to 90 percent less) to process c-Si feedstock from recycled silicon than it does to
process raw silica.78 Furthermore, in recent years a silicon shortage has made recycling silicon PV an even more
attractive option. A company located in Freiburg, Germany, is one of the few in the world that operates a c-Si recycling
plant to reuse defective and used c-Si for new panels.79
C. Amorphous Silicon (a-Si)
End-of-life hazardous waste issues: Amorphous silicon PV panels contain no EPA-regulated toxic materials, aside
from those contained in the circuit boards (as noted above).
Recycling options: Since most a-Si PV panels are currently found in consumer products, they are typically disposed of
in household waste streams. As with other small electronic devices, these products contribute to the overall e-waste
load on local landfills. Amorphous silicon cells are also being used in combination with other materials to make
multijunction panels (see below). The a-Si panels on these consumer products can be recycled through standard
glass recovery/recycling processes, but they rarely are because they are attached to consumer products that are
typically just thrown in the trash.
D. Cadmium Telluride (CdTe)
End-of-life hazardous waste issues: While the hazards of cadmium are well known, the toxicity of cadmium telluride
(CdTe) is not as clear. It is believed to be less toxic than cadmium compounds (cadmium hydroxide) found in nickel
cadmium (NiCd) batteries because it does not dissolve in water as readily.80 However, tests to date are inconclusive.
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Early studies of how metals may leach into groundwater show that CdTe modules failed both the TCLP and DEV† tests.81,82,83,84 More recent studies indicate that CdTe panels marginally pass TCLP standards,85,86 and one
manufacturer reports that its panels currently pass TCLP and DEV tests.87,88 Potential future applications include
CdTe quantum dots, shown to cause damage to cell biology and cell death.89
Recycling options: Even though recycling technologies and processes are being developed, no company is yet reusing discarded CdTe panels as a manufacturing input for new ones. CdTe panels will go to the smelters that treat television cathode ray tubes (CRTs), fluorescent lights, and Ni-Cad and lead-acid batteries. There are several recycling methods in development by private industry and government labs to recover the metals in CdTe panels instead of burning them, but these are limited to pilot projects.90, 91 These methods include the use of strong acids (such as sulfuric acid) to strip off metals from crushed PV modules, providing a solution rich in metals that is further
processed with sodium hydroxide, sodium carbonate, sodium metabisulfite, zinc, or iron to recover cadmium and
tellurium.92
Some of the intermediate compounds that could enter the waste stream from the recycling process above include sodium sulfide and tellurium sulfide. Potential waste products include tellurium dioxide, sulfur dioxide, and potential emissions from the polymer laminate and casing. Since these recycling efforts are still at the pilot scale, it is unclear what kinds of tasks will be automated and which will put workers at risk. It is also unclear if recovered cadmium will be economically competitive for reuse, or simply treated as hazardous waste. Recovery of tellurium, however, is very important because of low global availability.
E. Copper Indium Selenide (CIS) and Copper Indium Gallium Selenide (CIGS)
End-of-life hazardous waste issues: Selenium is a regulated substance that bioaccumulates in food webs and forms
compounds such as hydrogen selenide, which is considered highly toxic and carcinogenic by the EPA.93 CIGS has
toxicity levels similar to CIS with the addition of gallium, which is associated with low toxicity. CIS and CIGS
semiconductors also use cadmium sulfide (CdS) as a buffer layer, so cadmium is also a potential hazard. In
addition, cadmium telluride (CdTe) is often used as a buffer material in these modules, which introduces the CdTe
toxicity issues discussed above. In an acute toxicity comparison of CdTe, CIS, and CIGS, researchers found CIGS to
have the lowest toxicity, and CdTe to have the highest.94
Recycling options: No recycling processes to recover elements for reuse have been explored beyond the pilot scale.95
Indium, a by-product of zinc mining, is extremely rare, and it has competing uses in the flat screen television industry.
The high value of this metal will make recycling important for the success of CIS/CIGS PV technologies.
† The German “DEV S4” (Deutsches Einheitsverfahren) test, similar to the U.S. TCLP, is used by the E.U. to ensure that
potentially toxic materials do not leach into the groundwater near waste disposal sites.
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F. Gallium Arsenide (GaAs) and Multijunction Panels
End-of-life hazardous waste issues: The limited toxicological data on gallium arsenide (GaAs) suggest that it could
have profound effects on lung, liver, immune, and blood systems.96 It is also considered likely that these crystals
would release arsine or arsenic if deposited in landfills; arsenic is highly toxic and carcinogenic.97 As noted above,
there is little toxicological data on gallium, but it is believed to be safe in small doses.
Recycling options: There are no pilot-scale recycling facilities for GaAs and multijunction PV (which also incorporates
materials such as cadmium telluride and amorphous silicon). Other potentially toxic materials under development for
use in multijunction PV include zinc manganese tellurium, indium gallium phosphide/germanium, and indium
gallium nitride. As noted previously, the global rarity of metals such as indium and tellurium will make recycling
essential to the success of solar PV based on these materials.
G. Emerging Solar PV Technologies
End-of-life hazardous waste issues: Most of the end-of-life hazards for emerging solar PV technologies have not been
analyzed. In some cases, emerging products simply combine existing semiconductors (or advanced forms of existing
semiconductors), and they will therefore carry the hazardous waste issues of all the technologies employed. For
example, a multijunction cell of amorphous silicon and gallium arsenide will entail hazards posed by all of the
materials and processes used.
Even less is known about the hazards of newer PV technologies. Dye-sensitized solar cells are based on a combination of a dye and titanium dioxide (which is not considered toxic), so the hazards of these technologies will be based on the toxicities of the dyes used, which at this point are not clear. Silver cells will pose hazards related to the mild toxicity of silver, as well as any new hazards presented by the use of silver nanocrystals.
Recycling options: Because of the diversity of materials used, recovery of semiconductor materials in multijunction
cells will be complicated unless the different crystals are mechanically or manually disassembled, at which point their
recovery processes will be similar to those described above. It is too early to say how dye-sensitive cells are going to
be recycled. Organic, carbon-based, solar PV will pose little if any risk since it would be biodegradable. Understanding
the end-of-life impacts of hybrid cells will depend on knowing which technology is being utilized.
Of particular concern for emerging solar cell technologies’ end-of-life are the uncertain hazards associated with the
use of nanomaterials and technologies. As previously noted, the fate of nano-sized particles can be much different
than that of larger sized particles of the same materials. Materials not considered hazardous may, in fact, become
hazardous if their bioaccumulative or toxicity characteristics change at the nanoscale. It is also unclear how
nanoparticles found in ink suspensions or nanoparticles (such as quantum dots) sprayed onto surfaces will degrade
when exposed to cracks in the solar cells’ protective layers.
.......
Reduce and Eventually Eliminate the Use of Toxic Materials
Based on the information presented in this report, SVTC recommends that the following actions be taken by U.S. solar
PV manufacturers to reduce the environmental and health risks presented by the PV industry:
Green Chemistry
Green chemistry takes a lifecycle approach, in which every
step from raw material extraction through product use and
end-of-life are considered in the design of products. The 12
principles of green chemistry† include precautionary and
pollution prevention measures to ensure that products are
designed to incorporate safer chemicals, renewable raw
materials, and minimal energy use and waste.
As detailed in this report, many of the chemicals used in
the PV industry are far from green. Application of green
chemistry principles will benefit everyone. Solar PV
companies can save on the costs of energy and regulatory
compliance, and workers and communities will risk less
exposure to potential toxins. This approach is already
viewed as a competitive advantage for companies seeking
to market products to the E.U. and to U.S. states with
proactive chemicals policies, such as California.††
† P. Anastas and J. Warner, Green Chemistry: Theory and
Practice, Oxford University Press, New York, 1998.
†† Michael Wilson, “Green Chemistry in California: A Framework for
Leadership in Chemicals Policy and Innovation,” Report to the
California Senate Environmental Quality Committee, California
Policy Research Center, Berkeley, 2006.
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• Phase out use of chemicals already restricted by the E.U.’s Restriction of Hazardous Substances (RoHS).
These chemicals—including cadmium, lead, mercury, brominated flame retardants, and chromium—are considered highly dangerous and should be phased out in the U.S. as well.
• Develop chlorine-free methods for making polysilicon feedstock that eliminate the use of trichlorosilane
(which results in waste silicon tetrachloride, an extremely toxic substance). This is the most toxic and energyintensive
phase of silicon production, and several methods are being developed to potentially replace it.101
• Phase out use of sulfur hexafluoride (SF6). One ton of sulfur hexafluoride has the greenhouse effect equivalent
of 25,000 tons of CO2.102 It is imperative that a replacement for sulfur hexafluoride be found, because accidental or
fugitive emissions will greatly undermine the greenhouse gas reductions gained by the use of solar power.
• Phase out use of hydrogen selenide. This highly toxic material is used in the production of CIS/CIGS PV. New
processes to make CIS/CIGS have been developed that avoid using hydrogen selenide.103
• Phase out use of arsenic. Arsenic, used in production of gallium arsenide PV, is highly toxic and carcinogenic.
• Phase out phosphine and arsine. Phosphine and arsine are highly toxic gases used in the production of GaAs
crystals (although they are not found in the final PV cells).
• Reduce fugitive air emissions from facilities. Reduce fugitive air emissions by PV manufacturing facilities,
which include such chemicals as trichloroethane, acetone, ammonia, and isopropyl alcohol and greenhouse gases
such as sulfur hexafluoride and nitrogen trifluoride 104
B. Hold the Solar PV Industry Accountable for the Lifecycle Impacts of Its Products
The best opportunity to minimize the end-of-life hazards of solar PV lies in Extended Producer Responsibility (EPR),
which makes manufacturers responsible for their products’ end-of-life disposal. PV companies should take back their
solar panels and recycle them responsibly without exporting waste overseas or using U.S. prison labor.
.....
Overview of Chemicals Associated with Solar Photovoltaic (PV) Manufacturing and Disposal
• Ammonia (NH3) is used to produce anti-reflective coatings for solar PV modules. High-level exposures may irritate the
skin, eyes, throat, and lungs and cause burns. Lung damage and death may result from exposure to very high
concentrations. Ingesting ammonia can burn the mouth, throat, and stomach, and ammonia in the eyes can cause burns
and blindness.
• Argon (Ar) gas is used in thin-film solar cell manufacturing to apply a semiconductor onto a surface or as an inert cooling
gas. Although considered non-toxic, it is known to result in death due to asphyxiation in confined spaces. In such cases,
mental alertness is diminished, muscular coordination is impaired, judgment becomes faulty, and all sensations are
depressed. Emotional instability often results and fatigue occurs rapidly. As the asphyxia progresses, there may be
nausea and vomiting, prostration and loss of consciousness, and finally convulsions, deep coma, and death.
• Arsenic (As) can be released from the decomposition of discarded GaAs solar PV cells. Inhalation of high levels of
arsenic causes throat soreness, lung irritation, increased lung cancer risk, nausea and vomiting, decreased production of
red and white blood cells, abnormal heart rhythm, damage to blood vessels, and “pins and needles” sensations in hands
and feet. Ingesting or breathing low levels of inorganic arsenic for an extended period causes skin darkening, and small
“corns” or “warts” appear on the palms, soles, and torso. Skin contact may cause redness and swelling. Ingestion can
increase skin, liver, bladder, and lung cancer risks. Ingesting very high levels can result in death.
• Arsine (AsH3) is a doping gas used to add impurities to PV semiconductors. When inhaled, it attacks red blood cells,
causing headaches, vertigo, and nausea. It can cause critically affect the kidneys and blood. Arsine is a recognized
carcinogen and is similar in toxicity to the methyl isocyanate released in Bhopal. Arsine can be phased out and replaced
with the less toxic tertiary butyl arsine (TBA).
• Boron trifluoride (BF3) gas is used to dope silicon semiconductors. Exposure to large amounts over short periods of
time can affect the stomach, intestines, liver, kidney, and brain and can eventually lead to death.
• Brominated Flame Retardants (BFRs) are chemicals that inhibit the ignition of combustible organic materials. BFRs are
commonly used in computers, electronic products, televisions, insulating foams, and other building materials to reduce
product flammability. BFRs bioaccumulate and are found at high concentrations in human breast milk. BFRs known as
polybrominated diphenyl ethers (PBDEs) are used in polymers such as polystyrene foams, high-impact polystyrene, and
epoxy resins (see PBDE item below).
• Cadmium (Cd) is a by-product of zinc, lead, or copper mining. Workers can be exposed through cadmium smelting and
refining or through the air in workplaces that make Cd-based semiconductors. Acute symptoms vary depending on the
specific cadmium compound, but can include pulmonary edema, cough, chest tightening, headache, chills, muscle aches,
nausea, vomiting, and diarrhea. Cd is chronically toxic to the respiratory system, kidneys, prostate, and blood and can
cause prostate and lung cancer. NIOSH considers cadmium dust and vapors as carcinogens. California has also
determined (under AB 1807 and Proposition 65) that cadmium and cadmium compounds are carcinogens.
• Cadmium chloride (CdCl2) is a soluble form of Cd that vaporizes more readily than other cadmium compounds. It is
extremely toxic to workers exposed during feedstock preparation or through maintenance and fugitive emissions.
Information for this appendix was compiled from the International Labor Organization (ILO), NOAA’s Office of Response and Restoration, the Intergovernmental Panel on Climate Change (IPCC), U.S. EPA, California EPA, U.S. OSHA, and
California OSHA.
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• Cadmium sulfate (CdSO4) is used to apply CdS in CdTe and CIS/CIGS production. Cadmium compounds are toxic by
inhalation and skin contact, and exposure may cause cumulative and irreversible effects. Cadmium sulfate causes nose,
throat, and lung irritation, and lung edema may also occur. Symptoms are usually delayed for several hours and
aggravated by physical effort. Repeated, prolonged exposure to dust may cause discoloration of teeth, loss of smell,
shortness of breath, damage to liver and kidneys, and mild anemia.
• Cadmium sulfide (CdS) is used in CdTe and CIS/CIGS thin-film solar PV production. It is a suspected human
carcinogen and is toxic to kidney, lungs, and liver. Some bacteria found in nature produce CdS, and research is underway
to investigate possible use of these bacteria in solar PV manufacturing.
• Cadmium telluride (CdTe) is a thin-film semiconductor. Inhalation, ingestion, and dermal contact with CdTe are
considered toxic, though very little CdTe toxicological data exists. The highly reactive surface of cadmium telluride
quantum dots could trigger extensive reactive oxygen damage to the cell membrane, mitochondria, and cell nucleus.
• Carbon nanotubes (CNTs) are carbon allotropes (like diamonds and graphite) measured at the nanometer scale.
Exposures are linked to mesothelioma in animals, and nanotubes are believed to present inhalation hazards similar to
those of asbestos.
• Carbon tetrachloride (CCl4) is used to manufacture c-Si PV cells. Exposure to very high amounts of carbon tetrachloride
can damage the liver, kidneys, and nervous system (including the brain). CCl4 can cause cancer in animals, and the
Department of Health and Human Services (DHHS) has determined that it may be considered a human carcinogen.
• Chromium VI (Cr VI) is used in PV modules for chrome-plated hardware such as screws and frames. High levels of
chromium have provoked asthma attacks, and long-term exposure is associated with lung cancer. Handling liquids or
solids containing Cr VI can cause skin ulcers. Swallowing large amounts will cause upset stomach, ulcers, convulsions,
kidney and liver damage, and even death. The EPA classifies Cr VI as a known human carcinogen.
• Copper (Cu) can be poisonous or fatal at high exposures. Inhalation exposures may occur through the vaporization of
copper in CIS/CIGS production. Breathing high levels of copper can cause nasal and throat irritation. Ingestion of high
levels of copper can cause nausea, vomiting, and diarrhea. Very high doses of copper can cause damage to the liver and
kidneys and can ultimately cause death.
• Copper indium diselenide (CIS) is used in thin-film PV cells. There is limited toxicity information on CIS. Measurements
of airborne concentrations of copper, indium, and cadmium from mechanical scribing and deposition operations on
CIS/CdS modules were well below threshold levels. The main health issue related to CIS is the highly toxic hydrogen
selenide feedstock gas (also called selenium hydride, see below).
• Copper indium gallium diselenide (CIGS) is similar to CIS but also contains gallium (Ga) (see below).
• Diborane (B2H6) is a doping gas used to manufacture a-Si cells. It is highly flammable and is considered highly irritating
to skin tissues. In rare cases, it may cause liver and kidney damage.
• Ethyl vinyl acetate (EVA) is used to encapsulate solar PV cells. It is a non-toxic alternative to soft plastics like polyvinyl chloride (PVC) and bisphenyl A, but may release volatile organic compounds during manufacture.
• Gallium (Ga) is a rare soft metal used in GaAs PV and recovered from zinc and aluminum mining. It is not considered
toxic, but may cause skin irritation after prolonged exposure. Scaling up of GaAs production is limited by the global
scarcity of gallium. For use in manufacturing, Ga is converted into trimethylgallium (Ga(CH3)3).
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• Germane (GeHH4) is often deposited with silane to dope a-Si layers with germanium. It is extremely toxic and can kill red
blood cells and cause anemia and kidney failure.
• Helium (He) is a colorless, odorless, non-toxic gas used in solar PV to propel thin films onto a surface. Helium is
absorbed by inhalation or skin contact. Inhalation causes a high voice, dizziness, dullness, headache, and possible
suffocation. Containment failure can cause suffocation by displacing oxygen in confined areas. Skin frostbite is possible
through contact with liquid He.
• Hexafluoroethane (C2F6) is used to etch semiconductors. It is an asphyxiant and in high concentrations may cause
dizziness, nausea, vomiting, disorientation, confusion, loss of coordination, and narcosis. Very high concentrations may
cause suffocation. Liquid hexafluoroethane may cause frostbite. Harmful amounts may be absorbed if skin contact is
prolonged or widespread. It is listed as a potent greenhouse gas by the IPCC.
• Hydrochloric acid (HCl) is used to clean and etch semiconductors and to produce electrical grade silicon. Concentrated
HCl is corrosive to the skin, eyes, nose, mucous membranes, and respiratory and gastrointestinal tracts. Inhalation can
lead to pulmonary edema. Ingestion can cause severe injury to the mouth, throat, esophagus, and stomach. Other
possible effects include shock, circulatory collapse, metabolic acidosis, and respiratory depression.
• Hydrofluoric acid (HF) is used to etch and remove oxidation from semiconductors. Low levels of HF gas can irritate the
eyes, nose, and respiratory tract. Inhalation at high levels or in combination with skin contact can cause death from
irregular heartbeat or lung fluid buildup. Splashes of HF on the skin can be fatal, but may cause no immediate signs of
exposure. Swallowing even a small amount of highly concentrated HF affects internal organs and may be fatal.
• Hydrogen (H2) is used to manufacture a-Si solar cells. It is considered non-toxic but is extremely flammable and
explosive.
• Hydrogen sulfide (H2S) is used in the manufacture of CIS/CIGS. It is considered an irritant and is extremely flammable.
• Indium (In) is a rare metal used as the semiconductor for CIS/CIGS, indium gallium phosphide, or indium gallium nitride
solar PV. It is also used in lead-free solders. It is made from the highly reactive trimethylindium, which can spontaneously combust.
• Indium gallium nitride (InGaN) is a PV semiconductor. The toxicology of InGaN is not well documented, but the dust is
a known skin, eye, and lung irritant. It is produced from trimethylindium, trimethylgallium, and ammonia.
• Indium phosphide (InP) is used in multijunction solar PV. It is listed under California Proposition 65 as a chemical known
to cause cancer.
• Lead (Pb) is used to solder photovoltaic electrical components. Lead exposures occur in smelting and refining industries, soldering, and battery manufacturing. Workers can inadvertently bring home lead via clothing and possibly expose those most vulnerable: pregnant women and children. People who reclaim heavy metals from "recycled" electronics are also
exposed. Lead is most toxic to the nervous system. Lead exposure may cause weakness in fingers, wrists, or ankles, and
can also cause anemia. At high exposure levels, lead severely damages the brain and kidneys and may ultimately cause
death. In pregnant women, high levels of exposure to lead may cause miscarriage. Lead is also considered a probable
human carcinogen.
• Nitric acid (HNO3) is used in solar PV manufacture to clean wafers, remove dopants, and clean reactors. Major
occupational concerns relate to the potential for chemical burns.
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• Nitrogen (N2) is used to dope semiconductors. Rapid release of nitrogen gas in an enclosed space can displace oxygen,
and it therefore represents an asphyxiation hazard.
• Nitrogen trifluoride (NF3) is used to clean reactors and etch polysilicon semiconductors. It emits toxic fumes when
burned or reacted and can cause asphyxiation. The IPCC considers NF3 a significant greenhouse gas, making fugitive
emission control very important.
• Phosphine (PH3) is a doping gas used to add impurities to photovoltaic semiconductors. It is extremely flammable and
explosive and is considered a severe respiratory irritant. Phosphine can be replaced by less toxic tertiary butyl phosphine.
• Polybrominated diphenyl ethers (PBDEs) are flame-retardant chemicals added to plastics and foam products. Because
they are mixed into plastics and foams rather than bound to them, PBDEs can leave the products and enter the
environment. PBDEs undergo long-range transport and deposition, appearing in ringed seals found in the Canadian
Arctic. Very little is known about the human health effects of PBDEs, but toxicity to the liver, thyroid, and
neurodevelopment is reported in animals, and concerns are raised because of persistence and bioaccumulation in
humans. The EPA requires special procedures for the transport, storage, or disposal of PBDE. California outlawed the
sale of PBDEs and products containing them effective January 1, 2008.
• Polysilicon is the feedstock material used to produce silicon PV cells. It is obtained by heating silane or trichlorosilane gas.
• Polyvinyl fluoride (Tedlar®) is used in solar PV module backing sheets to extend product life and increase efficiency.
These are preferred backing sheets due to strength and weather, moisture, and UV light resistance. Tedlar® dust may
cause eye irritation, and skin contact may also produce irritation. Some formulations contain small amounts of one or
more of the following compounds: lead, chromium, cadmium, selenium, arsenic, and antimony.
• Selenium (Se) is found in CIS/CIGS as an alloy of diselenide. Short-term exposure to high concentrations of selenium may cause nausea, vomiting, and diarrhea. Chronic exposure to high concentrations of selenium compounds can produce a disease called selenosis. Major signs of selenosis are hair loss, nail brittleness, and neurological abnormalities
(such as numbness and other odd sensations in the extremities). Brief exposures to high levels of Se can result in respiratory tract irritation, bronchitis, difficulty breathing, and stomach pains.
• Selenium dioxide (SeO2) is a by-product of CIS/CIGS manufacturing and an intermediary in the recovery of selenium
from waste CIS/CIGS modules. It is highly toxic when inhaled and may cause skin burns and eye irritation. Chronic
exposure may cause selenium-related diseases. Brief exposure to high levels of SeO2 can result in respiratory tract
irritation, bronchitis, difficulty breathing, and stomach pains.
• Selenium hydride (H2Se) is used to apply the diselenide layer in CIS/CIGS. It is highly toxic and can cause respiratory
irritation and selenium-related diseases. Inhalation causes a burning sensation, nausea, and sore throat. Skin contact can
cause frostbite. It is extremely flammable. Methods are being developed to produce CIS/CIGS without H2Se. Also called
hydrogen selenide.
• Silane (SiH4) gas is used to apply silicon thin films and make silicon crystal semiconductors. Major health hazards
include respiratory tract, skin, and eye irritation. Silane gas is extremely explosive. At room temperature, silane is
pyrophoric—it spontaneously combusts in air without external ignition.
• Silicon (Si) is the most widely used solar PV semiconductor. Crystalline silica (silicon dioxide, SiO2) is a potent
respiratory hazard, irritating skin and eyes on contact. Inhalation causes lung and mucus membrane irritation. Eye
irritation results in watering and redness. Lung cancer is associated with occupational exposures to crystalline silica
among miners, diatomaceous earth workers, granite workers, pottery workers, brick workers, and others.
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• Silicon tetrachloride (SiCl4) is a corrosive and toxic by-product and intermediary in silicon-based PV cell production. It
reacts with water to form hydrochloric acid and can cause tissue damage. It causes severe respiratory problems when
inhaled. Skin contact causes severe pain, and eye contact can cause permanent damage. It is one of a group of
chemicals known as chlorosilanes.
• Silver (Ag) is used in solar PV electrical contacts or as the semiconductor in silver cells. Exposure to high levels of silver over long time periods may cause a condition called argyria, a blue-gray discoloration of the skin and other body tissues. Argyria is permanent, but it appears to be only a cosmetic problem. Exposure to high levels of silver can result in breathing problems, lung and throat irritation, and stomach pains. Skin contact with silver can cause mild allergic
reactions such as rash, swelling, and inflammation.
• Sodium hydroxide (NaOH) is used to clean and etch semiconductors. Even very low levels can produce skin and eye
irritation. High-level exposure can cause severe burns to the eyes, skin, and gastrointestinal tract, which may cause
death.
• Sulfur hexafluoride (SF6) is used to etch semiconductors and clean reactors in PV manufacturing. It is relatively inert
and is considered an asphyxiant. The IPCC considers SF6 the most potent greenhouse gas known.
• Tetrobromo bisphenol A (TBBPA) is a reactive brominated flame retardant used in the printed wiring boards of more
than 90 percent of electrical and electronic products. The main use of TBBPA in solar PV is in inverters. Occupational
exposure may occur from contact during production or through dust inhalation. Recent concerns focus on TBBPA as an
endocrine disruptor; it is similar to bisphenol A, a known estrogen mimic. TBBPA also bioaccumulates in organisms.
• Thiourea (CH4N2S) is used to manufacture CdTe and CdS PV semiconductors. It is toxic to blood and causes thyroid and
liver tumors. California recognizes thiourea as a carcinogen.
• Trichlorosilane (HSiCl3) is the main source of electrical grade silicon. It is formed in the presence of silicon and
hydrochloric acid and is toxic and flammable. Inhalation causes acute effects such as burns, difficulty breathing,
headache, dizziness, bluish skin color, and lung congestion. Blurred vision results from eye contact, and ingestion can
cause burns, vomiting, and diarrhea. |
