United States
Environmental Protection
Agency
Industrial Environmental Resea
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S7-82-066 Mar. 1983
Project Summary
Photovoltaic Energy Systems:
Environmental Concerns and
Control Technology Needs
Paul D. Moskowitz, Paige Perry, and Israel Wilenitz
Technical and commercial readiness
for alternate photovoltaic energy sys-
tems, and waste streams from three
different photovoltaic systems are exam-
ined. At present, specific emission
standards for this industry do not exist
and measurements of wastes produced
by existing manufacturers are not avail-
able. Thus, emission estimates pre-
sented are based upon design engineer-
ing studies of hypothetical facilities.
Because of the widespread use of many
of the materials used in this industry,
available control experience and tech-
nologies used in other industries may
ultimately be applied to photovoltaic
plants. This analysis suggests that
some uncontrolled waste streams could
be declared toxic or hazardous under
various provisions of the Clean Air,
Clean Water, and Resource Conserva-
tion and Recovery Acts. Although some
processes could emit large quantities of
pollutants, these can be controlled using
available technology. Other processes
may emit small quantities of more toxic
pollutants which will probably not be
directly controlled unless significant
hearth hazards are identified. Environ-
mental problems in installation and
operation are probably associated with
large central-station applications; no
significant effects are expected from
small decentralized applications. De-
commissioning of broken or degraded
photovoltaic systems will generate large
quantities of solid waste which can be
sirnply disposed of in a landfill or per-
haps recycled. Disposal of spent photo-
voltaic devices containing cadmium
may present unique hazards.
This Project Summary was devel-
oped by EPA's Industrial Environmen-
tal Research Laboratory, Cincinnati, OH,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
Identification and analysis of environ-
mental concerns and ways to mitigate
them for any energy industry before it
becomes fully commercialized can limit
potential investment costs while simul-
taneously minimizing environmental and
public health risks. This report updates
previous studies by the U.S. Environ-
mental Protection Agency (EPA) which
examine potential health and environ-
mental risks and control methodology
related to photovoltaic energy systems.
This analysis should provide background
information about potential health and
environmental effects to planners con-
cerned with research and regulatory
priorities, and federal, state, and county
officials engaged in pollution control per-
mitting programs.
In this spirit, this study reviewed the
technological readiness and examined
environmental concerns related to com-
mercialization of photovoltaic energy
systems. The final report describes the
technical and commercial readiness of
photovoltaic energy systems; reviews re-
fining, fabrication, installation, operation
and maintenance, and decommissioning
alternatives associated with the industry;
identifies methods which are likely to be
used to reduce pollutant release; de-
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scribes environmental regulations that
are or might be applied to an installed
industry; and examines the hazard poten-
tial of wastes generated during the refin-
ing of specific materials and the fabrica-
tion of different photovoltaic cell types.
The information presented is based upon
an extensive analysis of the literature,
supplemented by discussions with dif-
ferent individuals in the governmental
and private sectors.
Of the several phases in the life cycle of
photovoltaic systems, the refining of
materials and subsequent cell manufac-
ture were most intensively examined be-
cause they represent the major steps
from which pollutants are released. Waste
streams and pollution control methods
for the following three different photo-
voltaic systems were considered: (1.)
silicon n/p cells produced by ingot
growing; (2.) silicon metal/insulator/
semiconductor cells produced by ribbon
growing; (3.) cadmium sulfide/copper
sulfide backwall cells produced by spray
deposition. These three systems cover a
range of manufacturing options and
materials likely to be used in near-term
commercialization activities.
Measurements of waste streams from
existing manufacturers of photovoltaic
devices are not publicly available, and
therefore design engineering studies of
expected typical facilities were prepared.
From these, sources and types of pollu-
tants were estimated for each of the
production processes, as well as from the
installation, operation and maintenance,
and decommissioning of photovoltaic sys-
tems. Estimates were based on a 10
MWp/year plant and for a national annual
production rate of one gigawatt peak.
Plant emission rates are presented on a
kg/day basis and provide background
information for personnel engaged in
pollution control permitting programs.
Estimates presented on a per GWp basis
reflect national production rates in 1990
and should be more useful for adminis-
trators in determining research and regu-
latory priorities.
Conclusions
Large growth in the photovoltaics in-
dustry is expected in the next two de-
cades. In the year 2000, it is estimated
that total installed capacity will range
from (0.2 to 2.0) x 105 MWe. A variety of
materials and cell concepts are now
being examined for use in different mar-
kets: small-remote (10 kWp) for non-grid-
connected applications, and small (10
kWp) to large (100 MWp) systems for use
in residences, commercial and industrial
settings, and central-station electricity
generation.
Single-crystal silicon cells are current-
ly produced commercially and serve as
the standard of comparison for new
materials and concepts being developed.
Production of these cell types is costly;
several alternatives are being investi-
gated. Processes near commercial appli-
cation include both ingot casting and
ribbon growing for use in semicrystalline
silicon solar cells. Inexpensively pro-
duced thin films from such specialized
materials as cadmium sulfide/copper sul-
fide, polycrystalline gallium arsenide, and
amorphous silicon have the potential to
yield photovoltaic cells at comparatively
low production costs.
Presently, specific emission standards
for this industry do not exist, and regu-
lations on existing facilities range from
none to specification of methods of
hazardous waste disposal. Standards
developed for related industries, pro-
cesses, or for specific pollutants, may
affect control technology requirements in
this industry. Potential requirements
under review by the EPA include National
Emission Standards for Hazardous Air
Pollutants (NESHAPs) for arsenic and
possibly cadmium, and New Source Per-
formance Standards (NSPS) for particu-
lates from electric arc furnaces and vola-
tile organic compounds from degreasing
operations; Clean Water Act effluent limits
applicable to the electronics industry;
and. Resource Conservation and Recov-
ery Act standards for control of a variety of
specific toxic and hazardous wastes, in-
cluding a numberfrom electroplating and
degreasing operations.
Estimates of uncontrolled emission
rates from production of silicon ingot
photovoltaic cells are presented in Table
1. Similar tables of pollutant emission
rates are presented in the full report for
cadmium sulfide and silicon ribbon cell
production processes.
Results of the completed analyses
suggest that several processes could
emit potentially large quantities of pollu-
tants. Large quantities of fine particulates
are discharged from electric arc furnaces
in producing metallurgical-grade silicon
(MG-Si) for a number of uses (e.g., in
semiconductors). However, silicon de-
mand by the photovoltaic industry repre-
sents only a small fraction of total prc-
ducton and therefore is not expected to
result in a significant increase in these
emissions. Further refinement of MG-Si
by existing techniques consumes large
quantities of hydrochloric acid, which
must ultimately be disposed of. Etching
of single-crystal silicon ingots generates
large quantities of spent acids, including
hydrofluoric, which may require controll-
ed disposal. Plasma etching may eliminate
the need to use wet etching processes.
Silicon ribbon production, as hypothe-
sized, is a much cleaner production pro-
cess than ingot growing. Nevertheless,
small quantities of solvents and silver-
based inks may require careful control.
Cadmium sulfide photovoltaic cell pro-
duction is characterized by the use and
release of cadmium and the production of
large quantities of spent plating solu-
tions containing various metals. These
may require controlled disposal.
Table 2 summarizes control alterna-
tives that may be used in this emerging
industry. Because of the widespread use
of many of the materials in other indus-
tries, available control experience and
technologies may ultimately be applied
to the photovoltaics industry. The final
degree of control is likely to be more
precisely defined by specific design en-
gineering studies seeking compliance
with specific standards.
Other processes may emit small quan-
tities of more exotic pollutants (e.g.,
boron trichloride, phosphorous oxychlo-
ride, phosphine) which will probably not
be directly controlled unless significant
health hazards are identified. To the
degree that processes are integrated
within plants and automated, controls
implemented to reduce major pollutant
waste streams may also reduce discharges
of these more exotic pollutants.
The most significant environmental
problems in operation of photovoltaic
devices are expected to be associated
with large central-station applications.
Herbicides may be used to control plant
growth near photovoltaic arrays. Also, it
has been speculated that these facilities
may produce micro- or meso-scale
changes in the physical environment.
Subsequent effects on species diversity,
standing biomass, wind, temperature,
and humidity have been hypothesized.
Decommissioning of broken or de-
graded photovoltaic systems will gener-
ate large quantities of solid waste. Most
of these wastes will be nonhazardous and
can be disposed of in a landfill or recycled.
Disposal of spent photovoltaic devices
containing cadmium may present unique
problems. Centralized collection by a
utility owning a central-station array or
maintaining a large number of decentral-
ized systems will probably require dis-
posal in controlled landfills. Decentral-
ized disposal by individual homeowners,
however, could result in the release of
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Table 1.
Activity
Silicon
Production
Cell
Manufacture
Pollutant Emission Rates from
Process
Step
Carbothermic
Reduction of
Silica
Silicon
Purification
by Siemans
Process
Silicon
Purification
by Union
Carbide
Process
Ingot Forming
and Doping
Wafer Cutting
and Etching
the Production of Silicon Ingot
Pollutant
SiO as SK)2
Ash
CO
Si/icon dust loss from
size reduction
Distillation
bottoms (SiC/jJ
Noncondensibles
(hydrogen)
Vapor Deposition by-
product (63% SiClj)
Silicon dust loss from
size reduction
Waste settler discharge
(79% SiCIJ
Filter waste stream
(43% H2, balance
chlorosilanes)
Stripper overhead
(73% chlorosilanes)
Product melter loss
(Silane and hydrogen.
Argon not included)
Dust loss from crushing
BC/3
Crucible scrap (Si)
Silicon chips and dust
Slurry (oil, clay, and SiC)
Photovoltaic Cells
Medium
Vapor
Vapor
Vapor
Vapor
Liquid
Vapor
Liquid
Vapor
Liquid
Vapor
Vapor
Vapor
Vapor
Vapor
Solid
Solid
Liquid
(kg/Day*) /Plant
1,377
33
5,895
0.51 - 1.06
1,160-2,000
283
8,753
3.5
369
38.6
27.6
2.3
1.7
0.0009
25.7
197
30.6
(MT/YR) /GWp
48, 180
1,140
206,340
18-37
40,600 - 70,000
9,900
306,370
124
12,921
1,351
965
81
60
0.031
900
6,890
1,070
Etching liquor (12% SiF4
88% mixed acids)
Etching vapors (hydrogen
rate given, but also
some fraction of liquor
Liquid
1,647
57,640
Junction
Formation
Wafer Edge
Grinding and
Etching
Electroless
Plating and
Soldering
Application of
Ant/reflective
Coating
Testing,
Interconnecting
and Encapsulating
vaporized}
POC/s dopant
Si/icon dust (under
water spray)
Etching liquor
(mixed acids)
Etching vapors
(SiF4 and H^
Spent Ni plating
solution
Acetone
Photoresist
(urethane varnish
and titanium dioxide)
Rinse water
Exhaust (60% HCI, 33%
SiH2C/2)
Si3N4 deposit
on reactor walls
Vapor
Vapor
Liquid
Liquid
Vapor
Liquid
Liquid
Liquid
Liquid
Vapor
Solid
NEGLIGIBLE
7.7
0.0009
1.7
(?)
42.3
85
61
21 L
28
0.15
0.013
270
0.03
61
m
1,480
2,990
2,140
[740 m3]
1,000
5.2
0.45
"Plant Capacity 10 MWp/yr., and 350 working days/yr.
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Table 2. Review of Control Technology Alternatives
Media/Category Pollutants
Control Technology
Comments
1. Atmospheric
./. 7 Gas - Combustible
1.2 Gas - Other
1.3 Dust
2. Liquid
2.1 Acid
2.2 Metals
2.3 Other
3. Solid
3.1 Hazardous
3.2 Nonhazardous
CO, H, Chlorosilanes
BCI3, POC/s, PH3, acids,
solvents, (HCN)*, F
Metals, Si, Cd,
HF, HCI, Acetic,
HN03, H2S04
Cd, Cu, As, Ni, Si
Chlorosilanes, solvents, slurry,
cutting oils
Cd, F and other compounds
Si compounds
CO combustion, air dilution,
Chlorosilanes combustion to
form muriatic acid
Air dilution, treat in lime scrub-
ber and discharge liquor to lagoon
Bag filters or cyclones
Neutralization
Flocculation (lime, alum, ferric
salts, polyelectrolytes)
Process revisions, distillation
Three alternatives - resale, re-
cycle, disposal in controlled
landfill
Resale or disposal in municipal
landfill
Technology commonly employed;
limits must be identified.
Design studies required
to achieve limits.
97 to 99% removal.
Impervious lagoon, overflow
liquid may be hazardous; sludge
will be hazardous.
Flocculation technique must be
identified. Effective standards
must be met and sludge will
require control.
Chlorosilanes could be feedstock.
Metals and F noted under RCRA
guidelines.
*HCN may be a by-product of CdS cell production.
small quantities of cadmium to the at-
mosphere (from combustion at municipal
incinerators) or to terrestrial and aquatic
systems (from disposal in municipal land-
fills).
Recommendations
On the basis of this analysis, the fol-
lowing topics may require further investi-
gation:
(i) Measurement of Existing Waste
Streams - Analyses of risks from
photovoltaic energy systems are
based upon design engineering
estimates of wastes emitted from
expected typical facilities. Sampling
and chemical analyses from existing
facilities are required to support the
findings of these engineering stud-
ies or to identify inadequacies.
(ii) Regulation of Existing Industry -
At the present time, efforts to
control wastes from the existing
industry vary. Some state and
county officials engaged in the
regulation of the existing indus-
try need information relating to
problems likely to be encount-
ered, and methods which could
be employed to control these prob-
lems. A large number of regulations
exist, or are being developed, for
related industries, processes, and
pollutants. The potential applica-
bility of these regulations to this
industry needs to be examined in
greater detail.
(iii) Technology Transfer - Manufac-
ture of photovoltaic devices may
require use and disposal of large
numbers of chemicals; some may
be toxic or hazardous. Control
experience obtained for these ma-
terials in related industries should
be made available to manufactur-
ers of photovoltaic systems before
facilities are actually constructed.
Design engineering studies and
field application of control tech-
niques may ultimately be required
to demonstrate their cost-effec-
tive applicability to this industry.
(iv) Evaluation of New Processes -
Alternative materials and fabrica-
tion processes are being rapidly
developed. Environmental data,
however, are not being assembled
at the same rate. Thus, existing
knowledge about processing tech-
niques, materials, and potential
control methods is limited. On-
going efforts are required to elimin-
ate this void. Identification of con-
trol needs, prior to full-scale com-
mercialization of these new tech-
nologies, can reduce total design
engineering cost while minimizing
potential health and environment-
al risks.
(v) Micro- and Meso-scale Biological
and Climatic Effects - A number of
analysts have suggested that opera-
tion of large central-station photo-
voltaic plants in the Southwest may
create micro- and meso-scale ef-
fects on biological communities
and climate. Research and analysis
are required to evaluate the mag-
nitude of these risks.
•&U. S. GOVERNMENT PRINTING OFFICE:1983/65S»-095/590
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PaulD. Moskowitz, Paige Perry, and Israel Wilenitz are with Brookhaven National
Laboratory, Upton, NY 11973.
Benjamin L. Blaney is the EPA Project Officer (see below).
The complete report, entitled "Photovoltaic Energy Systems: Environmental
Concerns and Control Technology Needs," (Order No. PB 83-137 380; Cost:
$10.00, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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