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
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300

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