United States
                    Environmental Protection
                    Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
                    Research and Development
EPA-600/S7-83-021  Apr. 1983
SERA          Project  Summary
                    Preliminary Assessment  of  the
                    Use  of  Heat  Transfer  Fluids  for
                    Solar  Thermal  Energy  Systems

                    Stephen E. Petty, Bobi A. Garrett-Price, and Gary L. McKown
                     This report contains a preliminary
                    assessment, based on available data, of
                    the extent to which various materials
                    will be used as heat transfer media in
                    solar energy  systems  and  of
                    mechanisms for  their release  to the
                    environment. The emphasis is on solar
                    thermal energy systems for industrial,
                    agricultural and electrical production
                    applications over the next 5-10 years.
                    The study provides an assessment of
                    consequences  associated  with
                    transport and fate of the materials in the
                    environment, identifies available
                    pollution  control techniques, and cites
                    areas where further research may be
                    required.
                     This Project Summary was developed
                    by EPA's Industrial Environmental He-
                    search Laboratory, Cincinnati,  OH, to
                    announce key findings of the research
                    project that is  fully documented in a
                    separate report of the same title (see
                    Project Report ordering information at
                    back).

                    Introduction

                     Over the next  5  to  10 years,  the
                    potential  exists for  widespread
                    deployment of concentrating solar
                    thermal  energy systems using high
                    molecular weight hydrocarbons, silicone
                    oils, and other heat transfer agents. The
                    use of such materials could result in
                    significant insult to the environment if
                    leaks, spills, or other releases occurred.
                    The purpose of the present study is to
                    assemble background information on the
                    anticipated use of  heat transfer fluids in
                    solar  energy systems and to determine
                    pathways by which fluids could enter the
                    environment.
  The report  describes  the types  of
concentrating solar energy collectors that
are likely to be used during the 1980s and
1990s  and  the  conventional  energy
systems  which  they  may  replace.
Emphasis  is placed on solar collectors
operating at temperatures above 100°C,
because they frequently require special
heat transfer fluids.
  The study determined  the extent  to
which solar energy development would
result in increased production of  heat
transfer fluids. It also identified the rates
at which leaks and spills could occur
during the manufacture, transport, use,
and disposal of these fluids and compared
these rates with those for general use of
heat transfer fluids. In addition, the study
analyzed transport mechanisms for fluids
once they entered the environment and
existing techniques for controlling  fluid
release. The study did not examine the
toxicity of heat transfer fluids.

Findings and Conclusions
Estimates of Solar Thermal
System Development
  It is projected that the primary United
States markets  for  solar thermal
applications will require  approximately
6.5 x 1017 joules (0.62 quads) of energy
annually in the latter half of the 1980s. Of
this, the greatest demand is expected for
supplying electricity to displace peak-load
gas and oil units. Some demand is antici-
pated in southern California for enhanced
oil recovery. During the 1990s,  it  is
estimated that solar thermal applications
will supply 1.2 x 1018 joules of electric
power and 1.0 x 1018 joules of industrial
process heat (IPH).  Siting  of these
facilities will be predominately in the

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Southwest and Hawaii, although some
plants may be installed in the South and
Southeast.
  During  the  1980s  and 1990s, it is
expected that water and water/glycol-
based  heat  transfer  fluids  will  be
displaced  by hydrocarbon and  silicone
oils  as  the chief  heat transfer fluids.
Some electric generating stations may
use molten salts or liquid sodium.
  The extent  to  which  solar  thermal
energy development will place a strain on
current  production of heat transfer fluids
is dependent upon the types of fluids used
and   upon  how  rapidly the   energy
technology is deployed.  The projected
demand of 1.0 x 10'8 joules for IPH in the
1990s would require quantities of com-
mercially  available,  non-aqueous heat
transfer fluids (such as Dowtherm and
Therminol) that are one or two orders of
magnitude above present-day production
capacities for any one fluid. However, the
quantity of heat transfer fluid  is only a
fraction of today's production  rates for
more common materials such  as  the
glycols. In either case, it is anticipated
that the ten-year lead time  available to
increase production  before  widespread
deployment of solar systems should allow
for orderly development of new manufac-
turing facilities to meet demand.

Source of Spills
  Heat  transfer fluids can enter  the
environment  as a result  of leaks and
spills. In terms of volume,  the  annual
spillage or leakage of heat transfer fluids
in the 1980s will be small. The greatest
loss  of fluid is expected to occur during
fluid transfer and transport, situations for
which containment of large spills may be
difficult. Since most solar systems will be
located  in the Southwest while many
heat  transfer fluid producers are in  the
East, the  spillage  rate during transport
may be  above average.
  Heat transfer fluids can enter the envi-
ronment as a result of leaks and spills. In
terms of volume, the annual spillage or
leakage of heat transfer fluids in  the
1980s  will be small. For  1990, it is
estimated that annual  spillage rates on
the order of  16,000 kg/year will occur
from manufacture, transfer, use, and
storage operations. Thus, spillage of all
heat  transfer  fluids  used  for solar
systems in 1990 would be comparable to
the  annual spillage at an  oil  refinery
which  processes  100,000  barrels  per
day.
  Spillage and leakage are  expected to
account for less than 20 percent of the
volume of fluid lost during the life cycle of
a solar power site. Most of this loss will be
from storage facilities, where spills can
be  controlled with  containment
structures.
  It is concluded that a relatively small
volume of fluid will be released from the
use of solar energy for industrial process
heat or moderate power applications. For
the fluids which will be used in the 1980s,
no engineering problems were found in
this study that could not be addressed and
solved by careful attention to potential
environmental  effects  during  design,
operation,  and  maintenance  of solar
thermal systems.
Environmental Transport
and Fate
  The potential for migration in  the
environment varies  depending on  the
heat transfer fluid being used. A majority
of the solar system designs being consid-
ered for the near term make use of fluids
such  as water or water-glycol mixtures
which are  quite mobile  in the environ-
ment.
  The other principal fluids— silicone and
organic  hydrocarbons—are  generally
quite low  in  mobility.  However,  data
related  to  environmental  mobility  are
incomplete or unknown for a number of
materials that  have been proposed.
  In many cases, heat transfer fluids can
be disposed of readily by standard tech-
niques. However, the lack of toxicity data
for some fluids suggests that the use of
special disposal techniques (e.g., secured
landfills)  may be  indicated  by  future
research. Inert, inorganic fluids such as
silicones will  need  to  be confined  in
containers, since they are not amenable
to biological or thermal degradation.
  Heat transfer  fluids tend to be high
molecular  weight,  non-volatile
compounds and  mixtures. Therefore, air
pollution is not  generally a significant
factor   in  evaluating  potential
environmental impact. Thefluorocarbons
are an exception to this  rule. However,
fluorocarbons have been considered only
in a  few designs of large-scale or high-
temperature   systems,   and  potential
impacts are thus expected to be low.

Recommendations
  Based on the findings of this study, a
number of  areas were identified where
incomplete  knowledge   exists  of  the
factors influencing  the  impact of heat
transfer fluids on the environment. The
areas described below are considered to
be the most important ones to address in
further research on the use of these fluids
in solar energy systems.
    It is recommended that specific studies
  be instituted to explore toxic effects and
  migratory  potential  of those  materials
  judged  to be primary candidates for use
  as heat transfer fluids. Toxicity studies of
  the actual fluids, as well as of their major
  constituents,  are   needed.  Migration
  effects  should be evaluated by octanol-
  water  partitioning  and soil column
  leaching  determinations  for  those
  materials for  which  such data are non-
  existent.
    Since few of the solar system designs
  that have  been  proposed have reached
  the demonstration stage, periodic studies
  to  reevaluate  environmental   impact
  potential need to be continued. This is
  particularly true since the environmental
  effects  of currently proposed fluids vary
  widely,   and   since  widespread
  deployment of any  given  system may
  occur rapidly if the demonstration phase
  is  successful. A  continuing program to
  evaluate  potential  for  environmental
  insult should  be  planned to parallel the
  demonstration efforts.
    Since the evaluation of potential envi-
  ronmental  impact is  nearly always only a
  secondary   objective  of  solar  energy
  research and development programs and
  sponsoring  agencies,  EPA should
.  consider continuing  support  of  timely
  studies that focus on that  aspect. This
  would  provide   assurance  that
  environmental effects are properly con-
  sidered, while allowing the  developer to
  focus attention on system development.
    Finally, a study is needed of the  impact
  of pollution control  and environmental
  monitoring   on  design,   siting,  and
  operation of solar energy systems. This
  exercise  would   include   cost-benefit
  analyses and  an evaluation  of  impact on
  projected  deployment schedules  that
  result  from  applicable  laws  and
  regulations.  Such an analysis may be
  critical  to shaping environmental policy
  and to arriving  at overall  economic
  analyses for an industry which currently
  appears to have only  marginal profit
  potential.

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     Stephen E. Petty, Bob/A. Garrett-Price, and Gary L McKown are with Battelle-
       Pacific Northwest Laboratory, Richland, WA 99352.
     Benjamin L. Blaney is the EPA Project Officer (see below).
     The complete report, entitled "Preliminary Assessment of the Use of Heat Transfer
       Fluids for Solar Thermal Energy Systems," (Order No. PB 83-170 597; 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
       iHJ.S.  Government  Printing  Office:  1983-659-017/7053
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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