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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