Concentrated solar radiation is now a viable alternative source for many advanced manufacturing processes. Researchers at the National Renewable Energy Laboratory (NREL) have demonstrated the feasibility of processes such as solar induced surface transformation of materials (SISTM), solar based manufacturing, and solar pumped lasers. Researchers are also using sunlight to decontaminate water and soils polluted with organic compounds; these techniques could provide manufacturers with innovative alternatives to traditional methods of waste management. The solar technology that is now being integrated into today's manufacturing processes offer greater potential for tomorrow, especially as applied to the radiation abundant environment available in space and on the lunar surface

Clyne, Richard J.

Hauser, Steven G.

Murphy, Lawrence M.

English

NASA Technical Reports Server

N92=22448
MANUFACTURING WITH THE SUN
Lawrence M. Murphy
Steven G. Hauser
and
Richard J. Clyne
National Renewable Energy Laboratory
(formerly the Solar Energy Research Institute)
1617 Cole Blvd.
Golden, CO 80401
ABSTRACT
Concentrated solar radiation is now a viable ahemative energy source for many advanced manufacturing
processes. Researchers at the National Renewable Energy Laboratory (NREL) have demonstrated the feasibility
of processes such as solar-induced surface transformation of materials (SISTM), solar-based manufacturing, and
solar-pumped lasers. Researchers are also using sunlight to decontaminate water and soils polluted with organic
compounds; these techniques could provide manufactures with innovative alternatives to traditional methods of
waste management. The solar technology that is now being integrated into today's manufacturing processes
offers even greater potential for tomorrow, especially as applied to the radiation-abundant environment available
in space and on the lunar surface.
INTRODUCTION
Researchers at the Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL) are
developing advanced manufacturing processes that are powered by the sun. These processes are offering
industry viable alternatives for accomplishing many of today's manufacturing tasks, and they are likely to be a
key ingredient in solving energy problems in tomorrow's advanced manufacturing environment. The advanced
solar manufacturing research is managed through NREL's Mechanical and Industrial Technology Division, which
is dedicated to bringing American industry practical renewable alternatives that reduce or replace fossil-fuel-
based sources of energy.
Currently, the most promising results related to materials manufacturing have come from using
concentrated solar radiation to modify the surface properties of materials used in advanced technology
applications. Applications such as transformation hardening of steel, cladding, self-propagating high-temperature
synthesis, thin-film deposition, and electronic materials processing have been successfully demonstrated and
analyzed at NREL.
The advanced manufacturing research is centered around NREL's high-flux solar furnace, which can
achieve solar intensities of up to 50,000 times normal ambient conditions. While using directed energy beams
for advanced manufacturing has been understood and integrated in certain applications for more than a decade,
researchers are now demonstrating that solar-energy-based processes are economically competitive with
traditional methods of materials processing [1].
These processes are also environmentally benign, as all the energy driving them comes directly from the
sun. High levels of energy efficiency are achieved because the energy conversion steps inherent in traditional
processing--fossil fuel to heat, heat to electricity, electricity back to heat--are eliminated. Reflected,
concentrated solar flux is applied directly to the materials being processed.
NREL researchers are also investigating solar-based methods to reclaim process water contaminated
with organic compounds. This solar detoxification process uses sunlight in combination with a photocatalyst to
destroy aqueous volatile organic contaminants. In the near future, as early as the middle of this decade, this
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process could be a viable waste management technique to cleanse water used in manufacturing processes and to
reclaim polluted water.
NREL's HIGH-FLUX SOLAR FURNACE
New techniques for manufacturing advanced materials are being explored through the use of NREL's
solar furnace. The solar furnace began operating in early 1990 and allows researchers to study the properties and
applications of very high solar flux. The facility currently has the ability to produce solar flux densities of up to
50,000 suns (5000 W/cm2). This upper limit rose dramatically recently with a new first-of-its-kind concentrator
design. New research directions and applications for this promising technology are continually being discovered.
Figure 1 shows the physical configuration of the solar furnace. The heliostat tracks the sun and reflects
incoming solar energy onto the stationary primary concentrator, which consists of 23 individual curved facets
(see Figure 2). These facets collectively focus the solar flux at a point in the test facility, which is located just
off the primary ,'txis. The long focal length of the primary concentrator produces a 10-centimeter-diameter
concentrated beam of approximately 2,500 suns at the center of the target area. When a secondary concentrator
is placed at the beam's focus, the peak flux can be increased 10 to 20 times, the upper limit applying to
dielectric-filled secondaries.
Three performance characteristics put the solar furnace at the cutting edge of solar industrial process
research. The first is the system's ability to produce very high temperatures directly from the sun. (For
example, we have melted through a 2-inch alumina fire brick, which has a melting point of 1800°C, in less than
1 minute.) The second is the extremely high rate of heating made possible by very high solar flux. In certain
applications this rate exceeds 1 million degrees Celsius per second. These heating rates produce thermal
conditions attainable only through radiant heating processes. The third characteristic is the furnace's ability to
deliver the entire solar spectrum (from 300 to 2500 nanometers); this allows researchers to study applications
requiring either broad spectrum radiation or a particular frequency, ranging from the infrared to the near-
ultraviolet.
-- = =
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• f/¢/ s,/
fI 1 w/_,_i,_il r ,-
Figure 1. NREL's high:flux solar furnace.
Left: Schematic view of system operat|on,
Right: The actual facility located on South Table Mountain in Golden, Colorado.
218 ORIL_INAL PAf"_,-E
Ji.ACK AND WHITE PHOTOGRAPh
MATERIALS PROCESSING APPLICATIONS
Materials processing is a major area of
research at NREL's high-flux furnace facility.
Specifically, research pertaining to the solar-induced
surface transformation of materials (SISTM), which is
ideally suited to the high-flux environment created by
the solar furnace, is at the center of these studies.
SISTM research uses the thermal energy (as opposed
to the photochemical energy) produced from solar
radiation. The key to SISTM is the rapid, controlled
heating that alters the surface of a workpiece without
affecting its base properlies. The processes we are
developing can be carried out without consuming
fossil resources ,and without producing a host of
environmental liabilities.
NREL researchers are refining ways to use
solar energy to produce surface modifications that are
critical to a number of materials technologies
including hardening, cladding, chemical vapor
deposition, and the manufacture of electronic
components and circuitry. These are currently being
fabricated using electron beams, arc lamps, lasers,
and induction heating. Preliminary economic
analyses indicate that concentrated solar flux, when
used in large-scale production applications, could
produce these materials at one-half to one-quarter of
the cost of production associated with the
conventional radiant methods in use today.
The transformation hardening of steel is
typically accomplished using lasers and is being
applied most noticeably in the automotive industry for
hardening drive-train components. Researchers at NREL
have demonstrated that steel
can be hardened using solar
energy, and have shown that
the process is competitive
with laser-based techniques
[2]. Hardened steel consists
of a hard, wear-resistant
layer surrounding a softer,
steel core. Figure 3 shows a
hardened steel sample
produced in the high-flux
furnace.
Using solar radiation
to clad preapplied powders to
steel substrates has generated
a considerable amount of
industrial interest. Solar
cladding produces excellent
Figure 2. The primary concentrator of NREL's
solar furnace. The 23 enhanced-aluminum front-
surface mirrors focus the reflected solar flux to a
10-cm-diameter beam inside the test building (not
shown). The reflection of the heliostat, which
tracks the sun and directs its energy to the
concentrator, is shown.
,i
........... .........................} ...................:......:: ...! ...........................
Figure 3. Cross section of solar-hardened steel. The fully hardened
region is 1 to 2 mm deep and about 20 mm in diameter.
219 ORIGINAL PAGE
BLACK AND WHITE PHOTOGRAPH
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t:tt_.CK AND WFIITEPHOTOGRAPH
Figure 4. Photomicrographs of alloy coatings formed by solar melting of preapplied powders on steel
substrates. Note the high density of the coatings and the good metallurgical bonds between the coatings
and their substrates. The images show an area measuring approximately 600 lam by 400 lum.
metallurgical bonds between the melted powder and the substrate. The desirable properties of an expensive
material such as a superalloy can be economically obtained by cladding relatively small amounts of this material
to a less expensive substrate base such as mild steel. Figure 4 shows microgmphs of solar-clad materials.
Concentrated sunlight is being applied to a number of chemical vapor deposition processes. Chemical
vapor deposition consists of generating sufficient levels of heat on or near the surface of a given workpiece in
the presence of selected gaseous reactants. The heat causes the reactants to form solid products on the surface.
Solar furnace technology is well suited to this process because the surface heating can be closely controlled,
eliminating the formation of solid product on surfaces other than the specific material of interest. NREL is
investigating the chemical vapor deposition process for the production of TiN, TiB z, SiC, and hard carbon films.
Rapid thermal annealing (RTA), a process that uses radiative heat to accomplish diffusion processes or
to remove defects from delicate electronic components such as semiconductors, has tradition_ly relied on
tungsten-halogen lamps as the source of energy. The high level of control required for RTA is easily obtained
using concentrated solar radiation; the solar furnace meets the precise requirements of this process. Depending
on the materials being annealed, the solar furnace rapidly heats a workpiece to operating temperature and
provides the required thermal treatment. RTA studies conducted at NREL's solar furnace include producing
high-temperature superconductor films on substrates such as SrTiO 3, ZrO 2, and MgO.
SOLAR-PUMPED LASER APPLICATIONS
Recent advances in secondary concentrator systems are causing researchers to reevaluate using
concentrated solar flux to pump lasers. The concept of solar-pumped lasers has been studied for more than two
decades, but low beam concentrations limited the conversion efficiencies to approximately 1%. With the upper
bounds of attainable concentration now approaching 50,000 suns, conversion efficiencies are approaching 5%,
which offers the potential for both high power and high efficiency for several types of lasers [3].
A solar-pumped laser would have all the performance characteristics of traditionally powered devices,
and a demonstration of a 5%-efficient solar-pumped laser should occur in mid-1992. Researchers are developing
innovative applications for solar-pumped lasers, such as the destruction of toxic compounds (polychlorinated
biphenyls, PCBs) and the manufacture of inorganic high-value substances (ceramic carbides and borides) [3].
220
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DESTROYING CHEMICAL WASTES
ORIGINAL P.__t-"
BLACK ANi._ _"',"i-tIr'_;:-_i-_,'.)TOGRAP[4
NREL researchers are studying two distinct
solar-based methods to destroy hazardous
environmental waste. The first process--the solar
detoxification of water--uses low solar concentrations
to breakdown organic compounds in contaminated
process water and groundwater. The second
method known as gas-phase detoxification--uses the
concentrated solar flux produced in the solar furnace
to destroy hazardous compounds that have been
desorbed from solids and exist in the gas phase.
The f'trst process destroys unwanted organic
compounds found in waste water or polluted
groundwater. The process works as follows: polluted
water is brought into contact with a semiconducting
photocatalyst, such as titanium dioxide, which in the
presence of sunlight creates highly reactive hydroxyl
radicals. These radicals react with the organic
compounds and convert them into water, carbon
dioxide, and easily neutralized mineral acids such as
hydrochloric acid. Because the process requires low
solar flux concentrations, the reaction can be initiated
using either flat-plate solar panels (one-sun
concentrations) or a transparent tube mounted at the
focus of a parabolic reflecting trough (up to 30-sun
concentrations). This latter design is shown in
Figure 5. This process is currently being field tested
at a Superfund site and could be available to industry
as a waste management tool soon.
Figure 5. Experimental solar decontamination
trough.
Gas-phase detoxification is a hazardous waste destruction method being applied to contaminated solids,
such as soils. This process, which is being studied at NREL's high-flux solar furnace, can use energy from
throughout the solar spectrum. Typically, a concentration of greater than 300 suns is required to drive the
reaction. During the process the contaminants are desorbed from the solid using either vacuum extraction or heat
(heat produced by the infrared portion of the solar spectrum can be used for this purpose). After being
desorbed, the contaminants are introduced into a reactor (shown in Figure 6) that is mounted at the focus of a
solar concentrator system. The near-ultraviolet portion (high-energy photons) of the flux then converts the
contaminants to end products such as CO 2, Ha0, and HCi. Catalysts are being studied that can greatly improve
the effectiveness of the process.
Both of these methods are remarkably efficient in destroying hazardous organic compounds (exceeding
the EPA's 99.9999% requirement), and neither produce the detrimental by-products associated with many of the
conventional waste remediation techniques [4]. By the latter part of this decade these methods could become
standard tools for decontaminating process waste water, soils, and other contaminated media.
SOLAR MANUFACTURING PROCESSES IN SPACE
The concentrated solar radiation applications that are now being proven and integrated into
manufacturing processes here on earth hold even greater potential for use in space. As we strive for a permanent
presence in space, the practical issues of energy logistics and efficiency will be crucial to the success of the
endeavor. Solar technology is remarkably well suited to supply a large portion of the energy needed in a
working space environment.
221
Concentrated solar
radiation technology would
produce greater efficiencies
in space th,'m attainable in
the terrestrial environment.
Available solar radiation
increases by 70% outside the
earth's atmosphere [5], and
the ultraviolet portion of the
spectrum expands down to
200 nm, providing more
energy for photolytic
interactions. Also, the direct
use of solar radiation would
employ a much smaller solar-
collecting system because of
the high efficiencies inherent
in the technology. For
exeanple, to attain the same
levels of usable power Ks a
direct solar beam system, a
photovolt_tic-driven ,arc lamp,
which experiences high
OR_GINA_ F A,3-E"
_LACK AND WHITE PNOTOG£APH
Figure 6. Solar gas-phase detoxification reactor.
energy losses converting
solar radiation to electricity, would require 10 times the amount of collector surface area; a photovoltaic CO 2
laser system operating at the same level would require a collector 25 times larger than that used for a direct solar
beam system. Additionally, the space environment would introduce complications in dissipating the excess heat
produced by these conventional technologies [6].
In addition to the surface modification applications discussed previously in the Materials Processing
section of this paper, a number of other applications are readily identified for using concentrated solar radiation
in a space environment. High solar flux could be applied to materials joining, welding, fabricating, repairing,
and surface cleaning operations. The technology could also be integrated in lunar mining operations to provide
bulk heating for extracting certain products from mined bulk materials. An artist's conception of a lunar-based
solar furnace is shown in Figure 7.
Water would be available in limited quantities in any space environment, and solar radiation could be
applied to extract water from human waste and reclaim water used in operating processes.
RESEARCH COLLABORATION AND TECHNOLOGY TRANSFER
The long-term success of NREL's research and development projects is tied to working closely with
industry and other outside research organizations.
NREL works with industrial partners through a variety of arrangements, including cost-shared demon-
strations, joint research, and Cooperative Research and Development Agreements (CRADAs). NREL technology
transfer is fostered through written material, presentations, workshops, training programs, and traveling exhibits.
Our participation in industry projects, and exchanges between our researchers and their industry counterparts,
also play an important role in disseminating technology advances.
Only through close cooperation and information exchange among researchers, manufacturers, and
operators will solar-based manufacturing processes continue to make inroads into U.S. industry.
222
Figure 7. Artist's conception of lunar-based solar furnace.
CONCLUSION
The solar-based manufacturing processes developed at NREL have advanced to the point where they can
be considered competitive energy alternatives for many conventional manufacturing applications. One of the
most attractive features of solar manufacturing systems is their immunity to fluctuations in the price of fuel;
operation and maintenance costs remain extremely stable over the life of a facility.
As this technology gains a foothold in the marketplace, other solar processes current,/ in the
developmental stage will mature. Certainly these advances will play a crucial role in the next generation of
advanced manufacturing technology, both on earth and in space.
REFERENCES
, Pitts, J.R., C.L. Fields, J.T. Stanley, and B.L. Peiton, "Materials Processing Using Highly Concentrated
Solar Radiation," Proceedings of the 25th Intersociety Energy Conversion Engineering Conference, Volume
6, American Institute of Chemical Engineers, 1990.
2. Stanley, J.T., C.L. Fields, J.R. Pitts, "Surface Treating with Sunbeams," Advanced Materials and Processes,
Vol. 138, no. 6, December, 1990.
3. Rosen, J., "Solar Furnaces: Concentrating 100,000 Suns," Mechanical Engineering, February, 1990.
223
, Gupta, B.P., J.V. Anderson, Solar Detoxification of Hazardous Waste: An Overview of the U.S. Department
of Energy Program, Solar Energy Research Institute, SERI/TP-253-3959, August 1990.
5. Riorden, C.J., D.R. Meyers, R.L. Hulstrom, Spectral Solar Radiation Data Base Documentation r Volume II,
Solar Energy Research Institute, SERI/TP-215-3513B, July, 1989. This figure assumes 1367 W/m z mean
direct normal radiation at earth orbit and air mass 0, and 800 W/m 2 direct normal availability at air mass
1.5 for the southwestern United States.
6. Pitts, J.R., T. Wendelin, J.T. Stanely, "Applications of Solar Beams for Materials Science and Processing in
Space," Proceedings of the 25th Intersociety Energy Conversion Engineering Conference TVolume 1,
American Institute of Chemical Engineers, 1990.
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