Journal of Power and Energy Engineering, 2013, 1, 29-39 Published Online December 2013 (
Copyright © 2013 SciRes. JPEE
Demonstra tion of Pil ot S cale Large Aperture Pa rabolic
Trough Organic Rankine Cycle Solar Therm al Power
Plant in Louisiana
Jonathan R. Raus h1, Terrence L. Chambers1, Ben Russo2, Kenneth A. Ritter III1
1College of Engineering, University of Louisiana at Lafayette, Lafayette, USA; 2CLECO Power LLC, Pineville, USA.
Received August 2013
During the calendar year of 2012 the University of Louisiana at Lafayette in conjunction with CLECO Power LLC
(CLECO) has constructed and commissioned a pilot scale parabolic trough solar thermal power plant for the first time
in Louisiana. The large aperture trough (LAT) solar collectors were provided by Gossamer Space Frames and are
coupled with an organic Rankine cycle (ORC) power block provided by ElectraTherm, Inc. for study of the feasibility
of cost-effective commercial scale solar thermal power production in Louisiana. Supported by CLECO and providing
power to the existing CLECO grid, the implementation of state-of-the-industry collector frames, mirrors, trackers, and
ORC power block is studied under various local weather conditions which present varied operating regimes from exist-
ing solar thermal installations. The solar collectors provide a design output of 650 kWth and preliminary actual perfor-
mance data from the system level is presented. The optimal size, configuration and location for such a plant in the given
solar resource region are being studied in conjunction with CLECO’s search for optimal renewable energy solutions for
the region. The pilot scale size of the facility and implementation of the simpler ORC allow remote operation of the
facility and flexibility in operating parameters for optimization studies. The construction of the facility was supported
by the Louisiana Department of Natural Resources, the U.S. Department of Energy, and CLECO. The continued opera-
tion of the plant is supported by CLECO Power LLC and the University of Louisian a at Lafayette.
Keywords: Concentrating Solar Power; Parabolic Trough; Solar Thermal; Organic Rankine Cycle; Power Plant
1. Introduction
The need for a diversified energy portfolio for stationary
power generation is widely accepted, and solar energy is
projected to provide a significant basis for this continued
diversification during the coming decades [1]. While sig-
nificant solar resource (greater than 6.0 kWh/m2/day)
exists in the southwest continental United States (US),
much of the country is covered by a band of moderate
solar resource (4.0 - 6.0 kWh/m2/day); it is in this band
that the US state of Louisiana resides. Currently, concen-
trating solar power (CSP) offers the most economical
commercial scale solar power option and there are many
examples of existing or planned commercial scale instal-
lations in areas of high solar resource [2]. There are very
few, however, commercial or pilot scale installations in
areas of moderate solar resource and none in Louisiana
[3]. The introduction of a pilot scale parabolic trough
solar thermal power plant in Louisiana will allow the
local demonstration of several key technical components
of solar power as well as further the field as a whole with
the development and validation of analytical models for
further planning and innovation. A pilot scale facility
would permit low-cost testing of various component tech-
nologies including concentrating solar collectors, thermal
storage, and power blocks. In addition, flexibility in op-
erational and testing configurations, including remote mo n-
itoring capabilities, would provide the opportunity for
generating the necessary data for development and vali-
dation of full scale analytical models and feasibility stu-
dies for the region.
2. Background
2.1. Project Development
The investigation of CSP installations in areas of mod-
erate solar resource is a need that has yet to be fully ful-
filled. In addition, the development of distributed genera-
tion, small scale (1 - 10 MW) solar installations offers
several potential advantages including savings in trans-
mission and distribution, improved reliability, and the
potential to offset retail costs of electricity as opposed to
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
wholesale [4]. On these scales, it has been suggested that
coupling a CSP installation with an organic Rankine cycle
(ORC) power block as opposed to a traditional Rankine
cycle power block is an attractive option [5,6]. In 2011,
the University of Louisiana at Lafayette was awarded a
grant through the Louisiana Department of Natural Re-
sources, originating from the US Department of Energy,
to design, install, and commission a pilot scale solar
thermal power plant. The construction and commission-
ing of the facility was completed during the 2012 calen-
dar year.
2.2. Solar Resource in Lou isiana
Louisiana resides in an area of the United States where
the solar resource is substantially less than that of the
current commercial scale CSP installations of the south-
west US [3]. Figure 1 shows a map of the US Solar Re-
source developed by the National Renewable Energy
Laboratory (NREL). Economical utilization of the solar
resource in this region would significantly increase the
footprint of viable areas for commercial development.
Louisiana has an average solar resource between 4 and 5
kWh/m2/day. NREL Typical Meteorological Year (TMY3)
data [7] resulted in a median peak direct normal irradi-
ance (DNI) for the 6 months beginning in April of 688
W/m2 for the Lafayette area, with a 15 percent error band.
While these levels are substantially lower than those of
the southwest US, the insolation still represents a sig-
nificant level of energy. Indeed, based on the existing
installed power capacity of Louisiana [8], one square
mile of installed CSP projects would generate about one
percent of the current capacity, based on a solar-to-elec-
tric efficiency of 20 percent.
2.3. Project Goals
The pilot solar thermal power plant was developed at the
CLECO Alternative Energy Center in Crowley, Louisi-
ana, and is operated by the University of Louisiana at
Lafayette with the aim of installing and operating a pilot
scale solar thermal facility for the first time in Louisiana.
The overarching goal of the installation was to encourage
the development, implementation and deployment of cost-
effective renewable energy technologies in Louisiana, to
support the creation of additional employment opportuni-
ties, and to stimulate market demand for other emerging
renewable energy systems. In addition, the research op-
portunities provided by the facility includ e the evaluation
of the feasibility and commercial viability of full scale
Figure 1. Concentrating solar resource of the US source: National renewable energy laboratory solar data center.
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
solar thermal power plants in Louisiana, the study of dis-
tributed generation facilities for small and medium-sized
municipalities, and to develop a laboratory where high
fidelity analytical models could be created and validated.
This project will also develop an accurate database of
solar DNI values where to date the best available data is
modelled from the NREL database.
3. Plant Design
3.1. Design Objectives
Several design objectives were identified in the devel-
opment of the pilot scale parabolic trough power plant,
while the major design constraints were issued by the
grant program. The primary objective was that a para-
bolic trough solar collector field was to supply thermal
energy to a power block for conversion to electricity.
This electricity was to be supplied to an existing power
grid. A secondary design objective was the inclusion of a
thermal storage system to act as a thermal buffer for in-
termittent cloudy periods or when the solar irradiation
exceeded design values. Installation of the thermal sto-
rage system had to be postponed, how ever, for bud getary
reasons. The major constraints (in addition to the con-
struction budget) were that all installed equipment were
to be commercially available at the time of construction,
and the net electricity produ ction was to be limited to 20
kW net to the grid. Due to the limited output of the pow-
er plant, it was determined that an organic Rankine cycle
(ORC) power block would be advantageous for several
reasons, including simplicity, reliability, low mainten-
ance, and remote monitoring [9]. This system would
have the advantages of utilizing medium and low grade
temperature thermal energy (66˚C - 260˚C or 150 - 500
˚F) and would operate at low pressures (less than 1380
kPa or 200 psig). Additional constraints included adhe-
rence to the “Buy America” provision of US Federal
procurement policy. Due to the geographic proximity to
the Gulf of Mexico, local design codes required a wind
load rating of 169 km/h (105 mph) for a three second
gust for the installed solar collectors.
3.2. Power Block Techn ology
The selected ORC power block was the Green Machine
series 4000 provided by ElectraTherm, Inc. The Green
Machine was designed to accept low grade temperature
water between 66 and 121˚C (150˚F and 250˚F) as the
thermal energy input and could produce up to 50 kW of
electricity (kWe); although the newest models are capa-
ble of 65 kWe. The Green Machine is one of the few
available ORC power blocks with power production ca-
pacity under 100 kW, which also made it an attractive
option f or t he facility.
The Green Machine utilizes R245fa as the organic
working fluid in a Rankine cycle and can be either dry
cooled or liquid cooled. For the current installation, due
to the availability of municipal water service, an evapor-
ative cooling tower was chosen as the cooling method. In
the Green Machine working cycle, the working fluid is
evaporated by heat exchange with the heat transfer fluid
(HTF) and then expanded in a twin-screw expander. The
twin-screw design provides low susceptibility to con-
densation and has low sensitivity to varying inlet condi-
tions [5]. The expander is directly coupled to an electric
generator producing 480 volts of AC power. Following
expansion, the low pressure vapor is condensed by heat
exchange with the cooling water and then accumulated
before being pumped through a pre-heater and back into
the evaporator. The hot water-to-refrigerant heat exchang-
er in the current model was designed for a hot water flow
rate of 379 - 758 l/min (100 - 200 gpm). The overall
thermal efficiency was expected to be about eight percent.
This means that at design load, the ORC would need to
be provided 6 50 kW of the rmal power (kW th) in orde r to
produce 50 kWe power. Utilizing this figure and the
minimum flow rate,
the desired temperature drop
(ΔT) through the ORC could be calculated from the clas-
sic equation [10]:
Q mC T= ∆
is the energy flux and Cp is the specific heat
of the fluid. From this it was determined that a 28˚C (50
˚F) ΔT through the ORC (and collector field) was re-
quired in order to provide the requisite 650 kWth energy
flux needed to produce the design capacity of 50 kWe.
3.3. Solar Collector Technol ogy
The selected solar collector technology was the large
aperture trough (LAT) parabolic trough solar collectors
produced by Gossamer Space Frames (GSF). The GSF
LAT, with an aperture of 7.3 meters, is the largest aper-
ture trough curre ntly available in commercial production.
The current installation represents the second demonstra-
tion facility for the LAT. The collectors utilize an all-
aluminum space frame which provides high rigidity for
improved accuracy while also minimizing weight. The
collectors also satisfied the local building codes for wind
load rating. The reflectors consisted of thin film polymer
technology provided by 3 M with silver as the reflective
Schott PTR70 heat collection element (HCE) tubes
with 70 mill imeter outs ide d iameter w ere e mployed which
result in an industry leading concentration ratio (the ratio
of the area of collected radiation to the area of concen-
trated radiation) of 104. Due to the design of the ORC,
water could be used as the HTF for the collector field.
NREL laboratory testing of the GSF collectors demon-
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
strated a slope error of less than 1.5 milliradian with ov er
99% intercept factor.
The LAT collector drives were designed for a single
solar collector assembly (SC A) consisting of 16 collector
frames, each 12 meters in length. For the current in stalla-
tion a loop was designed with 12 total collector frames;
two SCAs of 6 frames each were employed due to space
constraints. Additional key design parameters and me-
trics are listed in Table 1.
4. Installation
Construction of the facility began in June 2012 and was
completed in December 2012. Approximately one acre of
university property (4050 m2) was utilized. Ground prepa-
ration included leveling and grading with the collector
field installed on cast concrete pylon foundations. Col-
lector assembly and install were completed onsite with
local labor resources used for nearly all of the skilled and
unskill e d work.
5. Modeled Output
Figu re 2 shows the modeled output of the solar field per
loop based on DNI, and the TMY3 dataset. For the de-
sign output of 650 kWth, a summer DNI of about 800
DNI would be expected to be required to maintain a con-
stant output. Significant variability was expected due to
seasonal weather conditions. Figure 3 uses the TMY3
dataset to model daily output over the course of one year.
It should be noted the significant number of days fore-
casted with zero energy produced due to local weather
6. Preliminary Performance Data
In an effort to quantify the solar collector efficiency, a
local hourly measurement of the DNI was required. In-
stallation of a tracking pyreheliometer was completed in
mid-July, 2013. DNI measurements from the first full
Table 1. Plant characteristics.
Plant Location Crowley, LA
Yearly Direct Normal Solar 1590 kWh/m2
Plant Size (nominal) 50 kWe
ORC Gross Output 50 kWe
Solar Field Heat Transfer Fluid Water
Inlet Temperature 93˚C
Outlet Temperature 121˚C
ORC Working Fluid R245fa
ORC Design Point Efficiency 8%
Solar Field Size 1051 m2
Land Area 4050 m2 (1 acre)
Solar to Electric Design Point Efficiency 6%
Figure 2. Collector field output vs. DNI. Source: 3 M.
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
Figure 3. Modeled energy collected per day per loop. Source: 3 M.
month of installation resulted in an average daily peak of
771 W/m2. This compares to the TMY3 data 652 W/m2
for the same time period, or an 18 percent increase from
the predicted value. Figure 4 shows the measured solar
insolation in kWh/m2/day versus predicted data.
Due to the installation date, pyroheliometer data for
the local area was not available for the first six months of
operation of the sola collectors. During this period, the
local global normal irradiance (GNI) was measured manu-
ally with a DBTU1300 Digital Solar Power Meter by
General Tools which utilizes a silicone photovoltaic de-
tector. In order to generate a DNI data point, a DNI/GNI
ratio was employed. A review of the literature revealed
this ratio could range anywhere from 0.5 to 0.8 [11]. Al-
though more recent studies have shown the ratio to be
above 0.8, especially considering GNI values above 1000
W/m2 [12]. Kurtz, Muller, Marion, and Emery found a
ratio of 0.78 for GNI values between 975 and 1025 W/m2
in a study of 30 different sites [12]. This range (975 to
1025 W/m2) closely approximates the GNI values found
for the days presented in this paper and thus the ratio of
0.78 was used to determine the DNI when direct meas-
urement was not available.
Figure 5 gives the temperature distribution through
the collector field vs. time for a typical day in April,
2013. Several peaks can be identified where one SCA
was defocused in order to prevent temperatures in excess
of the high temperature limit of the ORC. The apparent
noise (rapid fluctuation) in the temperature measurements
was possibly due to two phenomena. First, upon start-up,
regions of fluid in the collector field were significantly
hotter than fluid in the balance of plant and in the piping
cross-over between SCAs. This is due to the secondary
reflection of solar radiation onto the receiver tube even
while not tracking. Without a thermal buffer in the sys-
tem, there exists a period of time for the regions of
higher temperature fluid to diffuse into the remaining
areas, so that the temperature was uniform throughout the
system. The second reason for temperature fluctuations
was the continual balancing of the heat addition and heat
removal of the ORC, again a result of a lack of thermal
buffer in the system. The temperature distribution was
found to be regular across the collector field as would be
expected. Wind effects we re found to be ne gligible.
Figure 6 presents the solar collector field energy out-
put (flux) vs. time relative to the approximated DNI val-
ues. Figure 7 depicts solar collector field energy flux
relative to measured DNI values for a day later in the
su mme r . The fluctuation in temperature measurements
also had the effect of creating noise in the calculated
energy flux, which is a function of the temperature rise
through the system. To offset this effect, the outlet tem-
perature measurements of the collector field would need
to be shifted in time, so that the inlet temperature mea-
surement of a given fluid particle would correlated to its
outlet temperature measurement, resulting in an accurate
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
Figure 4. Measured solar insolation vs. actual.
Figure 5. Collector field temperature distribution.
ΔT calculation. This adjustment has not been made to
Figure 6 and so additional noise in the calculated energy
flux is observed, yet was adjusted in Figure 7, where
substantial fluctuations still exist, yet are dampened and
dissipate more quickly for constant inlet conditions. An
error band of five percent is displayed as a conserva tive
estimate of the actual DNI and a linear trend line for the
energy output is given for visualization in Figure 6. It
can be seen that the design output of 650 kWth was
reached and maintained on this day with design solar
irradiation. In contrast, the design output was not reached
for the second day presented. Here, several degrading
conditions are present that have not been quantified, in-
cluding but not limited to the cosine effect of the sun
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
Figure 6. Collector field energy output.
angle later in the year and the build-up of dirt from col-
lector usage. The thermal efficiency of the collector field
could then be evaluated by the given formula:
() ()
nAperture Area
Here ηth represents the thermal efficiency and
is the
thermal energy flux from the flow field. The efficiency
of the solar field, based on the approximated DNI values,
ranged between 70 and 80 percent (Figure 8), while the
efficiency of the second day, based on measured DNI
values, ranged between 65 and 75 percent (Figure 9).
When considering the degrading factors mentioned ear-
lier that have not been accounted for in the measurement,
the efficiency values represent an industry standard, even
after accounting for the low thermal losses which would
Figure 7. Collector field energy output, day 2.
Figure 8. Collector field efficiency.
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
Figure 9. Collector field efficiency, day 2.
be expected due to the low temperature operating regime.
Additionally, the cross-over piping between the two
SCAs remain uninsulated, which is estimated to account
for a one to two ˚C (2˚F - 4˚F) temperature drop based on
measured data, which would further increase overall
thermal efficiency when insulated.
Figures 10 and 11 show the measured DNI for the
second day presen ted, averaged by the minute and hourly,
respectively, which highlights the variable conditions
seen in the collector field data.
Figure 12 presents data depicting the ORC performance
for the same day presented for the solar field in Figures
6 and 8. The ORC p ower production is pr imarily a fun c-
tion of the temperature difference between the heat
source and the cooling source. Depicted also is the power
production in kWe relative to the ΔT mentioned above.
Figure 13 depicts the performance of the evaporative
cooler. The low humidity and moderate temperatures
result in effective cooling relative to the ambient tem-
perature. Finally, the thermal efficiency of the ORC was
determined by simply calculating the ratio of electric
power produced to thermal power supplied. Figure 14
presents the thermal efficiency of the ORC, which was
between 7 and 8 percent, within the design conditions.
Also shown is the theoretical Carnot efficiency for the
cycle and 75 percent of the Carnot efficiency, which is
commonly considered the engineering limit.
7. Results and Future Work
The University of Louisiana at Lafayette, in conjunction
with CLECO Power LLC, has installed and commis-
sioned a pilot scale solar thermal power plant in Louisi-
ana for the first time. Following commission in Decem-
ber, 2012, testing and operation of the facility commenced.
Initial preliminary performance data has been presented
which demonstrates that the collector field and ORC
power block are operating at or near the design point on
an efficiency and power output basis. In the case of the
collector field, initial performance has in some cases ex-
ceeded expected values. Improvements to the performance
will be expected when additional work is completed in-
cluding adding insulation to exposed piping at the cross-
over between SCAs (15 linear meters) and a regime for
cleaning the mirrors is introduced. Regarding the ORC,
the initial performance at or near design point is hig-
hlighted by the fact that the input flow rate of the ORC
requires a minimum of 379 l/min while the current HTF
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
Figure 10. Measured DNI for day 2, averaged by minute.
Figure 11. Measured DNI for day 2, averaged hourly.
Demonstration of Pilot Scale Large Aperture Parabolic Trough Organic Rankine Cycle Solar Thermal Power Plant in Louisiana
Copyright © 2013 SciRes. JPEE
Figure 12. ORC performance data.
Figure 13. ORC cooling data.
Figure 14. ORC efficiency .
flow rate is at a maximum at this value. Future work will
include adding variable frequency drives to the HTF pump
to modulate and optimize the HTF flow rate for improved
ORC heat removal. Losses in the system must be quanti-
fied for optimization, including quantifying the level of
degradation in specularity due to dirt build-up on the
mirrors. Pumping losses for the HTF and the evaporative
cooler tot a led about 3.5 kWe.
In addition, the current data represents operation in
moderate ambient temperatures and low humidity, lead-
ing to effective evaporative cooling. The summer months
of the local area will bring higher humidity and ambient
temperatures which will adversely affect cooling and
overall thermal efficiency. Considerable fluctuations in
the thermal output of the collector field were due to a
lack of thermal buffer. Future work calls for the installa-
tion of a thermal storage/buffer system which will act to
remove the high levels of variability due to cloudy con-
ditions and collector field-ORC balancing acting to fur-
ther optimize the system. Additional work will also in-
clude the continued collection and study of measured
DNI data, which will serve to improve efficiency calcu-
lations, create a database for local conditions which will
replace TMY3 data in analytical models, and inform lo-
cal DNI/GNI ratios.
8. Acknowledgements
This work was funded by a grant from the Louisiana
Department of Natural Resources under the EmPower
Louisiana Renewable Energy Grant Program, award
number RE-06, the United States Department of Energy
through the American Recovery and Reinvestment Act of
2009 and CLECO Power LLC.
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