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Eurotrough - Parabolic Trough Collector Developed for Cost Efficient Solar Power Generation

Conference Paper

Eurotrough - Parabolic Trough Collector Developed for Cost Efficient Solar Power Generation

Abstract and Figures

The high-performance EuroTrough parabolic trough collector models ET100 and ET150 have been developed for the utility scale generation of solar steam for process heat applications and solar power generation. With corresponding receiver tubes they can be used in combination with various heat transfer fluids in large solar fields. With an optical concentration of 82:1 operating temperatures over 500°C may be reached. The ET100 and ET150 structure geometry has included wind channel and finite element method validation and is compatible with the standard receiver tubes and mirror panels of the market. The loop and field concept is also fully compatible with the proven solar field technology of the successful Solar Electric Generating Systems (SEGS) in California and can be integrated to field sizes for up to 200 MW el solar plants. The collector modules have been fully qualified in the years 2000 – 2002 with a synthetic heat transfer fluid for 395°C operation at the Plataforma Solar in Almeria with independent performance test certificates from the research laboratories. 14% solar field cost reduction are anticipated due to weight reduction and collector extension to 150 meters. A 50 MW solar power plant with 549 000 m 2 of EuroTrough collectors and 9h-thermal storage is projected for South Spain.
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EUROTROUGH - Parabolic Trough Collector
Developed for Cost Efficient Solar Power Generation
Michael Geyer b, Eckhard Lüpfert f,
Rafael Osuna a, Antonio Esteban a, Wolfgang Schiel c, Axel Schweitzer c, Eduardo Zarza e, Paul Nava b,
Josef Langenkamp b, Eli Mandelberg d
a INABENSA Instalaciones Abengoa S.A., Avenida de la Buhaira 2, E-41018 Sevilla, Spain
b FLABEG Solar International GmbH, Mühlengasse 7, D-50667 Köln, Germany
c Schlaich Bergermann und Partner, Hohenzollernstr.1, D-70178 Stuttgart, Germany
d SOLEL Solar Systems, P.O. Box 811, Beit Shemesh 99107, Israel
e CIEMAT Plataforma Solar, Apartado 22, E-04200 Tabernas (Almería), Spain
f DLR Plataforma Solar, Apartado 39, E-04200 Tabernas (Almería), Spain
Abstract - The high-performance EuroTrough parabolic trough collector models ET100
and ET150 have been developed for the utility scale generation of solar steam for process
heat applications and solar power generation. With corresponding receiver tubes they can be
used in combination with various heat transfer fluids in large solar fields. With an optical
concentration of 82:1 operating temperatures over 500°C may be reached. The ET100 and
ET150 structure geometry has included wind channel and finite element method validation
and is compatible with the standard receiver tubes and mirror panels of the market. The loop
and field concept is also fully compatible with the proven solar field technology of the
successful Solar Electric Generating Systems (SEGS) in California and can be integrated to
field sizes for up to 200 MWel solar plants. The collector modules have been fully qualified
in the years 2000 – 2002 with a synthetic heat transfer fluid for 395°C operation at the
Plataforma Solar in Almeria with independent performance test certificates from the
research laboratories. 14% solar field cost reduction are anticipated due to weight reduction
and collector extension to 150 meters. A 50 MW solar power plant with 549 000 m2 of
EuroTrough collectors and 9h-thermal storage is projected for South Spain.
1. Technical Features
Figure 1: Working Principle of the EuroTrough collector
Figure 1 shows the working principle of the EUROTROUGH collector at the Plataforma Solar. By tracking
the sun from sunrise to sunset, the parabolic EuroTrough collectors concentrate the sun’s radiation with
their parabolic mirror facets on the absorber tubes along their focal line. Through these absorber tube
circulates a heat transfer fluid (HTF), usually synthetic oil, which is heated to a temperature of nearly
400°C.
presented at: 11th Int. Symposium on Concentrating Solar Power and Chemical Energy Technologies,
September 4-6, 2002, Zurich, Switzerlan
d
2
EuroTrough Model ET100 ET150
Focal Length 1.71 m 1.71 m
Absorber Radius 3.5 cm 3.5 cm
Aperture Width 5.77 m 5.77 m
Aperture Area 545 m² 817.5 m²
Collector Length 99.5 m 148.5 m
Number of Modules per Drive 8 12
Number of Glass Facets 224 336
Number of Absorber Tubes (4.1 m) 24 36
Mirror reflectivity 94% 94%
Weight of steel structure and pylons, per m2 aperture area 19.0 kg 18.5 kg
Table 1: Main characteristic parameters of EuroTrough 100 m and 150 m
The EuroTrough collector models are made up of identical 12 m long collector modules. Each module
comprises 28 parabolic mirror panels - 7 along the horizontal axis between pylons and 4 in a vertical
cross-section. Each mirror is supported on the structure at four points on its backside. This permits the
glass to bend within the range of its flexibility without effect on the focal point. The 100 m long ET100
has 8 collector modules and an aperture area of 545 m², the 150 m long ET150 has 12 collector modules
and an aperture area of 817.5 m².
Detailed wind tunnel tests have been conducted for obtaining a reliable database for the expected wind
loads at different locations in the collector field. Bending and torsion forces have been determined in
these experiments. Horizontal forces and pitching moments have been evaluated for different wind
speed and direction, different collector positions in the field and various elevations of the collector.
Existing Regular Version Torque Tube Design A Torque Box Design A
Bending Load Torsion Load
Figure 2: Concentrator deformation analysis for different support structures
Detailed FEM investigations (see Figure 2) on the structural behaviour under various load cases (dead
load, wind loads for a range of pitching angles of the collector and wind directions) for alternate
designs, complex computer modelling and ray tracing were performed to obtain the best possible
relationship of optical accuracy and collector cost.
3
Figure 3: Computer Model of the EuroTrough Collector with Torque-Box Design
Based on these studies a so-called torque-box design has been selected for the EuroTrough, with less
weight and less deformations of the collector structure due to dead weight and wind loading than the
reference designs (LS-2 torque tube or the LS-3 V-truss design, both commercial in the Californian
plants). This reduces torsion and bending of the structure during operation and results in increased
optical performance and wind resistance. The weight of the steel structure has been reduced about 14%
as compared to the available design of the LS-3 collector.
The central element of the box design is a 12-m long steel space-frame structure having a squared cross
section that holds the support arms for the parabolic mirror facets. The torque box is built out of only 4
different steel parts. This leads to easy manufacturing, and decreases required efforts and thus cost for
assembling on site. Transportation volume has been optimized for maximum packing. The structural
deformation of the new design is considerably less than in the previous design (LS-3), which results in a
better performance of the collector. Thus the spillage during operation can be reduced by approximately
2-10 percentage points.
abcd e
Figure 4: EuroTrough collector element consisting out of (a) 2 endplates; (b) 4 simple steel frames
screwed to a torque box; (c) 3 absorber tube supports; (d) 28 cantilever arms and (e) 28 mirror facets.
The design utilizes mirror supports that make use of the glass facets as static structural elements, but at
the same time reduce the forces on the glass sheets by a factor of three. This promises less glass
4
breakage with the highest wind speeds. Absorber tube supports were designed such to reduce the
breakage risk and to ease mirror cleaning in comparison to the LS-3 collector.
The accuracy of the concentrator is achieved by a combination of prefabrication with jig mounting on
site. The majority of the structural parts are produced with steel construction tolerances. The accuracy
for the mirror supports is introduced with the glass brackets on each of the cantilever arms. This concept
allows minimum assembly manpower and cost in series fabrication of solar fields.
The ET100 and ET150 are tracked with the sun during operation along their long axis with a hydraulic
drive. The drive system consists out of two hydraulic cylinders mounted on the central drive pylon.
From a control box mounted on the drive pylon signal and power lines lead to the hydraulic unit, the
rotational encoder, limit switches and temperature sensors.
The tracking system developed for the ET100 and ET150 on the Plataforma Solar is based on 'virtual'
tracking. The traditional sun-tracking unit with sensors that detect the position of the sun has been
replaced by a system based on calculation of the sun position using a mathematical algorithm [2]. The
unit is implemented in EuroTrough with a 13-bit optical angular encoder (resolution of 0.8 mrad)
mechanically coupled to the rotation axis of the collector. Comparing both sun and collector axes
positions by an electronic device, an order is sent to the drive system, inducing tracking. The latest
version of the solar coordinates calculation algorithm was checked against the Multiyear Interactive
Computer Almanac (MICA), a software product of the United States Naval Observatory. Errors in
longitude and/or latitude of the site below 10 km do not provoke a significant positioning error, if the
parabolic trough collectors are correctly aligned.
Following cost reduction potentials have been exploited:
1. Cost reduction by simplification of the design:
less different profiles, parts, better transportation; assembly concept; cost reduction by weight
reduction of the structure; frame work structure, closed profiles, corrosion protection; finite element
method for structural design calculations; wind analyses for proper definition of the load cases
2. Cost reduction by improvement of the optical performance of the collector:
rigid support structure --> frame work torque box; manufacturing, assembly accuracy
3. Cost reduction achieved in additional steps: possible tilt of the collector and extension of collector
length per drive unit (ET150).
The anticipated overall cost reduction for the solar field is 14% for ET150 collectors. Additional
reduction of solar electricity cost will be achieved by the higher annual performance due to improved
optical parameters.
2. Performance
Tests were carried out and evaluated on thermal performance and structural torsion under external load.
The EuroTrough collector showed a performance of 3 % points higher than LS-2 reported by Sandia,
see Figure 5.
Because of the fact that the efficiency definitions used by Sandia for the LS-2 collector evaluation [5]
are the same as used for the EuroTrough, both collector types can be compared directly. The measured
specific thermal losses of the EuroTrough and the LS-2 collector are almost identical, which is
explained by the use of the same heat collection element as absorber (Solel HCE tubes with Cermet
coating). That leads to a similar thermal efficiency of both collectors. The EuroTrough collector
behavior for incident angles of more than 30° is more efficient than the LS-2 collector. This is due to the
larger collector module, higher geometric precision of the parabola, and less shading due to improved
absorber support design.
Collector torsion under load was analyzed from the measurements of the angular encoders of each
collector pylon.
A test with photogrammetric surface analysis has been performed. Its results served for detailed 3-
dimensional insight in the reflector and support structure properties and improvements towards higher
collector efficiency.
5
(a)
(b)
Figure 5: Global Collector Efficiency (a) and Incident Angle Modifier (b) for the EUROTROUGH
collector (upper line) and the LS-2 reference measurements (Sandia, USA), both using previous version
of Solel HCE absorber tubes, for clean mirrors, reference area 4 x 11.98 x 5.77 m2, and DNI = 900
W/m2.
The new model of absorber tube – the UVAC (Universal vacuum collector, SOLEL), has the same
external size and shape as the previous model (HCE), but higher performance and better durability. The
following product improvements were achieved:
1. Coefficients of absorptivity α and emissivity ε are improved to give additional thermal annual
output of up to 20% (depending on site conditions).
2. The original selective coating was designed to be stable at high temperature and in vacuum but the
stability at exposed environment (air & humidity) was relatively limited. The applied UVAC
selective coating is designed to work at vacuum and exposed outdoor conditions, with no oxidation
or oxide deposit on the glass tubes. Operating temperature at exposed environment (air) is 400°C.
3. A new solar radiation shield set was designed in such a way, that it shields the glass to metal
connection zone and the bellow connections, maintaining the fixed relative position in spite of the
axial displacement of the tube during heat up. The design specification demands of the shield set are
to protect the glass-to-metal connection even at extremely low radiation angles of the sun, of both
direct and reflected sunrays, while it interferes as little as possible with the effective collecting area
of the UVAC, so as not to deteriorate the overall efficiency of the solar system.
Possible heat transfer fluids are ranging from the proven synthetic oils to silicon oil, water/steam and
molten salts.
6
3. Solar Field Design with EuroTrough Collectors
The ET100 and ET150 EuroTrough collector models can be serially connected with flexible ball joints
to loops. Each loop can consist of six to eight ET100 EuroTrough collectors or four to six ET150
EuroTrough collectors, depending on the site conditions and solar field size.
Figure 6 shows a layout example of a solar field with the 100 m long ET100 EuroTrough collectors. The
two collector loops located at the outside borders of the solar field are reinforced, so-called “strong”
ET100 models to withstand the higher wind loads; the inner ET100 loops are of regular type.
Cold HTF flows from the power block area into a cold heat transfer fluid (HTF) header that distributes it
to the parallel loops of EuroTroughs in the solar field. Two adjacent rows of collectors are connected by
a crossover pipe near the edge of the solar field and form a loop. HTF is heated in the loop and enters
the hot header, which returns hot HTF from all loops to the Power Block area.
Power
Block
Area
100m EuroTrough
SCA
SCAs with regular SCE'sSCAs with strong SCE's
Figure 6: Principle layout of solar field with strong and regular 100m EuroTrough collectors
4. EuroTrough Costs and Market Perspectives
The industrial EuroTrough partners are prepared to offer solar fields with the EuroTrough collectors
ET100 and ET150 on a turn-key basis to utilities, IPP developers and process heat users; they have been
prequalified with EuroTrough solar field offers for the Integrated Solar Combined Cycle projects in
Mathania (India) and Kuraymat (Egypt). EuroTrough solar field cost depends on field size and specific
site. For a first of ET150 solar field with at least 500 000 m2 in Southern Spain, the EuroTrough partners
count with solar field cost of 206 €/m² including HTF system and installation.
Under the contract of the Solar Millennium AG of Germany, the EuroTrough industrial partners are now
engineering the Andasol project, a 50 MW solar only plant with 549 360 m2 EuroTrough solar field and
9 hours of storage for implementation in Southern Spain under the framework of the Royal Decree 2818
and its expected premium for solar thermal power. With a measured annual direct normal irradiation of
2200 kWh/a, this field of ET150 EuroTrough collectors will annually supply 594 312 MWhth/a of solar
steam to a Rankine cycle of 38% gross annual efficiency, which feeds 181 700 MWhe/a of net solar
electricity to the grid. The cost of the EPC contract (without land and without contingencies) amount to
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181 M€. With an expected lifetime of 25 years, an annual depreciation of 6.7%, an annual discount rate
of 9.0%, an annual insurance rate of 1.0% and an annual income tax rate of 35%, the Levelized
Electricity Costs according to the IEA method are 0.15 €/kWh for this project.
5. EUROTROUGH Consortium
Mediterranean Solar Process heat applications of the EuroTrough technology have been investigated by
the independent consultant Fichtner Solar GmbH (Germany) and the research laboratory CRES
(Greece). Power equipment costs have been verified by the Spanish utility partner Iberdrola. The
EuroTrough technology and engineering is fully backed by the industrial supply partners of the
EuroTrough consortium, i.e. the companies Abengoa/Inabensa (Spain), Flabeg Solar International
GmbH (Germany) and Schlaich Bergermann & Partner (Germany). Solel (Israel) contribute the high
efficient UVAC absorber tubes for the ET100 and ET150 modules at the PSA. Ciemat (Spain) and DLR
(Germany/Spain) support the development mainly with their experience on collector development and
testing on PSA. The development and qualification testing of the EuroTrough was financially supported
by the European Commission within the 4th and 5th Framework Programs under contracts JOR3-CT98-
0231 and ERK6-CT-1999-00018. The development was further supported by the Spanish and German
Governments to Ciemat and DLR respectively.
References
[1] EuroTrough Project. Final Public Report, European Commission Contract No. JOR3-CT98-00231,
Sevilla/Almería/Brussels, 2001
[2] Manuel Blanco-Muriel, Diego C. Alarcón-Padilla, Teodoro López-Maratalla, Martín Lara-Coira:
„Computing the Solar Vector“, Solar Energy 2001;70 (5):431-441.
[3] Lüpfert E, Geyer M, Schiel W, Esteban A, Osuna R, Zarza E, Nava P. EuroTrough Design Issues
and Prototype Testing at PSA. Proceedings of the ASME International Solar Energy Conference –
Forum 2001, Solar Energy: The Power to Choose (R. Campbell-Howe, Ed.), Washington, DC,
April 21-25, 2001, pp. 389-394. www.eren.doe.gov/troughnet/
[4] Pilkington Solar. Status Report on Solar Thermal Power Plants - Experience, Prospects and
Recommendations to Overcome Market Barriers of Parabolic Trough Collector Power Plant
Technology. Cologne 1996. ISBN 3-9804901-0-6.
[5] Dudley VE, Kolb GJ, Mahoney AR, Mancini TR, Matthews CW, Sloan M, Kearney D. SEGS LS-
2 Collector Test Results. Sandia National Laboratories, SAND94-1884, USA 1994
[6] www.eurotrough.com
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EuroTrough Design Issues and Prototype Testing at PSA. Proceedings of the ASME International Solar Energy Conference – Forum Solar Energy: The Power to Choose
  • E Lüpfert
  • M Geyer
  • W Schiel
  • Esteban A Osuna
  • R Zarza
  • E Nava
Lüpfert E, Geyer M, Schiel W, Esteban A, Osuna R, Zarza E, Nava P. EuroTrough Design Issues and Prototype Testing at PSA. Proceedings of the ASME International Solar Energy Conference – Forum 2001, Solar Energy: The Power to Choose (R. Campbell-Howe, Ed.), Washington, DC, April 21-25, 2001, pp. 389-394. www.eren.doe.gov/troughnet/
Status Report on Solar Thermal Power Plants -Experience, Prospects and Recommendations to Overcome Market Barriers of Parabolic Trough Collector Power Plant Technology
  • Pilkington Solar
Pilkington Solar. Status Report on Solar Thermal Power Plants -Experience, Prospects and Recommendations to Overcome Market Barriers of Parabolic Trough Collector Power Plant Technology. Cologne 1996. ISBN 3-9804901-0-6.
EuroTrough Design Issues and Prototype Testing at PSA. Proceedings of the ASME International Solar Energy Conference – Forum Solar Energy: The Power to Choose (R. Campbell-Howe
  • E Lüpfert
  • M Geyer
  • W Schiel
  • A Esteban
  • R Osuna
  • E Zarza
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