garrigues report 05 jul 2011 ingles (2)
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REPORT ON THE TECHNICAL ASSESSMENT OF THE STRUCTURE
FOR COLLECTORS ALBIASATROUGH
5th July, 2011
Report on the technical assessment of the structure Page 2 of 41 Albiasa-Trough
TABLE OF CONTENTS
1. INTRODUCTION 3
1.1 Aim 3
1.2 Scope and sources of information 3
1.3 Recipient 4
1.4 Liability 4
2. TECHNICAL ASSESSMENT OF THE STRUCTURE 6
2.1 Background 6
2.2 Albiasa Solar experience 7
2.3 Collector specifications, design and technology 8
2.4 Tests results 16
2.4.1. Mechanical Characterization Tests 17
2.4.2 Tests carried out by CIEMAT 20
2.5 Manufacturing process and suppliers. 26
2.6 Assembly process and maintenance for the collector 30
2.7 Auditing structural calculations and foundations type 34
2.7.1 Structural calculations 34
2.7.2 Foundation types 36
3. CONCLUSIONS 37
APPENDIX: DOCUMENTS UNDER REVISION 40
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1. INTRODUCTION
1.1 Aim
Garrigues Medio Ambiente, at the request of ALBIASA SOLAR, S.L.
(hereinafter, Albiasa) has made an objective and independent technical revision
report of the structure for the parabolic collector Albiasa Trough, developed by
Albiasa.
1.2 Scope and sources of information
The work included in this report consists of the technical assessment on the
structure for parabolic collectors developed by Albiasa, so any other component
in the collector is out of the scope of this report.
The technical assessment of Albiasa Trough carried out by Garrigues Medio
Ambiente in this document is based on the Technical assessment of parabolic
collector Technical assessment of parabolic collector “Albiasa Trough” carried
out by the engineering company Alatec on 25th May, 2010, as well as on
complementary information about constructive details and tests carried out on
the structure, supplied by Albiasa.
Additionally, Garrigues Medio Ambiente had telephone conversations on the
28th July, 2010 with Mr. Eduardo Zarza, Head of the Concentrated Solar
Systems Unit, CIEMAT, in order to extend the information regarding the tests
on the collector in the PSA, as well as with Mr. Santiago Segovia, Development
Manager of Avdel and Mr. Alayn Redondo, Development Manager of Faro to
collect information about the riveting and the laser scanner system supplied by
those companies respectively.
The documentation on revision to carry out this report is listed in Appendix I.
Report on the technical assessment of the structure Page 4 of 41 Albiasa-Trough
1.3 Recipients
This report issued with the aim stated in section 1.1 and the recipients of the
report are exclusively Albiasa, its clients and the financing entities cooperating
with Albiasa.
The report cannot be delivered to any other person or organization, nor
reproduced by any other means, totally or partially and/or used with any other
aim without our written consent.
1.4 Liability
This report is based on the sources of information listed in section 1.2.
The following hypotheses have been assumed for this work:
The documents and information supplied and examined are truthful,
complete, remain in force and do not contain false information, they have
not been modified or extinguished by any other document and no
relevant information or document has been concealed with the aim of
modifying or altering the documents and information object of this
revision.
The photocopied, scanned and electronic documents are complete and
true copies of the original documents.
There is no appendix or modification to the revised documents to be at
our disposal.
The signatures in the documents correspond to the natural persons, who
according to the documents under analysis took part in the documents
elaboration. Likewise, the dates established in the documents correspond
Report on the technical assessment of the structure Page 5 of 41 Albiasa-Trough
to the dates of their effective creation, emission, signature, execution or
production.
There is no document modifying, contradicting or altering the documents
under analysis.
The assessment must consider the following limitations and reservations:
According to section 1.2, Garrigues Medio Ambiente has not audited the
calculations of the structure’s design.
No document and/or information outside those listed in the appendix or
created after the report’s emission date have been analysed.
Garrigues Medio Ambiente liability in relation to this document will not exceed
the honoraries received for its services, and will not include indirect damages,
loss profits, consequential damages or opportunity costs.
Report on the technical assessment of the structure Page 6 of 41 Albiasa-Trough
2. TECHNICAL ASSESSMENT OF THE STRUCTURE
2.1 Background
The structure in Albiasa-Trough consists of a central beam made of one
cylindrical axis or main tube (torque tube) from which the arms are designed to
hold the mirrors making up the cylindrical-parabolic receiver surface, which is
activated through hydraulic actuators and rotate to orientate the mirrors towards
the sun position along the day.
The main difference with other collector models is that the torque tube is made
up of four galvanized torque tube quarters which are fixed among them by
clinching. The other models having a torque tube have a beam with helicoidal
welding, which must be shipped after being pre-manufactured up to the field
assembly location. Therefore, Albiasa-Trough lowers manufacturing and
transportation costs of the beam up to the thermosolar plant location. Once the
collector is at the location, the torque tube is assembled by clinching, using no
welding procedure on field.
Garrigues Medio Ambiente has based the structure analysis on the technical
assessment report of “Albiasa-Trough” carried out by Alatec, dated the 25th
May, 2010, as well as on data and complementary information regarding
constructive details and the tests carried out, which have been supplied by
Albiasa. Alatec conclusions derive from the assessment of the following aspects:
i) Albiasa experience
ii) Collector specifications, design and technology
iii) Tests results
iv) Manufacturing process and supplier
Report on the technical assessment of the structure Page 7 of 41 Albiasa-Trough
v) Collector assembly process and maintenance
vi) Sales-purchase contract and warranties
vii) Audit on structural calculations and foundations type
Garrigues Medio Ambiente has made report following a similar guideline,
although the sales-purchase contract and warranties have not been analysed, for
they are out of the scope of this report.
2.2 Albiasa Solar experience
Albiasa Solar has designed the parabolic collector Albiasa-Trough. Albiasa
Solar was founded in 2004 with the objective of designing, promoting and
executing photovoltaic and thermosolar plants. The company belongs to Albiasa
Group, which has wide experience in designing, developing, manufacture,
supplying and selling machinery and equipments for the industrial sector,
especially the iron and steel sector.
Nowadays, Albiasa has five photovoltaic plants under operation with a total
power of 14MW, and one plant under construction with 22,7 MW. Regarding
the thermosolar sector, Albiasa has developed the collector Albiasa-Trough and
has participated in several thermosolar plants which are under promotion, such
as 50 MW thermosolar plant in Saucedilla and 16 plants, 16 MW each, in
Bienvenida, Caceres. These plants are not included in the pre-assignment
registry for 2013 issued by the Ministry of Industry, Tourism and Commerce.
Moreover, Alatec declares in its report that Albiasa has photovoltaic and
thermosolar projects in USA under promotion. Thus, Albiasa, through its
subsidiary company Albiasa Corp, with offices in San Francisco and Phoenix, is
promoting a thermosolar plant 220 MW with parabolic trough technology and 6
hours thermal storage near Kingman (Arizona). Additionally, Albiasa will
Report on the technical assessment of the structure Page 8 of 41 Albiasa-Trough
supply Albiasa-Trough for a10 MW thermosolar plant in Kauai (Hawaii) to the
companies PLP and Ram Power.
Albiasa is also collaborating with the North-American companies PG&E and
NV Energy for a project of 5 plants 20 MW with ORC1
2.3 Collector specifications, design and technology
technology, which have
different locations.
Regarding Albiasa-Trough supply, nowadays there is no thermosolar plant using
this model under operation, for it is a new development, but half-collector has
been installed in Almeria Solar Platform (hereinafter, PSA,) for 30 months in
order to carry out the tests described and assessed in this report.
Garrigues Medio Ambiente considers that Albiasa has experience in the design
and construction and metallic structures due to its activity in the steel and iron
sector from 1974, so it has the technical background and experience required to
design and to construct the structure for thermosolar parabolic collectors.
The main characteristics of the structure for collectors designed by Albiasa are
summed up in this section. The structure can be supplied with two different
lengths, 100 m and 150 m. Depending on the length, the collector will be divided
into 8 or 12 modules, 12 m each, which will support 28 mirrors distributed into 4
rows with 7 mirrors each and 3 absorber tubes.
The following figure shows the collector Albiasa-Trough:
1 Organic Rankine Cycle
Report on the technical assessment of the structure Page 9 of 41 Albiasa-Trough
Figure 2.1: Structure for collector Albiasa-Trough
The main components in the collector structure are the following:
• Torque tube. Made up by 4 torque tube quarters of hot galvanized steel
fixed by clinching. The torque tube quarters are of circular section and
have half T flanges to join them and support the arms.
• Cantilever arms. They are made up of welded hot galvanized square
section profiles. There are 28 arms starting from the central beam and
support the reflective mirrors.
• Heat collector element supports. Each module has 3 brackets to maintain
the absorber tube in the parabola focus position. They are joined by means
of screws to the central beam.
• Pylons. The torque tube is supported by pylons, from the foundations in
the terrain. Each loop is made up by 6 central pillars, 36 intermediate
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pillars (between modules), 4 final pillars and 4 double pillars shared by the
adjoining collectors.
• End plates. The torque tube has two plates at it ends which also join the
modules. There are 3 types of end plates depending on the position they
hold in the collector’s module.
Alatec does not include a description of the torsion transmission system in its
report. This system transfers the rotary movement form one module to another
one by means of end plates. In order to complete the structure analysis of this
report, Albiasa has provided additional documentation describing the
transmission system between modules in a collector, that is, axis set. Its main
functions are: joining the modules, supporting the pillars and transferring the
rotary movement between modules.
Figure 2.2: Axis set. Source: Albiasa Solar.
As it can be seen, the axis set if made up of three pieces joined among them by
welding: one axis and two metal sheets. The lateral metal sheets are joined
through screws at each module. The axis, is supported by a flat ferrule located
Report on the technical assessment of the structure Page 11 of 41 Albiasa-Trough
on the central beam, and serves to transfer the module weight and offers low
resistance to torsion rotation.
According to the report by Alatec, the novelty in this structure consists of the
reduction on welding units as well as the material and number of pieces in use.
The torque tube in Albiasa-Trough is the only torque tube having no helicoidal
welding which makes that the manufacturing process be easier and cheaper.
Likewise, the assembly process is more automated, easier and faster than the
process in torque box structures. Alatec remarks that collectors 100 m long have
lower risk of efficiency reduction at medium-long term due to the deformations
made by the wind than in collectors 150 m.
Torque tube collectors have been widely tested in SEGS plants (LS-2 model).
Likewise, other manufacturers such as Solel or Sener use this type of structure
for collectors. The diameter and thickness in Albiasa-Trough torque tube is
similar to those in other suppliers of collectors. However, the design in Albiasa-
Trough is innovative, for it is the only structure using four torque tube quarters
of hot galvanized steel, fixed by clinching. As it is stated in this report, other
manufacturers use clinching in other parts of the structure which are exposed to
similar stress data. Nowadays, there is no thermosolar plant under operation
using the clinching joint technology used by Albiasa Trough.
The additional information regarding the axis set, which was requested by
Garrigues Medio Ambiente to Albiasa, is here summed up.
The following table include the number of main elements required to assembly
one loop.
Report on the technical assessment of the structure Page 12 of 41 Albiasa-Trough
Elements N. of pieces Beam quarters 192
End plates 48 Bridge 1 48 Bridge 2 48 Axis set 48
Arms 1.344 Mirrors support 5376 External mirrors 672 Internal mirrors 672 Tube supports 144
Tube 144 TOTAL 8.736
Table 2.1: Number of main elements per loop.
Moreover, according to the information provided by Albiasa, each module
weights about 1.436 kg.
The arms are fixed through screws directly to the central beam without using any
other intermediate element, thanks to the half T flanges in the beam quarters.
The collector is designed to support a maximum wind velocity of 19,4 m/s (70
km/h), where the maximum survival wind velocity is 33,3 m/s (120 km/h). On
the other hand, the velocity of 8,11 m/s is the point at which the collector’s
efficiency is no longer 100%. The following table shows the structure’s
efficiency losses as the wind velocity increases.
Report on the technical assessment of the structure Page 13 of 41 Albiasa-Trough
Wind velocity (m/s Efficiency 8,2 85% 8,3 78% 8,4 74% 8,5 69% 8,6 67% 8,7 63% 8,8 61% 8,9 58% 9 56% 10 42% 11 32%
Table 2.2: Structure’s efficiency for wind velocities.
The assembly process for torque tube structures is easier than torque box
structures, for the total number of elements to assembly is lower. With this
respect, table 2.1 lists the number of main elements required to assembly a
whole loop for this structure model.
Regarding the main novelty of Albiasa design, it is a torque tube made up of
four quarters of tube joined by rivets, and these are the main advantages and
disadvantages of the solution proposed by Albiasa:
a) Advantages
The torque tube does not have helicoidal welding, so it simplifies its
manufacturing process and galvanizing, avoiding future corrosion
problems due to helicoidally welding. Moreover, the welding between
the arm supports and the torque tube are avoided. This results in lower
manufacturing costs.
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Easiness and costs saving for transportation to the field, for the four
quarters of torque tubes can be piled, thus making better use of the
space available in the trucks.
The half T flanges between the four quarters facilitates the torque tube
fixing to the cantilever arms, avoiding anchorage between welded lugs
on the torque tube.
Torque tube higher resistance to flexion, thanks to the flanges between
the tube quarters.
b) Disadvantages
Riveted joints can be sensible to corrosion, but according to the
information provided by Albiasa, they are made of materials corrosion-
resistant (stainless steel and hot dip galvanizing) to minimize this risk.
The supplier for this element is Avdel. According to the information
provided by Mr. Santiago Segovia, Avdel Development Manager,
riveted joints are used in the open such as AVE railways or air-
conditioning systems. Regarding the thermosolar sector, Avdel joints
are used at different points of structures for collectors by different
suppliers (Grupo Samca, Abengoa Solar, Mann Solar Millenium,
Flagsol, Sener) in Spain and abroad.
The four tube quarters must be assembled on field, so the works in the
plant location and assembly supervision are increased. It is expected
that the manufacturing and transportation costs saving compensate the
extra-cost for its assembly on field.
Torque tube resistance to torsion and fatigue, as it is made of four
quarters joined by rivets instead of one element welded in the
manufacturing process as in the torque tubes existing in the market.
Report on the technical assessment of the structure Page 15 of 41 Albiasa-Trough
Regarding this aspect, we will comment on the in a different section on
the mechanical tests carried out on Albiasa Trough.
Regarding the deformations on the structure made by the wind, we have checked
that the wind velocity from which deformations start to appear in Albiasa-
Trough is higher than any other collectors of similar characteristics. Even though
an appropriate design must minimize deformation by wind, it is evident that the
longer a structure is, the higher efforts a structure must support at long term.
According to the data under revision, the efficiency reduction due to wind
velocity is similar to the rest of collectors in the market.
On the other hand, Garrigues Medio Ambiente considers that structures 100 m
have more accurate solar tracking than in 150 m, although shorter structures
require more actuators for the same solar field size and, consequently, an
increased initial investment is necessary, for maintenance, higher self-
consumption by the solar field which reduces net production, although the
impact in self-consumption can be regarded as negligible. With this respect,
Garrigues Medio Ambiente considers it necessary to carry out a cost-benefit
analysis to decide on the collectors’ length. It must be considered also that
structures 100 m long have an operation track record higher than structures
being 150 m long.
Therefore, we can say that a torque tube with rivets is a good technical option,
but it is important to make sure that the join between the tube quarters is
appropriate to resist maximum loads and reiterations (fatigue). In this sense,
Albiasa Solar has carried out mechanical tests to check this situation. Section
2.4.1 describes such tests and we offer our conclusions about the results.
Moreover, Albiasa has carried out optical tests to characterize the structure and,
even though Albiasa-Trough is not installed in any plant under operation, it has
been installed in PSA for 2 years and a half and it has not shown any meaningful
Report on the technical assessment of the structure Page 16 of 41 Albiasa-Trough
mechanical or operation incidence, according to Mr. Eduardo Zarza, Head of the
Concentrated Solar Systems Unit in PSA.
2.4 Tests results
Section 6 in the report by Alatec includes an analysis on the tests carried out on
Albiasa-Trough:
a) Mechanical characterization tests (torsion, breakage and fatigue) on the
torque tube Albiasa Trough carried out by Applus in LGAI
TECNOLOGICAL CENTER, S.A in Bellaterra (Barcelona), which have
been verified by ECA, Grupo Bureau Veritas.
b) Tests carried out by CIEMAT in Almeria Solar Platform.
As the structure Albiasa-Trough is a new development, the design and
verification process has been modifying the collector’s characteristics depending
on the results obtained from the different tests in order to make the necessary
improvements until the final commercial version has been obtained. Garrigues
Medio Ambiente has had access to tests results carried out after the report by
Alatec. Therefore, in order to adapt this report to the current characteristics of
the structure Albiasa, we present the data corresponding to the most recent tests,
carried out on the product in its commercial form. At the end of each section we
present our commentaries regarding the tests and the results, and, where
appropriate, the opinions by Alatec.
In general terms, Garrigues Medio Ambiente considers that testing the structure
or part of it is the best way to check the design and engineering whenever there
is no track record of operation, as it is the case.
Report on the technical assessment of the structure Page 17 of 41 Albiasa-Trough
2.4.1. Mechanical Characterization Tests
Now, we sum up the mechanical characterization tests results carried out
by Applus in LGAI TECNOLOGICAL CENTER, S.A in the
Autonomous University of Barcelona in Bellaterra. The tests have been
verified by ECA (Grupo Bureau Veritas).
The tests were carried out on the testing material which were received on
the 23rd February, 2011, consisting of the torque tube assembled by
Albiasa, made up of four sections of torque tube, joined by clinching and
TOX type joints, with the end plates joined by means of screws to the
torque tube, as well as the axis set joined to the end plate. The torque
tube has no welding of any type.
The tests on the torque tube complied with the specifications present in
the Technical dossier testing protocol, dated on the 3rd of February,
2011. Garrigues Medio Ambiente has revised such protocol and
considers it correct and appropriate for the proposed objectives.
According to the report by Albiasa, the torque tube is not under flexion
loads, so the torsion test is considered to be enough. In this respect,
Garrigues Medio Ambiente considers that, although it would have been
recommendable to carry out flexion tests, performance to flexion is
expected to be better than other torque tube collector due to the
reinforcement provided by the half T flanges in the tube.
2.4.1.1 Torsion Tests
The mechanical characterization tests consisted of applying ten cycles of
load and unload to torsion with increases of 10% load (4,1 kN) and back
to zero load, until the maximum lineal load is 41 kN, corresponding to a
maximum torque pair of 72 kNm. According to the information supplied
Report on the technical assessment of the structure Page 18 of 41 Albiasa-Trough
by Albiasa, such tests considered the weight of each element supported
by the torque tube, including the mirrors. The torsion test was carried out
on the 1st of March, 2011.
The cycles are carried out under displacement control at a velocity of 0,2
mm/s. The load and position of the force applicator is continuously
registered with a frequency of 5 Hz.
The results show that, the residual displacement of the active part is 9
mm for the total load of 41 kN, which produces a residual rotation angle
of 5 mrad, whereas the passive part has almost no displacement after the
test.
The report by ECA concludes that the results coincide with the results
expected by Albiasa.
2.4.1.2 Breakage test
The breakage tests consisted of applying load at 0,2 mm/s constant
velocity on the torque tube, in order to identify the mechanical fuses and
limit loads before the yield point. The load application has three possible
results: breakage of the sample, end-of-charge for the actuator (250 kN)
and route ending of the actuator (±150 mm). The load and displacement
values for the piston are registered at a frequency of 5 Hz.
The breakage test was carried out on the 22nd March, 2011. The results
show that the plastic phase for the torque tube starts between 90 and 100
kN. The elastic limit is around 92 kN, which corresponds to a
momentum of 160 kN, which is the product of the force and the distance
at which it is applied, 1,75 m. Likewise, a minimal displacement of the
sample of 0,1 mm at 55 kN is observed. The breakage of the torque tube
Report on the technical assessment of the structure Page 19 of 41 Albiasa-Trough
takes place at around 100 kN, corresponding to a momentum of
approximately 175 kNm.
The conclusions by ECA show that the results obtained in the tests are
within the results expected by Albiasa.
2.4.1.3 Fatigue test
The fatigue test consisted of applying two different cyclic loads, one to
torsion and another one to flexion. The loads were synchronized so that
the maximum and minimum values coincide, up to a total of 1,300,000
cycles. The test was carried out on the 3rd of March, 2011 until the 19th
of March. During the test, the maximum and minimum values for
displacement and force of the two actuators (torsion and flexion) are
registered. After finishing the test, the load applicators return to zero
force and maintain this position until the final visual inspection.
The results show a constant displacement on the flexion and torsion
actuators along the cycles of the test, which results in a uniform
performance of the torque tube, and no collapse at all. The graphs
included in the report by ECA show that the values for the force applied
on the torsion and flexion actuators are constant during the cycles of the
fatigue test.
In conclusion, the report by ECS states that the constant performance the
torque tube during the cycles of the test is satisfactory.
As a final conclusion, the report by ECA states that the torque tube has
shown a mechanical performance not only within the expected
parameters but also higher values than those calculated in the technical
dossier and testing protocol by Albiasa.
Report on the technical assessment of the structure Page 20 of 41 Albiasa-Trough
Garrigues Medio Ambiente considers that the mechanical tests carried
out on the torque tube Albiasa Trough are complete and their results
show an appropriate mechanical performance.
2.4.2 Tests carried out by CIEMAT
The tests carried out by CIEMAT are the following:
b.1) Geometric characterization of the collector by photogrammetry.
b.2) Incidence angle modifier determination.
b.3) Thermal tests to obtain the collector’s global efficiency.
2.4.2.1 Geometric characterization
According to the geometric characterization results, which state that there
is no meaningful optical difference between vertical and horizontal
position, CIEMAT concludes that the module shows good performance
towards gravity of wind deformations. On the other hand, CIEMAT has
pointed out some misalignments between one mirror and its adjoining
mirror and between modules and their adjoining modules. Even though
CIEMAT thinks they are irrelevant, we consider it appropriate to pay
special attention to the modules assembly to avoid any possible out of
focus.
The obtained intercepting factor is over 96%. Alatec informs that such
value is among the highest values measured in collectors. In order to
obtain this value in a thermosolar plant, the assembly procedure must
guarantee the same geometric quality as the module tested in PSA.
Garrigues Medio Ambiente thinks that the intercepting factor of Albiasa-
Trough is within the highest values for collectors in the market.
Likewise, we coincide with Alatec in that it is necessary for the assembly
Report on the technical assessment of the structure Page 21 of 41 Albiasa-Trough
process to guarantee the same geometric quality as the module tested in
PSA for a thermosolar plant.
According to the information provided, the improvements made in
Rioglass mirrors during the last few years, have increased the benefits in
relation to the mirrors installed in the collector at PSA. In this sense, we
consider that the photogrammetry test results would be higher with these
new mirrors would provide higher values than the previous ones.
2.4.2.2 Incidence angle modifier
Up to the issue of the report by Alatec, there were only preliminary
results regarding the global efficiency test and there were no tests to
determine the incidence angle modifier and nominal optical efficiency.
In order to complete the information in Alatec report, Albiasa Solar
provided us with a preliminary report by Mr. Eduardo Zarza, Head of the
Concentrated Solar Systems Unit, dated the 22nd July, 2010, including
the theoretical results of those parameters obtained at PSA. The
preliminary report states that, according to PSA experience, there were
no meaningful differences to be expected between the tests results and
the values for peak optical efficiency and incidence angel modifier, as it
has been confirmed by the report dated the 21st October, 2010.
The main considerations about the preliminary report dated the 22nd
July, 2010 regarding the peak optical efficiency and the incidence angle
modifier are summed up.
• Peak optical efficiency: The following table shows the values used to
calculate this parameter.
Report on the technical assessment of the structure Page 22 of 41 Albiasa-Trough
Parameter Value Source Glass cover transmissivity 0.96 Tube Schott PTR-70 Specifications
Selective coating absorptivity 0.96 Tube Schott PTR-70 Specifications Mirror reflectivity 0.93 Measurements carried out in PSA
Intercepting factor of modules 0.96 Photogrammetry and measurements carried out in
PSA Intercepting factor of receiver tubes 0.96
Intercepting factor due to torsional rigidity of structure 0.97
Table 2.3: Parameters used to calculate the peak optical efficiency.
Taking into account the parameters, the peak optical efficiency is 0,76,
when the tubes are appropriately placed and the collector is clean.
Depending on the expected dirtying level, the terrain conditions for
installation and the mirrors degradation, this value must be adjusted.
On the other side, and according to the report revised by Garrigues
Medio Ambiente, this value is slightly higher than the peak optical
efficiency in Eurotrough collector.
• Incidence angle modifier. This parameter depends on the gap existing
between the collector’s elements and the arms’ shape supporting the
tubes. The preliminary report provided by PSA stated that, considering
that both parameters are similar to those of Eurotrough, a similar
incidence angle modifier was expected.
As we have already stated, Garrigues Medio Ambiente has revised the report
dated the 21st October, 2010, regarding the experimental results obtained in
PSA.
• Peak optical efficiency: The peak optical efficiency experimentally
obtained is 0,756. This value is 0,4% lower to that theoretically
calculated, so it validates the initial estimation. Likewise, the value 0,756
is within the usual range in the market.
Report on the technical assessment of the structure Page 23 of 41 Albiasa-Trough
• Incidence angle modifier: In order to determine this parameter, the
collector has been operating with a constant inlet fluid temperature at
320ºC and a flow at 14m3/h during 10 minutes, 4 hours before and after
the solar midday.
The following figure shows a comparison between the theoretical and
experimental intercepting factor.
Figure 2.3: Comparison between the theoretical and experimental intercepting
factor of Albiasa Trough.
According to this figure, the experimental curve is always over the theoretical
curve. Both curves are very closed within the range of incidence angles, 0º -
30º, with errors lower than 1,05%. For those angles between 31º - 50º, the
difference between both curves is always lower than 2,34% and for angles
between 51º - 65º, the maximum difference between the theoretical and
experimental curves is 5,68%. The fact that the experimental curves is always
Report on the technical assessment of the structure Page 24 of 41 Albiasa-Trough
above the theoretical curve for the whole range of angles, implies that the
theoretical approximation to define the incidence angle modifier was
conservative.
According to the report by PSA, Albiasa Trough incidence angle modifier is
defined by:
2.4.2.3 Thermal tests to obtain collector’s global efficiency.
Global efficiency relates the useful thermal power provided by the
collector to the thermal oil, using the solar energy falling on the collector.
To obtain this parameter experimentally, it is necessary to know the
incidence angle modifier and the collector’s thermal efficiency. These
tests were not carried out before because PSA had problems to face these
tests. According to the information provided by Mr. Eduardo Zarza, on
the 28th July, 2010, they were studying the possible effect produced by
the tube expansion due to high temperatures on structures 150 m. At
ambient temperature, the tubes supports are not perpendicular to the
structure, which implies that the tubes are not located in the parabola’s
focus made by the mirrors and, therefore, they do not receive the
pertinent concentrated radiation. The structures have been designed for
the supports to be placed perpendicular to the structure when the tube
expands at operating temperatures. As a result of this phenomenon, when
the operation temperature is not achieved, the tube receives lower amount
of radiation, having a lower efficiency. Thus, this test is only valid and
has coherent results if it is carried out at operation temperature.
Report on the technical assessment of the structure Page 25 of 41 Albiasa-Trough
Nevertheless, PSA technicians solved this problem and the global
efficiency is defined, in the report dated on21st October, 2010, by the
following expression:
Where x is the difference the fluid average temperature and ambient
temperature. This expression is valid for a range of temperature
differences between 260ºC - 380ºC, which covers the operation range of
collectors in thermosolar plants. The following figure shows the
experimental performance of this parameter.
Figure 2.4: Global efficiency of Albiasa Trough.
This figure shows that global efficiency decreases as the difference
between the average temperature and ambient temperature increases.
From the straight line onwards, Garrigues Medio Ambiente has
calculated the global efficiency for differences between the fluid ambient
Report on the technical assessment of the structure Page 26 of 41 Albiasa-Trough
and average temperature within the operation range for the collector. The
following table shows the results:
Fluid average Temp- ambient Temperature (ºC)
Global efficiency (%)
260 72,00 270 71,72 280 71,44 290 71,14 300 70,84 310 70,53 320 70,20 330 69,87 340 69,53 350 69,17 360 68,81 370 68,44 380 68,05
Table 2.4: Collector’s global efficiency.
According to the values present in the table, global efficiency is between
68% and 72% for the whole range of temperatures under analysis.
Considering that the peak optical efficiency value is 75,7%, the global
efficiency value is good.
Garrigues Medio Ambiente considers that Albiasa-Trough characterization
through the tests carried out by CIEMAT at PSA is complete.
2.5 Manufacturing process and suppliers.
Regarding the quality control and manufacturing process for the structure Albiasa-
Trough, alatec includes in its report the procedure carried out by albiasa Solar
from the point in which a client places an order up to the structure reception on
site.
Report on the technical assessment of the structure Page 27 of 41 Albiasa-Trough
Albiasa Solar quality management system was certified according to ISO
9001:2008 by Bureau Veritas on the 21st April, 2010. Moreover, Albiasa-Trough
has the CE marking.
The elements making up the structure are manufactured according to the planes
supplied by albiasa. The elements are supplied together with a quality dossier
which contains information related to materials, geometric analysis, coatings used
on the surfaces and tests to chek they fulfill all the requirements requested by
Albiasa. Moreover, Albiasa will have personnel on site at the structure reception
to check visually the supplied elements and assess any possible shipment damage.
Albiasa quality control system is positively valued by Alatec in its report.
Now, we present a summary of the information contained in Alatec’s report
related to the suppliers of the elements for the collector and we complete it with
information provided by Albiasa Solar. The following table contains the suppliers
for the main elements2:
Element Supplier Torque Tube Welser Profile Arms Algasa Mirror support, L form Algasa Axis Ideas en Metal HCE tube support Ideas en Metal End plates IA Técnica
Table 2.5: Suppliers for main equipments.
Here you can find a short description for each supplier:
2 According to the information provided, Albiasa has alternative suppliers to those stated in Table 0.5.
Report on the technical assessment of the structure Page 28 of 41 Albiasa-Trough
a) Welser Profile
The origin of this company dates back to 1664, in a blacksmith’s workshop.
Being a factory, it started to work with cold rolled sections in 1958 and in 1980
it started to manufacture special welded sections. In 1999 it absorbed the
German companies RP Technik and Hoesch, devoted to steel profiles
manufacture. Nowadays, the company has 1.790 employees with 415.000 tons
of steel consumption.
The headquarters are located in Austria, between Salzburg and Vienna. The
production centres have more than 160.000 m2 of area. Since 2001 there is
another production centre in Bönen (Germany) with an area of 80.000 m2. 70-
75% production is sold abroad through its 11 sales offices scattered in Europe,
and in Spain is also present since 1990.
Welser Profile has manufactured more than 17.000 different profiles to be used
in different industrial areas. Moreover, it has been certified according to quality
standards ISO 9001 and environmental management system ISO 14001.
b) Algasa
Asturiana Galvanizadora, S.A. focus its activity on steel and iron galvanizing.
Algasa’s work consists on profile manufacture and its later galvanizing
process.
Since 1995, its Management System has been certified according to ISO 9001,
and in 2004, according to ISO 14001 and OHSAS 18001 specifications
regarding Labour Risk Prevention.
The headquarters is located in Gijon and has one galvanizing plant, one area
devoted to storage and the main offices.
Report on the technical assessment of the structure Page 29 of 41 Albiasa-Trough
Within the thermosolar area, this company has supplied profiles for Andasol
III.
c) Ideas en Metal
Ideas en Metal is an Asturian company founded in 2001, from Hevia Corte
Group. Its main activity is to design and manufacture metal products. It has
more than 24.000 m2 for production centres in Gijon and 180 employees, with
an invoicing of 19 million euros in 2007.
Ideas en Metal supplied the collectors and torsion transmission systems for
Ibersol thermosolar lant. Likewise, has supplied some components in
Eurotrough for Andasol 1 and is the supplier of structures for helyostates in
Torresol Energy and the pillars and main tube for Extresol II and Manchasol I.
d) IA Técnica
This company belongs to Iriarte group, made up of Iriarte Manutención, IA
Técninca Energías Renovables and IA Técnica. In the 50s, Pedro Iriarte Artola
founded a small blacksmith’s, which was the origin for Talleres Iriarte and
Iriarte Manutención in 2003.
IA Técnica was founded in 1990, devoted to mechanized boilermaking for the
areas of construction and automotive. The subdivission IA Técnica Energías
Renovables was founded in 2008 and supplies supports for photovoltaic sun-
trackers and arms for parabolic collectors. However, we do not know whether
this company has supplied any component for collectors in any plant under
operation.
Garrigues Medio Ambiente considers that the suppliers chosen by Albiasa are a
good technical option, as they have a consolidated career in steel components
manufacture.
Report on the technical assessment of the structure Page 30 of 41 Albiasa-Trough
On the other hand, the fact that the structure components are supplied by different
manufacturers implies that Albiasa has to make sure they fulfill all the tolerances
required to avoid any possible problem in the assembly process. Therefore, we
consider it should be paid special attention to this aspect. Moreover, using one
sole manufacturer for the supply of all the elements may cause a delay in the time
delivery, so having several manufacturers may be considered advantageous in a
way.
According to the information supplied, Albiasa asks each supplier for a certificate
of conformity in which each supplier declares that the products conform to
contract requirements regarding mechanical properties, breakage stress, elastic
limit, strength and chemical composition, being part of the quality dossier.
Moreover, the quality dossier will include a dimensional checking report.
Depending on the element, the supplier will check the relevant critical
measurements and that deviations are within the tolerance limits according to the
manufacture plane. Likewise, suppliers must submit a certificate stating the
superfical treatments applied on each element and the pertinent checking tests.
Lastly, critical elements will require a revision of 100% elements.
Garrigues Medio Ambiente considers that the quality control by Albiasa is
appropriate and usual for this type of supply.
2.6 Assembly process and maintenance for the collector
Now, we present a summary describing the assembly process according to the
analysis by Alatec. Albiasa has informed us that the assembly process has been
designed to optimize the efficiency values and intercepting factor as they have
been obtained in PSA. This approach is appropriate has to be checked with the
assembly process to be used when executing commercial plants.
Report on the technical assessment of the structure Page 31 of 41 Albiasa-Trough
Albiasa solar will build an assembly bay in the location of the thermosolar plant to
assembly the collector’s structure. The bay will have 5 assembly and control
stations to carry out the different tasks. In this way, the same assembly line will
serve to assembly the structure and to position the mirrors on the structures.
The following table, included in Alatec report, presents a summary of the tasks for
each station:
Station Task Function Machinery and equipments
N. of operatives
Total time
1 Torque tube assembly
Assembly of torque tube and bridges for the later
placement of the receiver tube
Two tools similar to those used in the torque tube
assembly. Hydropneumatic guns.
4 12 min
2 TR supports assembly
Assembly of 3 supports for receiver tube on the
bridges.
Fixture focus tools, focalizer and focus
centralizer. 2 14 min
3 Arms assembly Arms assembly on the torque tube set. Hydropneumatic guns. 2 14 min
0 Mirrors supports
pre-assembly with arms
Presentation of the mirrors on the arms.
Final tightening is not done.
Specific tables where the arm is fixed to. 4 15 min
4 Mirrors assembly
External and internal mirrors assembly on the
module structure.
Two structures of semi-grades at both sides of the
rail mounted track. 5 12 min
5 Optical checkpoint
Optical checkpoint to certify each module has the guaranteed optical
efficiency.
Digital projector and control unit 3 12 min
Table 2.6: Description of assembly stations.
Once the modules are assembled, they are shipped from the assembly bay to their
location in the solar field where they are placed by means of cranes on the
previously installed pillars. When all the modules of a collector are assembled,
they are aligned and levelled with a special tool. Albiasa has planned that the
assembly process for each module takes 15 minutes and must be shipped to the
solar field at this time interval.
Report on the technical assessment of the structure Page 32 of 41 Albiasa-Trough
Albiasa Solar has chosen the scanning method to measure the collector’s optical
efficiency. This aspect and additional information about the mirrors’ assembly
process will be analysed.
The mirrors are placed on the structures using steel semi-grades which facilitate
the parabola to adopt the ideal position. The grades have 10 contact points per
mirror, 2 of which guarantee transversal position to the module’s axis, 4 of them
guarantee longitudinal position regarding the module’s axis and the 4 remaining
ones guarantee vertical position and the parabola’s shape. Contact points are made
of nylon to prevent the mirrors from suffering any damage during the positioning.
A laser will check that the position and orientation of mirrors on the semi-grades
is correct.
Mirrors are placed using a manipulator, which takes them out of the piles and
place them on the semi-grade, having bumpers to secure the mirrors’ appropriate
position. Once the two semi-parabolas are assembled, two suction pads suck the
mirrors (4 pads per mirror) and place the parabola on the set made up of the
torque tube and the arms’ supports. The operatives screw the mirrors to the
structure and the suction pads release the mirrors.
Placing the mirrors on the structure is an automated process whereas tightening
teh flanges, which are the joint between the mirrors and arms, is done manually by
the operatives.
Finally, the last step consists on measuring the intercepting factor of each module.
According to the information provided by Albiasa solar, it is done by a laser
scanner. It measures the parabola’s accuracy at the back of the collector and it
generates a 3 dimensional image with ±2 mm accuracy. According to Faro, the
laser supplier, the factors affecting measurement accuracy are distance, light and
the element colour, among others. In this sense, Albiasa has planned to carry out
the measurements at a distance lower than 10 m and the back of the mirrors, from
Report on the technical assessment of the structure Page 33 of 41 Albiasa-Trough
which measurements are taken, will be white. According to the information
provided by Faro, reflectivity factor in this element is 90% and in these
conditions, the measurement accuracy can be ±1 mm.
This image can be later exported to a computer to be compared with the
theoretical image and check the assembly quality. According to the information
provided, this system has good performance under light temperature variations.
This scanner system accuracy has been assessed in the half-collector installed at
PSA. The intercepting factor obtained with this system is similar to that measured
at PSA. The reading procedure at the mirrors’ back requires the introduction of a
correcting factor to eliminate the signal blockage of the structure, which is located
between the scanner and mirrors. Albiasa has estimated the losses due to that
blockage which results in 1,8% losses. Therefore, the intercepting factor measured
by the scanner must be raised proportionally.
One collector Albiasa-Trough 150 m long, is made up of 12 modules of 3
different types. So, one collector has 2 initial modules, 8 central modules and 2
final modules. The assembly order to be followed is: 1 initial module, 4 central
modules and 1 final module.
In relation to the commentaries made by Alatec, Garrigues Medio Ambiente
shares the following:
• It would be advisable to have at least 2 assembly lines so as to reduce
assembly periods and to avoid any delay in case of breakdown.
• Using cranes to assemble the modules is usual for thermosolar plants,
however, on windy days the assembly process can get complicated.
• Using semi-grades and automated media makes sure that the mirrors position
on the structure will follow a parabola shape. However, as the joints between
mirrors and the arms are manually reinforced, we consider that the operatives
Report on the technical assessment of the structure Page 34 of 41 Albiasa-Trough
should receive specific information about the process. The automated
assembly process has not been tested in any plant under operation. The
collector installed at PSA was assembled following a manual assembly
procedure; therefore, Garrigues Medio Ambiente recommends that the testing
results from PSA should be corroborated when they are installed following
this procedure. Likewise, the time periods devoted for each assembly station
must be checked when they are installed in a commercial plant.
• We consider that having a station to check that the optical efficiency is
appropriate to the guaranteed value is suitable, for the geometric quality is
linked to the assembly process. The system liability has been tested in a
module from the half-collector installed in PSA.
• Finally, it would be desirable to check each collector’s module alignment
once they are installed on field to avoid misalignment.
2.7 Auditing structural calculations and foundations type
2.7.1 Structural calculations
Alatec has revised the structural calculations making up the structure for
collectors developed by Albiasa solar. The calculations under revision
correspond to a collector 150 m long, made of 12 modules, 12 m each.
Taking into account that there is no specific regulation for collectors’ structures,
Alatec considers it advisable to estimate wind action according to the Technical
Building Code. Likewise, the application of the wind and stress hypotheses
taken into account for the structural calculation as well as the earthquake
resistance regulations is reasonable.
Regarding the materials of the elements, Alatec considers they are appropriate
and has checked they fulfil the safety coefficients under application.
Report on the technical assessment of the structure Page 35 of 41 Albiasa-Trough
Moreover, Alatec thinks that the elements modeling, using Catia software is
appropriate and the results for the main pillar, torque tube and arms confirm the
resistance for those elements.
Regarding the intermediate pillar, depending on its position in the solar field, it
is designed to support 90 km/h wind velocity when it is protected or more than
100 km/h when it is exposed to wind. In both cases, the modeling justifies the
design for each of them.
Garrigues Medio Ambiente considers Alatec revision appropriate regarding the
structural calculation, although we think it lacks an analysis of the elements’
joints in the structure for they are a critical part. Garrigues Medio Ambiente
coincides with Alatec conclusions in general terms and specifically with the fact
that the arms, girders and pillar are designed to support the stresses they will be
subjected to along their useful life.
To complete Alatec analysis in relation to the joints, Albiasa Solar provided
Garrigues Medio Ambiente with an additional report about the calculations for
the screwed joints in Albiasa-Trough. This report includes theoretical
calculations of arms and end plates in the collector.
According to the supplied information, Albiasa Solar has calculated the joints
between the module and axis and between the supports joints in the absorber
tube, using traditional formulae used to calculate elements in machinery or
empirical methods, for these calculation procedures are considered more reliable
than computer programs. We think it would have been advisable to compare
results from both procedures.
Calculations of the screws for the end plates have been carried out taking into
account the maximum stress hypothesis regarding wind and tracking position,
maintaining a safety factor of 1,96 in the worst case. Albiasa solar declares that
Report on the technical assessment of the structure Page 36 of 41 Albiasa-Trough
the collector tested at PSA has been under operation for more than 20 months
and has faced wind velocities higher than 110 km/h having no incidence at the
joints.
Besides, the stress applied by the absorbed tubes’ weight when the collector is
focusing the parabola is taking into account for the arms supports. In this case,
the screws keep a safety factor of 8,9.
Even though the possible differences between the results from the calculation
procedures used by Albiasa and those from computer programs are missing,
Garrigues Medio Ambiente considers that the methodology used by Albiasa to
design the joints is appropriate. Likewise, the safety factors are also appropriate.
2.7.2 Foundation types
Pillars foundations will consist on reinforced concrete circular isolated piles 85
cm diameter, with steel structure. They will be between 4 and 6 meters long,
depending on the terrain features where the thermosolar plant is to be located.
Piles will protrude upwards 20 cm over land level.
Garrigues Medio Ambiente considers that, depending on the terrain type and the
results from a geotechnical study, it should be checked that foundations are
resistant to subsidence and the stresses transferred to the terrain are appropriate
to its bearing capacity to adapt the foundations design if necessary.
Report on the technical assessment of the structure Page 37 of 41 Albiasa-Trough
3. CONCLUSIONS
The conclusions by Garrigues Medio Ambiente during the technical revision of the
structure collectors Albiasa-Trough are:
i. Albiasa experience. Garrigues Medio Ambiente considers that Albiasa Solar has
experience in the design, construction and installation of structures that are
similar to its characteristics and complexity, for which we conclude that it has all
the technical resources required to design and construct structures for
thermosolar plants. Regarding thermosolar plants promotion, Albiasa Solar has
experience in promoting several plants in USA. It must be noted that, although it
does not have commercial plants under operation, Albiasa Solar has half
collector installed in PSA for 30 months, to carry out the texts under revision in
this report, having no incidence.
ii. Albiasa-Trough design. The structure design is torque tube type. The torque tube
is made up of four sections or quarters of torque tube, having flanges joined by
clinching and TOX joints. Its main advantages are the eradication of helicoidally
welding which is present in other structures with central tube, which lower down
manufacture and transportation costs to the solar field, as well as facilitating the
arms fixing to the flanges in the torque tube. Garrigues Medio Ambiente
considers that this design present advantages regarding manufacturing and
transportation costs, which should compensate for the cost increase in the
assembly on field. Likewise, choosing one of the versions offered by Albiasa
(100 m or 150 m) should depend on a cost-benefits study.
Report on the technical assessment of the structure Page 38 of 41 Albiasa-Trough
iii. Tests results
a) Mechanical test. Garrigues Medio Ambiente considers that the tests carried
out by Albiasa for the mechanical characterization of the structure are
complete and the results show an appropriate mechanical performance.
b) Optical tests. Garrigues Medio Ambiente considers that the intercepting
factor, higher than 96%, resulting from the tests in PSA, is within the
highest range in the market. The definitive report by PSA, dated the 21st
October, 2010, shows the peak optical efficiency, 0,757. The formula used
to calculate the incidence angle modifier is valid for the range of incidence
angles between 0º and 65º, which is, according to the report, the operation
range for collectors in thermosolar plants. Additionally, the formula used to
calculate the global efficiency ( ) covers the range 260º-380º C,
which is the operation interval for parabolic collectors. Taking into account
that the peak optical efficiency is 75,7%, we think that the value for global
efficiency is good. Garrigues Medio Ambiente considers that, according to
the tests carried out in PSA, the experimental characterization of Albiasa-
Trough can be considered as complete.
iv. Manufacture and assembly.
a) Garrigues Medio Ambiente considers that the suppliers for the main
components chosen by Albiasa Solar have the experience required for such
supply.
b) Regarding the quality control, we think it has the elements required to check
the equipments specifications when they are received at the assembly point.
Among these elements, we can highlight Albiasa Solar decision of
providing its staff for the equipments reception and also demanding a
Report on the technical assessment of the structure Page 39 of 41 Albiasa-Trough
quality dossier about the components under supply to their suppliers, to
check the requirements demanded by Albiasa Solar.
c) The assembly process described in the report has not been tested yet,
although we understand from the analysis that it is well designed and the
time and procedures are reasonable. Garrigues Medio Ambiente considers
that automatization, using semi-grades to facilitate the parabolic shape and
the intercepting factor measurement for each module inside the assembly
bay before been shipped to the solar field are outstanding features. We
recommend Albiasa to check the assembly time periods and the compliance
of the guaranteed values regarding geometric quality when assembling the
first Albiasa-Trough collectors on field.
v. Structural calculations. Garrigues Medio Ambiente considers that the
conclusions provided by Alatec regarding calculations auditing are appropriate.
Regarding foundations, Garrigues Medio Ambiente recommends revising and, if
necessary, adapting foundations design when the geotechnical features of the site
terrain are known. Regarding the joints, Garrigues Medio Ambiente considers
that the methodology and safety factors used by Albiasa for its design are
appropriate.
Report on the technical assessment of the structure Page 40 of 41 Albiasa-Trough
APPENDIX: DOCUMENTS UNDER REVISION
• Technical assessment of “Albiasa-Trough” carried out by Alatec, dated the 25th
May, 2010.
• Complementary documentation to carry out the technical assessment of the
structure Albiasa-Trough provided by Albiasa to Garrigues Medio Ambiente on
the 16th July, 2010.
• Assembly bay for parabolic collector. Document written by Albiasa Solar on the
20th July, 2010.
• First results on peak optical efficiency and incidence angle modifier for Albiasa
Trough carried out by Eduardo Zarza on the 22nd July, 2010.
• Calculations for the screwed joints by Albiasa Solar, provided to Garrigues
Medio Ambiente in August, 2010.
• Appendix on the pair transmission between modules in a collector Albiasa
Trough, provided by Albiasa solar to Garrigues Medio Ambiente in August
2010.
• Torsion test report on the torque tube carried out by Applus on the 3rd of March,
2010.
• Torsion test report on the torque tube carried out by Applus on the 8th of
October, 2010.
• Technical specifications of Rioglass mirrors, provided by Albiasa Solar to
Garrigues Medio Ambiente on the 15th October, 2010.
• Experimental calculation of peak optical efficiency, incidence angle modifier
and global efficiency, carried out at PSA on the 21st October, 2010.
Report on the technical assessment of the structure Page 41 of 41 Albiasa-Trough
• Station 5: Optical checking, document written by Albiasa Solar on the 21st
September, 2010.
• Appendix explaining the document “Station 5: Optical checking”, written by
Albiasa Solar and sent to Garrigues Medio Ambiente on the 26th October, 2010.
• Justification/Demonstration of impossibility for fatigue failure due to torsion in
any part of the torque tube set Albiasa Trough V.2, carried out by Albiasa on the
12th November, 2010.
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