Garrigues Report 05 Jul 2011 INGLES (2)

REPORT ON THE TECHNICAL ASSESSMENT OF THE STRUCTURE

FOR COLLECTORS ALBIASATROUGH

5th July, 2011

Report on the technical assessment of the structure 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


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.


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


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.


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


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


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


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


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


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.


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.


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.


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.


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


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.


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


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


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.


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


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.


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.


• 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


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.


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


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.


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.


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.


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.

http://www.mecsa.org/en/mecsa/obras.php?id=244&categoria=MECHANIZED%20BOILERMAKING�


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.


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.


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


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


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.


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


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.


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.


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


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.


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.


• 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.

Garrigues Report 05 Jul 2011 INGLES (2)

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