Skip to main content

New solar collector concept for high temperature operation in CSP applications

Final Report Summary - HITECO (New solar collector concept for high temperature operation in CSP applications)

Executive Summary:
According to the EC’s Strategic Energy Technology Plan (SET-Plan), there are several pathways that will lead to a los carbon economy, since no single measure or technology will be enough to achieve the 2020 objectives. Therefore, solar energy, including concentrated solar power (CSP), needs to become more competitive and gain mass market appeal. It is expected that with the necessary technological development, this technology might meet up to 7% of the world’s power needs. The most mature and promising technology of all CSP designs is currently the parabolic-trough solar collector, with more than 1.000 MW operating world-wide and more than 3.000 MW under construction or planned to be commissioned in the next 5 years. However, in order to accelerate the implementation of this technology, the produced electricity cost has to be reduced by increasing the thermo solar plants’ efficiency.
The HITECO Project was focused on that, increasing the operating temperature of the heat transfer fluid (HTF) up to 600 °C and therefore raising the overall efficiency of the process. The current state-of-the-art designs are prevented to reach such temperatures without a dramatic efficiency drop by several key components. The HITECO design has re-assess all these concepts and research on new solutions that will allow the HTF to reach the aforementioned temperature and the overall process to increase its performance at the same time. In order to develop such a receiver, several research lines will have to be explored. Research on new materials and deposition methods will be developed in order to provide a system that will be able to endure such temperatures and maintain the optical, mechanical and thermal performance of the receiver; a new vacuum system will be introduced to maintain and monitor an acceptable vacuum level and the desired composition inside the tubes; new HTFs will have to be researched; and new supports, union systems and contact points will be developed. All these new concepts and designs will be validated through several modeling approaches and also through off-sun and field tests. The new design will also be assessed from a manufacturing point of view, in order to achieve a product that is easier and cheaper to fabricate, to assemble and to commission.
In order to achieve these ambitious goals, the HITECO consortium has brought together industrial partners and research organizations. The consortium has been coordinated by the SME ARIES, an independent engineering company specialized in the development of highly technological and efficient solutions that has broad experience in promoting CSP plants. There are several partners from Spain, the world leader in the development of CSP technology, and key partners from other countries to complement this thermo solar know-how with their intensive experience in other demanding sectors.
With the successful development of the HITECO concept, the efficiency of CSP plants will be increased, thus contributing to a reduction of the produced electricity cost and therefore accelerating the implementation of this technology. Furthermore, by offering an easier and cheaper to manufacture technology, in addition to its 25-year life cycle, the CSP plants using the HITECO design will be more attractive for investors even without the help of feed-in tariffs, which will also help to the development of CSP plants. By developing these new technologies, this project will help Europe continue its reign in the CSP world market.

Project Context and Objectives:
In order to accelerate the implementation of the concentrated solar power (CSP) technology, electricity costs must be reduced by increasing the plant’s efficiency. The HITECO Project aims at doing so by increasing the operating temperature of heat transfer fluid (HTF) up to 600 °C, which would raise the overall efficiency of the process.
Current designs are prevented of reaching such high temperatures without it experiencing a drastic efficiency drop by several of its key components. The HITECO design will re-assess all these concepts and research new solutions able to allow the HTF to reach the aforementioned temperature and the overall process to increase its performance at the same time.
In order to develop such a receiver, several research lines will be explored. Research on new materials and deposition method will be developed in order to provide a system able to endure such high temperatures, maintaining the optical, mechanical and thermal performance of the receiver; a new vacuum system will be introduces to maintain and monitor an acceptable vacuum level and the desired composition inside the tubes; new HTFs will be researched; and new supports, union systems and contact points will be developed in order to better accommodate the thermal expansion of steel and glass tubes. All these new designs and concepts will be validated through several modeling approaches and also through off-sun and field tests. The new design will also be assessed form a manufacturing point of view, in order to achieve an easier product to manufacture, assemble and commission.
Summarizing, this new concept of absorber tube will be capable to operate at temperatures of up to 600 °C and also allow to a much higher efficiency in the solar radiation to electrical energy conversion process, due to the increased optical and thermal performance expected for this new design.

Science and Technology Objectives
General objective:
• Develop and validate a new concept of absorber tube and develop a Solar Assembly Collector that allows the operating temperature of the transfer fluid to reach 600 °C while increasing the performance.
Specific Objectives:
• Find alternative concepts to fulfill operating requirements for higher temperatures without the efficiency losses of today’s technology. These should include:
o A concept that eliminates optical losses due to vertical displacement of the tube from the theoretical focal point.
o A system to evacuate H₂ and maintain the chemical composition inside the tubes which is not sensitive to temperature.
o A design able to reduce the losses due to shadow affects and therefore increases the effective area of the tube. The objective that has been set, is to reach an effective length of the receiver of 98% (currently it’s between 95 and 96% for 400 °C, decreasing with temperature). As a result of this longer effective length and the avoidance of the tube flexion, a performance increase of 2.5% is expected.
• Develop a concept that guarantees sufficient durability (up to 25 years of continuous operation).
• Develop a new product easier and cheaper to manufacture and also presents an easier collector assembly. Manufacturing cost reduction of 20%.
• Develop a solution that allows to achieve an optimal energy cost (€/kWh).

Operative Objectives
• Research, develop and validate new receptor geometries and design for each one of the key elements, including among others:
o the supporting structure,
o the absorber tube-structure interface,
o flexible and expansion compensating elements,
o joint systems between solar collector elements and assemblies.
• Research, develop and validate new coating concepts (selective and antireflexive materials) for the new operating temperature, and to develop an application method for them (PVD). Emitance of 0.1 at 600 °C and absortance of 0.96.
• Research, develop and validate a new vacuum and composition maintenance system that includes and integrates the following points:
o New glass covers concepts, including new geometry and new composition of the glass tube.
o New protection and treatment concepts.
o New concepts of contact systems for high operating temperatures, including ceramic and polymeric materials with low thermal conductivity.
o Vacuum system continuously and externally controlled and monitored of a high thermal performance and at low vacuum level 1•10ˉ² mbar, avoiding the use of getter systems.
• Use of a HTF management system using a novel fluid able to endure the new operating conditions.
• Integrate all new concepts and developments in order to assure an optimal optical, thermal and mechanical performance of the collector. This will be done by modeling and correlating the optical, mechanical and thermal behavior of the developed technologies and designs.
• Develop a lab-scale prototype to validate the design and development of the HITECO concept by conducting off-sun tests and analyzing the re4sults obtained.
• Develop a pilot in an industrial plant in order to validate the new concept in terms of:
o Performance.
o Operating and product costs (CAPEX and OPEX).
• Design and develop the pre-industrial processes to manufacture the HITECO receiver and be able to later up-scale the processes.

Project Results:
The activities carried in HITECO have been focused in to develop a new device with new and advantageous technical properties for Solar Thermal Technology.
The results of these activities can be divided in five main parts according the evolution of the project:

1. Definition of the concept and previous design
2. Development of components and coatings
3. Modeling and Correlation
4. Testing in Laboratory and Solar Field
5. Validation and confirmation of results

These activities as well the results involved in it are described and explained below:

1. Definition of the concept and previous design

The main target in this stage was the definition of the absorber tube concept according the premises included in the objectives and the initial idea expressed in the DoW. These design bases are shown below:

• The Stainless Steel tube (SS tube) and the glass tube will be independent from each other. This introduces several differences from the state of the art: the differential thermal expansion does not impact on tube integrity having no welding between both materials; secondly, the axial expansion of the stainless steel tube is free from the glass tube, since there is no contact between the two tubes and continuous vacuum chamber is formed by each semicolector and, at the end, the vacuum is done in field (not in factory) using vacuum pumps.
• The accumulated thermal expansion of the SS tube is completely absorbed by a single bellow placed at the end of every semicolector. Also, the mechanical load of the bellow due to its self expansion is completely transmitted to the final vertical stiffened support. Thus, no appreciable stress is transmitted to the outer glass tube, therefore decreasing its breakage risk.
• The SS tube is supported in several contact points by a ceramic disc with low thermal conductivity, mounted in the flange connection. Due to the low thermal conductivity of ceramic materials, heat conduction from the inner tube is largely reduced.
• The connection of glass sections is done by flanges and vacuum seals to ensure a constant pressure on glass and joints; this reduces the breakage risk and sealing the vacuum chamber.
• The HITECO design reduces the number of welds, where only a few of them will be exposed to a vacuum environment. The connection system simplifies the HCE manufacturing process in terms of welding requirements, and therefore reducing costs.
• The system is designed to maintain the relative position of the HCE and the parabolic through constant, thus keeping the receiver tube always in the focal line. As a result, the vertical receiver-structure supports present an equal height.
• The Hiteco concept directly integrates the vacuum maintenance system in the HCE, enabling pressure control by vacuum pumps each semicolector. Hiteco HCE is designed to operate at higher pressure levels (compared to the current technology) and with an insulating gas inside the vacuum chamber capable to absorb the effect of high heat conductive gases potentially present inside of it. As a consequence, this system reduces the costs involved in manufacturing process and allows full-time monitoring of the vacuum chamber state. Moreover, since vacuum is dynamically controlled, getters are substituted by a more efficient system that also guarantees an appropriate vacuum level. By removing the getters, a relevant disadvantage concerning performance in increased temperature is solved.

According to these key points it has been fixed a definition of the new solar absorber tube based in the next guidelines that allowed working in the manufacturing lines for each component.

a) The tube will be formed with glass sections with a length of 6 meters. These sections will be coated with AR coating to improve the optical characteristics (around 96% of transmittance).
b) The internal steel tube will be coated with a selective stack that will provide good optical values (around 10% of emitance and 95% of absortance). The union of steel tubes will be done by welding.
c) There will be placed a ceramic piece each 6 meters of tube (union of glass sections).
d) The tribological performance of the ceramic piece will allow the survival of coating over the steel.
e) The working range pressure inside the chamber will be around 10-4 mbar and 10 mbar.
f) The union of section will be done by elastomeric pieces to allow working under vacuum conditions.
g) The vacuum on the tube will be done by an only connection at the end of semicolector.
h) The supporting of the absorber tube over the solar structure will be done in the bridle attachment area.

2. Development of components and coatings

Once the system was defined in work packages WP2, WP3 and WP4 started the detail design and manufacturing of prototypes.
a. Selective coating and anti-reflexive development

The target in the beginning of the activities was to obtain a proper solar selective coating able to work according the conditions defined in HITECO keeping the optical values defined (10% of emitance and 95% of absortance)
• Working temperature: between 350º and 600ºC.
• Pressure and composition: maximum partial pressure of 200mbar of air.

There have been developed coatings to work at high temperature assuring the chemical stability up to 600 ºC. The work was carried out in the two studied systems, a) oxide based selective coating (formed by Ag and Mo: SiO2 CERMET) and b) nitride based selective coating (formed by Ag and Mo: Si3N4 CERMET).
Between others, the criteria followed during the coating definition was to have a proper mechanical properties, as adhesion of the stack to the substrate and mechanical resistance, and to provide a formula able to be scalable up to 4 meters length unit in cylindrical geometries.
Regarding the structural properties the ageing of the stack at high temperature was a critical point. It becomes in an analysis of diffusion phenomena and the mechanism that avoids the oxidation of the stack for the foreseen presence of oxygen.
The initial results of the tasks didn’t provide a coating to be applied with guaranties in a 4 meters length tube because the degradation in normal conditions. A redesign of the stack, in with was change the silver (used as IR mirror) and the Cermet, provided a coating with good optical values (E400ºC= 8%; E600ºC=13% and A=94%) that was finally used during the validation process of the prototype.

A new antireflective coating was developed to be applied in the glass tubes to achieve the best optical values.
The new AR coating Sol-gel was based in mixture of components produced according to a recipe realized in 2 step: a) tetraethylorthosilicate (TEOS) + Non-ionic surfactant-Triton X-100 [C14H22O(C2H4O)10] (chemical name-Glycol Tertoctylphenyl ether) + HNO3 + H2O + colloidal silica (LUDOX) and after that we stir it 120 minutes. B) Addition to the mixture of acetylacetonate (ACAC) + Ethanol (EtOH) and stirring during for 60 minutes.
One target during the design included to be strong enough to support a typical cleaning process that is produced on field. It meant to introduce several chemical modifications to improve the life expectancy and reduce the influence of humidity.
The final results obtained for the coating were successful from the optical and mechanical points of view. The value for transmittance obtained was around 97% (from the initial 92%) and the mechanical ageing testing shown the capacity of keep the properties during long working periods.
b. Vacuum, connections and experimental control

The vacuum system to test the premises of HITECO was a key element during the project. The initial target in this point was to confirm the capacity to produce low pressures in a chamber placed on field keeping the conditions initially defined. According to that the analysis of the vacuum chamber and pressure level range has been carried and defined according the technology available for other industrial processes. The most important results were the next:
• According the conditions defined in HITECO where will be several flow conditions: a) molecular, b) Knudsen, and c) continuous flow inside the chamber.
• The pressure level to be achieved makes it necessary to operate the chamber with a two staged pumping concept. It means to use a rotator pump up values around 10-1 mbar and to use a molecular pump to achieve 10-5 mbar.
• The outgassing is a mechanism to consider as important when a system with high surface is working at high temperatures and with strict requirements.
• The length of the chamber has a higher influence on conductance. It means to consider the number of support elements and the pass sections for pumping.
The vacuum and gas control system designed and produced was based on the above mentioned analysis. During the project were developed several concepts of vacuum systems including a gas control system for the usage of insulating gas (two-pump vacuum system with filling gas system). Based on the conductance measurements performed, a DN40 metal hose has been selected for the off-sun test system.
The mechanical definition produced was used successfully during the testing in laboratory (WP6) and the testing on field (WP8).
According to the concept defined in HITECO it was developed a below (one below at the end of each semicolector was defined) able to work during all the working life producing minimum mechanical charges on the system. In order to fulfill specification for the final expansion component (FEC), a highly flexible bellows with very narrow corrugations was selected (produced by hydro forming process). To determine the detailed tool shape and to check the bellows production some tasks of finite element analysis were used. In addition, the bellows spring forces in compressed and elongated shape have been calculated as well as the bellows life time. Afterwards new hydro forming tools have been designed and produced. Using these tools bellows for the off-sun test for internal validation has been produced. The bellows for off-sun test was welded to end parts defined, the bellows for the validation was welded to special test adapters.
For the modular locking system (MLS) the same bellows corrugation shape was used than for the FEC, only the number of corrugations and the end cuff geometry are different. Using the new hydro forming tool, bellows for the MLS-validation have been produced.
With these bellows the spring force measurement in end positions and life time testing validation has been performed.
A metal hose (doing the function that it currently done by ball-joints) has been developed for the connection of the solar collector and the fixed piping system. During the first life time tests some failures in the weld seam between the corrugations and the tube ends occurred. At further tests there have been no failures in the optimized welding area. Life time tests (20.000 cycles) have been done with different installations.
c. Glass clouding, sealing and thermal insulation

The production of glass tube sections with a length of 6 meters with accurate values of parallelism and finishing was a key point of the activity. The thickness defined for tubes was 3mm).
During the project it was tested the welding of tubes and glass flanges following different paths: by laser, by laser and gas and only by gas. The optimal results show the welding by using of gas and oxygen.

Part of the activity was to modify the process of melting of glass and recipe of the composition of glass in order to achieve higher transmittance by 0.3%. At wall thickness of 3mm we have been achieving excellent integral transmittance of glass around 92.5% in wavelength 300-1100nm.
Mechanically was tested that glass welding tubing for the solidity and they meet the demanded criteria considering a tensile strength of glass welding and final tensile strength higher than a demanded 750Mpa.
Geometry was frozen considering the needs of HITECO and manufacturing capacity of the suppliers: length 6020 mm and diameter of 160 mm with to ends done by molding including the geometry to place the joints.

The sealing joints set was configured considering the target leakness values (around 10-4 mbar l/s) and the maximum expected values in them (around 150ºC).
During the design process and with validation procedures done some conclusion were achieved:

• The maximum GAP allowable for the combination of glass flange and inner lip seals is a critical value.
• The whole bridle system is very sensitive to the external loads which could appear in a parabolic trough.
• The glass flange roughness is a key point to improve a solution for the vacuum tightness.
• They could appear several problems when the glass flange is touching the metallic ceramic support.
The final configuration of sealing is based in the using of two seals to keep the vacuums on the chamber one axial and other radial. According to that, on each ceramic support have been assembled two axial seals that keep contact with the polished face of glass, having the function of maintaining the seal of the expansion chamber absorbing movements of the glass tube due to temperature changes.
In the same ceramic support, on a new specific area, the radial seal is mounted contacting with the inner cylindrical surface of the glass, reinforcing with that the sealing function of the axial seal and giving more rigidity.
For the validation of the sealing joints have been developed tests of temperature, permeation and leakage. All results were satisfactory.

The ceramic support is placed each 6 meters with a double function: a) place the steel tube in the center of the glass tube and b) avoid high thermal losses by conduction.
The component has suffered different evolution during the project development. The final design of the internal absorber tube supports has been produced using three steel shafts surrounded by ceramic bearing. Due to their good tribological performance, inner tube stands and slides on these radial bearings positioned in angle of 120º one to each other. The main ceramic piece, which provides mechanical strength to this set, is screwed to the ceramic support. This ceramic system offers a double thermal breakage. The first one is between the inner tube and the metallic shaft through the ceramic bearing. And the second one is the main ceramic piece which connects the metallic shaft to the ceramic support. Due to the experimental results taken out from previous prototypes, the ceramic material chosen for this piece is Zirconia (Magnesia stabilized zirconia oxide) because its high mechanical resistance and a the low thermal conductivity. The validation of the ceramic piece has been done by modeling and testing in the of-sun test. Regarding modeling, it was produce a model to define the map of temperatures in the set. The validation was considered for a ceramic piece working in the worse conditions (molten salts around 600ºC) being the limitation of the sealing (because of the material) 200ºC. The results obtained are the maximum temperature reachable in the ceramic support where sealing joints are located is 163ºCwhat is below the maximum sealing temperature working range.

3. Modeling and Correlation

There have been developed several analyses to characterize the mechanical behavior of the components and subsystems that were involved in HITECO project.
It has included the solutions for components and well the integrated performance of absorber tube and the supporting structure that has been used in the experimental tests.
The main activities and results obtained during mechanical analysis are the next:
• Mechanical analysis of the supporting structure: adaptation of the HITECO absorber tube to the supporting structure used in testing. Definition of new supporting arms and their designed for manufacturing. The maximum displacement obtained in maximum wind velocity in operation (10 m/s) was 15 mm in the position more unfavorable with a maximum stress of 140 MPa in Von Mises criteria.
• Mechanical analysis of the supporting structure to obtain the parable deformations due to gravity loads (its own weight) and wind loads (for several operating scenarios). The result of this analysis has been used in the optical modeling to analyze the optical losses due to parable distortions. These results have been considered to analyze the optical efficiency in other model with a typical position of 30°C degrees of the structure.
• A modal frequency analysis has been carried out in order to analyze and evaluate the dynamic response of structure under excitations. The first six natural modes has been calculated using finite elements analysis. The results obtained are between 2.53 Hz (first natural mode) and 7.325 Hz (sixth natural mode).
All components of the receiver tube were modeled by a thermal and mechanical analysis being the results the next:
• In the glass tubes has been obtained a maximum stress of -35 MPa in compression and 20 MPa in traction for the maximum displacement in operation in critical conditions of working.
• In the SS tube analysis a maximum bending of 9.9 mm has been as result in the conditions more unfavorable.
• In the set of the ceramic piece the results in maximum temperature of operation are 85 MPa as Principal Stress criteria in compression with a deformation maximum of 1.42•10-3 mm.

The optical results of the models with the deformation calculated of the parabola have a decrease of 3.25% between ideal and deformed with a normal incidence (θ=0°) and a decrease of 3.25% between ideal and deformed with a normal incidence θ=30°.

For thermal models, the results have been extracted from a base case with next specifics inputs; DNI (619.1 W/m2), Incident angle (30.13°), vacuum gas type(100% air), vacuum annulus pressure (0.01 Pa), HTF mass flow rate (5.05 kg/s), obtaining for this base case a results of: HTF temperature increase 24.6°C, Heat gain 1844.8 W/m; Heat loss 306.3 W/m, Optical efficiency of 62.5% and a Collector Efficiency or 53.6%. These model have been correlate with a experimental results obtained in field.

4. Testing in Laboratory and Solar Field

a. Testing in Laboratory Off-sun test
For the validation of the concept and to check the prototypes produced, there were designed and assembled a bench test for the off-sun test in laboratory.
The tooling included in the bench was: heating system, temperature sensors, pressure sensors, gas composition sensor, electrical sensors, data acquisition and control system a vacuum system. The testing activities were focused in to check the heat losses depending or vacuum chamber configuration and mechanical behavior of the components.
There have been evaluated all the intermediate selective coating designs and the values for real operation was done with the final design of coating. This selective coating provides with the last set of sealing joints the stability of selective coating under vacuum conditions the batch of tests carried out to characterize the performance of receiver tube (between 1•10-4 mbar in vacuum chamber at low temperature to 10 mbar using different configuration of gas with partial pressures of Kr).
The most important conclusion extracted from the thermal tests in OFFSUN is the influence of the gas composition of the vacuum chamber in thermal losses. The presence of a gas as Krypton allows to work at high pressure in vacuum chamber (test done at 300°C, 400°C and 500°C) with less or similar thermal losses than when the activity is done at low pressures.
Some relevant results are that the target working condition in HITECO (2.5•10-2 mbar with air) is similar in thermal losses terms to use Kr at pressure around 5 mbar. It means more conform and reliability during operation.
It was taken into account during testing that high air pressures at high temperature the oxygen present in the air could damage the selective coating, so that, in these cases nitrogen was used for the characterization of thermal losses avoiding oxidation.
For the energy consumption which means the energy losses by the receiver, the difference of voltage along the wires and in endings of tubes were discarded. These endings were also thermal isolated with a wool rock-cover not affecting the thermal losses in the surrounding parts of the receiver.
To ensure the tightness of sealing system, after all heat performance tests were finished, a final mechanical test was taken on the receiver. The bridle between both glass tubes was misaligned 20mm in atmospheric pressure and then, high vacuum (10-4mbar) was accomplished maintaining this rate 15 hours. No breakages on glass tubes or vacuum leakages appeared in this test. This condition was harder than limits of design.
Using the optical measurements of the selective coating samples of the second measurement campaign, a first attempt to validate the detailed heat transfer model was made. The agreement between the experimental data and the simulation results generated with the detailed heat transfer model is good for all temperatures.

b. Pre-industrial process development

The extrapolation of the results from laboratory to real conditions was a key part of the project it includes the assembly and validation of a new sputtering coating machine for selective coating a system to antireflexive coating and a preindustrial facture for producing the components.
The sputtering machine prototype has been designed and manufactured in order to test the industrialization of the solar absorber coating and to manufacture the tubes needed for the field tests. With the new device it was possible to apply by sputtering the different layers that make up the solar absorber coating, that is, the diffusion barrier, the infrared mirror, the absorbent cermet and the antireflective layer on 4 m long tubes.
The central chamber has been manufactured to support the 4 sputtering evaporators and the necessary vacuum pump and sensors. The evaporators are set two in each side of the chamber and the pump and sensors in the top of the chamber. It also includes 4 shutters to keep the target as clean as possible avoiding being coated while the front material is being evaporated. They will also let clean and stabilize the target prior to the deposition.
The vacuum system is composed of a rotary vane mechanical pump, a roots mechanical pump, a turbo molecular vacuum pump and a Pirani/Bayard-Alpert gauge. A capacitive gauge is used for the process pressure control. The base pressure of the system when it is cleaned is 1•10-6 mbar.
A gas diffuser system has been installed. The function of the diffuser is to have a good gas distribution, especially the reactive gases, along the evaporator, which is necessary to obtain a good film quality. For the best performance of the CSP system the tube must maintain the optical properties in all the length. This has been taken into account within the design of the PVD pre-industrial line.
This design guarantees the uniformity of the coating along the tube by moving the tube through the sputtering evaporators and rotating it at the same time. Just after the first processes a small shadow effect was seen in the tube sides due to the fixture system.
The antireflective coating is applying in a workplace including a glass apparatus for stirring of components. The glass apparatus has volume 100 liters, i.e. able to stir of 100 liters of sol-gel for AR coating on glass tubes. It has been equipped with the possibility of the regulation of rotation speed. The apparatus is mobile and the preparation of sol-gel is realized directly at the application basin. it has capacity 1 tube per 120 minutes (around 4 tubes per day).
The whole part of glass tube is dipped to the vessel with Sol-Gel. Dipping is done by speed which is 20 times higher than the pulling up. The tubes are pulled up by speed 6 cm/1 minute. After that follows the process of drying, this takes 90 minutes by the temperature of 20°C.
The dried glass part with applied and dried SOL-GEL layer is put on the conveyer of decorating (heating). The front part of decorating has 6m for easier placing of tubing. There can be 3 tubes side- by- side. Simultaneously there is done firing of AR layer and elimination of the temper in glass which was caused by the welding of glass part.

The integration line for the integration of absorber tubes according HITECO design as similar as possible to the foreseen industrial line. This line will be used for the production of absorber tubes for the testing in field.
This line will include some work-stations in the main path where HITECO solar tube will pass through each one sequentially, and finally the vacuum capability of each tube will be tested before transporting.
The design of the preindustrial assembly line has been carried out with the Lean Manufacturing philosophy. This is a strategy for achieving significant, continuous improvement in performance through the elimination of all wastes of time and resources in the whole manufacturing process, being the elimination of waste to remove all activities that do not add value such as transportation, inventory, motion, waiting, over production, over processing and defects/Rework.
One of the advantages of HITECO tube concept is its easy way of reducing the manufacturing costs. For the preindustrial line no more than 3 people will be needed for the assembly process that after a training period, will easily achieve the goal to assemble six units per 8 hours.
Solar tube to be assembled is made up to several components and pieces which are needed to be delivered with the specified quality, in a safe packaging and on time. There should be enough time for the manufacturers to be able to build them just in time so they would not waste money in storage pieces and could deliver them when it is required.
For the integration line design it has been defined a general lay-out. It has been thought considering that the tube will change its place at every assembly stage. It will be needed enough area for all workstations minimizing at the same time the motion between them. The whole space needed for the assembly process was around 100 m2.
All the tubes needed for the testing on field were assembled in the integration line designed.

c. Testing in real condition. On-sun.
This final validation stage was focused in to confirm the thermal results obtained in off-sun testing as well to produce valuable data in real conditions making the final product something near to the market needs.
Testing was based in mechanical and thermal testing being the results shown below:
Structure deflection: the measure has been done by deflectometry using the procedure (VISfield). This procedure needs to have the solar tube assembled and positioned with the collector facing north or south, and allows to adjust the inclination of the arm (high / low) in order to have the receiver tube parallel to the axis of rotation. The measure of the torsion of the manifold with VISfield by comparing the position reached by the receiver near the engine moving from 85 ° -> 90 ° and 95 ° -> 90 ° has shown a difference between positions of 2 mm maximum.
Measurement of thermal expansion and deflection of the SS tubes: it was done out during the phase of outgassing by molten salt flow, increasing the temperature in the inlet section of the solar collectors (positioned at 90°), up to the maximum temperature reachable by the electric heating systems of the plant. Thermal expansion and shrinkage of the steel tube vs the molten salt temperature gave information about geometrical position of support beams and receiver line’s bending, above all in the middle section of the module 12 m long showing little deviations due to the assembly process.
Validation of the FEC in 75 m: the measurements have been performed with molten salt circulation conditions, in the range of temperature 500°C - 350°C, reducing the temperature of the molten salt in the inlet section of the tube and measuring the thermal expansion in the outlet section, obtaining un maximum value of 0.71 meters of expansion for 510°C.
Leakness characterization: The values obtained shows very promising values (better than the objective placed). The minimum value of pressure inside the chamber obtained using a dynamic vacuum procedure was in the range of 10-5 mbar (maximum capacity of the vacuum pumps).

Outgassing process: The phenomenon of outgassing has been testing at different conditions being the next the conclusion:
a) The effect of Leakness is constant and not depending of temperature
b) The Outgassing is highly dependent of the temperature and pressure
c) The permeation is highly dependent of temperature
d) In a dirty clamber at room temperature the main effect that increase the pressure is the Outgassing
e) In a clean chamber at room temperature the main effect that increase the pressure is the leakness
f) A dirty chamber a high temperature is biggest influence of pressure increase is the outgassing
g) In typical working conditions, and stable situation with a clean chamber the effect is share by the permeation 50% and leakness and outgassing 25% each.
The values obtained for this parameters is the next: Room temperature with dirty chamber: 8.5•10-5 mbar l/s, Room temperature clean: 7.6•10-6 mbar l/s, High temperature dirty chamber: 5.7•10-4 mbar l/s; High temperature clean chamber: 3.5•10-5 mbar l/s.
Thermal losses: There have been carried out the thermal performance test with air and Kr and air/Kr at different pressures, compositions and temperatures. The testing procedure is based on to have steady state conditions during a minimum time. The values and the testing were repeated to confirm the results and to ensure the homogeneity of results.
According to the results obtained, it has been confirmed the results obtained during the off-sun testing. It means that the thermal losses are similar at 10-2 mbar with air and with 10 mbar of Kr. In addition the difference in all the range of temperatures show the little difference (but increasing) of the thermal losses when the operations done at 1, 5 and 10 mbar.
The consequence of this results is that is advisable to use as high pressure as possible with an atmosphere of Kr (around 5-10 mbar of Kr). This is because when the increase of pressure due to leakness, outgassing and permeation. The number of repumping operations is reduced compared to working at 1 mbar and as consequence the OPEX is also minor.
The tests of energy gain and thermal efficiency on field was based in heating the fluid using the solar radiation from the sun following with the tracking system the movement of the sun.
The energy gain: has been tested at 400°C with the next compositions in the chamber: Air at pressure <10-2 mbar and with 100% of Kr at: 1 mbar, 5 mbar and 10 mbar. The results have been affected by the optical efficiency of the parabolas used. In any case they show the promising of the new concept and the need to consider other approaches to make the solar market more reliable.

Potential Impact:
CSP is a large-scale, commercially viable way to make electricity. It is best suited to those areas of the world with the most sun; Southern Europe, Northern Africa and the Middle East, parts of India, China, Southern USA and Australia, where many are suffering from peak electricity problems, blackouts and rising electricity costs. In these regions, 1 sq km of land is enough to generate as much as 100-130 gigawatt hours (GWh) of solar electricity a year using solar therman technology. This is the same as the power produced by a 50 MW conventional coal or gas-fired mid-load power plant. Over the total life cycle of a solar thermal power system, its output would be equivalent to the energy contained in more than 5 million barrels of oil. CSP does not contribute to climate change and the source will never run out. The technology is mature enough to grow exponentially in the world’s ‘sun-belt’. By using a mere 0.4% of the total surface of the Sahara desert, the European demand for electricity could be entirely met, and the global demand by using only 2% of that surface.
According to the Global CSP Outlook 2009, under an advanced industry development scenario, with high levels of energy efficiency, CSP could meet up to 7% of the world’s projected power needs in 2030 and a full quarter by 2050. Even with a set of moderate assumptions for future market development, the world would have a combined solar power capacity of over 830 GW by 2050, with annual deployments of 41 GW. This would represent between 3.0 and 3.6% of global demand in 2030 and between 8.5 and 11.8% in 2050.
Under just a moderate scenario, the countries with the most sun resources could together:
• Create €11.1 billion (USD 14.4) investment in 2010, peaking at €92.5 billion in 2050.
• Create more than 200,000 jobs by 2020, and about 1187 million in 2050.
• Save 148 million tones of CO₂ annually in 2020, rising up to 2.1 billion tones in 2050.
CSP technologies could reduce global emissions. During the 1990s, global investment in energy infrastructure was around €158-186 billion each year; a realistic CSP figure would represent approximately on 5% of that total. This is a technology that, along with wind energy, can contribute to a ‘New Green Deal’ for the economy.
The successful implementation of this project will allow to reach operating temperatures beyond the current state-of-the-art 400 °C, therefore increasing the efficiency and therefore the power level for a given plant size. This will also reduce costs.

The main causes for the costs reduction in the energy cost in CSP plants are:
• The increase in the scale of the plants and their capacity.
• A decrease on the components price to the scale effect as a result of the technology implementation.
• An improvement of the optical and thermal sun field output.
• The alternatives for the thermal storage with new methods.
• The reduction of the operation and maintenance costs mainly because of the decrease in the Heat Collector Element (HCE) failure and the use of a new thermal fluid. These factors allow the increase of the world temperature with the consequent output improvement and in some cases the elimination of the components such as the heat exchanger.
Furthermore, the HITECO concept not only addresses and increase in operating temperature, which will lead to an increase in efficiency and therefore in the power level for a given plant size. By integrating several innovative concepts to its design, this new solar receiver will also be easier and cheaper to manufacture. Furthermore, the logistics for the HCE and its assembly process in the SCE will be simplified.
The assembly operations to manufacture the heat collector element will be simple enough not to need high technology assembly plants, so they will be able to be carried out in the same location of the CSP plant or in a nearby location. This concept increases the production capacity without the need of constructing new plants for HCE production.
So with the successful implementation of this project, the improvement of the CSP technology will be twofold. Investors will be more willing to put their money into thermo solar plants, with a faster return on investment. Furthermore, by making sure that the new components will have a life of at least 25 years, the rate of return will be warranted.

Main Dissemination Activities
The dissemination activity plan has been focused on spread project information and materials for potential users and beneficiaries. Industrial and research communities have been identified as a primary target. The dissemination activities performed during the whole project will rely on two main pillars:
• Project corporate image and strategy: definition of standards, norms and templates to be used within the dissemination activities aimed to assure the quality and consistency of the materials produced.
• Action plan: with perfectly identified actions, agreed with every WP leader. Evaluation of the most suitable channels and messages for our target. The main objectives for the dissemination activities are:
• General strategy definition to be followed by partners to disseminate the results achieved within the project to the society.
• Gather all dissemination materials developed during the project execution.
• Summarize all dissemination activities performed during the whole project, providing a clear view of the activities carried out.
The HITECO project Consortium distinguishes between internal and external dissemination actions, taking into account the channel to distribute the message: Internal Dissemination: communication actions carried out among project partners with the scope of sharing the developed know-how. Internal project website: Specific site with contents agreed by all the partners and with limited access to ensure confidentiality protection. This website has ensure the proper information availability and visibility of the correct activities progression for all the partners. It is also used as database and knowledge management tool, a gathering knowledge base on HITECO related scientific topics, reports, state-of-the-art and outputs of the project, and any information on specific resources that is available to all different partners. Internal meetings: Internal meetings organized to share information and to strengthen the cooperation among the partners in the Consortium.

External Dissemination: strategic action to ensure visibility and improve project results awareness (outside the consortium border), with a special focus on the exposure of the project results to the CSP European scientific and research communities. Thus project results could be used and become the basis for further research. External visibility and public awareness and knowledge of the HITECO project will be ensured through the following actions:
• Project Website: HITECO site contains general project information, scientific publications, news and events as well as public deliverables. Public documents can be used by “third parties” to enhance their projects but also give these “third parties” the possibility to provide feedback and thus to further improve the HITECO project’s results.
• Publications and printed media: project results and innovations have been submitted in scientific journals, conferences, and workshops relevant to the topic of the research activity to be carried out during the project.
• Workshops: Two workshops have been organized by HITECO to share public results and conclusions with stakeholders and experts outside the consortium. Electricity producers that are willing to expand on renewable energy in their area of business, CSP manufacturers, regulatory bodies, research community, ONGs are some of the target we identified for these events. First workshop took place in June 2012 with the first key points of the research and the last one was held on October 2014 with the conclusions and main insights about CSP technology in the future.
The scope of the dissemination plan through external communication activities was to maximize the impact on our target groups. Main tools used to ensure our goals were: promotional material massive distribution, website, relevant events, direct marketing materials, key conferences, endorsers for our project (professors, enterprise associations, partners’ network, etc.)
Relations with other stakeholders
Dissemination team of the HITECO project is also actively seeking links and interaction with other RTD projects and stakeholders in the area of CSP. The goal is not only the exchange of information, but also the creation of any possible synergies on the development of the technical work.

Project Leaflet
A project leaflet was created to introduce the HITECO project and to disseminate its main objectives. The leaflet could be downloaded at HITECO website ( Hard copies have been distributed in the events the consortium attended to (e.g. conferences, workshops, etc.) and organized. The information provided in the leaflet is addressed both to experts and non-experts. The main aim of the leaflet is to address the interested people to HITECO website, where more in-depth information can be found, and where the latest achievements and public deliverables of the project will be available.
Relevant publications like technical magazines (Photon, Renewable Energy,…), as well as newspapers will be used to disseminate project insights and results. Though we have been more focused on technical publications, we have also based our dissemination tasks on general media to share this information with general public.
We have distributed every project piece of news through official press releases with the main information and press contact to deal with editors. Every press release was also published on HITECO website and LinkedIn group.

Conferences, tradeshows and workshops
During the project life, two public dissemination workshops were organized by the HITECO consortium. These Workshops aimed at dissemination purposes, at the creation of awareness on relevant communities (industries, universities, etc.) on the project results and opportunities provided by HITECO project, in knowledge-transfer activities through the provision of material (included educational material produced during the project). These dissemination workshops will also become platforms to promote potential synergies and collaborations between projects, while the achievements of HITECO project will be presented.

Other Dissemination Events
Members of HITECO consortium participated in several events offering an overview of the project focused on the vision, the objectives and the impact of the results for the particular event targeted field.

Exploitation of Results
The CSP market has suffered up and down movements during the last years, which in the end haven’t allowed the technology to become a mature and stable sector. In addition, certain movements in the legislation of several governments have meant the slow down of solar plants construction and, as consequence, have reduced the attractiveness of this technology.
In any case, interest shown on this technology and the construction of new solar plants are strong enough to consider CSP technology as a good sector to invest in.
The biggest obstacles faced by the technology are:
• Changes and uncertainties in the regulatory frames that put investments in risk and reduce the attractiveness of it.
• High cost of the technology and, in particular, the reduced reliability of critical components, as the solar absorber tubes.
On the other hand, the potential of the technology is huge and the possibilities to implement R&D solutions wide, being the main paths to improve the technology:
• To achieve higher operation temperatures, higher conversion efficiency, new solutions for the thermal storage.
• To reduce operating costs by new designs of critical components. In addition the possibilities of hybridizing are becoming a new open field in the technology.

Summarizing, for the survival of the market in the medium term, the technology must become competitive by reducing energy costs, which means:
• Making simpler and packaged solutions.
• Decreasing the required CAPEX (Capital Expenditures).
• Decreasing the required OPEX (Operational Expenditures).
• Increasing efficiency.
• Improving predictability.
• Improving net electrical output based on reliable low-risk storage.
• Using experience to become similar to conventional and proved technologies.
The HITECO project bits in the targets of the market shown previously, validating a more efficient solar receiver, less expensive to fabricate and easier to assemble, reducing the cost of the energy produced. In general terms the project is focused to follow a design-to-cost strategy providing new possibilities to impel the technology.
The future in the implementation of the developments done in HITECO will strongly depend of the market available in the next years. This available market will come from the possibilities to supply tubes for new solar plant to be constructed or, from a general movement of making a repowering of the old plants with obsolete absorber tubes.
Detailed plans for the use (exploitation and further research) of the HITECO results are detailed in the Consortium Agreement, covering all aspects related to Intellectual Property Rights (IPRs), exploitation, dissemination, etc.

Furthermore, below, details on exploitation targets for the different partners in the project if demonstration is successful are given:
• As a result of the project a new generation of absorber tubes will be developed. This new concept will contribute to generate electric energy reducing productions costs. This target will be reached increasing the efficiency, meanwhile, operational expenditure and capital expenditure of projects are reduced.
• Flexible union elements with a wide application.
• New glass (borosilicate) compositions and new geometries more fit for solar purposes. New commercial developments for unions, in vacuum and a good hermeticism conditions, of glass tubes.
• Vacuum system capable to work in external conditions with a minimum need of maintenance.
• New selective absorber coating with the capacity to work at high temperatures (near 600 ºC).

List of Websites:

The public website developed for the project is opened to be used by all possible interested users, allowing them to know the project HITECO contents, objectives and main expected results. The address of the website is as follows: