The centrifugal particle receiver (CentRec®) developed by DLR for high-temperature solar applications, previously tested on sun in a 500 kWth prototype at the solar tower in Jülich was further developed and tested at slightly smaller scale of 300 kWth. The test with artificial sunlight provided more stationary and controllable boundary conditions. Outlet temperature of 681 °C was reached at an irradiating input power of 214 kW. The performance was determined with particle mass flow and temperature measurement systems. The data confirms the thermodynamic model for this receiver, indicating an extrapolated performance of 81% at nominal conditions.

The production of dispatchable renewable energy will be one of the most important key factors of the future energy supply. Concentrated solar power (CSP) plants operated with molten salt as heat transfer and storage media are one opportunity to meet this challenge. Due to the high concentration factor of the solar tower technology the maximum process temperature can be further increased which ultimately decreases the levelized costs of electricity of the technology (LCOE). The development of an improved tubular molten salt receiver for the next generation of molten salt solar tower plants is the aim of this work. The receiver is designed for a receiver outlet temperature up to 600 degrees C. Together with a complete molten salt system, the receiver will be integrated into the Multi-Focus-Tower (MFT) in Jalich (Germany). The paper describes the basic engineering of the receiver, the molten salt tower system and a laboratory corrosion setup.

The centrifugal particle receiver technology (CentRec (R)) is predicted to contribute significantly to reduction in levelized cost of electricity / heat (LCOE / LCOH) for concentrating solar power (CSP) and concentrating solar thermal (CST) applications. Main drivers are derived from the benefit offered from solid particles as heat transfer medium (HTM) and storage medium which are reduced receiver cost, increased operating temperature range and lower cost for the HTF itself. Previously, the CentRec (R) receiver was tested at the Solar Tower Jtilich under significant part load due to optical restrictions of the facility. The results confirmed the expectation into receiver performance and motivated further projects to improve systems understanding as well as full load operational experience. This paper provides an overview over the currently ongoing projects aimed at improving the understanding of the CentRec (R) receiver through operation in a lab-environment at the DLR's Synlight facility and a test campaign at the National Solar Thermal Test Facility (NSTTF) of the Sandia National Laboratories. Initial results from a study of increasing the receiver size are shown. Lastly, two new commercial scale CentRec (R) installations are introduced. These include a full test loop at the DLR's new Multi Focus Tower in Jttlich, Germany, and a complete plant being developed and built as a technology demonstrator in Foggia, Italy.

The present work is part of an approach targeted on demonstrating a concentrated solar energy-driven thermochemical cycle employing solid elemental sulphur as a chemical energy vector and a seasonal solar energy storage medium. In exploring the concept of coupling this cycle to a centrifugal particle solar receiver, bauxitebased particles, commercial and composition-modified, were tested and validated with respect to their suitability for simultaneous operation as solar energy harvesting media and sulphur trioxide splitting catalysts. Long-term catalytic activity tests exceeding 1000 h of operation at 850 degrees C, demonstrated that properly composition-modified bauxite particles were capable of achieving stable SO3 conversion exceeding 70% (about 80% of equilibrium value under conditions studied) and exhibiting no or negligible loss of catalytic performance after this extended operation. In addition, such composition modification enhanced the particles' solar irradiation absorptance, which resulted in substantially higher than that of their commercial, non-modified bauxite counterparts. Commercial bauxite particles on the other hand, demonstrated much better mechanical strength, flowability, and attrition- and thermal shock resistance together with measurable, yet lower catalytic activity, which deteriorated with prolonged on-stream exposure. The combined results obtained advocate for the eventual selection of an "allothermal" cascaded sulphur trioxide splitting/sulphuric acid decomposition reactor, containing a non-moving catalytic bed that is heated indirectly by a moving bed of high-temperature (>= 900 degrees C) nonmodified commercial bauxite particles irradiated in the centrifugal solar particle receiver.

The centrifugal particle receiver “CentRec” is a solar tower receiver development by DLR based on a direct absorption receiver concept especially suitable for high temperature process heat and electricity generation applications. Ceramic particles are used as heat transfer and storage medium for temperatures up to 1000°C. A centrifugal particle receiver system including a CentRec receiver prototype has been tested up to 965°C average receiver outlet temperature in the research platform of DLR’s test facility Juelich Solar Tower, Germany. This paper describes the first test results with a focus on first operational experiences.

A direct absorption receiver using ceramic particles (CentRec) has been successfully developed by DLR and tested under solar conditions at the Juelich Solar Power Tower, demonstrating receiver outlet temperatures of more than 900 °C. The next step towards commercial application of the technology is to demonstrate a cost-effective, high temperature heat extraction and transfer to a process medium. Besides e.g. steam for electricity generation in a steam turbine, hot air can be used to supply heat to industrial processes with energy demand at high temperature level. A great potential for higher efficiencies and lower costs has been identified for a moving bed heat exchanger. Several concepts of direct contact heat exchangers have been analyzed and evaluated. The selected concept is a combination of several crossflow-sections that are arranged in series with fluid-mixing-chambers between each crossflow-section. Based on the selected design a heat exchanger prototype with 10 kW thermal power and a design air outlet temperature of 750 °C has been built and integrated into a test setup. The test setup provides particles at 900 °C that are heated up electrically inside a hopper on top of the heat exchanger. Hot particles are then moving downwards (moving bed) from the hopper through the direct contact heat exchanger driven by gravity. Cold air supplied by a compressor flows through the particle bed in cross-flow and is heated up. The hot air flow leaves the heat exchanger with a temperature of 750 °C. The particle mass flow is controlled by an oscillating mass flow controller, positioned under the heat exchanger. The cold particles are collected in a container on the bottom. The particle cycle is closed by transporting them back to the hopper. A measurement and control system is implemented to carry out the tests. The test setup has undergone successful commissioning in October and an extensive testing phase started in January 2019. This paper presents the development and manufacturing as well as the successful commissioning of the heat exchanger prototype.

One direct absorption receiver concept currently investigated at the DLR is the Centrifugal Particle Receiver (CentRec®). Successful tests and promising results of this receiver design have been achieved in a Proof-of-Concept scale with 7.5 kW thermal power and 900°C particle temperature in 2014. Based on these results the prototype has been scaled up to 2.5 MW thermal power for a future pilot plant. Lab tests have been carried out with infrared heaters. In a next step the prototype has been prepared to be tested on-sun in a test setup in the Juelich Solar Tower, Germany. The tests aim to demonstrate high temperature operation and to evaluate the performance of the system. The test setup consists of a centrifugal receiver integrated into the tower and a closed loop particle transport system. The transport system includes an air cooling system to cool down the particles at the receiver outlet, cold particle storage, belt bucket elevator, hopper and particle metering system. While the 2.5 MWth receiver prototype has been developed in a former project, the further infrastructure for the on-sun tests needed to be designed, manufactured and installed. The system is equipped with measurement instrumentation, data acquisition system and control software. Manufacturing of all main components has been completed. Installation of the test setup started in November 2016 and finished in June 2017. Cold and hot commissioning have been carried out from July 2017 until September 2017. On-sun tests started in September 2017. Receiver tests up to 775°C/1,430°F receiver outlet temperature and more than 900°C/1,650°F particle temperature in the receiver have already been achieved. Tests up to 900°C particle outlet temperature are planned at different load levels and will be conducted until summer 2018. This paper describes the test setup for a centrifugal particle receiver system, presenting design, installation and commissioning of the system. It presents test results of first on-sun tests and gives an outlook on further steps regarding solar tests planned for 2018.

Particle receivers achieve significantly higher temperatures than state of the art molten salt solar towers. The centrifugal particle receiver is a direct absorption receiver with a simple control of the residence time of the particles in the receiver. The paper describes the cold testing including mechanics of the particle film and first hot testing using a 100 kW(el) infrared heater.

Turmkraftwerke weisen einen hohen Wirkungsgrad und grose Kostensenkungs-potenziale auf. Zur Bestimmung der Wirkungsgrade und Eintrittsleistung und zur Optimierung des Betriebs dient die Messung der solaren Flussdichteverteilung in der Ebene der Eintrittsapertur des Receivers. Flussdichtemesssysteme nutzen haufig einen diffus reflektierenden Schwenkbalken, der sich vor dem Receiver vorbeibewegt, wahrend eine CCD-Kamera die Helligkeitsverteilung der am Balken reflektierten solaren Strahlung aufnimmt. Anschliesend wird das Bild mit Radio-meterwerten kalibriert. An kommerziellen Turmkraftwerken hoherer Leistung und entsprechend groserer Apertur sind mechanische Schwenkbalken sehr gros und daher nur bedingt geeignet. Aus diesem Grund werden Messmethoden untersucht, die ohne Schwenkbalken auskommen [1]. Eine Methode kombiniert eine Raytracing-Simulation mit einer vereinfachten Messung im Bereich des Strahlungsschutzes. Die Messung dient dabei zur Validierung der Simulationen. Aus dem Simulationsergebnis lassen sich dann alle wichtigen Grosen zur Charakterisierung des Kraftwerkes ableiten. Dieses Poster prasentiert die Anwendung dieser Methode an dem Demonstrationskraftwerk SOLUGAS, einem Cavityrohrreceiver mit Mikrogasturbine [2].

This paper describes a method for the efficiency determination of a cavity receiver using the example of the solar hybrid gas turbine system SOLUGAS. Major focus is given on the improvement of a new approach of the solar flux density determination based on a measurement-supported simulation technique where an acceptable uncertainty of the solar input power of -1.3%...+6.3% is achieved. For the thermal evaluation an uncertainty of 2.4% is determined that leads to an overall uncertainty of the thermal receiver efficiency of -2.8%...+7.7%. Detailed uncertainty propagation is presented and conclusions discussed. (C) 2016 Elsevier Ltd. All rights reserved.

Quantification of abrasion, erosion and corrosion is important to determine operation costs for solar particle receivers, including particle replacement, maintenance, and especially the need for replacement of components during lifetime of the solar particle plant. This paper deals with the assessment of the quantities of abrasion and erosion of particles during operation and the resulting costs for particle replacement. Firstly, the assessment of expected loads on the particles during abrasion are discussed as well as the transfer of these parameters to experimental setups. Secondly, the conducted experiments and the results are described. Finally, the experimental results are transferred to the application by scaling and conversion into cost data. The results indicate particle replacement costs of less than 0.32 €/MWhth (0.36 $/MWhth1). First corrosion experiments indicate, as expected, a siginficant effect of combined high temperature corrosion of metallic structural material in combination of abrasion due to relative movement of particles to structural material.

Previous successful tests and promising results of a Centrifugal Particle Receiver (CentRec) for high temperature solar applications has been achieved in a lab scale prototype with 7.5 kW(th) [1, 2, 3]. In a next step this receiver technology is scaled up to higher thermal power for a future pilot plant.This paper presents the optimization methodology of the design and technical solutions. It describes the manufacturing and assembly of the prototype and first tests and results of the commissioning including cold particle tests and prototype costs. Finally the paper gives an outlook on the planned further steps regarding hot lab tests and solar tests.

In the last years more experience has been achieved with long time operation of solar tower receivers increased in size. The insulation of these receivers shows higher complexity and importance compared to small prototypes [1, 2]. Both insulation of tubular cavity receiver and inner insulation of piping are safety-relevant components as they protect e.g. support structures and pressurized tubes and connections against overheating. Besides safety, operating reliability is one of the most important requirements to meet as down times, maintenance and repairs cause high costs. This paper describes the new development of the insulation for a tubular cavity receiver with air as heat transfer medium, where costs and thermal heat loss should be reduced. The prototype has been designed, built and tested for 100 operating hours at receiver outlet temperatures of up to 800 degrees C at the test facility Plataforma Solar de Almeria (PSA), Spain. The results of a thermal model, of material tests and the evaluation of the thermal heat loss are presented. (C) 2015 The Authors. Published by Elsevier Ltd.

CSP hybridisation is one of the most promising concepts for cost reduction and dispatchability, and also one of the most competitive with conventional electricity generation systems. The Solugas project, first solar hybrid system topped with a gas turbine at megawatt scale, was commissioned in May 2012 in Abengoa's Sol car Platform near Seville.Numerous operation objectives of the project have been tackled since the operation started and the project is running for several hundred solar operation hours already, yet for the technology assessment the stable operation and evaluation of long time behaviour are crucial. In 2012 the maximum receiver outlet temperature objective was achieved: the temperature of the heat transfer medium - pressurised air-has been heated up to 800 degrees C in one receiver, reaching a temperature gradient of almost 500 K.Current objectives include obtaining the tubular receiver efficiency accurately and optimisation of plant operation and control, in order to be able to characterise the behaviour of the plant and the production of the future plants. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Flux density measurement applied to central receiver systems delivers the spatial distribution of the concentrated solar radiation on the receiver aperture, measures receiver input power, and monitors and might control heliostat aimpoints. Commercial solar tower plants have much larger aperture surfaces than the receiver prototypes tested in earlier research and development (R&D) projects. Existing methods to measure the solar flux density in the receiver aperture face new challenges regarding the receiver size. Also, the requirements regarding costs, accuracy, spatial resolution, and measuring speed are different. This paper summarizes existent concepts, presents recent research results for techniques that can be applied to large-scale receivers and assesses them against a catalog of requirements. Direct and indirect moving bar techniques offer high measurement accuracy, but also have the disadvantage of large moving parts on a solar tower. In the case of external receivers, measuring directly on receiver surfaces avoids moving parts and allows continuous measurement but may be not as precise. This promising technique requires proper scientific evaluation due to specific reflectance properties of current receiver materials. Measurement-supported simulation techniques can also be applied to cavity receivers without installing moving parts. They have reasonable uncertainties under ideal conditions and require comparatively low effort.

Parabolic trough power plants today represent the state of the art in solar thermal electricity generation. A large number of plants have been realized in Spain based on the same principle as the first systems in the U.S. back in the 1980s. The market today is characterized by a strong need for cost reduction as competing technologies like PV showed remarkable improvements in terms of economics. For solar thermal power plants, several paths to higher profitability are open. Line focusing systems with either direct steam generation (DSG) or molten salt as a heat transfer fluid aim at higher process temperatures and thus better cycle efficiency. The same motivation holds for the activities in solar tower plants. Along with these “big” technological innovations it is important to optimize the performance of each single component. Detailed knowledge of physical effects is essential to identify potential for improvement. This paper focuses on the topic of flow stratification in horizontal tubes. Since the diameter to length ratio of absorber tubes in parabolic trough or Linear Fresnel systems is very small, a common assumption is that the temperature and flow are equally distributed over the cross section. In many cases, this assumption is appropriate to simplify calculation procedures. Nevertheless, there are applications for which this assumption is not valid any more. The paper will describe two such examples observed at DLRs test facilities. The first one deals with accurate measurement of the temperature rise within a collector efficiency test bench. It is shown how temperature stratification in the absorber tubes could lead to severe errors in the temperature measurement. The second example is a collector test facility for direct steam generation. During the start-up procedure we observed a damage of two absorber tube glass covers which was caused by large temperature gradients over the pipe cross section.

The air receiver technology, which is demonstrated at the solar tower of Julich, uses ceramic honeycomb structures to absorb concentrated solar radiation and transfer the heat to an air flow. Therefore, the absorbers have to be highly porous to let the radiation penetrate deeply into the structure but must also feature a large internal heat transfer surface. The paper reveals the basic correlation between geometry and performance by means of a simplified mathematical model. New developments of honeycomb absorbers are presented and their thermal efficiency measured in a laboratory test is shown. The absorber development is accompanied by a thermal shock and cycle test program to assure sufficient mechanical stability