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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.

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.

This article presents the first megawatt scale solar-hybrid plant with a solarized gas turbine. The works and improvements that made the Solugas project succeed during design, construction and long-term solar operation are described and explained. More than 1000 operation hours and receiver outlet temperatures of 800 °C were achieved. The operation behaviour and performance of the key components – the solar pressurised air receiver and the gas turbine – are presented here as a proof of the high potential of the technology.

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 kWel infrared heater.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 kWel infrared heater.

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 kWth [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.

The present work describes the realisation and successful test operation of a 100 kW pilot plant for two-step solar thermo-chemical water splitting on a solar tower at the Plataforma Solar de Almeria, which aims at the demonstration of the feasibility of the process on a solar tower platform under real conditions. The process applies multi-valent iron based mixed metal oxides as reactive species which are coated on honeycomb absorbers inside a receiver–reactor. By the introduction of a two-chamber reactor it is possible to run both process concepts in parallel and thus, the hydrogen production process in a quasi-continuous mode. In summer 2008 an exhaustive thermal qualification of the pilot plant took place, using uncoated ceramic honeycombs as absorbers. Some main aspects of these tests were the development and validation of operational and measurement strategy, the gaining of knowledge on the dynamics of the system, in particular during thermal cycling, the determination of the controllability of the whole system, and the validation of practicability of the control concept. The thermal tests enabled to improve, to refine and finally to prove the process strategy and showed the feasibility of the control concept implemented. It could be shown that rapid changeover between the modules is a central benefit for the performance of the process. In November of 2008 the absorber was replaced and honeycombs coated with redox material were inserted. This allowed carrying out tests of hydrogen production by water splitting. Several hydrogen production cycles and metal oxide reduction cycles could be run without problems. Significant concentrations of hydrogen were produced with a conversion of steam of up to 30%.

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 °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.

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.

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 Solucar 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 °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.