DESIGN AND COST STUDY OF IMPROVED SCALED-UP CENTRIFUGAL PARTICLE RECEIVER BASED ON SIMULATION

A numerical model of the CentRec® receiver has been developed and validated using the measurement data collected during the experimental test campaign of the centrifugal particle system at the solar tower Jülich. The model has been used to calculate the thermo-optical efficiency of a scaled-up 20 MWth receiver for various receiver geometries. A cost function has been deduced and was used to perform a technoeconomic optimization on an LCOH (levelized cost of heat) basis of the CentRec® receiver concept. Attractive LCOH as low as 0.0209 €/kWhth for a system with thermal storage, or as low as 0.0150 €/kWhth for the LCOH without storage, are predicted. This study has shown that the optimal configuration from an LCOH perspective for a 20 MWth centrifugal particle receiver reaches specific receiver costs of 35 €/kWth. Hereby the costs of the receiver can be reduced by 60 % compared to the original configuration

Operational Experience of a Centrifugal Particle Receiver Prototype

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

Entwicklung eines Rohrreceivers für ein solar-hybrides Mikroturbinensystem

In this work a metallic tube receiver with an air outlet temperature of 800°C for a solar-hybrid microturbine system was developed. This solar tower system can displace expensive diesel generators in areas without electricity in an equal and ecological way. The use of additional fuels guarantees availability around the clock independent of the solar insulation. Additional benefits are low water use, the production of process heat and significantly lower safety demands compared to competing systems, as no pressurized quartz window like in a volumetric pressurized receiver is used. However a pressure-less window is deployed to minimize convection and thermal radiation losses. After a discussion of the different receiver loss mechanism an overview of the state of art of solar tower receivers with different heat carriers and different heat transfer types is given. For the calculation of the 3D temperature field of a pressurized air cooled tube receiver a finite-element-model was developed. Based on own preliminary considerations and the analysis of already constructed receiver different layouts were developed and analyzed in detail. With the receiver layout “tipi” a configuration was found, which satisfied the requirements tube temperature 80% for a given heliostat field at all time points. This receiver was tested in a system with a Turbec T100 microturbine on the Cesa-1 tower of the Plataforma Solar de Almeria in Spain and the results were compared to the results of the simulations. The development of the receiver was successful and showed the technical feasibility of a system, which could accomplish a significant contribution to the reduction of worldwide energy poverty. As a next step a demo system could be built in an off-grid location and a storage system could be added

Development of a tube receiver for a solar-hybrid microturbine system

Solar-hybrid microturbine systems with cogeneration offer new possibilities for the generation of electricity and heat or air conditioning. The solar receiver is an important component of such a system. For a prototype system demo project a tube receiver for a 100kWe microturbine system is currently under development. The receiver is designed for air preheating up to 800°C at a pressure of 4.5 barabs. The challenge of the design is to find the right compromise between high efficiency, low pressure drop, high durability and low cost. The receiver consists of multiple metallic tubes, arranged in a cavity and connected in parallel. For the design the knowledge of local flux density, fluid and material temperature is required. A finite-element program coupled with a ray tracer was used for the layout. The final receiver design is described, which was optimized with respect to efficiency, material temperatures and pressure drop. Expected performance data for nominal load and off-design conditions will be presented, including the expected annual receiver and system performance. In addition, several possibilities for future improvements will be outlined

Direct absorption receivers for high temperatures

Three concepts of direct absorption receivers for concentrating solar power (CSP) systems are compared. They are characterized by advantages like simple design, high working temperatures and good storage possibilities leading to a potential reduction of the levelized electricity costs. The design of the first concept, the liquid film receiver, is based on a face-down cylindrical barrel, whose inner surface is cooled by a directly irradiated molten salt film. Detailed investigations regarding film stability and system management strategies reveal increased receiver efficiency by implementing a slow rotation and inclined receiver walls. The second concept resembles the first one, but instead of molten salt small ceramic particles are used as heat transfer medium. The solar radiation is directly absorbed by a falling particle curtain whereas appropriate recirculation strategies of the particles can lead to high receiver efficiencies for all load conditions. While the above described systems are suitable for the 50 to 400 MWth power range the third concept – also a particle receiver – can be applied in decentralized small-scale CSP plants ranging from 100 kWth to 1 MWth as well as in larger systems with up to 200 MWth. Due to centrifugal acceleration the particles are forced against the cylindrical receiver wall where they form a thin layer which is directly heated up by incoming radiation. The particle retention time and with it the mass flow can be adjusted to all load conditions by regulating the rotation speed. Heliostat field layout calculations for different design power levels were carried out comparing the annual performance and levelized cost of heat for a face-down receiver and a receiver with an optimized inclination angle. Only small differences between both concepts could be noticed. However, simplified assumptions regarding thermal receiver losses were made neglecting e.g. convection losses. Thus, in order to give reliable information about the thermal efficiency of the introduced concepts, computational models considering the main heat loss mechanisms are developed. The models are accompanied by experimental validation and support the numerical findings

Cost Analysis of different Operation strategies for falling particle receivers

The potential for highly efficient and cost competitive solar energy collection at high temperatures drives the actual research and development activities for particle tower systems. One promising concept for particle receivers is the falling particle receiver. This paper is related to a particle receiver, in which falling ceramic particles form a particle curtain, which absorbs the concentrated solar radiation. Complex Operation strategies will result in higher receiver costs, for both investment and operation. The objective of this paper is to assess the influence of the simultaneous variation of Receiver costs and efficiency characteristics on levelized cost of heat (LCOH) and on levelized cost of electricity (LCOE). Applying cost assumptions for the particle receiver and the particle transport system, the LCOE are estimated and compared for each considered concept. The power level of the compared concepts is 125 MWel output at design point. Thesensitivity of the results on the specific cost assumptions is analyzed. No detailed evaluation is done for the thermal storage, but comparable storage utilization and costs are assumed for all cases

Solar gas turbine systems with centrifugal particle receivers, for remote power generation

There is a growing demand from remote communities in Australia to increase the amount of decentralised renewable energy in their energy supply mix in order to decrease their fuel costs. In contrast to large scale concentrated solar power (CSP) plants, small solar-hybrid gas turbine systems promise a way to decentralise electricity generation at power levels in the range of 0.1- 10 MWe, and reduce to cost of energy production for off-grid, isolated communities. Thermal storage provides such CSP Systems with an advantage over photovoltaic (PV) technology as this would be potentially cheaper than adding batteries to PV systems or providing stand-by back-up systems such as diesel fuelled generators. Hybrid operation with conventional fuels and solar thermal collection and storage ensures the availability of power even if short term solar radiation is not sufficient or the thermal storage is empty. This paper presents initial modelling results of a centrifugal receiver (CentRec) system, using hourly weather data of regional Australia for a 100 kWe microturbine as well as a more efficient and cost effective 4.6 MWe unit. The simulations involve calculation and optimisation of the heliostat field, by calculating heliostat by heliostat annual performance. This is combined with a model of the receiver efficiency based on experimental figures and a model of the particle storage system and turbine performance data. The optimized design for 15 hours of thermal storage capacity results in a tower height of 35 m and a solar field size of 2100 m² for the 100 kWe turbine, and a tower height of 115 m and solar field size of 50 000 m² for the 4.6 MWe turbine. The solar field provides a greater portion of the operational energy requirement for the 100 kWe turbine, as the TIT of the 4.6 MWe turbine (1150°C) is greater than what the solar system can provide. System evaluations of the two particle receiver systems, with a selection of cost assumptions, are then compared to the current conventional means of supplying energy in such remote locations