High-Temperature Thermal Storage System for Solar Tower Power Plants with Open-Volumetric Air Receiver Simulation and Energy Balancing of a Discretized Model

This paper describes the modeling of a high-temperature storage system for an existing solar tower power plant with open volumetric receiver technology, which uses air as heat transfer medium (HTF). The storage system model has been developed in the simulation environment Matlab/Simulink®. The storage type under investigation is a packed bed thermal energy storage system which has the characteristics of a regenerator. Thermal energy can be stored and discharged as required via the HTF air. The air mass flow distribution is controlled by valves, and the mass flow by two blowers. The thermal storage operation strategy has a direct and significant impact on the energetic and economic efficiency of the solar tower power plants

High-Temperature Thermal Storage System for Solar Tower Power Plants with Open-Volumetric Air Receiver Simulation and Energy Balancing of a Discretized Model

This paper describes the modeling of a high-temperature storage system for an existing solar tower power plant with open volumetric receiver technology, which uses air as heat transfer medium (HTF). The storage system model has been developed in the simulation environment Matlab/Simulink®. The storage type under investigation is a packed bed thermal energy storage system which has the characteristics of a regenerator. Thermal energy can be stored and discharged as required via the HTF air. The air mass flow distribution is controlled by valves, and the mass flow by two blowers. The thermal storage operation strategy has a direct and significant impact on the energetic and economic efficiency of the solar tower power plants

Jülich Solar Power Tower – System Behavior During Downtime

At the Jülich Solar Power Tower, two new shut-off dampers have been installed in the hot air piping system in order to reduce thermal losses during downtime of the plant. The thermodynamic behavior of the thermal energy storage and the steam boiler has been investigated with respect to heat losses after shut-down of the plant. Also, the change of temperature and the pressure drop at both shut-off dampers during downtime has been analyzed. Results show that for the storage, a reduction of thermal losses can be achieved by closing the damper overnight. Regarding the steam boiler, no improvements on heat losses were observed. If only two of the four storage chambers have been charged during operation, heat transfer between the chambers is observed after shut-down. It is concluded that natural convection is not the main source of thermal overnight losses, however, it can be lowered thanks to the dampers. Heat conduction and convectional heat transfer at the surfaces also contribute to the decrease of thermal energy, which can be lowered by thicker insulation layers in the future

Annual Performance Assessment of a 50 MWe Commercial Solar Tower Plant with Improved Open Volumetric Receiver

Central receiver systems with open volumetric air receiver and packed bed thermal storage are an alternative to the currently deployed salt and steam receiver plants. The air receiver technology is being tested as a complete system at the 1 MWe test and demonstration plant Solar Tower Jülich since 2009 and shows high robustness and availability. Recent developments focused on increasing the thermal receiver efficiency. Changing the receiver geometry to a cavity type and further structural improvements resulted in an efficiency increase to above 85%, as experiments and CFD simulation models show. The high dynamic flexibility could be further enhanced. A commercial reference plant with 50 MWe power level was defined for a potential location in South Africa. An LCOE analysis based on an annual performance simulation was conducted for several design and operational alternatives. Under good conditions, results show LCOE values below 90 €/MWh for the single 50 MWe standard unit. Higher power levels can be reached by multiplying such standard units, leading to further cost savings

Innovative 3D-Shaped Structures as Volumetric Absorbers

As proven by the continuous operation of the Solar Tower Juelich, central receiver power plants with open volumetric receivers are a valid alternative to other receiver types. Evolving new manufacturing techniques will allow to advance the technology further by improving its core component, the porous absorber structures. Using ceramic 3D screen printing, the new StepRec absorber design is fabricated out of siliconized silicon carbide and is presented along with the second new structure, the Emitec absorber made of very thin metal sheets. Based on experiments in the high-flux solar simulator Synlight, the thermal efficiency of both new designs is derived for reduced-size absorber probes. The new structures outperform the state-of-the-art HiTRec absorber with efficiencies above ninety percent at air temperatures of 650°C. Full-size absorber modules have been tested under real irradiation conditions at the research platform of the Solar Tower Juelich. The thermal efficiencies of the full modules will be quantified with further experiments in the Synlight facility in the near future

Experimentally assessed efficiency improvement of innovative 3D-shaped structures as volumetric absorbers

Solar tower plants are predicted to take on a significant role in the ongoing global energy transition. The open volumetric air receiver technology can provide an alternative to molten salt receivers due to its proven and effective storage capabilities. The key component of this technology are porous absorber structures which are responsible for the absorption of the solar irradiation. Research of porous structures has consistently shown that 3D-shaped absorber designs offer the highest efficiency potential. The realization of such designs is made possible by newer manufacturing techniques. In this publication, experimental results for two groups of new volumetric absorbers are presented. The StepRec absorber is manufactured via ceramic 3D screen printing, its characteristic step-pin sections allow for deep penetration of the solar irradiation. Additionally, metallic foil absorbers were evaluated, they exhibit particularly high specific surface areas due to low wall thicknesses. The new absorbers were tested for flux densities up to 650kWm2 and air exit temperatures up to 735°C. The experiments successfully confirmed the new absorbers' great potential: They outperformed the HiTRec reference, a ceramic honeycomb structure, for all air temperatures. At 650°C, thermal efficiencies up to 91.8% were recorded, an improvement of 6.5%-points w.r.t. to the HiTRec result

Transient Simulation for Hybrid Solar Tower Power Plant with Open-Volumetric Receiver in Algeria

This work describes the procedure of transient simulation for a solar tower power plant with open-volumetric receiver for a site in Northern Algeria. The simulation models have been developed in the simulation environment MATLAB/Simulink. Basic design calculations have been conducted on basis of meteorological data provided by satellites to investigate different concepts. For the concept that is most auspicious a transient annual simulation using local measured meteorological data has been conducted to yield detailed and accurate results