Optimal year-round operation of a concentrated solar energy plant in the south of Europe

Direct steam generation (DSG) in parabolic-trough collectors (PTC) is one of the most attractive technologies in concentrated solar power plants. Its appeal stems from its ability to reduce the operational and maintenance costs compared with other heat transfer fluids. Modelling and simulation (M&S) tools, together with the development of experimental real-scale set-ups have played a key role in the advancement of this solar technology. The aim of this review is to summarize and analyse the thermohydraulic, thermal and optical models implemented in M&S tools for DSG in PTC in order to identify the contribution that these models could provide towards the improvement of the technology in the future. Thermohydraulic models have been, in most cases, developed under the three-equation homogeneous equilibrium model (HEM) approach, successfully for recirculation mode. The more complete six-equation two-fluid model (TFM) approach, has also been properly applied, to a lesser extent, to modelling the once-through solar field operation mode, considering water/steam two-phase flow patterns. Although these advancements have contributed to the design and operation of the first commercial solar steam power plant with PTC for electricity generation, there are however some technological gaps still to be overcome to consolidate the technology. In recirculation solar field operation mode, the use of HEM has shown to be adequate to model the DSG process in PTC integrated with thermal energy storage systems and into solar hybrid power plants. For once-through operation mode, the distributed-parameter thermohydraulic models, especially under TFM approach, involving a detailed flow pattern map, have demonstrated to be suitable tools for solving the uncertainties related to the two-phase flow, especially at the endpoint of the evaporation section.

Modelling and simulation tools for direct steam generation in parabolic-trough solar collectors: A review

http://math.univ-lyon1.fr/~saleh/papers/BN_Energie_CHSS.pdf

A positive and entropy-satisfying finite volume scheme for the Baer-Nunziato model

Among the diverse technologies for producing clean energy through concentrated solar power, central tower plants are believed to be the most promising in the next years. In these plants a heliostat field collects and redirects solar irradiance towards a central receiver where a fluid is heated up. Afterwards, the same fluid or eventually another one heated in a heat exchanger develops a thermodynamic cycle that produces a mechanical power output, transformed in electrical energy through an electrical subsystem. Quite high temperatures can be reached in the solar receiver, above 1000 K, ensuring a high cycle efficiency. This review is focused to summarize the state-of-the-art of this technology and the open challenges for the next generation of this kind of plants. An actualized review of the plants working nowadays as well as the plants under development and research projects is presented. Updated thermo-economic data are collected in a comprehensive way. Each of the subsystems of a typical plant are surveyed, putting the emphasis on the more relevant research lines and the issues to be solved in the next years. Heliostat field margin of improvement, high temperature receivers and the most suitable thermodynamic cycles to take advantage of high temperature heat are detailed. Thermal storage and hybridization concepts are also surveyed. It is stressed the importance to design the plant as a whole, optimizing subsystems and their coupling to improve overall plant performance. Finally, a prospect for future R&D in this field is performed.

High temperature central tower plants for concentrated solar power: 2021 overview

Among the diverse technologies for producing clean energy through concentrated solar power, central tower plants are believed to be the most promising in the next years. In these plants a heliostat field collects and redirects solar irradiance towards a central receiver where a fluid is heated up. Afterwards, the same fluid or eventually another one heated in a heat exchanger develops a thermodynamic cycle that produces a mechanical power output, transformed in electrical energy through an electrical subsystem. Quite high temperatures can be reached in the solar receiver, above 1000 K, ensuring a high cycle efficiency. This review is focused to summarize the state-of-the-art of this technology and the open challenges for the next generation of this kind of plants. An actualized review of the plants working nowadays as well as the plants under development and research projects is presented. Updated thermo-economic data are collected in a comprehensive way. Each of the subsystems of a typical plant are surveyed, putting the emphasis on the more relevant research lines and the issues to be solved in the next years. Heliostat field margin of improvement, high temperature receivers and the most suitable thermodynamic cycles to take advantage of high temperature heat are detailed. Thermal storage and hybridization concepts are also surveyed. It is stressed the importance to design the plant as a whole, optimizing subsystems and their coupling to improve overall plant performance. Finally, a prospect for future R&D in this field is performed. 

A class of non-equilibrium models for compressible multi-component fluids in multi-dimensions is investigated taking into account viscosity and heat conduction. These models are subject to the choice of interfacial pressures and interfacial velocity as well as relaxation terms for velocity, pressure, temperature and chemical potentials. Sufficient conditions are derived for these quantities that ensure meaningful physical properties such as a non-negative entropy production, thermodynamical stability, Galilean invariance and mathematical properties such as hyperbolicity, subcharacteristic property and existence of an entropy–entropy flux pair. For the relaxation of chemical potentials, a two-component and a three-component models for vapor–water and gas–water–vapor, respectively, are considered.

/pdf/closure-conditions-for-non-equilibrium-multi-component-1kkfdypngl.pdf

Closure conditions for non-equilibrium multi-component models

Robust optimal aiming strategies in central receiver systems

The exploitation of solar power for energy supply is of increasing importance. While technical development mainly takes place in the engineering disciplines, computer science offers adequate techniques for simulation, optimisation and controller synthesis.

In this paper we describe a work from this interdisciplinary area. We introduce our tool for the optimisation of parameterised solar thermal power plants, and report on the employment of genetic algorithms and neural networks for parameter synthesis. Experimental results show the applicability of our approach.

/pdf/optimisation-of-concentrating-solar-thermal-power-plants-4atdfam2ao.pdf

Optimisation of concentrating solar thermal power plants with neural networks

In solar tower power plants aiming strategies are used to distribute the heat flux on the receiver surface. An optimal strategy maximizes the mass flow while avoiding thermal overloading to prevent the risk of damage to receiver components. This problem has been modeled as an integer program (IP) to provide deterministic solutions. To consider disturbances caused by the tracking error, the aiming strategy is extended to ensure a robust solution.

Pascal Richter

Papers

Closure conditions for non-equilibrium multi-component models

Robust optimal aiming strategies in central receiver systems

Optimisation of concentrating solar thermal power plants with neural networks

Optimization of robust aiming strategies in solar tower power plants

Dynamic aiming strategy for central receiver systems