José González-Aguilar

Performance comparison of different thermodynamic cycles for an innovative central receiver solar power plant

The potential of using different thermodynamic cycles coupled to a solar tower central receiver that uses a novel heat transfer fluid is analyzed. The new fluid, named as DPS, is a dense suspension of solid particles aerated through a tubular receiver used to convert concentrated solar energy into thermal power. This novel fluid allows reaching high temperatures at the solar receiver what opens a wide range of possibilities for power cycle selection. This work has been focused into the assessment of power plant performance using conventional, but optimized cycles but also novel thermodynamic concepts. Cases studied are ranging from subcritical steam Rankine cycle; open regenerative Brayton air configurations at medium and high temperature; combined cycle; closed regenerative Brayton helium scheme and closed recompression supercritical carbon dioxide Brayton cycle. Power cycle diagrams and working conditions for design point are compared amongst the studied cases for a common reference thermal power of 57 ...

Numerical analysis of radiation propagation in innovative volumetric receivers based on selective laser melting techniques

Volumetric absorbers constitute one of the key elements in order to achieve high thermal conversion efficiencies in concentrating solar power plants. Regardless of the working fluid or thermodynamic cycle employed, design trends towards higher absorber output temperatures are widespread, which lead to the general need of components of high solar absorptance, high conduction within the receiver material, high internal convection, low radiative and convective heat losses and high mechanical durability. In this context, the use of advanced manufacturing techniques, such as selective laser melting, has allowed for the fabrication of intricate geometries that are capable of fulfilling the previous requirements. This paper presents a parametric design and analysis of the optical performance of volumetric absorbers of variable porosity conducted by means of detailed numerical ray tracing simulations. Sections of variable macroscopic porosity along the absorber depth were constructed by the fractal growth of sing...

A new laboratory-scale experimental facility for detailed aerothermal characterizations of volumetric absorbers

This paper describes a new modular laboratory-scale experimental facility that was designed to conduct detailed aerothermal characterizations of volumetric absorbers for use in concentrating solar power plants. Absorbers are generally considered to be the element with the highest potential for efficiency gains in solar thermal energy systems. The configu-ration of volumetric absorbers enables concentrated solar radiation to penetrate deep into their solid structure, where it is progressively absorbed, prior to being transferred by convection to a working fluid flowing through the structure. Current design trends towards higher absorber outlet temperatures have led to the use of complex intricate geometries in novel ceramic and metallic elements to maximize the temperature deep inside the structure (thus reducing thermal emission losses at the front surface and increasing efficiency). Although numerical models simulate the conjugate heat transfer mechanisms along volumetric absorbers, they lack, in many ca...

Numerical Modeling of Thermal Energy Storage System

Thermal energy storage in the form of latent heat of fusion of phase change material gained considerable attention in solar energy applications since it significantly increases the energy density and reduces the storage tank size compared to the sensible heat storage system. Several numerical and experimental studies have been conducted to enhance the performance of the system. In this study, 2-D continuous solid phase and effective packed bed models are developed to study the behavior and performance of a thermal energy storage system for high temperature applications, which is composed of spherical capsules encapsulated by phase change material (Sodium nitrate) and high temperature synthetic oil (Therminol 66) as heat transfer fluid. Temperature distribution, fluid flow, melting, solidification and thermocline behavior of the system are predicted and the influence of capsule size on the performance of the system is studied.Copyright

Numerical Study of a Beam-Down Solar Thermochemical Reactor for Chemical Kinetics Analysis

A lab-scale solar thermochemical reactor is designed and fabricated to study the thermal reduction of non-volatile metal oxides, which operates simultaneously as solar collector and as chemical reactor. The main purpose of this reactor is to achieve the first step in two-step thermochemical cycles. The chemical conversion rate strongly depends on the temperature and fluid flow distribution around the reactant, which are determined by the reactor geometry. The optimal design depends on the constraints of the problem and on the operating parameters. Hence, the objective of this investigation is to analyze the heat and mass transfer in the vertically-oriented chemical reactor by a CFD model and to optimize the reactor design. The developed numerical model is validated by comparing the simulation results with reported model. The influence of different technical and operating parameters on the temperature distribution and the fluid flow of the reactor are studied.Copyright

Ultra-modular 500m2 heliostat field for high flux/high temperature solar-driven processes

The main objective of the European Project SUN-to-LIQUID is the scale-up and experimental demonstration of the complete process chain to solar liquid fuels from H2O and CO2. This implies moving from a 4 kW laboratory setup to a pre-commercial plant including a heliostat field. The small power and high irradiance onto the focal spot is forcing the optical design to behave half way between a large solar furnace and an extremely small central receiver system. The customized heliostat field makes use of the most recent developments on small size heliostats and a tower with reduced optical height (15 m) to minimize visual impact. A heliostat field of 250kWth (500 m2 reflective surface) has been built adjacent to IMDEA Energy premises at the Technology Park of Mostoles, Spain, and consists of 169 small size heliostats (1.9 m × 1.6 m). In spite of the small size and compactness of the field, when all heliostats are aligned, it is possible to fulfil the specified flux above 2500 kW/m2 for at least 50 kW and an aperture of 16 cm, with a peak flux of 3000 kW/m2.The main objective of the European Project SUN-to-LIQUID is the scale-up and experimental demonstration of the complete process chain to solar liquid fuels from H2O and CO2. This implies moving from a 4 kW laboratory setup to a pre-commercial plant including a heliostat field. The small power and high irradiance onto the focal spot is forcing the optical design to behave half way between a large solar furnace and an extremely small central receiver system. The customized heliostat field makes use of the most recent developments on small size heliostats and a tower with reduced optical height (15 m) to minimize visual impact. A heliostat field of 250kWth (500 m2 reflective surface) has been built adjacent to IMDEA Energy premises at the Technology Park of Mostoles, Spain, and consists of 169 small size heliostats (1.9 m × 1.6 m). In spite of the small size and compactness of the field, when all heliostats are aligned, it is possible to fulfil the specified flux above 2500 kW/m2 for at least 50 kW and an ap...

19 Concentrating Solar Thermal Power

Robert McConnell National Renewable Energy Laboratory 23.1 Photovoltaics ..................................................................... 23-

Identification model and PI and PID controller design for a novel electric air heater

ABSTRACT In this article, the software and hardware control architecture for a novel high-temperature three-phase electric air heating furnace is presented. It consists of a multiple-input single-output (MISO) nonlinear plant designed to heat air at flow rates in a range between 10 and 60 Nm3/h, from ambient temperature up to 1000 °C. A divide-and-conquer (D&C) approach is applied. It consists in discretizing the air flow rates and working temperatures in intervals where the system behaviour is considered as single-input single-output (SISO) linear plant. Process identification techniques have been used to obtain empiric models for different operation ranges of the electric furnace. The controller parameters have been calculated using the Ziegler–Nichols tuning method. The resulting output air temperature control is composed of a set of 12 PI and PID controllers. The switch among controllers as a function of air flow rates and temperatures is carried out using programming logic and gain scheduling technique, respectively. The resulting multiple controller has been tested under real conditions and the results are presented and discussed.