High-flux Solar Simulator Research Articles

Use of concentrated radiation for solar powered glass melting experiments

To investigate the feasibility of using concentrated solar radiation to provide process heat for glass production, a high flux solar simulator was used to melt glass forming batches. Initial experiments involved melting various glass forming batches which demonstrated that rapid and full conversion of the crystalline raw materials into an X-ray amorphous vitreous state was possible. A pure silica batch produced an X-ray amorphous product but it was not possible to refine the melt in these exploratory tests. A powdered, ternary soda–lime–silica (SLS) glass forming batch melted vigorously, with rapid gas removal, resulting in a completely transparent glass. Industrial SLS pellets were subsequently used in semi-continuous melting experiments, whereby the batch was intermittently fed into the melting zone while the beam was kept on. Additional secondary heating and insulation around outlet of the melting zone was required to achieve a semi-continuous flow of molten glass to an output crucible.

Optical Analysis of a Hexagonal 42kWe High-flux Solar Simulator

A 42-kWe high-flux solar simulator with hexagonal reflector symmetry has been designed, built and optically characterized at IMDEA Energy Institute, Spain. This facility makes possible the lab-scale generation of a quasi-uniform high radiation flux density and high stagnation temperatures and it will be used as a platform for analyzing processes under concentrating solar energy conditions; for instance, central receivers in concentrating solar power plants and solar fuel production process in thermochemical reactors. The high-flux solar simulator consists of seven reflector-lamp pairs arranged in the center and vertices of a regular hexagon. The 6-kWe Xe short arc lamps are allocated in the primary focus of the corresponding truncated ellipsoidal reflector. This hexagonal symmetry provides compactness and quasi-uniform spatial distribution of the radiation at the system common focal plane.This work presents the experimental characterization of the solar simulator optical performance. Preliminary measurements indicate an average flux density at the focal plane of 3.5 MW/m2 that means 3,500 suns (1 sun = 1kW/m2) and stagnation temperature of approximately 2,800K.

Proof of Concept Test of a Centrifugal Particle Receiver

As a proof of concept a Centrifugal Particle Receiver (CentRec) prototype in laboratory scale (∼10 kWth) was designed, built and tested in the High-Flux Solar Simulator in Cologne, Germany. Since they can be heated up to 1000°C without sintering in the storage, small bauxite particles produced for the oil and gas industry are used as the absorber, the heat transfer and storage media at the same time. A defined rotation is used to form a thin direct absorbing particle film on the inner surface of the cylindrical receiver. Depending on the incoming heat flux the particle residence time can be adjusted by controlling rotation speed and mass flow. A constant particle outlet temperature for all load conditions can be therefore ensured. First experiments were conducted with various power levels and mass flows at two different receiver inclinations. Particle outlet temperatures of up to 900°C were demonstrated and the expected simple control capability of the receiver concept was verified.

Design and Validation of a Low-cost High-flux Solar Simulator using Fresnel Lens Concentrators

A systematic design procedure for a high flux solar simulator is presented in this paper. The 84 kWe solar simulator is based on an array of 12 commercially available xenon-arc lamps (each 7 kWe) coupled with silicone-on-glass Fresnel lenses as the optical concentrator. A ray-tracing model of the xenon lamp has been developed based on the real emitter shape and the Fresnel lens optics; simulations performed using a non-sequential Monte Carlo technique have been validated against experimental test data. The results show that 19.7kW of radiative power is delivered on a 200mm diameter target with and a peak flux of 6.73 MW/m2 and an electricity to radiative power efficiency of 23.4%. This research facility will be used as an experimental platform for high flux solar receiver and thermochemical reactor research, as well as for advanced high-temperature material testing.

Description and characterization of an adjustable flux solar simulator for solar thermal, thermochemical and photovoltaic applications

A high flux solar simulator for indoor performance assessment of systems in solar thermal, thermochemical and high concentration photovoltaic research offers repeatability under controlled climate conditions. This paper presents a new high flux solar simulator where a 7kW xenon short arc lamp coupled with a truncated ellipsoid reflector is used as the light source. The flux mapping method is used to evaluate performance of this high flux solar simulator on the basis of flux distribution, temporal instability, spatial non-uniformity, peak flux, conversion efficiency and power intercepted on a circular target placed at the focal plane. The input current of the simulator is adjusted in the range of 113–153A to quantify the maximum and minimum peak flux output per power settings of the solar simulator, which yield different flux distribution at different power level. A theoretical comparative analysis of manufacturer’s sensor scaling factor of the circular foil heat flux gage with literature is performed and an optimum scaling factor of 491.46kWm−2/mV is selected to relate measured incident flux with CCD (charge-coupled device) camera’s greyscale value of acquired image. It was observed that at an input current of 153A, the simulator delivers a peak flux of 3583kWm−2, temporal instability of radiative output less than 3%, and cumulative beam power of 1.642kW at a circular target radius of 110mm placed at the focal plane. A conversion efficiency at 153A and 110mm radius was determined to be 47%. For a photovoltaic cell size of 1.5mm radius, the solar simulator provides an average incident flux in the range of 1200–3000 suns with class ‘A’ temporal instability and class ‘B’ spatial non-uniformity. The simulator is capable of adjusting peak flux in the range of 2074–3583kWm−2 and can produce a theoretical black body stagnation temperature of 1857K.

Design of Ellipsoidal Specular Reflectors of 70 kW High-Flux Solar Simulator

With the constraint of maximum light-concentrating efficiency, we designed a condenser for a 70 kW high-flux solar simulator. The mathematical models of the optical condenser unit and system were established to determine the condenser shape parameters.The Monte Carlo ray-tracing method was applied to compute the the light-concentrating efficiency for the condenser. It is shown that the truncation angle is the major parameter to influence the light-concentrating efficiency.When the truncation angle is 60 degrees, the condenser aberration is balanced by the truncation loss to reach the maximum light-concentrating efficiency.

A two-zone solar-driven gasifier concept: Reactor design and experimental evaluation with bagasse particles

A two-zone solar reactor concept for the steam-based gasification of biomass particles using concentrated solar energy has been developed and experimentally evaluated with particles of sugarcane bagasse at a 1.5kW solar input scale. The gasifier has been designed with the objective to provide pyrolysis and gasification conditions yielding high carbon conversion into syngas and suppressing the formation of tars and gaseous hydrocarbons. It consists of two zones. In the upper drop-tube zone, a high radiative heat flux to the dispersed particles induces their fast pyrolysis. In the lower trickle bed zone, a structured packing provides the residence time and temperature required for the char gasification and the decomposition of the other pyrolysis products.A series of 20min gasification experiments comparing the two-zone reactor vs. a drop-tube reactor were performed in a high-flux solar simulator with a maximum particle flux of 16g/sm2. It has been demonstrated that the former allows for more efficient decomposition of CH4 and C2 hydrocarbons at comparable reactor temperatures. The LHV of the product gas leaving the two-zone gasifier was significantly higher than those typically obtained in conventional autothermal gasifiers. Solar energy was chemically stored in the product gas, resulting in energetic upgrade of the biomass by 5% and a maximum energy conversion efficiency of 21%.

Operational Performance of the University of Minnesota 45 kWe High-Flux Solar Simulator

The University of Minnesota's high flux simulator delivers radiative power of approximately 9.2 kW over a Ø60 mm circular area located in the focal plane, corresponding to an average flux of 3200 kW m−2, with a peak flux of 7300 kW m−2.

Error Analysis of the Radiative Power Determined From Flux Distributions Measured With a Camera in a Xe Arc Lamp-Based Solar Simulator

The CCD camera-based flux measurement at Paul Scherrer Institute's (PSI) high flux solar simulator (HFSS) is influenced by a spatially variable spectrum of the concentrated radiation characteristic for arc lamp-based solar simulators. This results in a substantial error in the radiative power determined by integration of the flux distribution. This systematic error is assessed by numerically modeling the response of the CCD camera in use. Measured spectra of concentrated radiation obtained at different points in the flux distribution, measured transmission characteristics of all optical elements, and published data for the spectral sensitivity of the CCD chip are applied in the model. The response of a water calorimeter is used as baseline case. It is shown that the magnitude of the error depends strongly on the region analyzed, i.e., on aperture size, on the wavelength band analyzed, and, unfortunately, also on the number of lamps in operation. A relative error in the range of 10–30% is observed if an aperture with 1 cm in diameter covering the region of peak concentration is considered. It will be shown that the error arises due to the fact that a photon counter (CCD camera) is used to determine the thermal power.

A novel beam-down, gravity-fed, solar thermochemical receiver/reactor for direct solid particle decomposition: Design, modeling, and experimentation

A novel solar-thermochemical reactor for the reduction of ZnO powder using concentrated sunlight has been designed, constructed and tested. The purpose of the reactor is to accomplish the first step in a two-step water-splitting process to generate hydrogen renewably from sunlight using the ZnO redox cycle. Abbreviated as GRAFSTRR (Gravity-Fed Solar-Thermochemical Receiver/Reactor), the reactor is closed to the atmosphere, and features an inverted conical-shaped reaction surface along which reactant powder descends continuously as a moving bed, undergoing a thermochemical reaction at high temperature upon exposure to highly concentrated sunlight within the reaction cavity. Heat transfer and Zn production within the cavity have been modeled, as well as the influence of effective reactant particle size on reactive surface area. Initial experiments using a high-flux solar simulator successfully demonstrated the mechanical stability of the reactor and primary systems, namely particle entrainment in the vortex flow, moving bed adhesion to the reaction surface, and the solid particle delivery and exit mechanism. This paper presents the GRAFSTRR concept, select design choices, and a summary of pertinent findings from experimental and numerical investigations.

非共轴椭球面聚光阵列式高焦比太阳模拟器

非共轴椭球面聚光阵列式高焦比太阳模拟器

Thermoelectric Oxide Modules (TOMs) for the Direct Conversion of Simulated Solar Radiation into Electrical Energy

The direct conversion of concentrated high temperature solar heat into electrical energy was demonstrated with a series of four–leg thermoelectric oxide modules (TOM). These temperature stable modules were not yet optimized for high efficiency conversion, but served as proof-of-principle for high temperature conversion. They were constructed by connecting two p- (La1.98Sr0.02CuO4) and two n-type (CaMn0.98Nb0.02O3) thermoelements electrically in series and thermally in parallel. The temperature gradient ΔT was applied by a High–Flux Solar Simulator source (HFSS) which generates a spectrum similar to solar radiation. The influence of the graphite layer coated on the hot side of the Al2O3 substrate compared to the uncoated surface on ΔT, Pmax and η was studied in detail. The measurements show an almost linear temperature profile along the thermoelectric legs. The maximum output power of 88.8 mW was reached for a TOM with leg length of 5 mm at ΔT = 622 K. The highest conversion efficiency η was found for a heat flux of 4–8 W cm-2 and the dependence of η on the leg length was investigated.

Heat transfer model of a solar receiver-reactor for the thermal dissociation of ZnO—Experimental validation at 10 kW and scale-up to 1 MW

A transient heat transfer model is developed for analyzing the thermal performance of a thermochemical reactor for the solar-driven dissociation of ZnO in the 1600–2136 K range. The reactor consists of a rotating cavity-receiver lined with ZnO particles that are directly exposed to concentrated solar radiation. The model couples radiation, convection, and conduction heat transfer to the reaction kinetics for a shrinking domain and simulates a transient ablation regime with semi-batch feed cycles of ZnO particles. Validation is accomplished in terms of the numerically calculated and experimentally measured temperature profiles and reaction extents for a 10 kW reactor prototype tested in a high-flux solar simulator and subjected to peak solar concentration ratios exceeding 5000 suns. Scaling-up the reactor technology to 1 MW solar thermal power input has the potential of reaching a solar-to-chemical energy conversion efficiency of 56%.

CO2 capture from atmospheric air via consecutive CaO-carbonation and CaCO3-calcination cycles in a fluidized-bed solar reactor

Abstract A thermochemical cyclic process and associated reactor is presented for the continuous removal of CO2 from ambient air via consecutive CaO-carbonation and CaCO3-calcination steps using concentrated solar energy as the source of high-temperature process heat. A fluidized-bed solar reactor is applied to accomplish the carbonation at 365–400 °C and the calcination at 800–875 °C, with reacting particles directly exposed to high-flux solar irradiation. Water vapor was introduced during the carbonation step to enhance its kinetics. Five consecutive cycles were performed, yielding complete removal of CO2 from a continuous airflow containing 500 ppm of CO2 within a residence time of 1.3 s during each carbonation step, and subsequent complete release of CO2 and regeneration of the CaO reacting particles during the calcination step. The reactor design, set-up, and experimentation using a high-flux solar simulator are described.

A Receiver-Reactor for the Solar Thermal Dissociation of Zinc Oxide

An improved engineering design of a solar chemical reactor for the thermal dissociation of ZnO at above 2000K is presented. It features a rotating cavity receiver lined with ZnO particles that are held by centrifugal force. With this arrangement, ZnO is directly exposed to concentrated solar radiation and serves simultaneously the functions of radiant absorber, chemical reactant, and thermal insulator. The multilayer cylindrical cavity is made of sintered ZnO tiles placed on top of a porous 80%Al2O3–20%SiO2 insulation and reinforced by a 95%Al2O3–5%Y2O3 ceramic matrix composite, providing mechanical, chemical, and thermal stability and a diffusion barrier for product gases. 3D computational fluid dynamics was employed to determine the optimal flow configuration for an aerodynamic protection of the quartz window against condensable Zn(g). Experimentation was carried out at PSI’s high-flux solar simulator with a 10kW reactor prototype subjected to mean radiative heat fluxes over the aperture exceeding 3000suns (peak 5880suns). The reactor was operated in a transient ablation mode with semicontinuous feed cycles of ZnO particles, characterized by a rate of heat transfer—predominantly by radiation—to the layer of ZnO particles undergoing endothermic dissociation that proceeded faster than the rate of heat transfer—predominantly by conduction—through the cavity walls.

Numerical and experimental study of gas–particle radiative heat exchange in a fluidized-bed reactor for steam-gasification of coal

A heat transfer numerical model is developed for the steam-gasification of coal in a fluidized bed contained in a quartz tubular reactor that is directly exposed to concentrated thermal radiation. The Monte Carlo method is applied for solving the radiative exchange within the reactor quartz walls, the bed particles, and the gas phase. The reaction kinetics are described by Langmuir–Hinshelwood type rate laws. Steady-state mass and energy conservation equations that link heat transfer to the chemical kinetics are formulated and solved iteratively by the finite volume method and Newton algorithm. Numerically computed temperature profiles, product gas composition, and conversions are compared to experimentally measured values in a directly irradiated tubular quartz reactor, tested in a high-flux solar simulator. At above 1450 K, the gas composition consists of a nearly equimolar mixture of H 2 and CO, with less than 5% of CO 2. Heat is transferred to the particles predominantly by thermal radiation and to the gas by particle–gas convection, since radiation absorption by particles is three orders of magnitude higher than that of the gas phase.

A Novel 50kW 11,000 suns High-Flux Solar Simulator Based on an Array of Xenon Arc Lamps

A novel high-flux solar simulator, capable of delivering over 50kW of radiative power at peak radiative fluxes exceeding 11,000 suns, is operational at the Paul Scherner Institute. It comprises an array of ten Xe arcs, each close-coupled with ellipsoidal specular reflectors of common focus. Its optical design, main engineering features, and operating performance are described. The Monte Carlo ray-tracing technique is applied to optimize the geometrical configuration for maximum source-to-target transfer efficiency of radiative power. Calorimeter measurements indicated an average flux of 6800kW∕m2 over a 60-mm-diameter circular target, which corresponds to stagnation temperatures above 3300K. This research facility simulates the radiation characteristics of highly concentrating solar systems and serves as an experimental platform for investigating the thermochemical processing of solar fuels and for testing advanced high-temperature materials.

Experimental Investigation of the Solar Carbothermic Reduction of ZnO Using a Two-cavity Solar Reactor

Zinc production by solar carbothermic reduction of ZnO offers a CO2 emission reduction by a factor of 5 vis-a`-vis the conventional fossil-fuel-based electrolytic or Imperial Smelting processes. Zinc can serve as a fuel in Zn-air fuel cells or can be further reacted with H2O to form high-purity H2. In either case, the product ZnO is solar-recycled to Zn. We report on experimental results obtained with a 5 kW solar chemical reactor prototype that features two cavities in series, with the inner one functioning as the solar absorber and the outer one as the reaction chamber. The inner cavity is made of graphite and contains a windowed aperture to let in concentrated solar radiation. The outer cavity is well insulated and contains the ZnO-C mixture that is subjected to irradiation from the inner graphite cavity. With this arrangement, the inner cavity protects the window against particles and condensable gases and further serves as a thermal shock absorber. Tests were conducted at PSI’s Solar Furnace and ETH’s High-Flux Solar Simulator to investigate the effect of process temperature (range 1350-1600 K), reducing agent type (beech charcoal, activated charcoal, petcoke), and C:ZnO stoichiometric molar ratio (range 0.7–0.9) on the reactor’s performance and chemical conversion. In a typical 40-min solar experiment at 1500 K, 500 g of a ZnO-C mixture were processed into Zn(g), CO, and CO2. Thermal efficiencies of up to 20% were achieved.

A New 75 kW High-Flux Solar Simulator for High-Temperature Thermal and Thermochemical Research

A new high-flux solar simulator, capable of delivering up to 75 kW of continuous radiative power at peak fluxes exceeding 4250 kW/m2, is operational at the ETH-Zurich. Its optical design and performance are described. This unique facility serves principally as an experimental platform for investigating thermal and thermochemical processes at temperatures up to 3000°K.