Search

Computing the flux densities provided by solar concentrators or focusing heliostats can be done in two different ways: A grid ray-tracing (GRT) procedure that makes use of a large number of ray bundles, starting from the solar disk and finally impinging the focal plane of the concentrator. The method is reliable and accurate, but requires extensive computing times. Alternatively, the flux densities can be estimated by using convolution algorithms. This latter method requires much less computing time, but is known to be less accurate when the incidence angle of the sunrays on the reflector increases. The objective of this contribution is to define an algorithm based on convolution products and fast Fourier transforms having high accuracy. The results show that RMS error differences between both models are typically lower then 1%.

Particle flow structure and associated heat transfer coefficient are examined as a function of temperature in a single-tube fluidized bed solar receiver operating in upward particle flow mode. It is found that temperature has a strong effect on both fluidization regimes and wall-to-bed heat transfer coefficient that varies in the range 800-1200 W/(m2.K). Turbulent fluidization regime results in the most intense heat transfer between the irradiated wall and the fluidized particle.

This study presents a comparison of both modelling and experimental results obtained on the solar field and the receiver of the MW-scale particle driven CSP unit implemented at the Themis solar tower (France) in the framework of the Next-CSP H2020 European project. At partial load, ~900 kW, the simulated data concerning the incident power at the receiver aperture are consistent with the measured values with less than 5% difference from the experimental results. The difference is higher for the particle temperature and the thermal efficiency as a function of particle mass flow rate. It ranges between 12 and 98°C for measured particle temperature of 430 and 300°C respectively. For the thermal efficiency, the difference varies strongly with the experiments from approximately 12% to 50% (relative). The main cause of discrepancy between the experimental and the calculated results is attributed to the heterogeneity of the solar flux distribution on the receiver tubes.

Concentrated solar power is a promising technique enabling renewable energy production with large scale solar power plants in the near future. Estimating quantitatively the reflectivity of a solar concentrator is a major issue, since it has a significant impact on the flux distribution formed at the solar receiver. Moreover, it is desirable that the mirrors can be measured during operation in order to evaluate environmental factors such as day/night thermal cycles or soiling and ageing effects at the reflective surfaces. For that purpose, a backward gazing method that was originally developed to measure mirror shape and misalignment error was developed. The method operates in quasi real-time without disturbing the heat production process. It was successfully tested at the Themis solar tower power plant in Targasonne, France. Its basic principle consists in acquiring four simultaneous images of a Sun-tracking heliostat, captured from different observation points located near the thermal receiver. The images are then processed with a minimization algorithm allowing the determination of the reflectance and slopes errors of the mirrors. In this communication, it is shown that the algorithm allows one to get quantitative reflectivity maps at the surface of the heliostat. The measurement is fully remote and is used to evaluate surface reflectivity that depends on optical coatings quality and soiling effects. Preliminary results obtained with a Themis heliostat are presented. They show that reflectivity measurements can be carried out within repeatability about ± 5% Peak-to-Valley (PTV) and 1% RMS. Ways to improving these numbers are discussed in the paper.

Recycling Li-ion batteries is a delicate but strategic operation that can be performed by either pyrometallurgy, hydrometallurgy or a combination of methods. This paper presents, for the first time, an innovative solar pyrometallurgical route that consists in three steps. They are pyrolysis, mechanical separation and smelting. The process is applied to LiNixMnyCo1-x-yO2 (NMC) cathode material. After pyrolysis at 580°C and smelting at 1000°C, the final product is a Ni-based alloy containing Co, Li and Mn.

A fluidized particle single-tube solar receiver has been tested for investigating the gas-particle characteristics that enable the best operating conditions in a commercial-scale plant. The principle of the solar receiver is to fluidize the particles in a vessel – the dispenser – in which the receiver tube is plunged. The particles are flowing upward in the tube, irradiated over 1-meter height, by applying an overpressure in the dispenser. Experiments with a concentrated solar flux varying between 188 and 358 kW/m² are carried out, and the particle mass flux varied from 0 to 72 kg/(m²s). The mean particles and external tube wall temperatures in the irradiated zone are heated from the ambient to respectively 700°C and 940°C. It is shown that the temperature rise leads to a decrease of the particle volume fraction. Furthermore, a self-regulation of the system is evidenced with a short transient regime. This characteristic is essential from the operational viewpoint. The thermal efficiency of the receiver increases with the particle flow rate, reaching between 60 and 75% above 30 kg/(m²s). Several fluidization regimes are identified thanks to pressure signal analyses, like slugging, turbulent and fast fluidization, showing that regimes transitions are strongly affected by the temperature.

A fluidized-particles two-tube solar receiver was tested at ambient temperature at PROMES Laboratory to investigate the influence of an inhomogeneous solar flux density on the particle mass flow rate between the tubes. The principle of this 3rd generation solar receiver is to fluidize the particles in a container, called dispenser, in which the tubes’ bottom are immersed. The fluidized particles are flowing upward the tubes by applying an overpressure in the dispenser. Air velocities are changed inside the tubes, thanks to air mass flow controllers, to represent temperature heterogeneity between the tubes. Air velocities from 0.05 up to 0.52 m/s were tested, both in homogeneous and heterogeneous conditions. In the heterogeneous ones, the differences in air velocity between the tubes aim to mimic a difference in temperature from 20 to 100 % with homogeneous air flow rates injected. The following conclusions were drawn. First, the particle mass flux in the tubes are the same with homogeneous air velocities, each one following a calibration map previously obtained. Second, different air velocities lead to different particle mass flux. Third, the rise of the total particle mass flux diminishes the pressure in the dispenser. Four, this diminution of pressure leads to a decrease of the particle mass flow rate of the tube with the lower air velocity. This influence can lead in some cases to the stop of the fluidized bed circulation in the affected tube.

This work presents the experimental evaluation of pilot-scale thermocline that integrates a layer of phase change material (PCM) at the top of a sensible heat storage material in a thermocline thermal energy storage (TES) tank. The TES is integrated to the MicroSol-R parabolic trough pilot plant at the PROMES research facility in Odeillo, France. The tank is filled with alumina spheres as sensible heat storage. The PCM is NaNO3 encapsulated in stainless steel horizontal tubes that fill about 5.5% of the tank volume. The charge is evaluated at three mass flow rates 2600, 3000, and 3900 kg/h at two different operating temperature ranges 285-315 ºC and 295-330 ºC. The discharge is studied at three mass flow rates 1600, 2000, and 3000 kg/h from 315 to 220 ºC and 330 to 225 ºC. The performance of the TES is analyzed with two main indicators: the thermocline thickness and the efficiency during the charge and discharge. The results indicate that lower mass flow rates during the charging process result in smaller thermocline thickness. Similarly, during discharge, the thermocline thickness reduces with lower discharge rates. Efficiency evaluation during discharge suggests that an optimal flow rate could be achieved.

After many years of fruitful collaboration in the field of research infrastructures (RIs) for concentrated solar power/solar thermal energy applications, several European countries decided to apply to the European Commission to go a step forward and create a European Research Infrastructure Consortium (ERIC), a new legal form of association which poses a number of advantages in the endeavour for a further development of this technology in Europe at all levels. This new consortium, EU-SOLARIS ERIC, is likely to be legally implemented in October 2022, after a long negotiation and evaluation process, where the support of the respective Governmental research agencies of the countries involved has been crucial. EU-SOLARIS ERIC will be a legal entity and its main goal will be the improvement of the interoperability, accessibility and quality of services provided by the existing European research infrastructures to the CSP/STE research communities and industrial stakeholders. Although the current Members of the EU-SOLARIS consortium are Germany, France, Cyprus and Spain (Statutory Seat at Plataforma Solar de Almería, Spain), plus Portugal as an Observer, it is open to any other country willing to participate as Member or Observer.