Politicizing immigration in Western Europe

Immigration has become a hot topic in West European politics. The factors responsible for the intensification of political conflict on this issue are a matter of considerable controversy. This holds in particular for the role of socio-economic factors and of radical right populist parties. This article explores the politicization of immigration issues and its driving forces in the electoral arena. It is based on a comparative study using both media and manifesto data covering six West European countries (Austria, France, Germany, Netherlands, Switzerland, and the UK) for a period from the early 1990s until 2017. We find no association between socio-economic factors and levels of politicization. Political conflict over immigration follows a political logic and must be attributed to parties and party competition rather than to ‘objective pressures.’ More specifically, we provide evidence that the issue entrepreneurship of radical right populist parties plays a crucial role in explaining variation in the politicization of immigration

Numerical investigations of advanced volumetric reseiver materials

This paper presents the results of a numerical analysis of the mass transport and the heat flow through a volumetric solar receiver as a candidate component for a central receiver system for solar electricity generation. The receiver investigated was an extruded honeycomb structure made out of Silicon carbide. The objective of the study is to investigate the influence of slight geometric changes on to the overall performance of the receiver. The results are compared with those of an experimental study. Two numerical models have been developed. One makes use of the real geometry of the channel (single channel model), the other one considers the receiver to be “porous continuum”, which described with homogenized properties such as permeability and effective heat conductivity. The experimental parameters such as average solar heat flux and mass flow were taken into account in the models as boundary conditions. Various parameters such as the average air outlet temperatures, the temperature distributions and the solar-to-thermal efficiency were used for the comparison. The good correspondence between the experimental and numeric results of the both numeric investigations confirms the usefulness of the approach for further studies

Review of heliostat calibration and tracking control methods

Large scale central receiver systems typically deploy between thousands to more than a hundred thousand heliostats. During solar operation, each heliostat is aligned individually in such a way that the overall surface normal bisects the angle between the sun’s position and the aim point coordinate on the receiver. Due to various tracking error sources, achieving accurate alignment ≤1 mrad for all the heliostats with respect to the aim points on the receiver without a calibration system can be regarded as unrealistic. Therefore, a calibration system is necessary not only to improve the aiming accuracy for achieving desired flux distributions but also to reduce or eliminate spillage. An overview of current larger-scale central receiver systems (CRS), tracking error sources and the basic requirements of an ideal calibration system is presented. Leading up to the main topic, a description of general and specific terms on the topics heliostat calibration and tracking control clarifies the terminology used in this work. Various figures illustrate the signal flows along various typical components as well as the corresponding monitoring or measuring devices that indicate or measure along the signal (or effect) chain. The numerous calibration systems are described in detail and classified in groups. Two tables allow the juxtaposition of the calibration methods for a better comparison. In an assessment, the advantages and disadvantages of individual calibration methods are presented

Modeling of heat conduction processes in porous absorber of open type of solar tower stations

An analysis of existing methods for calculating heat and mass transfer processes in porous absorbers of receivers of tower solar power plants is carried out. It is shown that the resulting thermophysical properties of the material are influenced not only by the porosity but also by the location of the pores in the material volume. The criterion of the dislocation vector is proposed as a mathematical indicator of various porous structures. The shortcomings of the existing dependences of the effective thermal conductivity of a material on the type of porosity are shown. The most reliable dependences for determining the thermophysical parameters of a porous medium are also determined and independent factors are proposed on which the mathematical model of heat and mass transfer in open-type solar receivers should be based. The current state of research on the effective thermal conductivity of the porous structure of solar receivers is described in detail. A new formula for calculating the effective thermal conductivity of a porous structure with regard to the dislocation vector and a method for calculating the processes of heat transfer in open solar receivers based on the proposed formula are proposed. The proposed equation has been tested. It is determined that for simple channel structures it is sufficient to use the existing equations to calculate the thermal conductivity coefficient, while for more complex porous structures, such as the StepRec absorber, it is better to use the proposed equation. Among the strengths of this study is a new calculation formula that allows us to build an analytical model of heat transfer in a porous medium. The use of the analytical model can significantly reduce the complexity of modern calculations of heat transfer processes in a porous absorber and will help improve the quality of optimization models of solar receivers

Towards an optimal aiming for molten salt power towers

Finding a suitable aiming strategy for receivers of power towers can be challenging, especially for receivers using molten salt as heat transfer fluid as the allowable flux density decreases dramatically with increasing salt temperature. In this paper a very fast, steady-state model for the molten salt receiver is presented. This model is combined with a ray-tracing software and a metaheuristic optimization procedure. The thermal model is used to calculate the actual temperature and mass flow in the receiver which are then used to calculate the operational limits for the flux density. It is demonstrated that such an optimized aiming strategy can outperform a parameter based aiming strategies by more than 2%

Potential high-temperature industrial process heat applications for concentrating solar technology in South Africa

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.South Africa has the largest and most developed economy and the highest energy consumption on the continent. 72% of the primary energy is provided by coal, making South Africa the leading carbon dioxide emitter in Africa and the 13th largest in the world. As the amount of South Africa’s proved crude oil reserves is very small, synthetic fuels derived from coal and natural gas in its coal-to-liquid and gas-to-liquid plants make up roughly 90% of the country’s domestic petroleum production. However, just one third of the total petroleum demand can be met by the production and the other two third has to be imported and processed in the local oil refineries. Using Concentrated Solar Thermal (CST) technology, especially solar tower systems, could have the potential to substitute fossil fuels by solar energy, as South Africa is exposed to one of the highest direct normal irradiance (DNI) in the world. There are several technologies able to deliver high temperature heat. They differ by heat transfer media, system temperature and the system pressure. Direct or indirect heat storing allows a high solar share while an easy hybridization with fossil fuels guarantees 100% availability. One promising technology, for example, uses small ceramic particles as heat transfer and storage media. The particles can be heated up to 1000°C and later be used for production of hot air. A very simple and therefore robust technology uses ambient air which is heated up to 750°C for direct use in a pre- heating process or storing the heat in regenerator storage. Another technological approach uses the rejected heat of a solarized gas turbine with temperatures up to 650°C as process heat. The benefit of such a system is the combined generation of electricity and heat. Storage can be included at the pressurized side allowing high solar share or by using a regenerator on the hot exhaust stream. The diversity of processes and consumers requires an individual selection of the technology and a layout adapted to the specific consumer needs. The paper presents the different available technologies to show the potential using CST for process heat using air with temperatures above 600°C.cf201

Static optimal control: Real-time optimization within closed-loop aim point control for solar power towers

Many aim point optimization techniques exist to control Solar Power Towers (SPTs). However, SPTs exhibit optical losses that cannot be exactly modeled. Moreover, cloud passages cause transient incident flux distributions. Due to these modeling errors and disturbances, aim point optimization may exceed the Allowable Flux Density (AFD); consequently, these efficient aiming strategies are seldom applied at commercial plants. In this paper, an innovative closed-loop aim point control technique, the Static Optimal Control, is proposed. Flux density measurements close the open control loop of aim point optimization. Based on this feedback, the Static Optimal Control estimates weights that are embedded in the cost function of the aim point optimization. This GPU-based optimizer finds good aim point configurations in a few seconds even for large plants. Thus, the Static Optimal Control compensates for modeling errors and rejects disturbances to observe the AFD while maximizing the intercept. The performance of the Static Optimal Controller is evaluated for inaccurately modeled mirror errors and under a real cloud scenario. Aim of this control is not to exceed the AFD by more than 5% i.e. the accuracy of the flux density measurements. The aim is achieved for static modeling errors while improving the intercept by 1.7-8.6% compared to a heuristic control. In the cloud scenario, the Static Optimal Control reaches its limits. Even mapping all-sky-imager-based nowcasts in a feed forward manner on the heliostat field does not improve the control quality due to high prediction errors