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Biasca, Switzerland

Bader R.,ETH Zurich | Pedretti A.,Airlight Energy Holding SA | Steinfeld A.,ETH Zurich | Steinfeld A.,Paul Scherrer Institute
Journal of Solar Energy Engineering, Transactions of the ASME

A large-span solar parabolic trough concentrator is designed based on a multilayer polymer mirror membrane mounted on a rotatable concrete structure. The multilayer membrane is contained in a transparent protective air tube and generates a multicircular profile that approaches the trough parabolic shape. An analytical model of the mechanical behavior of the membrane mirror construction coupled to a Monte Carlo ray-tracing simulation is formulated and applied for design and optimization and for elucidating the influence of manufacturing and operational parameter variations on the radiative flux distribution. It is found that the parabolic shape can be well approximated with four stacked membranes that generate an arc-spline of four tangentially adjacent circular arcs. A 45-m-long 9-m-aperture full-scale prototype concentrator was fabricated and experimentation was carried out to validate the simulation model. Highest measured peak solar radiative flux concentration was 18.9, corresponding to 39% of the theoretical maximum value for an ideal parabolic trough concentrator. © 2011 American Society of Mechanical Engineers. Source

Bader R.,ETH Zurich | Pedretti A.,Airlight Energy Holding SA | Barbato M.,University of Applied Sciences and Arts Southern Switzerland | Steinfeld A.,ETH Zurich | Steinfeld A.,Paul Scherrer Institute
Applied Energy

A tubular cavity-receiver that uses air as the heat transfer fluid is evaluated numerically using a validated heat transfer model. The receiver is designed for use on a large-span (9m net concentrator aperture width) solar parabolic trough concentrator. Through the combination of a parabolic primary concentrator with a nonimaging secondary concentrator, the collector reaches a solar concentration ratio of 97.5. Four different receiver configurations are considered, with smooth or V-corrugated absorber tube and single- or double-glazed aperture window. The collector's performance is characterized by its optical efficiency and heat loss. The optical efficiency is determined with the Monte Carlo ray-tracing method. Radiative heat exchange inside the receiver is calculated with the net radiation method. The 2D steady-state energy equation, which couples conductive, convective, and radiative heat transfer, is solved for the solid domains of the receiver cross-section, using finite-volume techniques. Simulations for Sevilla/Spain at the summer solstice at solar noon (direct normal solar irradiance: 847Wm-2, solar incidence angle: 13.9°) yield collector efficiencies between 60% and 65% at a heat transfer fluid temperature of 125°C and between 37% and 42% at 500°C, depending on the receiver configuration. The optical losses amount to more than 30% of the incident solar radiation and constitute the largest source of energy loss. For a 200m long collector module operated between 300 and 500°C, the isentropic pumping power required to pump the HTF through the receiver is between 11 and 17kW. © 2014 Elsevier Ltd. Source

Mian A.,Ecole Polytechnique Federale de Lausanne | Ensinas A.A.,Ecole Polytechnique Federale de Lausanne | Ambrosetti G.,Airlight Energy Holding SA | Marechal F.,Ecole Polytechnique Federale de Lausanne
Chemical Engineering Transactions

Catalytic hydrothermal gasification is a promising technology which allows the conversion of wet biomass into methane rich syngas. It consists of three major steps, in which thermal energy has to be supplied at different temperature levels, leading to multiple products, such as clean water, nutrients/salts and methane rich syngas. Microalgae have an important potential as a new source of biomass, principally due to the fact that they can grow much faster than others biomass feedstock available in nature. Considering the energy balance of the algae cultivation step, the gasification process and thecrude product upgrading step, part of the converted syngas has to be used to close the energy balance. In this context, solar heat can be considered as an alternative to replace the heat that has to be generated from product or crude product burning. This would lead to higher fuel production, higher carbon conversion efficiency and in general a better sustainable use of energy sources. In this paper, the goal is to show the integration potential of solar thermal energy use in the catalytic hydrothermal gasification of microalgae. In order to maximize the fuel production, thermal energy requirements of the gasification and SNG upgrading process can be generated in concentrating solar systems, coupled with thermal energy storage. This allows to continuously provide heat for the process at different temperature levels. A superstructure of design models will permit the estimation of the optimal size and integration of the solar utility for different process configurations. The optimal design configurations are evaluated by solving a multi objective optimization problem which aims at the maximization of conversion efficiency and the minimization of operating and total production costs. Copyright © 2013, AIDIC Servizi S.r.l. Source

Zanganeh G.,ETH Zurich | Pedretti A.,Airlight Energy Holding SA | Zavattoni S.,University of Applied Sciences and Arts Southern Switzerland | Barbato M.,University of Applied Sciences and Arts Southern Switzerland | And 2 more authors.
Solar Energy

A thermal energy storage system, consisting of a packed bed of rocks as storing material and air as high-temperature heat transfer fluid, is analyzed for concentrated solar power (CSP) applications. A 6.5MWh th pilot-scale thermal storage unit immersed in the ground and of truncated conical shape is fabricated and experimentally demonstrated to generate thermoclines. A dynamic numerical heat transfer model is formulated for separate fluid and solid phases and variable thermo-physical properties in the range of 20-650°C, and validated with experimental results. The validated model is further applied to design and simulate an array of two industrial-scale thermal storage units, each of 7.2GWh th capacity, for a 26MW el round-the-clock concentrated solar power plant during multiple 8h-charging/16h-discharging cycles, yielding 95% overall thermal efficiency. © 2012 Elsevier Ltd. Source

Cooper T.,Sonneggstrasse | Schmitz M.,Sonneggstrasse | Good P.,Sonneggstrasse | Ambrosetti G.,Airlight Energy Holding SA | And 3 more authors.
Optics Letters

We consider the limit of geometric concentration for a focusing concave mirror, e.g., a parabolic trough or dish, designed to collect all radiation within a finite acceptance angle and direct it to a receiver with a flat or circular crosssection. While a concentrator with a parabolic cross-section indeed achieves this limit, it is not the only geometry capable of doing so. We demonstrate that there are infinitely many solutions. The significance of this finding is that geometries which can be more easily constructed than the parabola can be utilized without loss of concentration, thus presenting new avenues for reducing the cost of solar collectors. In particular, we investigate a low-cost trough mirror profile which can be constructed by inflating a stack of thin polymer membranes and show how it can always be designed to match the geometric concentration of a parabola of similar form. © 2014 Optical Society of America. Source

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