Airlight Energy Holding SA

Biasca, Switzerland

Airlight Energy Holding SA

Biasca, Switzerland
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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 | Year: 2011

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.


Bader R.,ETH Zurich | Barbato M.,University of Applied Sciences and Arts Southern Switzerland | Pedretti A.,Airlight Energy Holding SA | Steinfeld A.,ETH Zurich | Steinfeld A.,Paul Scherrer Institute
Journal of Solar Energy Engineering, Transactions of the ASME | Year: 2010

A cylindrical cavity-receiver containing a tubular absorber that uses air as the heat transfer fluid is proposed for a novel solar trough concentrator design. A numerical heat transfer model is developed to determine the receiver's absorption efficiency and pumping power requirement. The 2D steady-state energy conservation equation coupling radiation, convection, and conduction heat transfer is formulated and solved numerically by finite volume techniques. The Monte Carlo ray-tracing and radiosity methods are applied to establish the solar radiation distribution and radiative exchange within the receiver. Simulations were conducted for a 50 m-long and 9.5 m-wide collector section with 120°C air inlet temperature, and air mass flows in the range 0.1-1.2 kg/s. Outlet air temperatures ranged from 260°C to 601°C., and corresponding absorption efficiencies varied between 60% and 18%. Main heat losses integrated over the receiver length were due to reflection and spillage at the receiver's windowed aperture, amounting to 13% and 9% of the solar power input, respectively. The pressure drop along the 50 m module was in the range 0.23-11.84 mbars, resulting in isentropic pumping power requirements of 6.45 × 10-4 -0.395% of the solar power input. Copyright © 2010 by ASME.


Cooper T.,ETH Zurich | Ambrosetti G.,Airlight Energy Holding SA | Malnati F.,Airlight Energy Holding SA | Pedretti A.,Airlight Energy Holding SA | Steinfeld A.,ETH Zurich
Progress in Photovoltaics: Research and Applications | Year: 2016

A new approach to high-concentration photovoltaics (HCPV) based on a parabolic trough primary concentrator is presented. The design diverges from the standard HCPV arrangement of a two-axis tracking point-focus concentrator, and rather employs a simpler parabolic trough primary concentrator to reduce cost. To break the 2D limit of concentration, and bring the system into the realm of HCPV, the system employs an array of rotating secondary concentrators is arranged along the focal line of the parabolic trough. The resulting line-to-point (LTP) focus geometry allows the system to achieve a geometric concentration of 590×, yet still maintains the advantages of having a linear trough primary concentrator, namely manufacturability, economy, and scalability. A full-scale prototype of the system was constructed in Biasca, Switzerland. During on-sun tests a flux concentration of 364 suns was measured at the exit of the secondary concentrator, the highest reported concentration for any parabolic-trough-based system. Moreover, the system reached a peak efficiency of 20.2%, the highest measured solar-to-DC efficiency for a parabolic trough-based solar collector. Long-term performance is estimated by means of a coupled optical-electrical model validated vis-à-vis the experimental results. This work serves as an experimental proof-of-concept for high-concentration trough-based collectors, thereby opening new avenues for reducing the cost of HCPV systems. © 2016 John Wiley & Sons, Ltd.


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 | Year: 2012

We report on the field testing of a 42 m-long full-scale solar receiver prototype installed on a 9 m-aperture solar trough concentrator. The solar receiver consists of a cylindrical cavity containing a tubular absorber with air as the heat transfer fluid (HTF). Experimental results are used to validate a heat transfer model based on Monte Carlo ray-tracing and finite-volume techniques. Performance predictions obtained with the validated model yield the following results for the receiver. At summer solstice solar noon, with HTF inlet temperature of 120 °C and HTF outlet temperature in the range 250-450 °C, the receiver efficiency ranges from 45% to 29% for a solar power input of 280 kW. One third of the solar radiation incident on the receiver is lost by spillage at the aperture and reflection inside the cavity. Other heat losses are due to natural convection (9.9-9.7% of solar power input) and re-radiation (6.1-17.6%) through the cavity aperture and by natural convection from the cavity insulation (5.6-9.1%). The energy penalty associated with the HTF pumping work represents 0.6-24.4% of the power generated. © 2012 American Society of Mechanical Engineers.


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 | Year: 2015

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.


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 | Year: 2012

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.


Zanganeh G.,ETH Zurich | Bader R.,ETH Zurich | Pedretti A.,Airlight Energy Holding SA | Pedretti M.,Airlight Energy Holding SA | And 2 more authors.
Solar Energy | Year: 2012

The design of a solar parabolic dish concentrator is proposed based on an array of polyester mirror membrane facets that are clamped along their edges by elliptical rims and focused by applying a slight vacuum underneath the membranes, creating an ellipsoidal shape. The axes ratio of the elliptical rims varies with the position on the dish to approach the paraboloidal shape. The elastic mirror membrane deformation under uniform pressure load is simulated by finite element structural analysis and the resulting radiative flux distribution at the focal plane of the dish is determined by the Monte Carlo ray-tracing technique. Optimization of the membrane deflection is accomplished for maximum solar flux concentration at the focal plane. Two dish geometries are examined: (i) a 1.5-m radius 3-m focal length small dish, comprising 19 facets of 0.275-m radius with four different curvatures, yielding a peak solar concentration ratio of 5515 suns and a mean solar concentration ratio of 1435 suns with an intercept factor of 90% over a 3-cm radius disk target and (ii) a 10.9-m radius 11-m focal length large dish, comprising 121 facets of 0.9-m radius with 15 different curvatures, yielding a peak solar concentration ratio of 23,546 suns and mean solar concentration ratio of 8199 suns with an intercept factor of 90% over a 10.4-cm radius disk target. The performance of the second geometry is compared to that of the more conventional design of a multi-facet dish concentrator consisting of identical circular facets and shown to reach - on the same target area - a 12% higher mean solar concentration ratio as well as a 6.6% higher intercept factor. The simulated membrane shape is experimentally verified with photogrammetrical measurements carried out on a prototype facet of the small dish. © 2011 Elsevier Ltd.


Cooper T.,ETH Zurich | Ambrosetti G.,Airlight Energy Holding SA | Pedretti A.,Airlight Energy Holding SA | Steinfeld A.,ETH Zurich | Steinfeld A.,Paul Scherrer Institute
Applied Optics | Year: 2013

The two-stage line-to-point focus solar concentrator with tracking secondary optics is introduced. Its design aims to reduce the cost per m2 of collecting aperture by maintaining a one-axis tracking trough as the primary concentrator, while allowing the thermodynamic limit of concentration in 2D of 215× to be significantly surpassed by the implementation of a tracking secondary stage. The limits of overall geometric concentration are found to exceed 4000× when hollow secondary concentrators are used, and 6000× when the receiver is immersed in a dielectric material of refractive index no 1.5. Three exemplary collectors, with geometric concentrations in the range of 500-1500× are explored and their geometric performance is ascertained by Monte Carlo ray-tracing. The proposed solar concentrator design is well-suited for large-scale applications with discrete, flat receivers requiring concentration ratios in the range 500-2000×. © 2013 Optical Society of America.


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 | Year: 2013

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.


Cooper T.,Sonneggstrasse | Schmitz M.,Sonneggstrasse | Good P.,Sonneggstrasse | Ambrosetti G.,Airlight Energy Holding SA | And 3 more authors.
Optics Letters | Year: 2014

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.

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