Global Change Abstracts The Swiss Contribution - SCNAT

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198 Global Change Abstracts – The Swiss Contribution | Mitigation and Adaptation Technologies 08.1-424 Towards an improved architectural quality of building integrated solar thermal systems (BIST) Munari Probst M C , Roecker C Switzerland Engineering , Energy & Fuels Architectural integration is a major issue in the development and spreading of solar thermal technologies. Yet the architectural quality of most existing building integrated solar thermal systems (BIST) is quite poor, which often discourages potential new users. In this paper, the results of a large web survey on architectural quality, addressed to more than 170 European architects and other building professionals are presented and commented. Integration criteria and design guidelines established and confirmed through the analysis of these results are proposed. Subsequently, a novel methodology to design future solar thermal collectors systems suited to building integration is described, showing a new range of design possibilities. The methodology focuses on the essential teamwork between architects and engineers to ensure both energy efficiency and architectural integrability, while playing with the formal characteristics of the collectors (size, shape, colour, etc.). Finally a practical example of such a design process conducted within the European project SOLABS is given; the resulting collector is described, and integration simulations are presented. Solar Energy, 2007, V81, N9, SI, pp 1104-1116. 08.1-425 Biofuels must deliver on their promise of sustainability Opal C Switzerland Energy & Fuels , Engineering Power Engineer, 2007, V21, N3, JUN-JUL, p 18. 08.1-426 A methodology for thermo-economic modeling and optimization of solid oxide fuel cell systems Palazzi F, Autissier N, Marechal F M A, Favrat D Switzerland Modelling , Energy & Fuels , Engineering In the context of stationary power generation, fuel cell-based systems are being foreseen as a valuable alternative to thermodynamic cycle-based power plants, especially in small scale applications. As the technology is not yet established, many aspects of fuel cell development are currently investigated worldwide. Part of the research focuses on integrating the fuel cell in a system that is both efficient and economically attractive. To address this problem, we present in this paper a thermoeconomic optimization method that systematically generates the most attractive configurations of an integrated system. In the developed methodology, the energy flows are computed using conventional process simulation software. The system is integrated using the pinch based methods that rely on optimization techniques. This defines the minimum of energy required and sets the basis to design the ideal heat exchanger network. A thermo-economic method is then used to compute the integrated system performances, sizes and costs. This allows performing the optimization of the system with regard to two objectives: minimize the specific cost and maximize the efficiency. A solid oxide fuel cell (SOFC) system of 50 kW integrating a planar SOFC is modeled and optimized leading to designs with efficiencies ranging from 34% to 44%. The multi- objective optimization strategy identifies interesting system configurations and their performance for the developed SOFC system model. The methods proves to be an attractive tool to be used both as an advanced analysis tool and as support to decision makers when designing new systems. Applied Thermal Engineering, 2007, V27, N16, NOV, pp 2703-2712. 08.1-427 Dynamics of a solar thermochemical reactor for steam-reforming of methane Petrasch J, Steinfeld A Switzerland Engineering , Modelling , Plant Sciences A nonlinear dynamic model is developed for a steam/methane-reforming reactor that uses concentrated solar radiation as the source of high- temperature process heat. The model incorporates a set of lumped- parameter reservoirs for mass and energy. For each reservoir, the unsteady mass and energy conservation equations are formulated, which couple conduction, convection, and radiation heat transfer with the temperature dependent chemical conversion. Radiative exchange, the dominant heat transfer mode at above 800 K, is solved by a band- approximation Monte Carlo technique. The dynamic model is applied to predict the transient behavior of a 400kW prototype solar reformer in operational modes of purging, thermal testing, startup, chemical reaction, shutdown, and cyclical operation. Time constants vary between 2 s for species transport and 1 x 10(5) s for thermal energy transport through ceramic insulation. Validation is accomplished by comparing
Global Change Abstracts – The Swiss Contribution | Mitigation and Adaptation Technologies modeled and experimentally measured outlet gas temperatures obtained from reactor tests in a solar tower facility. Chemical Engineering Science, 2007, V62, N16, AUG, pp 4214-4228. 08.1-428 Development steps for parabolic trough solar power technologies with maximum impact on cost reduction Pitz P R, Dersch J, Milow B, Tellez F, Ferriere A, Langnickel U, Steinfeld A, Karni J, Zarza E, Popel O Germany, Spain, France, Switzerland, Israel, Russia Energy & Fuels , Engineering Besides continuous implementation of concentrating solar power plants (CSP) in Europe, which stipulate cost reduction by mass production effects, further R&D activities are necessary to achieve the cost competitiveness to fossil power generation. The European Concentrated Solar Thermal Roadmap (ECOSTAR) study that was conducted by European research institutes in the field of CSP intends to stipulate the direction for R&D activities in the context of cost reduction. This paper gives an overview about the methodology and the results for one of the seven different CSP system concepts that are currently under promotion worldwide and considered within ECOSTAR. The technology presented here is the Parabolic trough with direct steam generation (DSG), which may be considered as an evolution of the existing parabolic systems with thermal oil as heat transfer fluid. The methodology is explained using this exemplary system, and the technical improvements are evaluated according to their cost- reduction potential using a common approach, based on an annual performance model. Research priorities are given based on the results. The simultaneous implementation of three measures is required in order to achieve the cost-reduction target: Technical improvement by R&D, upscaling of the unit size, and mass production of the equipment. Journal of Solar Energy Engineering Transactions of the Asme, 2007, V129, N4, NOV, pp 371-377. 08.1-429 Optimum battery size for fuel cell hybrid electric vehicle - Part I Sundstrom O, Stefanopoulou A Switzerland, USA Energy & Fuels , Engineering This study explores different hybridization levels of a midsized vehicle powered by a polymer electrolyte membrane fuel cell stack. The energy buffer considered is a lead-acid-type battery. The effects of the battery size on the overall energy 199 losses for different drive cycles are determined when dynamic programming determines the optimal current drawn from the fuel cell system. The different hybridization levels are explored for two cases: (i) when the batter), is only used to decouple the fuel cell system from the voltage and current demands from the traction motor to allow the, fuel cell system to operate as close to optimally as possible and (ii) when regenerative braking is included in the vehicle with different efficiencies. The optimal power-split policies are analyzed to quantify all the energy losses and their paths in an effort to clarify the hybridization needs for a fuel cell vehicle. Results show that without any regenerative braking, hybridization will not decrease, fuel consumption unless the vehicle is driving in a mild drive cycle (city drive with low speeds) . However, when the efficiency of the regenerative braking increases, the fuel consumption (total energy losses) can be significantly lowered by choosing an optimal battery size. Journal of Fuel Cell Science and Technology, 2007, V4, N2, MAY, pp 167-175. 08.1-430 Optimum Battery Size for Fuel Cell Hybrid Electric Vehicle With Transient Loading Consideration—Part II Sundstrom O, Stefanopoulou A Switzerland, USA Engineering , Energy & Fuels This study presents a simplified model of a midsized vehicle powered by a polymer electrolyte membrane fuel cell stack together with a leadacid battery as an energy buffer. The model is used with dynamic programming in order to find the optimal coordination of the two power sources while penalizing transient excursions in oxygen concentration in the fuel cell and the state of charge in the battery. The effects of the battery size on the overall energy losses for different drive cycles are determined, and the optimal power split policies are analyzed to quantify all the energy losses and their paths in an ‘effort to clarify the hybridization needs for a fuel cell vehicle with constraints on dynamically varying variables. Finally, a causal nonpredictive controller is presented. The battery sizing results from the dynamic programming optimizations and the causal controller are compared. Journal of Fuel Cell Science and Technology, 2007, V4, N2, MAY, pp 176-184.
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Global Change Abstracts The Swiss Contribution - SCNAT

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