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SPS : Projet d’une minicentrale pilote électro-thermo-solaire de 10 kWe - Partie A : Centrale solaire hybride
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Thermal solar power plants using Rankine cycles closely approach the present economical electricity prices, at least in the large power range. One of the advantages currently explored is the integration with other fuel based technologies in order to ascertain a given power disponibility and to increase the use of the investment in the power unit. This paper presents the analysis of an original design of small hybrid solar plant including: a) A power unit of Superposed Organic Rankine Cycles equipped each with hermetic scroll expander-generators (scroll orbital type) with an installed total capacity of 12 kWe. Each turbine works with a new lubrication system whose feasibility, simplicity and robustness are experimentally confirmed. b) A Solar Plate Concentrating Reflector (CEP) unit equipped with mirror bands fixed on a plane surface which focalize solar energy on the vacuumed collector tubes. Only one array of 50 m2 (against 100 m2) of the solar field is assembled and tested. The realization of the second line of collectors is planned. c) A 15 kWel cogeneration Diesel engine unit to ensure power availability independently from the variations of solar radiation with a self regulation system. A total thermal power of 34.5 kW can be recovered. The following performances are expected: 12% of efficiency for the solar operation mode (Electricity power / Solar thermal incident) and 22% for the solar hybrid operation mode (Total Electricity Power / Solar thermal incident + Fuel Power). This concept presented can be used for several applications such as industrial waste heat recovery, domestic cogeneration etc… - - - - - - - - - - - - - - - - - Dans le cadre des projets précédents, le LENI en collaboration avec COGENER et avec le support de l’Office Fédéral de l’Energie (OFEN) a étudié le concept d’une centrale électro-thermo-solaire de 10 kWe. Cependant l’analyse des coûts globaux de la centrale, dimensionnée à la base pour fonctionner avec du solaire seul, avait conduit à l’option d’une réduction de la taille du champ de capteurs solaires à 96.4 m2 au lieu des 159 m2 initialement prévus. Le cycle thermodynamique de conversion devait être réadapté en tenant compte d’une source d’appoint thermique pouvant garantir la disponibilité de puissance. D’où l’idée de réaliser une hybridation au moyen d’une unité moteur de cogénération qui, de toute façon, représente une des voies parmi les plus prometteuses d’introduction du solaire par la production d’électricité. Le présent projet vise deux points essentiels. D’une part développer des outils de recherche nécessaires pour le développement d’un système solaire énergétique intégré, et d’autre part valoriser ces outils dans le cadre d’une unité pilote de centrale hybride (HSPS : Hybrid Solar Power System) permettant de mesurer ses performances et de caractériser son potentiel d’amélioration. Différentes études (modélisation des composants, méthode de dimensionnement, programme Solar Power System...) présentées en détail dans le rapport précédent intitulé "CSIP3: Projet détaillé d’une minicentrale pilote électro-thermo-solaire de 10 kWe" ne seront pas reprises. L’analyse du concept global de la centrale hybride a été présentée dans le cadre de la conférence CISBAT99, Concept d’une minicentrale électro-thermo-solaire hybride adapté au pays en voies de développement. La description de certaines parties de cette publication (la machine thermique, l’unité de cogénération...) sera complétée avec des supports techniques présentés en annexes. Pour les aspects du champ de capteurs, nous faisons références au rapport fourni par COGENER.
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The five Solar Electric Generating Systems (SEGS) at Kramer Junction, California, now have nearly 30 years of cumulative operating experience. These 30 MW plants employ parabolic trough technology originally deployed by LUZ International in the late 1980`s and are now managed, operated and maintained by the Kramer Junction Company. In this paper, Sandia National Laboratories performed an analysis of the annual energy production from the five plants. Annual solar-to-electric conversion efficiencies are calculated and the major factors that influenced the results are presented. The generally good efficiencies are primarily attributed to the excellent equipment availabilities achieved at all plants.
Solar thermal power plants of the parabolic trough type have been successfully demonstrated for 10 years, the electricity costs, however, are still too high. For commercialization on a large scale these plants have to be integrated into fossil fired combined cycles. A strategy how to meet this goal is proposed. For further cost reduction three advanced concepts are presented: Direct steam generation in parabolic trough systems, preheating of combustion air for gas turbines and upgrading of natural gas by solar reforming in tower systems. These solar systems only serve as fuel saver (8 to 25% for full load operation hours of 4000 h/y), however, have high potential for cost reduction down to 5 cts/kWh. To demonstrate their technical feasibility, governmental and European Community-funded prototype systems are being built. The state of development and economic analysis and comparisons are reported.
Integrated solar combined cycle systems (ISCCS) represent, both economically and energetically, a promising alternative for the conversion of solar energy while offering a guarantee of a minimum power supply independant of the level of solar radiation. Their performances are however strongly dependant on the intensity of the solar input. The approach proposed in this paper allows, from the characteristics of the turbines (gas turbines and steam turbines) and of the solar field, to rationalize the choice of the pressure levels and of the massflows of a steam cycle with multiple pressure levels. It is based on the coupling of a pinch technology approach with a thermodynamic modeling allowing an optimisation with deterministic algorithms. Results are applied to a dual pressure steam cycle and accounts for the respect of the "cone law" for the steam turbines. It is shown that an increase of the exergetic losses linked to heat transfer in the steam generators is inevitable at certain operational regimes and depends directly on the level of solar supply. The variations of the main steam cycle parameters as a function of the thermal supply (combustion gases + solar thermal oil) are shown for an 80 to 120 MWel power plant equipped with two gas turbine and one steam turbine train.
The integration of a solar collector field generating steam into a conventional combined cycle in order to partially replace the fossil fuel required by the latter results in a substantial reduction in greenhouse gases, in an increase in the return on investments associated with the solar field and in an almost complete elimination of the need for solar energy storage. This paper discusses the design of such an integrated hybrid solar-fossil combined cycle with maximum daily and nightly power outputs of 88 MWe and 58 MWe, respectively. This cycle is currently being evaluated from a technical and economic risk feasibility standpoint for possible implementation as a pilot plant in Tunisia. This paper outlines pertinent design considerations utilized in the thermoeconomic optimization approach employed for developing the hybrid combined cycle proposed here. The approach shows that there are several advantages to this type of design when compared with a purely solar steam cycle or any of the several other hybrid solar concepts which exist today. In addition to these advantages, the design presented revolves around the definition of a number of degrees of freedom which allow the solar energy part of the cycle to be highly integrated into the conventional part. A discussion of them is given. Finally, from an environmental standpoint, the obvious advantage of this type of cycle is that due to the substitution of fossil fuel, there is a marked mitigation in CO2 and NOx emissions when compared to a conventional cycle and to other hybrid concepts. Pertinent results for these reductions are presented.
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