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Concept de centrale électrothermosolaire alpine.
Abstract
Cet article présente un concept original de centrale électrothermosolaire comprenant des unités de puissance modulaires à cycles de Rankine superposés utilisant pour la première fois des expandeurs-génératuers hermétiques de type scroll, des capteurs à concentration à lamelles ajourées, et une évaporation et condensation directe des fluides de travail. Les performances expérimentales des principaux composants sont présentées.
... Recent technological progress opens new perspectives for Integrated Solar Fossil Cycle Systems (ISFCS). In the context of increasing global environmental concerns, these perspectives offer the possibility of accelerating fossil fuel substitution (even if only partial), and therefore reducing emissions, while ensuring an adequate power availability [1,2]. ...
... For the SPS project decision was made to rely on earlier work [14], which demonstrated the use of expanders modified from standard hermetic scroll compressor units with potentially low costs as most components are produced by thousands worldwide [1,2]. The major limitations of the latter are the limited pressure range and the built-in volume ratio for efficient operation. ...
... ț at a range of pressure levels and pressure ratios close to the best expander efficiencies and unit volumes, and ț independently with one or the other cycle in function of the solar condition or of the heat demand requirements [1,15]. For this prototype unit (Fig. 2), the chosen fluids are HCFC 123 for the topping cycle and HFC l34a for the bottoming cycle. ...
This paper introduces a novel concept of mini-hybrid solar power plant integrating a field of solar concentrators, two superposed Organic Rankine Cycles (ORC) and a (bio-)Diesel engine. The Organic Rankine Cycles include hermetic scroll expander-generators1 and the sun tracking solar collectors are composed of rows of flat mirror bands (CEP) arranged in a plane, that focus the solar energy onto a collector tube similar to those used in SEGS plants in California. Waste heat from both the exhaust gases and the block cooling of the thermal engine are also heat sources for the ORCs. Such units meet electricity, cooling and pumping needs of remote settlements. The thermal engine guarantees a minimum level of both power and heat availability at night or during cloudy periods. Laboratory tests, made with the superposed ORCs only, confirmed adequate operational characteristics with good performances over a broad range of conditions. A few preliminary tests on the site of the solar power plant when coupled with the engine confirmed a reasonable behavior and the interest of the concept even at part load or during sharp variations of the thermal supply.
... One of the major limitations of standard scroll compressor units is the low built-in volume ratio, which restricts the effrcient expansion ratio to values lower than typically 8 within a pressure domain from 25 to 3 bars. However this can be compensated by considering superposed ORCs using each a different fluid to keep a high specific power within the pressure rangaof the scrolls and avoid sub atmospheric pressures (Favrat, 1995; Kane et a7. 1999). ...
A new concept of small hybrid solar power system (HSPS) has been successfully demonstrated in the context of a project called SPS (Solar Power System). This plant integrates two rows of solar collectors, two superposed Organic Rankine Cycles (ORC) each equipped with a scroll hermetic expander-generator and a heat engine. In operation with solar energy only, the heat is supplied by a thermal fluid (presently pressurized water) heated in the vacuum insulated focal tubes of sun following, flat concentrators made of series of thin plate mirrors (CEP). In hybrid mode additional heat is supplied by heat recovery from the exhaust gases of the engine in series with the solar network and by a separate network recovering heat from the cooling of the engine block at an intermediate temperature level. This paper presents the results of a multi-criteria optimization of a 22 kWe HSPS, including aspects such as energy performance, economic and financial analysis, and environemental aspects. The so called mini-maxi methodological approach with genetic algorithm is used considering three principal criteria such as the energy efficiency of the superposed ORCs, the minimal cost of the installation and the minimum emission of CO2 . Taking into account of the solar radiation time dependence, the elecricity supply variation and the change of configuration (night and day operation), the performance analysis is based essentially on the yearly energy simulation in which the off-design physical models of components are considered. A comparison of HSPS with pure fossil fuelled Plants (DEPU-Diesel Engine Power Unit) is reported for the same electrical power load curve, with an economic sensitivity analysis. Results show that the solar electricity costs are still high and depend considerably on the size of the Solar Field (the HSPS Levelized Electricity Cost with 5 to 16% of annual solar share is about 17% to 49% higher than a similar size Diesel Engine Power Unit). However, a reduction of CO2, emission up to 26% could be obtained when replacing the Diesel Engine Unit by a similar HSPS. Those hybrid solar thermal power systems may already be competitive if a tax of about 42 Swiss cts/kgCO2 would be considered.
This paper presents field tests of an original concept of a small hybrid solar power plant integrating three technologies: hermetic volumetric scroll expander-generators installed in two superposed Organic Rankine Cycles (ORC), a (bio-)Diesel engine with heat recovery exchangers and a solar field made of two rows of sun following flat plate concentrators with vacuumed isolated collector tubes. The basic idea of the concept is to exploit the synergy between equipment, use cheap and maintenance free expander- generators, guaranty power availability at all time and improve the efficiency of the engine when it has to operate alone at night time by converting the waste heat with the solar ORC. This type of hybrid power plant is intended for rural electrification purposes in developing countries or cogeneration in applications like heated swimming pools in other countries. Pressurized hot water is used at this time as a thermal fluid in the collectors with HCFC123 in the topping cycle and HFC134a in the bottoming cycle. The field tests have been performed during the summer 2001 in Lausanne (Switzerland) and the pland proved operationally reliable. However performance results (with exergetic efficiencies up to 45%) did not meet the expectations but measures to improve the concept have been identified.
This paper presents the analysis of an original design of small hybrid solar plant using Organic Rankine Cycles with hermetic scroll expander- generators. The hot supply is provided from vacuumed collector tubes along the focal line of solar concentrators made of mirror bands fixed on a plane surface (CEP). The plant is integrated with a cogeneration Diesel engine unit to ensure power availability independently from the variations of solar radiation. It is primarily intended for isolated sites in developing countries. Measurements on the power unit of 13 kWel show an excellent behavior over a broad range of parameters with an efficiency of the order of 18% (50% exergetic efficiency), which is very promising, particularly when considering that the concept of superposed cycles will allow operations at higher supply temperatures with further technological developments.
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.
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