Yassine Allani’s research while affiliated with Swiss Federal Institute of Technology in Lausanne and other places

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.

Au soleil de Californie, des centrales solaires à capteurs cylindro-paraboliques produisent du courant électrique depuis des années. Une huile caloporteuse est chauffée à 400°C, puis utilisée pour produire de la vapeur qui entraîne des générateurs. C’est l’une des techniques de conversion du rayonnement solaire en électricité qui rencontre le plus de succès.

p>Hybrid solar thermal power plants (with parabolic trough type of solar collectors) featuring gas burners and Rankine steam cycles have been successfully demonstrated by California's Solar Electric Generating System (SEGS). This system has been proven to be one of the most efficient and economical schemes to convert solar energy into electricity. Recent technological progress opens interesting prospects for advanced cycle concepts: a) the ISCCS (Integrated Solar Combined Cycle System) that integrates the parabolic trough into a fossil fired combined cycle, which allows a larger exergy potential of the fuel to be converted. b) the HSTS (Hybrid Solar Tower System) which uses high concentration optics (via a power tower generator) and high temperature air receivers to drive the combined cycle power plant. In the latter case, solar energy is used at a higher exergy level as a heat source of the topping cycle. This paper presents the results of a thermoeconomic investigation of an ISCCS envisaged in Tunisia. The study is realized in two phases. In the first phase, a mixed approach, based on pinch technology principles coupled with a mathematical optimization algorithm, is used to minimize the heat transfer exergy losses in the steam generators, respecting the off design operating conditions of the steam turbine (cone law). In the second phase, an economic analysis based on the Levelized Electricity Cost (LEC) approach was carried out for the configurations, which provided the best concepts during the first phase. A comparison of ISCCS with pure fossil fueled plants (CC+GT) is reported for the same electrical power load. A sensitivity analysis based on the relative size of the solar field is presented. This paper was presented at the ECOS'00 Conference in Enschede, July 5-7, 2000 </ul

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.

A multicriteria decision support system has been developed to evaluate alternatives for sustainable and integrated energy centres for rural development in the Mediterranean area. The search for the most suitable solution for a fixed site is a complex problem, due to the variety of the plausible alternatives, the changing points of view and the diversity of the different interest groups that are responsible for the choice. By using a participative approach, combining optimisation and multicriteria methods and structuring the decision process, the different positions are clearly expressed and their consequences on the proposed solutions are brought to the fore. The negotiation is made easier and can focus on the essential aspects of the problem that have been identified by the decision support system.

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.