Usual size of parabolic trough solar thermal plants being built at present is approximately 50
MW
e. Most of these plants do not have a thermal storage system for maintaining the power block ...performance at nominal conditions during long non-insolation periods. Because of that, a proper solar field size, with respect to the electric nominal power, is a fundamental choice. A too large field will be partially useless under high solar irradiance values whereas a small field will mainly make the power block to work at part-load conditions.
This paper presents an economic optimization of the solar multiple for a solar-only parabolic trough plant, using neither hybridization nor thermal storage. Five parabolic trough plants have been considered, with the same parameters in the power block but different solar field sizes. Thermal performance for each solar power plant has been featured, both at nominal and part-load conditions. This characterization has been applied to perform a simulation in order to calculate the annual electricity produced by each of these plants. Once annual electric energy generation is known, levelized cost of energy (LCOE) for each plant is calculated, yielding a minimum LCOE value for a certain solar multiple value within the range considered.
► Solar hybridization improves the performance of CCGT in a very hot and dry weather. ► The scheme analyzed is a DSG parabolic trough field coupled to the Rankine cycle. ► An annual simulation has ...been carried out for two locations: Almería and Las Vegas. ► Economical analysis shows that this scheme is a cheaper way to exploit solar energy. ► For that, solar hybridization must be limited to a small fraction of the CCGT power.
The contribution of solar thermal power to improve the performance of gas-fired combined cycles in very hot and dry environmental conditions is analyzed in this work, in order to assess the potential of this technique, and to feature Direct Steam Generation (DSG) as a well suited candidate for achieving very good results in this quest. The particular Integrated Solar Combined Cycle (ISCC) power plant proposed consists of a DSG parabolic trough field coupled to the bottoming steam cycle of a Combined Cycle Gas Turbine (CCGT) power plant. For this analysis, the solar thermal power plant performs in a solar dispatching mode: the gas turbine always operates at full load, only depending on ambient conditions, whereas the steam turbine is somewhat boosted to accommodate the thermal hybridization from the solar field.
Although the analysis is aimed to studying such complementary effects in the widest perspective, two relevant examples are given, corresponding to two well-known sites: Almería (Spain), with a mediterranean climate, and Las Vegas (USA), with a hot and dry climate. The annual simulations show that, although the conventional CCGT power plant works worse in Las Vegas, owing to the higher temperatures, the ISCC system operates better in Las Vegas than in Almería, because of solar hybridization is especially well coupled to the CCGT power plant in the frequent days with great solar radiation and high temperatures in Las Vegas. The complementary effect will be clearly seen in these cases, because the thermal power provided by the solar field compensates the gas turbine part load performance due to the high temperatures. The economical analysis points out that this hybrid scheme is a cheaper way to exploit concentrated solar energy, although it is limited to a small fraction of the combined cycle power. The analysis also shows that the marginal cost of solar electricity is strongly influenced by the goodness of coupling, so this cost is lower in Las Vegas than in Almería.
► Circular shape mirrors give as good results as parabolic for Fresnel applications. ► With specific reference for each mirror more constant radiation intensity is obtained. ► A focusing procedure is ...described. ► The maximum mirrors widths are obtained for limiting reflection lateral drifts. ► Linear Fresnel Reflectors have a great potential for cost reductions in CSP.
This paper is aimed at characterizing the concentration process for LFRs, and to analyze the use of different optical designs, including circular-cylindrical and parabolic-cylindrical mirrors with different reference positions. A new approach to analyze and optimize the performance of Fresnel arrays is presented, which is based on a newly formulated optical property that can be used to evaluate the drift of the reflected sunbeams from the mirrors as they rotate to follow the sun. This new optical-geometric property sets upper bounds for the deviation of the reflected sunbeams, in relation to trajectories of the reference situation. It is observed that the maximum deviation depends on the width of the mirror, which must be limited for maximizing the optical efficiency. From this theory an optical design process is suggested to minimize such lateral drifts and to minimize the concentration factor variation along the day. A new mirror layout is defined for keeping a constant value of the radiation impinging onto the receiver from effective sunrise to effective sunset.
This paper describes the influence of the solar multiple on the annual performance of parabolic trough solar thermal power plants with direct steam generation (DSG). The reference system selected is ...a 50
MW
e DSG power plant, with thermal storage and auxiliary natural gas-fired boiler. It is considered that both systems are necessary for an optimum coupling to the electricity grid. Although thermal storage is an opening issue for DSG technology, it gives an additional degree of freedom for plant performance optimization. Fossil hybridization is also a key element if a reliable electricity production must be guaranteed for a defined time span. Once the yearly parameters of the solar power plant are calculated, the economic analysis is performed, assessing the effect of the solar multiple in the levelized cost of electricity, as well as in the annual natural gas consumption.
•Linear Fresnel reflectors (LFRs) have great potential for cost reductions.•Concentration in the receiver central strip as high as in trough collectors.•Daily constant flux map in the receiver if the ...filling factor is adequately designed.•High concentration variation between summer and winter for N–S configurations.
The late exponential development of Concentrating Solar Power (CSP) technology has driven to a very high power installed worldwide, but with no time for global optimization of the technology. High feed-in-tariffs have concentrated investments on trough collectors and central towers, previously studied during the 1980s. Linear Fresnel reflectors (LFRs) are regarded as a low efficiency technology, which is mainly due to very little previous research. However, the use of slightly bent mirrors drives to high concentration ratios, with obvious cost advantages over other CSP technologies. This paper studies the radiation flux obtained in a flat receiver using different mirror shapes, and analyzes its variation along the year. Linear Fresnel reflector design variables are reviewed, and a Ray Tracing model of the Fresdemo prototype is carried out. Results show higher performances than expected.
•LFCs with secondary reflector receiver achieve higher concentration factors than PTCs.•Central tubes of LFCs with multitube receiver achieve similar concentration than PTCs.•Annual efficiency of ...PTCs is higher than such of LFCs, for any receiver technology.•Annual efficiency of multitube LFCs is lower than for secondary reflector receiver.•Main losses of multitube LFCs are due to low flux intensities during some periods.
Parabolic trough collectors (PTCs) are still today the most mature technology in concentrating solar power. However, linear Fresnel collectors (LFCs) have been identified by many authors as a candidate to reduce the levelized cost of electricity, although with lower efficiencies. Within Fresnel technology, two possibilities appear for the receiver: multitube receiver and secondary reflector receiver. In the present work a developed Monte Carlo Ray Trace code is used in order to compare the energy effectiveness and flux intensity map at the receiver for different days of the year and different orientations in Almería, Spain, and in Aswan, Egypt. The optical annual energy and exergy efficiencies are also obtained for PTCs and LFCs, with multitube or secondary reflector receiver, where the concentration at each tube is used to weigh the exergy efficiency. It results that the maximum efficiency is obtained by PTCs, while the lowest one corresponds to LFCs with multitube receiver. Also, it is concluded that, while for PTCs NS orientation leads to clearly higher efficiencies, this is not the case for LFCs, where both orientations achieve similar efficiencies even when the solar field has been designed for NS orientation.
Linear Fresnel collectors still present a large margin to improve efficiency. Solar fields of this kind installed until current time, both prototypes and commercial plants, are designed with widths ...and shifts of mirrors that are constant across the solar field. However, the physical processes that limit the width of the mirrors depend on their relative locations to the receiver; the same applies to shading and blocking effects, that oblige to have a minimum shift between mirrors. In this work such phenomena are studied analytically in order to obtain a coherent design, able to improve the efficiency with no increase in cost. A ray tracing simulation along one year has been carried out for a given design, obtaining a moderate increase in radiation collecting efficiency in comparison to conventional designs. Moreover, this analytic theory can guide future designs aiming at fully optimizing linear Fresnel collectors' performance.
•Errors due to off-axis aberration and to beam aperture depend on the mirror location.•Design of mirrors with sun reference increase the maximum flux intensity.•Shading and blocking errors vary across the solar field if constant shift design is used.•A design with variable shift of mirrors drives to an increase of efficiency.
► An innovative multitube receiver for linear Fresnel reflectors is presented. ► Higher performance is achieved thanks to better heat transfer conditions. ► A wide range of designs that maximize ...efficiency for different conditions is found. ► Heat transfer fluid inlet temperature must be lower for low radiation intensities. ► Fresnel performance may be close to trough collectors, with lower costs.
The study of the performance of an innovative receiver for linear Fresnel reflectors is carried out in this paper, and the results are analyzed with a physics perspective of the process. The receiver consists of a bundle of tubes parallel to the mirror arrays, resulting on a smaller cross section for the same receiver width as the number of tubes increases, due to the diminution of their diameter. This implies higher heat carrier fluid speeds, and thus, a more effective heat transfer process, although it conveys higher pumping power as well. Mass flow is optimized for different tubes diameters, different impinging radiation intensities and different fluid inlet temperatures. It is found that the best receiver design, namely the tubes diameter that maximizes the exergetic efficiency for given working conditions, is similar for the cases studied. There is a range of tubes diameters that imply similar efficiencies, which can drive to capital cost reduction thanks to the flexibility of design. In addition, the length of the receiver is also optimized, and it is observed that the optimal length is similar for the working conditions considered. As a result of this study, it is found that this innovative receiver provides an optimum design for the whole day, even though impinging radiation intensity varies notably. Thermal features of this type of receiver could be the base of a new generation of concentrated solar power plants with a great potential for cost reduction, because of the simplicity of the system and the lower weigh of the components, plus the flexibility of using the receiver tubes for different streams of the heat carrier fluid.
The analysis of the viability of Hydrogen production without CO
2 emissions is one of the most challenging activities that have been initiated for a sustainable energy supply. As one of the tracks to ...fulfil such objective, direct methane cracking has been analysed experimentally to assess the scientific viability and reaction characterization in a broad temperature range, from 875 to 1700
°C. The effect of temperature, sweeping/carrier gas fraction proposed in some concepts, methane flow rate, residence time, and tube material and porosity has been analysed. The aggregation of carbon black particles to the reaction tube is the main technological show-stopper that has been identified.
► CO
2-free Hydrogen production from methane. ► Experimental methane cracking analysis. ► Black carbon plug as drawback for industrial application.
•Performance of linear collectors is assessed via the impinging energy on the mirrors.•Analytic methods are established to design LFCs.•Innovative designs are proved to increase efficiency with EW ...orientation.•Energy effectiveness of LFCs and PTCs are compared for different latitudes and tilts.
Linear Fresnel collectors lead to a reduction of investment costs compared to parabolic trough collectors, but it is not yet certain whether this implies a reduction of levelyzed cost of electricity or not. In order to analyze the optical behavior of concentrators ray trace models are often used. However, such methodology leads to time-consuming codes that make difficult to optimize all design variables. In this work an analytic method is used in order to characterize the effect of the design variables on the annual energy impinging onto the reflecting surface, and results for two different locations are compared. The paper leads to the notable conclusion that the ratio of energy impinging onto the reflecting surface of Fresnel collectors is closer to that of parabolic troughs at low latitude locations.
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