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Among the different kinds of renewable energy sources, solar energy plays a major role because it is safe and inexpensive at all times. Several techniques are developed for steam and electricity generation by solar energy, in which the parabolic trough collector is an advantageous method for generating steam and electricity. Different types of collectors for various temperatures, in which PTCs are used to produce medium temperature ranges using the readily available solar energy, were developed, produced, and tests. Many theoretical and experimental studies have been carried out to improvise parabolic trough collectors' optical and thermal characteristics. The modifications are reviewed in this paper to enhance the design modification, optical and thermal properties utilized in the collector. This analysis paper also elucidates the use of PTC desalination, various integrated parabolic trough collector methods for power generation, and the economic aspects of parabolic trough collector.

Discusses the thermochemical conversion and storage of solar energy, focusing on the decomposition reaction of a solid powder into a solid plus gas in a mixed homogenous open solar reactor. Information on steady-state solutions; Statistical data on parameter values for solar chemical reactions.

Discusses thermal surface absorbers. Question concerning reabsorption of part of the thermal emissions; Ability of high concentration solar thermal systems to minimize the dominant radiative losses; Functions of the surface absorber.

Discusses volumetric thermal absorbers exposed to nonuniform irradiance. Investigation of the optimum adjustment of the mass flux; Comparison of three strategies; Functions of solar receivers.

The increase in the production efficiency of photovoltaic technology depends on its alignment in relation to the solar position. Solar tracking systems perform the tracking action by implementing control algorithms that help the reduction of tracking errors. However, conventional algorithms can reduce the life of actuators and mechanisms due to control action, significantly reducing operation times and profitability. In this article, an unconventional control scheme is developed to address the mentioned challenges, presenting the design and implementation of an extremum-seeking control to perform maximum power point tracking for a two-axis solar tracker instrumented with a solar module. The proposed controller is governed by the dynamics of a classic proportional-integral scheme and assisted by sensorless feedback. Also, it has an anti-wind-up-type configuration for the integral component and counts with a variable amplitude for the dither signal. The proposal is validated experimentally by comparison between a fixed system and a two-axis system in azimuth-elevation configuration. In addition, two performance indices are defined and analyzed, system energy production and tracking error. The results show that the proposal allows producing up to 27.75% more than a fixed system, considering the tracker energy consumption due to the tracking action and a pointing accuracy with ±1.8° deviation. Finally, an analysis and discussion are provided based on the results, concluding that the proposed algorithm is a viable alternative to increase the performance of tracked photovoltaic systems. [ABSTRACT FROM AUTHOR]

It is difficult to measure the concentrated solar radiation flux (CSRF) inside a cavity receiver directly due to the complex geometry of cavity receivers. At present, most reports measure the CSRF at the aperture plane (generally coinciding with the focal plane of solar concentrators) of the cavity receiver instead of at the absorber wall, which would result in serious aberration because of the obvious difference in configuration between the aperture plane and the absorber wall. To obtain the CSRF at the absorber wall with complex geometry, the vector characteristics (consisting of both directional distributions and spatial distributions) of the CSRF at the focal plane were measured using developed double water-cooled Lambertian targets together with a CCD (charge-coupled device) camera. Then the CSRF images at the absorber wall of a hemisphere cavity receiver were carried out by applying MCRTM (Monte Carlo ray-tracing method) in combination with the measured vector results of the CSRF at the aperture plane. Results show that the directional distributions of the CSRF at the aperture plane are rather nonhomogeneous along the zenith angle and the circumferential angle. The directional distribution performance of the CSRF at the focal plane plays an equally important role in the CSRF images of the cavity receivers. In addition, the relative error of the peak CSRF value of the cavity receiver between the uniform and the measured directional distribution cases is up to 16%. The conclusions provide an important reference for the development of the CSRF measurement. [ABSTRACT FROM AUTHOR]

Imaging concentrators like the parabolic trough solar concentrators have been widely employed for energy production in solar power plants. The conventional imaging solar concentrators form a non-uniform Gaussian distribution on receiving absorbers yielding the highest temperatures. The traditional CSP system normally truncated a peripheral region of heat flux to better use the central part. CPV/T systems using the waste heat recovery method can largely improve the total efficiency. However, for the CPV module, the coolant temperature was usually below 80 °C, which limited the applications of the thermal cycle such as the ORC system. In this article, a novel trough-type free-form secondary solar concentrator (TFSC) for PV/Thermal hybrid application has been proposed. Different from other CPV/T concepts using a combined PV panel and cooling tunnel/tube, the current concept separates the receiver in two parts. The secondary free-form reflector is generated by the geometric construction method, resulting in uniform heat flux in the edge region and high concentration in the central region. Through the ray tracing method, the optical properties have been verified. Sensitivity analysis of the concentrating structure is also conducted. The results provide supports for the design and applications of novel CPV/T systems. [ABSTRACT FROM AUTHOR]

The developmental tendency of parabolic trough collector (PTC) is larger aperture area for energy harvest and novel optical design for higher solar concentration. Larger aperture faces a higher demand in tracking accuracy and lower tolerances with respect to wind loads, quality of mirrors, control, and mounting imprecisions. With the increase of reflection angle, the divergence size of concentrated focal spot gets enlarged on receiving surface, forming a Gaussian distribution. Receiving more energy and making best use of the concentrated solar power have become a key problem. In current study, a novel trough free-form solar concentrator (TFFC) has been developed by extending the aperture size with the aid of freeform optics and combined PV/thermal utilization. The structure model is composed by traditional parabolic trough with thermal tube, and extended freeform reflector with solar panel in slope configuration. The free-form surface is generated by geometric construction method for the sake of uniform heat flux distribution. The optical characteristics are validated by ray tracing method. The advantages will be revealed by compared with traditional system. The sensitivity analysis and error factors would be discussed as well. The initial results are promising and significant for the enhancement of trough type solar concentrator systems. [ABSTRACT FROM AUTHOR]

Solar thermal power plants with central receiver systems are promising candidates for the harvest of solar energy. However, the development and application of volumetric receivers are restricted owing to the nonuniformity of incident heat flux distribution, which may reduce thermal efficiency and even lead to structural damage. In the present work, the influence of thermal conductivity and radiation distribution on the thermal response of porous receivers is studied. On this basis, a transient thermal model was developed. It was found that porous media receivers with larger thickness will ensure that the thermal energy of the receivers will be fully taken advantage of by flowing air and improve the efficiency of the whole system. For porous receivers exposed to concentrated solar radiation with a Gaussian distribution, the temperature distribution along the radial direction also distributes in a Gaussian shape, with a mean temperature the same as that of uniform distribution heat flux. In working conditions where the intensity of concentrated solar radiation changes rapidly, the rate of temperature increase/decrease may be too high, which may cause damage to receivers. [ABSTRACT FROM AUTHOR]

With the mass-manufacture and resulting low cost of silicon photovoltaics driven by Western government subsidy schemes and large-scale manufacturing, concentrated solar power for electricity generation is now at a turning point. The present cost of mirrors, lenses, support structure and plant for concentrated solar thermal power, and of the high-efficiency multi-junction cells, concentrating optics and two-axis tracking systems for concentrated photovoltaic power, has made operational concentrated solar power plants uncompetitive in most scenarios. This is changing the shape of optics as well as the materials from which they are constructed and the size of the components used. We aim to highlight the current research that is being carried out to reduce the cost of concentrated solar power and concentrate on the long-term potential for cost reduction of both concentrated solar power technologies. This review concentrates first on optical and thermodynamic fundamentals, and the technology choices imposed by real world materials. We then review the broad categories of optical concentrators. Developments in solar thermal power generation and heat and thermochemical storage are discussed before briefly describing recent research on thermoelectric generation. Recent trends in concentrated photovoltaics are summarised, and we conclude by considering the present situation for concentrated solar power in the context of mass-market silicon photovoltaics. [ABSTRACT FROM AUTHOR]

Background: An experimental work was reported to estimate the increase in distillate yield for a compound parabolic concentrator-concentric tubular solar still (CPC-CTSS). The CPC dramatically increases the heating of the saline water. A novel idea was proposed to study the characteristic features of CPC for desalination to produce a large quantity of distillate yield. A rectangular basin of dimension 2 m x 0.025 m x 0.02 m was fabricated of copper and was placed at the focus of the CPC. This basin is covered by two cylindrical glass tubes of length 2 m with two different diameters of 0.02 m and 0.03 m. The experimental study was operated with two modes: without and with air flow between inner and outer tubes. The rate of air flow was fixed throughout the experiment at 4.5 m/s. On the basis of performance results, the water collection rate was 1445 ml/day without air flow and 2020 ml/day with air flow and the efficiencies were 16.2% and 18.9%, respectively. Findings: The experimental study was operated with two modes: without and with air flow between inner and outer tubes. The rate of air flow was fixed throughout the experiment at 4.5 m/s. Conclusions: On the basis of performance results, the water collection rate was 1445 ml/day without air flow and 2020 ml/day with air flow and the efficiencies were 16.2% and 18.9%, respectively. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we present a theoretical model based on the detailed balance theory of solar thermophotovoltaic systems comprising multijunction photovoltaic cells, a sunlight concentrator and spectrally selective surfaces. The full system has been defined by means of 2 n + 8 variables (being n the number of sub-cells of the multijunction cell). These variables are as follows: the sunlight concentration factor, the absorber cut-off energy, the emitter-to-absorber area ratio, the emitter cut-off energy, the band-gap energy(ies) and voltage(s) of the sub-cells, the reflectivity of the cells' back-side reflector, the emitter-to-cell and cell-to-cell view factors and the emitter-to-cell area ratio. We have used this model for carrying out a multi-variable system optimization by means of a multidimensional direct-search algorithm. This analysis allows to find the set of system variables whose combined effects results in the maximum overall system efficiency. From this analysis, we have seen that multijunction cells are excellent candidates to enhance the system efficiency and the electrical power density. Particularly, multijunction cells report great benefits for systems with a notable presence of optical losses, which are unavoidable in practical systems. Also, we have seen that the use of spectrally selective absorbers, rather than black-body absorbers, allows to achieve higher system efficiencies for both lower concentration and lower emitter-to-absorber area ratio. Finally, we have seen that sun-to-electricity conversion efficiencies above 30% and electrical power densities above 50 W/cm2 are achievable for this kind of systems. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The present work introduces a novel integrated solar collector with direct absorption of solar radiation and self-energy storage. The proposed system has compact size without the need for any connecting pipes. The working fluid absorbs the incident solar radiation directly and passes it to the storing fluid container that has been implemented within the core of the novel system. A mathematical model has been presented to describe the thermal behavior of the proposed system. Moreover, an expression has been derived to predict the system efficiency, outlet temperature, and utilized heat transfer. Simultaneously, a comparison of the performance of the novel solar system with that of the conventional solar collector reveals that the performance of the proposed system is much better than that of the conventional collector. The proposed direct absorption collector has a collector efficiency factor, F' = 1 which is 20% more than that of well-manufactured conventional collectors. This yields about 20% increase in the heat removal factors and efficiency of the integrated system as compared with that of the conventional collectors over the entire range of overall heat loss coefficients and for the same operating conditions regarding working fluid mass flow rate, inlet fluid temperature, ambient temperature, and incident solar radiation. However, it is found that the performance of the integrated collector is more sensitive to the variation in the overall heat loss coefficient and working fluid mass flow rate as compared with the conventional collectors. [ABSTRACT FROM AUTHOR]

Normal luminescent solar concentrators (LSC) have a great limitation in their light transportation because the light produced by the recently reported LSCs is not a point light source. In order to enable LSCs to use optical fibers as the effective remote light transport media, a new design of LSC, which uses three color luminescent fibers for solar absorption and uses clear optical fiber bundles to transport the absorbed sunlight into a remote place, is fabricated and tested. Radiation flux ratios with a mean value of 5.7%, the luminous flux up to 114.1 lumens, and the light efficiency of 0.56% have been achieved during the trial run. The luminous efficacy as 0.643 lm W is higher than that of combusting candles (0.3 lm W) but lower than that of the incandescent light bulbs (16-40 lm W). Further, since the sun light is free, different from electrical light sources, the luminous efficacy of the new LSC does not result in any electricity consumption when it is under operation. A color analysis and spectrum test proves that the light produced by the new LSC performs a great match to the direct sun light in color. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this article, an atlas of solar electricity potential of Stirling dish power generation system is presented. Important parameters needed for solar power generation modeling are direct solar insolation, ambient temperature, wind speed, concentrator aperture area, rim angle, mirror reflectance, working fluid, operating temperature, receiver insulating material and intercept factor. The input data values averaged over a 10-year period is obtained from India Meteorological Department, Pune. The useful energy delivered by a collector is evaluated with consideration for various heat losses. An average value of solar electricity potential of a 25.3 kW parabolic dish collector is found to be maximum of 15.3 kW for Jodhpur and minimum of 12.7 for Calcutta. Maps of annual variation of solar electricity potentials, comparison of electricity potentials of Indian cities for different months, average electricity potentials and annual electrical energy generation for various Indian cities have been developed. To produce 25 kW of electrical power on all the days of a year, three different dishes are recommended for the Indian cities of Jodhpur, Trivendrum and Calcutta. This atlas provides knowledge and aids in exploitation of solar electricity generation for Indian climatic conditions. [ABSTRACT FROM AUTHOR]