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The global challenge of sustainable and affordable wastewater treatment technology looms large as water pollution escalates steadily with the rapid pace of industrialization and population growth. The photocatalytic wastewater treatment is a cutting-edge and environmentally friendly technology that uses photons from light source to degrade and remove organic and inorganic contaminants from water. Thus, utilizing solar energy for photocatalytic wastewater treatment holds great promise as a renewable solution to alleviate pressures on the global water crisis. Employing solar concentrators to intensify sunlight for photocatalysis represents a promising avenue for future applications of a low-cost and rapid sustainable wastewater purification process. This groundbreaking approach will unveil fresh technological avenues for a cost-effective, sustainable, and swift wastewater purification process utilizing sunlight. This review article explores diverse solar concentrating systems and their potential applications in the wastewater treatment process.

Concentrating photovoltaic (CPV) systems have emerged as a transformative technology that incorporates radiation concentrators into the photovoltaic system to enable radiation to be concentrated onto a receiver—the solar cells. Different concentrator configurations have different impacts on the performance of the solar photovoltaic system. This research work aims to analyze the impact of different concentrators, comparing and identifying the most efficient structures for capturing and concentrating solar energy. Aiming at a deep analysis and comparison among concentrators shapes, this research work presents a unique investigation and revision among different structures such as flat, triangular, LFR, and parabolic concentrators. Moreover, since, in the UV–visible–NIR region, metals’ reflectance varies with the incident wavelength, five metals were considered: aluminum, gold, platinum, copper, and silver. Additionally, the research focuses on studying the effects of parameters critical to the quality of the concentration on the power obtained and on the uniformity of the radiation distribution on the surface of the receiver, as well as on the number of solar rays that reach the receiver. The power on the receiver increases proportionally with the number of reflector concentrators in the system and their reflectance. For parabolic geometries, the optical efficiency is affected by the receiver’s shadow on the concentrator and, in the case of the LFR, by a non-ideal alignment of the reflectors in relation to the receiver. However, in parabolic concentrator geometries, uniformity is usually lower, since in these configurations, the radiation is focused on specific areas of the receiver, usually the central zone.

This study presents a solar-powered parabolic dish desalination system with a solar tracking system and conical receiver. It efficiently transforms solar radiation into heat and evaporates saltwater, producing fresh water. The system is sustainable and affordable, making it a viable solution for water desalination in areas with limited access to fresh water. It achieves a high conversion rate from saltwater to fresh water, while consuming minimal energy. The results indicate that the system effectively utilizes solar energy, exhibiting high efficiency levels ranging from 78.56% to 82.77%, with an average efficiency of 80.79%. This system offers an effective solution to meet the growing demand for fresh water in water-scarce regions.

Solar concentration is the ability to harness solar radiation in order to increase the temperature of a receiver. The receiver is a component into which a heat transfer fluid can flow in an ORC system, which produces electricity, or it can be used for high-temperature thermal storage or even to implement thermochemical cycles. The choice of material is critical to ensure optimal performance and long-lasting operation. It is also essential that such material can operate at high temperatures and high thermal gradients. In short, material identification involves high thermal stresses that result in structural deformation. Different metal alloys were used to verify that the yield strength limit was not exceeded due to thermal stress induced by concentrated solar radiation. Starting with the general heat equation, the problem was implemented in Matlab. The purpose was to test whether thermal stress exceeds the yield strength, which is the condition in which elastic bonds in the material are changed, causing deformation. This condition, if exceeded, is sufficient to discard the material; otherwise, it is a necessary but not sufficient condition to resist over time. The best material identified was Inconel 740H, which had a high yield strength value and the lowest temperature difference. Under extreme working conditions, it withstood induced thermal shocks.

Static solar devices have advantages over solar tracking systems. In pure reflective systems, solar reception is limited by the entry angle of the reflector. Many reflective systems are based on mirror Compound Parabolic Concentrators. The solar collection can be improved by placing a lens on top of the reflector. In this work, a static system is proposed, consisting of a mirror funnel concentrator with a prism on top. The system is designed using ray-tracing software and is subsequently built and experimentally evaluated. The system designed for an effective concentration factor of 4× reaches an effective concentration of 3.2× at 11:30 a.m. and has an acceptance angle of 60°. Considering the time interval from 8 a.m. to 4 p.m., the system harvests 30.7% more energy than the flat surface. If the time interval considered is from 9:30 a.m. to 2:30 p.m., the increase in harvest is ∼77%. The incorporation of the prism represents an increase of ∼6% compared to the bare reflective system.

The present research aims at promoting the stability and applicability of a hybrid daylighting system combining daylight and artificial light, which eventually enables a constant and pleasant luminous flux of the mixed light delivered by a terminal device installed indoors. That is, the present system allows a constant amount of luminous flux through its terminal device similar to an electric lamp, demonstrating its energy efficiency as well as comfortableness. The system effectively combines two different types of light, as solar rays are collected by a solar tracking sun light collector. The mixed light is transmitted indoors by optical fiber cables all the way to terminal devices installed indoors and discharged as needed. This feature enables the utilization of daylight to its full capacity, promoting solar availability. In this study, the photometry of hybrid lighting was experimentally measured and analyzed by using a spectrometer for different portions of sunlight when maintaining a constant luminous flux of mixed light. The effectiveness of hybrid lighting was explored for a number of cases in actual conditions, and the system was capable of delivering a constant illuminance of 1200 lux on a plane located 1.1 m away from the terminal device (light emitter). Finally, the system was installed in a test cell to verify its effectiveness for indoor illumination.

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.

Solar concentrator collectors have the potential of meeting the medium- and high-temperature thermal energy demands of the world. A heat transfer fluid (HTF) is a vital component of a concentrating system to transfer and store thermal energy. This paper presents the design development of a solar paraboloidal dish concentrator (SPDC) and a study of selected HTFs using the storage receiver system of the concentrator. The locally designed SPDC (diameter 1.21 m and height 0.20 m) has features like light weight, effortless tracking, convenient transportation along with high optical and thermal performance. Three HTFs, silicone oil (SO), engine oil (EO) and ethylene glycol (EG), are selected based on their favorable properties for medium temperature (150–300 °C) applications. The characteristic parameters of HTFs, heating rate (Rh), instant thermal efficiency (ηith) and the overall heat loss coefficient (UL), are illustrated and determined experimentally. A new characteristic parameter, the normalized maximum fluid temperature (Tnf), is also introduced in the paper. In the heating test, the maximum attained temperatures by fluids, SO, EO and EG are found to be 240 °C, 180 °C and 160 °C, respectively. The thermal efficiencies of SO, EO and EG are determined to be 45, 36 and 31%, respectively. The heating rate of 6.56 °C/s is found to be the maximum for SO. Through the cooling test, the overall heat loss coefficient (UL) is computed to be 14 W/mK, which is the least among the three fluids compared. The high thermal performance, environmental safety and chemical stability of silicone oil make it suitable for use in concentrators for medium-temperature heat transfer and storage applications.

We have proposed a fruitful design principle targeting a concentration ratio (CR) >1000× for a typical high concentrating photovoltaics (HCPV) system, on account of a two-concentrator system + homogenizer. The principle of a primary dual-lens concentrator unit, completely analogous basic optics seen in the superposition compound eyes, is a trend not hitherto reported for solar concentrators to our knowledge. Such a concentrator unit, consisting of two aspherical lenses, can be applied to minify the sunlight and reveal useful effects. We underline that, at this stage, the CR can be attained by two orders of magnitude simply by varying the radius ratio of such two lenses known from the optics side. The output beam is spatially minimized and nearly parallel, exactly as occurs in the superposition compound eye. In our scheme, thanks to such an array of dual-lens design, a sequence of equidistant focal points is formed. The secondary concentrator consists of a multi-reflective channel, which can collect all concentrated beams from the primary concentrator to a small area where a solar cell is placed. The secondary concentrator is located right underneath the primary concentrator. The optical characteristics are substantiated by optical simulations that confirm the applicability of thousands-fold gain in CR value, ~1100×. This, however, also reduced the uniformity of the illumination area. To regain the uniformity, we devise a fully new homogenizer, hinging on the scattering principle. A calculated optical efficiency for the entire system is ~75%. Experimentally, a prototype of such a dual-lens concentrator is implemented to evaluate the converging features. As a final note, we mention that the approach may be extended to implement an even higher CR, be it simply by taking an extra concentrator unit. With simple design of the concentrator part, which may allow the fabrication process by modeling method and large acceptant angle (0.6°), we assess its large potential as part of a general strategy to implement a highly efficient CPV system, with minimal critical elaboration steps and large flexibility.

Solar-pumped lasers (SPLs) allow direct solar-to-laser power conversion, and hence, provide an opportunity to harness a renewable energy source. Herein, we report significant improvements in end-side-pumped solar laser collection efficiency and beam brightness using a novel 1.5-m-diameter compound solar concentrator combining a Fresnel lens and modified parabolic mirror. A key component of this scheme is the off-axis-focused parabolic mirror. An original dual-parabolic pump cavity is another feature. To determine the dependence of the SPL performance on the distance between the focus and central axis of the modified parabolic mirror, several systems with different distances were optimized using TracePro and ASLD software. It was numerically calculated that end-side pumping a 5-mm-diameter, 22-mm-long Nd:YAG crystal rod would generate 74.6 W of continuous-wave solar laser power at a collection efficiency of 42.2 W/m2, i.e., 1.1 times greater than the previous record value. Considering the laser beam quality, a brightness figure of 0.063 W was obtained, which is higher than that of other multimode SPL designs with end-side pumping. Thus, our SPL concentrator offers the possibility of achieving a beam quality as high as that obtainable via side pumping, alongside highly efficient energy conversion, which is characteristic to end-side pumping.

Active building envelopes that act as energy converters—gathering on-site available renewable energy and converting it to thermal energy or electricity—is a promising technological design niche to reduce energy consumption in the building sector, cut greenhouse gas emissions, and thus tackle climate change challenges. This research adds scientific knowledge in the field of composite building envelope structures containing phase-change materials for thermal energy storage. In this study, the focus lies on the cooling phase of the diurnal gain and release of solar energy. The experimental setup imitates day and night environment. Six alterations of small-scale solar facade modules are tested in two different configurations—with and without the adjustable insulation layer on their outer surface during the discharging phase. Modules explore combinations of aerogel, air gap, and Fresnel lenses for solar energy concentration. The results allow us to compare the impact of the application of an additional insulation layer at “night” for different designs of solar facade modules. The results show that modules with an air gap provide higher heat gains but do not take full advantage of the latent heat capacity of phase-change materials.

Indonesia has been blessed with excellent solar heat distribution, which can be used as renewable energy to heat water. Various technologies have been developed to utilize these inexhaustible thermodynamic resources, in the form of photons arrays, converted into concentrated heat for daily use, i.e., solar water heater. This renewable-based water heating system can provide significant energy efficiency, benefit the environment, and reduce energy use costs. This experimental study attempts to harvest the energy from the sun using a cylindrical through collector (CTC) type solar concentrator. The CTC was made of the solar reflective film (SRF) affixed to concentrator collector surfaces which was then mounted on an adjustable angle frame of the concentrator collector support. The heat generated from the concentrator was stored in water, and phase change material is embedded in the system to retain the heat longer. The research was carried out in Langsa City, Aceh, Indonesia. The results showed that water heaters using CTC systems could produce 16 L of hot water retained at 40–60 °C for four hours. With the addition of beeswax, the water temperature of the same capacity can be maintained at 40–60 °C for around 5 h. This technology demonstrated an excellent result that produces as much as 60 L of water per day, increasing solar thermal energy efficiency. This technology presented a great potential for replication or even for further development on an industrial scale.

The Stirling engine together with a solar concentrator represents a solution for increasing energy efficiency. Thus, within the National Research and Development Institute for Cryogenic and Isotopic Technologies, an automation system was designed and implemented in order to control the processes inside the solar conversion unit using a programmable logic controller from Schneider Electric. The acquired parameters from the installed sensors were monitored using Unity Pro L software. The main objective of this paper is to solve the starting, operating, and shut-down sequences in safe conditions, as well as monitor the working parameters.

This paper presents the experimental investigation of a novel cross-compound parabolic concentrator (CCPC). For the first time, a CCPC module was designed to simultaneously work as an electricity generator and collect the thermal energy present in the module which is generated due to the incident irradiation. This CCPC module consists of two regions: an absorber surface atop the rig and a reflective region below that to reflect the irradiation onto the photovoltaic (PV) cell, coupled together to form an absorptive/reflective CCPC (AR-CCPC) module. A major issue in the use of PV cells is the decrease in electrical conversion efficiency with the increase in cell temperature. This module employs an active cooling system to decrease the PV cell temperature, optimizing the electrical performance and absorbing the heat generated within the module. This system was found to have an overall efficiency of 63%, which comprises the summation of the electrical and thermal efficiency posed by the AR-CCPC module.

The mirror unit installation error of the solar parabolic dish concentrator can adversely affect its optical performance causing optical intercept losses and hot spots on the absorber surface, which in turn affect safety. Thus, minimizing mirror installation error is considered very important. In this paper, a new method for the facet installation measurement and facet alignment of the mirror unit in the dish concentrator is presented. Firstly, a “clean” facet installation error measurement method using photogrammetry is presented. The photogrammetry measures the spatial coordinates of three feature points to reverse the mirror facet alignment error parameters. Next, two novel methods, a three-rotation alignment method and two-rotation alignment method for aligning the mirror facet are presented and corresponding mathematical models. The advantage of these alignment methods is that the adjustment value and order for each support bolt can be determined before the mirror facet is aligned, which could provide quantitative adjustment information to operator and avoid repeated adjustments. Finally, validity of the installation measurement and facet alignment method was verified by a numerical simulation and an experiment using a metal facet alignment. The presented methods do not rely on the geometry of the reflector mirror and could therefore have extensive uses in applications such solar tower and trough concentrator.

In this paper, we propose a side-absorption concentrated module with diffractive grating as a spectral-beam-splitter to divide sunlight into visible and infrared parts. The separate solar energy can be applied to different energy conversion devices or diverse applications, such as hybrid PV/T solar systems and other hybrid-collecting solar systems. Via the optimization of the geometric parameters of the diffractive grating, such as the grating period and height, the visible and the infrared bands can dominate the first and the zeroth diffraction orders, respectively. The designed grating integrated with the lens and the light-guide forms the proposed module, which is able to export visible and infrared light individually. This module is demonstrated in the form of an array consisting of seven units, successfully out-coupling the spectral-split beams by separate planar ports. Considering the whole solar spectrum, the simulated and measured module efficiencies of this module were 45.2% and 34.8%, respectively. Analyses of the efficiency loss indicated that the improvement of the module efficiency lies in the high fill-factor lens array, the high-reflectance coating, and less scattering.

Fiber-optic daylighting systems have been shown to be a promising and effective way to transmit sunlight in the interior space whilst reducing electric lighting energy consumption. To increase efficiency in terms of providing uniform illumination in the interior, the current need is to illuminate optical fiber-bundle with uniform light flux. To this end, we propose a method for achieving collimated light, which illuminates the fiber-bundle uniformly. Light is collected through a parabolic concentrator and focused toward a collimating lens, which distributes the light over each optical fiber. An optics diffusing structure is utilized at the end side of the fiber bundle to spread light in the interior. The results clearly reveal that the efficiency in terms of uniform illumination, which also reduces the heat problem for optical fibers, is improved. Furthermore, a comparison study is conducted between current and previous approaches. As a result, the proposed daylighting system turns out convenient in terms of energy saving and reduction in greenhouse gas emissions.

The significance of this work lies in the development of a novel code-based, detailed, and deterministic geometrical approach that couples the optimization of the Fresnel lens primary optical element (POE) and the dome-shaped secondary optical element (SOE). The objective was to maximize the concentration acceptance product (CAP), while using the minimum SOE and receiver geometry at a given f-number and incidence angle (also referred to as the tracking error angle). The laws of polychromatic light refraction along with trigonometry and spherical geometry were utilized to optimize the POE grooves, SOE radius, receiver size, and SOE−receiver spacing. Two literature case studies were analyzed to verify this work’s optimization, both with a spot Fresnel lens POE and a spherical dome SOE. Case 1 had a 625 cm2 POE at an f-number of 1.5, and Case 2 had a 314.2 cm2 POE at an f-number of 1.34. The equivalent POE designed by this work, with optimized SOE radiuses of 13.6 and 11.4 mm, respectively, enhanced the CAP value of Case 1 by 52% to 0.426 and that of Case 2 by 32.4% to 0.45. The SOE’s analytical optimization of Case 1 was checked by a simulated comparative analysis to ensure the validity of the results. Fine-tuning this design for thermal applications and concentrated photovoltaics is also discussed in this paper. The algorithm can be further improved for more optimization parameters and other SOE shapes.

A crossed compound parabolic concentrator (CCPC) is a non-imaging concentrator which is a modified form of a circular 3D compound parabolic concentrator (CPC) obtained by orthogonal intersection of two 2D CPCs that have an optical efficiency in line with that of 3D CPC. The present work is about the design and fabrication of a new generation of solar concentrator: the hybrid photovoltaic (PV)/thermal absorptive/reflective CCPC module. The module has a 4× CCPC structure truncated to have a concentration of 3.6× with a half acceptance angle of 30°. Furthermore, an experimental rig was also fabricated to test the performance of the module and its feasibility in real applications such as building-integrated photovoltaic (BIPV). 3D printing and Computer Numerical Control (CNC) milling technologies were utilized to manufacture the absorber and reflective parts of the module.

A novel on-axis general sun-tracking formula has been integrated in the algorithm of an open-loop sun-tracking system in order to track the sun accurately and cost effectively. Sun-tracking errors due to installation defects of the 25 m2 prototype solar concentrator have been analyzed from recorded solar images with the use of a CCD camera. With the recorded data, misaligned angles from ideal azimuth-elevation axes have been determined and corrected by a straightforward changing of the parameters’ values in the general formula of the tracking algorithm to improve the tracking accuracy to 2.99 mrad, which falls below the encoder resolution limit of 4.13 mrad.