Three-dimensional Compound Parabolic Concentrator Research Articles

Multirod Pumping Approach with Fresnel Lens and Ce:Nd:YAG Media for Enhancing the Solar Laser Efficiency

A multirod Ce:Nd:YAG solar laser approach, using a Fresnel lens as a primary concentrator, is here proposed with the aim of considerably increasing the efficiency of solar-pumped lasers. Fresnel lenses are cost-effective, rendering solar lasers more economically competitive. In this work, solar-pumped radiation collected and concentrated using the Fresnel lens is received by a secondary three-dimensional compound parabolic concentrator which transmits and funnels the light toward the Ce:Nd:YAG laser rods within a water-cooled tertiary conical concentrator that enables efficient multipass pumping of the rods. To explore the full potential of the proposed approach, the performance of various multirod configurations is numerically evaluated. Through this study, configurations with three and seven Ce:Nd:YAG rods are identified as being the most efficient. A maximum continuous wave total laser power of 122.8 W is reached with the three-rod configuration, marking the highest value from a Ce:Nd:YAG solar laser, leading to solar-to-laser conversion and collection efficiencies of 7.31% and 69.50 W/m2, respectively. These results represent enhancements of 1.88 times and 1.79 times, respectively, over the previous experimental records from a Ce:Nd:YAG/YAG single-rod solar laser with a Fresnel lens. Furthermore, the above results are also 1.58 times and 1.68 times, respectively, greater than those associated with the most effective three-rod Ce:Nd:YAG solar laser utilizing a parabolic mirror as the main concentrator. The present study also shows the great usefulness of the simultaneous pumping of multiple laser rods in terms of reducing the thermal stress effects in active media, being the seven-rod configuration the one that offered the best compromise between maximum efficiency and thermal performance. This is crucial for the applicability of this sustainable technology, especially if we wish to scale our system to higher power laser levels.

Temperature estimation of a receiver equipped with a 3D compound parabolic concentrator

Solar Tower Power Plant (STPP) require a high concentration ratio to provide high working fluid temperatures for power generation. Three-dimensional Compound Parabolic Concentrator (3D-CPC) can be used to increase the concentration ratio in the receiver. This paper estimates the air outlet temperature of an indirectly irradiated solar receiver equipped with a 3D-CPC for STPP. For this purpose, the STPP subsystems such as the heliostat field, the 3D-CPC and the receiver are sized for an electrical power of 30 kW. An in-house Matlab code is developed and executed the configuration of the heliostats in the field. The result of the Monte Carlo ray tracing (MCRT) method is used to provide boundary conditions to the Computational Fluids Dynamics (CFD) model. The CFD model is used to simulate the conjugate heat transfer in the receiver. Based on this, a heat source is created from the solar rays absorbed in the receiver. This heat source is implemented as a volumetric heat source in Ansys Fluent by UDFs functions. Thus, the in-house Matlab code is validated by simulating the PS-10 heliostat field and the CFD model is also validated by simulating the Weizmann heliostat field. The results show that the solar field is consisted of 175 heliostats of 2 m2 surface area and 1.5 m height each. The 3D-CPC truncated at 35° increased the concentration ratio by a factor of 4.91 for an optical efficiency of 80.66 %. A receiver mesh count of 1,076,958 gave convergence of the air outlet temperature. 1.5 × 106 rays are found to get independence of the absorbed heat flux in the receiver. The temperature found on the heated solid is 1063.4 K. For a porosity of 56.02 % and a mass flow rate of 0.11 kg/s, a temperature of 1218 K is reached at the outlet of the receiver. The results show that the use of a 3D-CPC increase the concentration ratio and, consequently improve the thermal performance of the receiver. It is important to note that, parameters such as mass flow rate and porosity have a strong influence on the air outlet temperature.

Design of a compound parabolic concentrator for a multi-source high-flux solar simulator

A three-dimensional compound parabolic concentrator (CPC) is designed for high-temperature solar thermochemical applications driven by radiation from a multi-source high-flux solar simulator. The basic geometrical parameters of the CPC including the acceptance angle and the entry aperture radius are determined using optical simulations. A cooling system for overheating protection is designed using engineering heat transfer correlations. A prototype CPC is manufactured using additive manufacturing and single point diamond turning techniques. The optical simulations show that the CPC increases the concentration ratio by a factor of 4.1 at an optical efficiency of 85.4%, reduces spillage loss from 78.9% to 32.1%, and reduces the flux non-uniformity on the target surface.

Multiple nonlinear regression model for predicting the optical performances of dielectric crossed compound parabolic concentrator (dCCPC)

As a typical type of three-dimensional compound parabolic concentrator (CPC), dielectric crossed compound parabolic concentrator (dCCPC) has drawn a significant research attention in these years to explore its angular characteristics in solar collection for concentrating photovoltaics and daylighting control in buildings. Optical efficiency and transmittance are the main performance indicators to evaluate a dCCPC which may be base-coated as a receiver or non-coated for daylighting. The most common way to accurately determine the performance of a dCCPC is through ray-tracing simulation which requires advanced optical analysis software and lots of time. To facilitate the annual performance evaluation of dCCPC, this study puts forward several mathematical models for multiple nonlinear regression based on a mass of simulation results. The models can predict the transmittance of non-coated dCCPC and the both of transmittance and optical efficiency of base-coated dCCPC from several sky parameters, respectively. The agreement between predicted and simulated values is generally satisfactory. The coefficient of determination (R2) for each model is higher than 0.94 and the mean square error (MSE) is less than 0.002. Six specific time among the whole year are selected to verify the reliability of the prediction models in practice. The limitation and significance of these models are discussed as well. The regression models provide a convenient and accurate approach to predict the optical performance of dCCPC.

Simulation model of a new solar laser system of Fresnel lens according to real observed solar radiation data in Helwan of Egypt

A new simulation model of a new solar pumped laser system was tested to be run in Helwan in Egypt (latitude φ=29°52′N, longitude λ=31°21′E and elevation=141m) as an example of an industrial polluted area. The system is based on concentrating the solar radiation using a Fresnel lens on a laser head fixed on a mount tracking the sun during the day and powered by a DC battery. Two cases of this model are tested; the first one is the model consisting of a Fresnel lens and a two-dimensional Compound Parabolic Concentrator (CPC), while the other is the model consisting of a Fresnel lens and a three-dimensional Compound Parabolic Concentrator (CPC). The model is fed by real actual solar radiation data taken in Helwan Solar Radiation Station at NRIAG in the various seasons in order to know the laser power got from such a system in those conditions. For the system of Fresnel lens and 2D-CPC, an average laser output power of 1.27W in Winter, 2W in Spring, 5W in Summer and 4.68W in Autumn respectively can be obtained. Accordingly, the annual average output power for this system is 3.24W. For the system of Fresnel lens and 3D-CPC, an average laser output power of 3.28W in Winter, 3.55W in Spring, 7.56W in Summer and 7.13W in Autumn respectively can be obtained. Accordingly, the annual average output power for this system is 5.38W.

Development of the Ecobalsas Solar Oven Based on a CPC and Cooking Power Estimation for Several Selective Surfaces on the Absorber

The Ecobalsas solar oven is presented as an alternative for generate economic savings for families living in dry climates, as it mitigates desertification and reduces the time people spend searching for firewood. It is an oven based on a three-dimensional compound parabolic concentrator that applies non-imaging optics and follows Trombe Meinel curves. The main materials used in its construction are: aluminum specular sheets in sections with high reflectance on the concentrator, a pressure pot (4-liter capacity) in the focal region as absorber, an acrylic panel (3 mm thick) as a cover at the opening area, polyurethane foam with a second waterproof layer as insulator on the exterior of the concentrator, and carbon steel in most of the structure and oven base. It is equipped on a rotative base that allows the hour angle path to be followed over 360° and solar altitude, and has a geometric concentration of about 4.1. Its average cost is $200 USD.Cooking power was determined following the Funk protocol. Merit factors and thermal efficiency were obtained as well [2]. The tests were repeated for four selective surfaces: resinous wood soot called “ocote,” black matte paint mixed with the aforementioned soot, copper oxide, and black matte paint, in order to determine which of these materials provides the best thermal performance and cooking power, thus allowing cooking time to be reduced.

Estimation of exergy efficiency of compound parabolic concentrator under time-varying cloud cover condition

The exergy budget in a solar collector has thus far been estimated under the condition of steady solar radiation intensity. In reality, solar radiation temporally varies depending on weather conditions. In particular, it remains to be elucidated to what extent cloud cover affects an exergy budget. To develop a method to evaluate the exergy efficiency with consideration of cloud cover, we studied the exergy budget of a three-dimensional compound parabolic concentrator (CPC) by constructing a model representing the heat budget of the CPC and by measuring temperatures at a few points in the CPC under a variety of cloud circumstances. We found reasonable validity in the thermal model through comparisons of the simulation with measurements. The temperature of the collector fluctuated owing to the appearance and disappearance of clouds, and in response, the input and output rates of the exergy temporally varied during cloudy days. By integrating the rates of exergy over a period including noon, we computed net input and output exergies. The exergy efficiency estimated was maximally 12%. The method developed in this study is also useful in quantifying the thermal performance of other types of solar collectors and improving their design.

Exergy analysis on solar heat collection of three-dimensional compound parabolic concentrator

This study presents a thermal model for the optimum design of the three–dimensional compound parabolic concentrator (CPC) considering the maximisation of exergy delivery. The model in this study has been validated by comparing the computed collector temperature with the measured one. A good agreement has been confirmed. The optimum temperatures of the collector and the thermal medium are calculated. Reduction of heat loss from the collector to ambient air can enhance the maximum exergy, but it is accompanied by shift of the optimum temperature. The heat extraction process has been examined by assuming that it is composed of two steps of heat flow: the first from the collector to the medium and the second from the medium to the final objective. The analysis shows how the exergy efficiency varies in response to the design change in the second step and where the overall optimised design can be found in a diagram between heat transfer coefficient and temperature.

Experimental and numerical investigation on solar concentrating characteristics of a sixteen-dish concentrator

The concentrated solar flux distributions of a sixteen-dish concentrator (SDC) were measured applying a thermal infrared imager in combination with water-cooled Lambert target, and predicted using a Monte Carlo ray tracing method (MCRT). A slope error of 2.2 mrad is detected by comparing the experimental and numerical results. Then, a two-stage concentrator system, formed by the SDC in tandem with a three-dimensional compound parabolic concentrator (3D CPC–SDC), is constructed based on the geometrical optics approach. The interception performances and the energy concentration ratio images (ECR) are presented for both the SDC and the 3D CPC–SDC. The results show that the ECR profiles of the SDC depend on the receiver sizes, whereas that of the 3D CPC–SDC is rather steady because most sunlight enters the receiver via several reflections with the 3D CPC mirror. The 3D CPC–SDC is capable of increasing the geometric concentration ratio (GCR) at the expense of a little interception efficiency.

Optical and thermal performance of a three-dimensional compound parabolic concentrator for spherical absorber

For medium range temperature applications, focusing type collectors like Compound Parabolic Concentrator (CPC) are most commonly used. Considerable research work has been carried out to improve the performance of the two-dimensional compound parabolic concentrator (2D CPC). The three-dimensional compound parabolic concentrator (3D CPC) was found to be more efficient than 2D CPC because of the higher concentration ratio. In the present work a 3D CPC was fabricated with a half acceptance angle of 4° for a spherical absorber of radius 100 mm. UV stabilized aluminized polyester foil having high reflectivity (0·85) was pasted on the reflector for a total height of 441mm and an aperture width of 540 mm. The optical efficiency was estimated theoretically and compared with the experimental value. Experimentally determined values of optical and thermal efficiencies were in good agreement with theoretically predicted value. The experimental results shown that the optical efficiency obtained from the 3D CPC (0·626) was significantly higher than that of the 2D CPC (0·570) of similar dimensions. Since the optical efficiency of the 3D CPC was increased, the thermal efficiency of the collector was also increased. In addition to that, time constant of the concentrator was also calculated. The time constant of the 3D CPC (431 s) was fairly high when compared with the 2D CPC (110 s). An attempt was made to generate low pressure steam using 3D CPC in the in situ steam generation mode. The efficiency of the steam generation was about 38%, which was one of the possible applications of 3D CPC module.

Micro 3-D CPC Solar Collector for Thermal Electric System

In this paper, the authors propose an innovative non-tracking three-dimensional compound parabolic concentrator (3-D CPC) solar collector, which has excellent thermal efficiency for a high-temperature range (100-200°C). The proposed 3-D CPC collector has a moderate concentration ratio and does not need tracking. First, the tentative 3-D CPC collector was fabricated and its thermal performance and principal characteristics were clarified. Next, numerical simulations of the optical characteristics of the 3-D CPC collector were carried out with the ray-tracing method. Finally, the specification of the optimal 3-D CPC collector will be shown.

Passive Q switching of a solar-pumped Nd:YAG laser

Passive Q switching is a preferable choice for switching the Q factor of a solar-pumped laser because it requires neither a driver nor an electrical power supply. The superior thermal characteristics and durability of Cr(4+):YAG single crystals as passive Q switches for lamp and diode-pumped high-power lasers has been demonstrated. Here we report on an average power of 37 W and a switching efficiency of 80% obtained by use of a solar-pumped Nd:YAG laser Q switched by a Cr(4+):YAG saturable absorber. Concentration of the pumping solar energy on the laser crystal was obtained with a three-stage concentrator, composed of 12 heliostats, a three-dimensional compound parabolic concentrator (CPC) and a two-dimensional CPC. The water-cooled passive Q switch also served as the laser rear mirror. Repetition rates of as much as 50 kHz, at pulse durations between 190 and 310 ns (FWHM) were achieved. From the experimental results, the saturated single-pass power absorption of the Cr(4+):YAG device was estimated as 3 ? 1%.

Using fiber optics to tap the sun's power

This paper discusses a solar energy collection system in which optical fibers are used to transport energy from a single-stage and a double-stage, three-dimensional Compound Parabolic Concentrator (CPC). After developing a thermo-mathematical model for the assembly of CPC and fibers, numerical simulations are used to optimize the system design. The modules filled with plastic and glass are shown to perform considerably better than those filled with air. A two-stage system performs better than a single-stage module. CPC surface reflectance improves the yield but an increase in fiber length decreases the performance.

Losses in a three-dimensional compound parabolic concentrator as a second stage of a solar concentrator

In this article, the losses due to reflection properties in a three-dimensional compound parabolic concentrator (3-D C.P.C.) are calculated and the effect of these losses on the concentration is analyzed. The 3-D C.P.C. is used as a second stage in two configurations of a two-stage concentrator: (a) a parabolic dish as a first stage, and (b) a Cassegrainian as a first stage. The nonplanar rays play an important role in 3-D C.P.C. losses. Thus, a ray-tracing procedure is needed to evaluate the losses. In this study, a rigorous three-dimensional ray tracing program was specially developed. The reflection losses and their effect on the concentration were determined from the reflection distribution derived by the developed ray-tracing program. As a result, the reflection losses were approximated by a simple empirical linear model useful in practical ranges of the 3-D C.P.C. acceptance angles and reflectivities. This model facilitates design and system optimization by analytical methods without resorting to a ray-tracing procedure. The approach presented in this article may be used to compare the performance of the two-system configurations, taking into account the 3-D C.P.C. losses.

Cone Compared to CPC as Secondary Concentrator in Tandem With a Paraboloidal Dish Primary

This paper reports that the three-dimensional compound parabolic concentrator (3-D CPC), a surface of revolution formed by rotating the 2-D CPC plane profile curve about its axis of symmetry, comes very close to achieving the maximum permissible geometric concentrator factor, given by: C = (D[sub 1]d[sub 2])[sup 2] = 1 sin[sup 2][theta][sub max] where d[sub 1] and d[sub 2] are the entrance and exit diameter, and [theta][sub max] is the half angle of maximum bean divergence. 3-D CPCs can be used as secondary elements to augment the concentration, relax optical tolerances and increase design flexibility of primary solar concentrators. Practical considerations sometimes demand the manufacture of a truncated cone, or compound cones, as a substitute to the 3-D CPC. Such a segmented approximation to the exact profile of the CPC has been previously investigated for the two-dimensional case. Transmission-angel curves, i.e., percentage of parallel rays, uniformly distributed over the entry aperture area, that reach the exit aperture area, were calculated for 3-D CPCs and for right circular cones.