Compound Parabolic Concentrator Reflectors Research Articles

A novel solution method for reflector shape of solar Compound Parabolic Concentrator and verification

In the existing studies, there are many methods to obtain the reflector shape equations of a CPC(Compound Parabolic Concentrator), but these methods are complicated and not unified. This paper aims to propose a novel method that is based on the edge-ray principle, the differential geometry theory, and the geometrical optical reflection law to get the reflector shape equations. Then, the reflector shape equations of an arc absorber CPC (A-CPC) which focuses light on the lower part of a circular absorber are calculated. The optical properties of such an A-CPC experimental model determined by these equations are studied via laser experiments. Afterward, the error between the calculated values obtained by MCRT(Monte Carlo Ray-Trace) method and experimental values are analyzed. The experimental results show that the optical properties of the A-CPC are in accordance with the theoretical expectations. They indicate also that the theoretical method is flexible and suitable for calculating a specific CPC reflector shape.

A New Approach for Design Optimization and Parametric Analysis of Symmetric Compound Parabolic Concentrator for Photovoltaic Applications

A compound parabolic concentrator (CPC) is a non-imaging device generally used in PV, thermal, or PV/thermal hybrid systems for the concentration of solar radiation on the target surface. This paper presents the geometric design, statistical modeling, parametric analysis, and geometric optimization of a two-dimensional low concentration symmetric compound parabolic concentrator for potential use in building-integrated and rooftop photovoltaic applications. The CPC was initially designed for a concentration ratio of “2×” and an acceptance half-angle of 30°. A MATLAB code was developed in house to provoke the CPC reflector’s profile. The height, aperture width, and concentration ratios were computed for different acceptance half-angles and receiver widths. The interdependence of optical concentration ratio and acceptance half-angle was demonstrated for a wide span of acceptance half-angles. The impact of the truncation ratio on the geometric parameters was investigated to identify the optimum truncation position. The profile of truncated CPC for different truncation positions was compared with full CPC. A detailed statistical analysis was performed to analyze the synergistic effects of independent design parameters on the responses using the response surface modeling approach. A set of optimized design parameters was obtained by establishing specified optimization criteria. A 50% truncated CPC with an acceptance half-angle of 21.58° and receiver width of 193.98 mm resulted in optimum geometric dimensions.

Performance analysis of hybrid solar desalination system using ETC and CPC

This paper present analytical and experimental analysis of hybrid solar desalination system using evacuated tube collector (ETC) and compound parabolic concentrator (CPC) to obtain the maximum amount of soft water for drinking and industrial purposes. In this paper, thermal performance of hybrid system with varying heights between ETC and CPC and flow rates are investigated with single effect boiling method. Water is used as working fluid for experimentation and tested for different climatic conditions of Pune city (located in western region in the Maharashtra state, India). The experimental set-up of thermosiphon solar water system mainly consists of ETC and CPC, condenser, inlet water tank, outlet collection jar etc. The CPC (reflector) is used to improve thermal performance of solar desalination system. Further, thermal performance of said solar desalination system has been improved with aluminium foil as CPC (reflector) material. From obtained results, it is concluded that for the climatic conditions of selected location, solar (ETC + CPC) hybrid desalination system could produce 1.5–2 l of fresh water per day and purity is validated as per ISO 12500-2012.

Life cycle assessment as a methodological tool for the optimum design of integrated collector storage solar water heaters

This study presents a simulation tool for the design optimization of Integrated Collector Storage (ICS) solar water heaters using a prototype solar device as reference. The prototype is a commercially available ICS with Compound Parabolic Concentrating (CPC) reflector, installed in the island of Crete, Greece. The aim of this study is to evaluate the optimal sizing of the CPC reflector, aiming at the highest performance of the system, the lowest environmental impacts and the minimization of the production cost. For the environmental profile of the model, Life Cycle Assessment (LCA) was employed. The implemented multi objective nonlinear optimum design of the ICS systems based on the results of the LCA. The environmental parameters in operation mode were evaluated using additional subroutines and functions of the code, which based on RETScreen Expert software examples. The analysis was implemented for different reflector configurations and storage types. The investigated configurations were compared with previous ICS models, in order to define the design specifications for the fabrication of new solar devices. The results imply that the redesigned models improve the energy and environmental performance of the original systems whilst at the same time the total production cost was minimized.

Design and analysis of a novel ICS solar water heater with CPC reflectors

In this paper, a new design of an integrated collector storage (ICS) solar water heater combined with compound parabolic concentrator (CPC) is presented. The ICS system consists of one cylindrical tank properly mounted in a stationary symmetrical CPC reflector through. In this solar system, the cylindrical storage tank surface is partially insulated at the back side at 50%, so as to suppress thermal losses from it to the ambiance. The system depth and aperture width are moderated. The optical efficiency of the ICS solar water heater was predicted using advanced ray tracing technique. The result shows that the acceptance angle is 40°. A theoretical study was carried out to predict the thermal behaviour of the system under Saharan climate. The results are presented and discussed.

Thermal performance of a new CPC solar air collector with flat micro-heat pipe arrays

A new type of compound parabolic concentrator (CPC) solar air collector (SAC) with flat micro-heat pipe arrays (FMHPA) was investigated in this study. A cylindrical absorber was constructed by inserting the FMHPA into an evacuated glass tube to transport heat during the working process. The new FMHPA-CPC SAC is an edge ray collector with a concentration ratio of 1.8. The core concept is the integration of the FMHPA, an absorber tube, and a CPC reflector as a heat-collecting unit. Thermal performance investigation was conducted theoretically and experimentally. This study mainly analyzed the effect of different factors on the thermal performance of the collector. The efficiencies and heat loss coefficients of the new collector were determined. Experimental curves with different testing conditions are presented. The optimal value of efficiency was determined for the SAC. The aperture area of each CPC collecting unit is approximately 0.4 m2. The new FMHPA-CPC SAC was tested in Beijing, China. The average efficiency was approximately 61% at a volume flow rate of 320 m3/h, with a radiation of 799 W/m2 (ambient temperature of 28.8 °C). The instantaneous efficiency reached 68%, depending on the solar radiation, air volume flow rate, and ambient temperature. In addition, the time constant of the collector was approximately 14.8 min, with an air volume flow rate of 260 m3/h.

Flexible Bench-Scale Recirculating Flow CPC Photoreactor for Solar Photocatalytic Degradation of Methylene Blue Using Removable TiO2Immobilized on PET Sheets

TiO2immobilized on polyethylene (PET) nonwoven sheet was used in the solar photocatalytic degradation of methylene blue (MB). TiO2Evonik Aeroxide P25 was used in this study. The amount of loaded TiO2on PET was approximately 24%. Immobilization of TiO2on PET was conducted by dip coating process followed by exposing to mild heat and pressure. TiO2/PET sheets were wrapped on removable Teflon rods inside home-made bench-scale recirculating flow Compound Parabolic Concentrator (CPC) photoreactor prototype (platform 0.7 × 0.2 × 0.4 m3). CPC photoreactor is made up of seven low iron borosilicate glass tubes connected in series. CPC reflectors are made of stainless steel 304. The prototype was mounted on a platform tilted at 30°N local latitude in Cairo. A centrifugal pump was used to circulate water containing methylene blue (MB) dye inside the glass tubes. Efficient photocatalytic degradation of MB using TiO2/PET was achieved upon the exposure to direct sunlight. Chemical oxygen demand (COD) analyses reveal the complete mineralization of MB. Durability of TiO2/PET composite was also tested under sunlight irradiation. Results indicate only 6% reduction in the amount of TiO2after seven cycles. No significant change was observed for the physicochemical characteristics of TiO2/PET after the successive irradiation processes.

Optical and thermal performances improvement of an ICS solar water heater system

With the aim to increase the quantity of absorbed energy and improve optical and thermal performances, a new design of an integrated collector storage (ICS) solar water heater combined with a compound parabolic concentrator (CPC) is presented. This model consists of two concentrating stages. The upper part contains two symmetrical parabolic sections with focal axes rotated by θ=48° in counterclockwise sens and θ=-48° in clockwise sens from vertical plane. The lower part is constituted by three involute reflectors. Its cylindrical storage tank covers the triangle formed by the three involute parts center’s. The geometric concentration is about 1.34. This design has a strong connection with a previous study where an old ICS system was designed and experimentally tested. A ray-tracing model was developed to simulate the reflection of the direct solar radiation on the CPC reflectors at different angles of incidence and compute the absorbed solar radiation distribution on the absorber surface. The obtained results, when compared with the old experimented model differing on the design of the lower stage concentrator, showed a significant improvement in optical efficiency, the distribution of the absorbed energy regarding the angle of incidence and the temperature level required.

Theoretical analysis of a novel, portable, CPC-based solar thermal collector for methanol reforming

In this paper we propose a new solar thermal collector which is suitable for providing heat for endothermic chemical reactions. The particular reaction that is considered is hydrogen production by menthol reforming. The design presented here is based on CPC (compound parabolic concentrator) technology, which can operate without complicated (and costly) tracking systems. It consists of a small, double-sided selective surface receiver in a vacuum envelope comprised of CPC reflectors and a glass aperture cover. Heat absorbed by the receiver is transferred to the working fluid inside micro tubes where the chemical reaction is occurring. This design, to the best of our knowledge, represents the first time that a vacuum package (which creates thermal concentration) has been combined with a CPC-based optical concentrator for thermo-chemical applications. This collector design can convert over 78% of incident solar radiation into heat with a concentration ratio of 1.75, allowing for a high solar-to-fuel efficiency in chemical reactions. This study establishes both the optical and thermal models needed to predict the performance of this type of collector. The results show that the collector stagnates at very high temperatures (up to 600°C), and can provide solar heat in the form of a small collector for a variety of portable applications – e.g. methanol reforming that requires temperatures of around 250°C.

Performance investigation on a novel single-pass evacuated tube with a symmetrical compound parabolic concentrator

Development of the cost-effective single-pass evacuated tubular collector (SPETC) for the solar processes heat is a particular topic of active research. A novel SPETC with a symmetrical compound parabolic concentrator (CPC) has been introduced, experimentally investigated and theoretically analyzed in this paper. The novel SPETC is mainly composed of a double-glass evacuated tube deposited the selective absorbing coating, as well as six expansion joints. Correspondingly, the symmetrical CPC has been designed and fabricated using the high-reflectivity 3M mirror films pasted over the stainless steel substrate. In addition, detailed numerical models for thermal behaviors of the SPETC with the CPC reflector, based on the three-dimensional CFD method, have been developed and validated with experimental data. The objective of this paper is to report the test results of the novel SPETC with the CPC, evaluate optical and thermal performances including the heat flux distribution on the absorber surface, heat losses, as well as thermal efficiencies, thereby providing useful data for practical solar process heat application. Experimental results indicate that a daily thermal efficiency of 48% can be reached at a difference of 59.6K between inlet and ambient temperatures under a volume flow rate of 0.0077m3s−1. Corresponding numerical prediction shows that the operational volume flow rate between 0.007 and 0.01m3s−1 is suggested to the SPETC using the HTF (air) under the geometry and operational conditions in this paper. These results suggested that the novel SPETC is feasible for industrial process heat and solar cooling system combined with the adsorption chiller or the desiccant wheel.

Numerical and experimental study of an integrated solar collector with CPC reflectors

The aim of this work is to develop a numerical code able to predict the thermal behavior of a double tank integrated collector storage system (ICS) with compound parabolic concentrator (CPC). The developed numerical model is based on the detailed analysis of the different forms of heat transfers occurring in the ICS system. The balance equations of each element of the system have been established and solved by means of a transient algorithm. A prototype of an ICS device was constructed and experimentally tested outdoors in order to observe the variation of water temperature in the storage tanks. The experimental results are presented and the validity of the model is examined by comparison of the theoretical results with experiments which demonstrates a good agreement. The numerical model is then used to perform theoretical study on the present ICS solar heater. The simulation results of the variation of the thermal efficiency are presented. The results of the yearly parametric study of the effect of the concentrators reflectivity, the absorber emissivity and the use of double glazing on the thermal performance of the ICS system are also presented and discussed. The developed numerical tool within this work can be considered as important for the study of double tanked ICS solar water heater regarding its transient thermal behavior.

A Study for the Use of Solar Energy for Agricultural Industry - Solar Drying System Using Evacuated Tubular Solar Collector and Auxiliary Heater -

Purpose: The objectives of this study were to construct the solar drying system with evacuated tubular solar collector and to investigate its performance in comparison with indoor and outdoor dryings. Methods: Solar drying system was constructed with using CPC (compound parabolic concentrator) evacuated tubular solar collector. Solar drying system is mainly composed of evacuated tubular solar collector with CPC reflector, storage tank, water-to-air heat exchanger, auxiliary heater, and drying chamber. Performance test of solar drying system was conducted with drying of agricultural products such as sliced radish, potato, carrot, and oyster mushroom. Drying characteristics of agricultural products in solar drying system were compared with those of indoor and outdoor ones. Results: Solar drying system showed considerable effect on reducing the half drying time for all drying samples. However, outdoor drying was more effective than indoor drying on shortening the half drying time for all of drying samples. Solar drying system and outdoor drying for oyster mushroom showed the same half drying time. Conclusions: Oyster mushroom could be dried easily under outdoor drying until MR (Moisture Ratio) was reached to about 0.2. However, solar drying system showed great effect on drying for most samples compared with indoor and outdoor dryings, when MR was less than 0.5.

Heat retaining integrated collector storage solar water heater with asymmetric CPC reflector

A novel integrated collector storage solar water heater (ICSSWH) was designed, optically analysed and experimentally studied. The unit was based around a heat retaining ICS vessel design consisting of two concentric cylinders mounted horizontally inside a stationary truncated asymmetric compound parabolic concentrating (CPC) reflector trough. The annulus between the cylinders was partially evacuated and contained a small amount of water, which changed phase at low temperature, producing a vapour and creating a thermal diode transfer mechanism from the outer absorbing surface to the inner storage vessel surface. The absorbing outer vessel surface covered with selective absorber film and was partially exposed to solar radiation. The remaining vessel surface area (including the vessel ends) was thermally insulated to improve heat retention during the night. Curved reflectors with a high reflectance along with high transmittance glazing were also used to improve effective operation of the ICS system. The thermal behaviour of the ICS system was compared to that of a Flat Plate Thermosiphonic Unit (FPTU). The experimental results showed that the ICS system is as effective during daily operation as it is during the night. Furthermore, the thermal loss coefficient during night gives similar values between the ICS system and FPTU.

CPC type integrated collector storage systems

Integrated collector storage (ICS) solar water heaters with stationary compound parabolic concentrating (CPC) reflectors are designed and test results are presented. The systems consist of single and double cylindrical horizontal tanks properly placed in truncated symmetric and asymmetric CPC reflector troughs. The suggested designs aim to achieve low cost systems with improved performance by the reduction of their thermal losses and the increase of water temperature rise by using the non-uniform distribution of solar radiation on the absorber surface. Four experimental models were constructed and tested outdoors to determine their mean daily efficiency and thermal losses during the night. Test results showed that asymmetric CPC reflectors contribute to lower thermal losses and the two connected in series cylindrical storage tanks result in effective water temperature stratification. The system with the single cylindrical storage tank and the symmetric CPC reflector performs satisfactorily during the day as well as during the night and regarding its simpler design it could be considered cost effective among the studied ICS systems. A typical thermosiphonic system with flat plate collector was tested for performance comparison, by which the improved daily efficiency of ICS systems and also their moderate water storage heat preservation during the night were confirmed.

Non-axisymmetric reflectors concentrating radiation from an asymmetric heliostat field onto a circular absorber

In solar tower plants, where a rotationally symmetric field of heliostats surrounds the tower, an axisymmetric secondary concentrator such as a compound parabolic concentrator (CPC) or a tailored concentrator or a cone is the obvious choice. For locations at higher latitudes, however, the reflecting area of the heliostats may be used more efficiently if the field of heliostats is located opposite to the sun as seen from the tower. Then the field is asymmetric with regard to the tower. In the case of an asymmetric field, an axisymmetric concentrator necessarily has a concentration significantly lower than the upper limit. Furthermore, the area on the ground from which a tilted axisymmetric concentrator accepts radiation is an ellipse, including also heliostats very distant to the tower producing a large image of the sun. For these reasons we investigate asymmetric secondaries. From the shape of the edge ray reflectors constructed for rays in the central south–north plane we conclude that a skew cone reflector might be appropriate for the field, and optimize its free parameters by means of ray tracing. Asymmetric concentrators may increase the concentration by up to 25% at the same efficiency compared to optimized axisymmetric CPC or cone reflectors.