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Acceptance Half Angle
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Runsheng Tang – One of the best experts on this subject based on the ideXlab platform.

A note on design of linear dielectric compound parabolic concentrators
Solar Energy, 2018CoAuthors: Guihua Li, Jingjing Tang, Runsheng TangAbstract:Abstract In this communication, threedimensional radiation transfer within linear dielectric compound parabolic concentrators (DCPC) is investigated based on vector algebra and solar geometry, and the design of DCPC oriented in eastwest direction is addressed. The analysis shows that, the projected incident and refractive Angles of solar rays on the crosssection of DCPC are not subjected to the correlation as Snell law except for incident rays on the crosssection, hence, the Acceptance Half–Angle (θa) of DCPC should be determined based on time variations of projected refractive Angle and minimum time (2tc) required to concentrate direct sunlight in all days of a year. It is also found that, to make all refractive radiation within θa are totally internally reflected onto the absorber, DCPC with a restricted exit Angle (DCPCθa/θe should be employed, and solar leakage from walls of DCPC θ a /90 can be avoided or reduced by increasing θa and number of periodical tiltAngle adjustment in a year. Calculations show that, the minimum θa of DCPC depends on tc and strategy of tiltAngle adjustment; and for a given tc, the ratio (Rc) of maximum geometric concentration of DCPC to that of reflective CPC (n = 1) is dependent on number of periodical tiltAngle adjustment in a year, but always larger than refractive index (n) of dielectric. Calculations also indicate that, for DCPCs with n > 1.4, when solar rays incident towards onto right/left wall, the radiation incident on its opposite wall (left/right) will be totally internally reflected, and multiple reflections of solar rays on way to the absorber will also be total internal reflection for radiation within its Acceptance Angle.

Irradiation distribution on solar cells inside CPCs with a restricted exit Angle
, 2016CoAuthors: Runsheng Tang, Chaofeng XiaAbstract:Abstract. In this work, irradiation distribution on the base of ideal twodimensional CPCs with and without a restricted exit Angle, to which solar cells are attached, are analyzed by the raytracing technique. Results show that, given an Acceptance Half–Angle ( a θ), for CPCs without a restricted exit Angle (CPC1), radiation flux distribution on the base depends on the incidence Angle of solar rays (θ); whereas for CPCs with a restricted exit Angle (CPC2), the flux distribution depends on θ and the restricted exit Angle ( e θ). For both CPC1 and 2 with identical geometric concentration factor (Ct=2) and Acceptance Half–Angle ( aθ =20), the peak flux concentration ratio on the base of CPC2 with e θ =6

Design and optical performance of CPC based compound plane concentrators
Renewable Energy, 2016CoAuthors: Feng Tang, Runsheng TangAbstract:To simplify the fabrication of compound parabolic concentrators (CPC) with a onesided flat absorber and make solar radiation on the absorber more uniform, an attempt is made here to use multiple plane mirrors in place of parabolic reflectors to construct a compound plane concentrator (CPCA, in short). The design procedure of such concentrator as an alternative to CPCs is presented based on the edgeray principle, and its optical performance and design optimization are theoretically investigated. Analysis shows that the effective Acceptance Half–Angle (θea) of CPCA, dependent on plane mirror’s number (N) and geometry of CPC based on which CPCA is designed, is always less than the Acceptance Half–Angle (θa) of CPC but gradually close to θa with the increase of N, and the optical efficiency of both CPCA and CPC is almost identical for solar radiation withinθea. Results revealed that the annual collectible radiation of CPCA oriented in the eastwest direction is almost identical to that of CPC only if the sun is kept withinθea for at least 7 h in all day of a year by periodically adjusting its tiltAngle. A further analysis indicates that CPCA designed based on the edgeray principle is not an optimal design but can be regarded as optimal geometry for maximizing its annual radiation collection.
Z. Hacker – One of the best experts on this subject based on the ideXlab platform.

Comparison of the optics of nontracking and novel types of tracking solar thermal collectors for process heat applications up to 300 °C
Solar Energy, 2003CoAuthors: C. Grass, W. Schoelkopf, L. Staudacher, Z. HackerAbstract:Abstract Evacuated CPC (compound parabolic concentrator) collectors with nontracking reflectors are compared with two novel tracking collectors: a parabolic trough and an evacuated tube collector with integrated tracking reflector. Nontracking low concentrating CPC collectors are mostly mounted in east–west direction with a latitude dependent slope Angle. They are suitable at most for working temperatures up to 200–250 °C. We present a tracking evacuated tubecollector with a troughlike concentrating mirror. Singleaxis tracking of the mirror is realized with a magnetic mechanism. The mirror is mounted inside the evacuated tube and hence protected from environmental influences. One axis tracking in combination with a small Acceptance Angle allows for higher concentration as compared to nontracking concentrating collectors. Raytracing analysis shows a Half Acceptance Angle of about 5.7° at geometrical concentration ratio of 3.2. Losses of well constructed evacuated tube collectors (heat conductivity through the manifolds inside the thermally insulated terminating housing are low) are dominated by radiation losses of the absorber. Hence, reducing the absorber size can lead to higher efficiencies at high operating temperature levels. With the presented collector we aim for operating temperatures up to 350 °C. At temperatures of 300 °C we expect with antireflective coating of the glass tube and a selective absorber coating efficiencies of 0.65. This allows for application in industrial process heat generation, high efficient solar cooling and power generation. A first prototype, equipped with a standard glass tube and a black paint absorber coating, was tested at ZAE Bayern. The optical efficiency was measured to be 0.71. This tubecollector is compared by raytracing with nontracking market available tubecollectors with geometrical concentration ratios up to 1.1 and with a low cost parabolic trough collector of Industrial Solar Technology (IST) with an Acceptance Half Angle about 1.5°, a geometrical concentration ratio of 14.4 and a measured optical efficiency of 0.69.
Nianyong Liu – One of the best experts on this subject based on the ideXlab platform.

Performance comparison of CPCs with and without exit Angle restriction for concentrating radiation on solar cells
Applied Energy, 2015CoAuthors: Nianyong Liu, Runsheng TangAbstract:Abstract To perform this comparison, the compound parabolic concentrator with a restricted exit Angle of 65° (CPC65) and the one without exit Angle restriction (CPC90) were fabricated and tested for concentrating radiation on multicrystalline solar cells. Both CPC65 and CPC90 are identical in the Acceptance Half–Angle (20°) and geometrical concentration factor (2×). Theoretical calculations showed that CPC90 based PV system (CPV90) annually concentrated about 3–5% more radiation on solar cells as compared to CPC65 based PV system (CPV65). For CPV65, all radiation would arrive on the solar cells at the incidence Angle less than 65°, but for CPV90, about 8–10% of annual collectible radiation would arrive on solar cells at the incidence Angle larger than 65°. Measurements at outdoor conditions showed that the CPV65 performed slightly better than CPV90 in terms of shortcircuit current and power output as the projection incidence Angle of solar rays on the crosssection of CPCtroughs (θp) less than the Acceptance Half–Angle, otherwise the CPV90 did better. Compared to CPV90, the power output at maximum power points from CPV65 were slightly higher, and increases of 2.1%, 5.4% and 8.17% were measured for θp = 0°, 10° and 16°, respectively. Analysis indicated that effect of solar flux distribution over solar cells on power output of both CPVs was almost identical and insignificant, and the CPV65 performed slightly but insignificantly better than the CPV90 in terms of annual power output except in areas with poor solar resources where the annual power output from both systems was almost identical.

Optical performance of CPCs for concentrating solar radiation on flat receivers with a restricted incidence Angle
Renewable Energy, 2014CoAuthors: Nianyong Liu, Runsheng TangAbstract:In some applications of compound parabolic concentrators (CPCs), the incidence Angle of solar rays on the absorber is restricted and must be less than a specified value (θe) for efficient energy conversion or transfer. For a flat receiver with a restricted incidence Angle (RWARIA, in short), two ideal concentrators designed based on onesided flat absorber can be employed for radiation concentration: one is the CPC without exit Angle restriction (CPC1), and another is the CPC with a restricted exit Angle (CPC2). In this work, the angular dependence of optical efficiency factor of both CPC1 and CPC2 for concentrating radiation on the RWARIA was derived, and a mathematical procedure to estimate daily radiation accepted by the RWARIA by using eastwest oriented CPC1 and CPC2 was suggested based on the solar geometry and monthly horizontal radiation. Results by numerical calculations show that, for fixed full CPC1 and CPC2 with identical Acceptance Half–Angle (θa), the CPC2 is slightly more efficient than CPC1 for concentration radiation on the RWARIA except periods of about 30 days before and after both equinoxes; whereas for fixed truncated CPC1 and CPC2 with identical geometric concentration factor (Ct) and θa, the CPC2 is always more efficient. Results also indicate that, for the case of the tiltAngle of the aperture of CPCs being yearly adjusted four times at three tilts, full CPC2 is less but truncated CPC2 is more efficient than CPC1 for concentrating radiation. In practical applications, CPCs are usually truncated due to less efficient of top portion of a CPC reflector for radiation concentration and less reflector material use, therefore, the CPC2 is more favorable and advisable for concentrating radiation on the RWARIA.