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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 concentratorsSolar Energy, 2018Co-Authors: Guihua Li, Jingjing Tang, Runsheng TangAbstract:
Abstract In this communication, three-dimensional 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 east-west direction is addressed. The analysis shows that, the projected incident and refractive Angles of solar rays on the cross-section of DCPC are not subjected to the correlation as Snell law except for incident rays on the cross-section, 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 (DCPC-θa/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 tilt-Angle adjustment in a year. Calculations show that, the minimum θa of DCPC depends on tc and strategy of tilt-Angle 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 tilt-Angle 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, 2016Co-Authors: Runsheng Tang, Chaofeng XiaAbstract:
Abstract. In this work, irradiation distribution on the base of ideal two-dimensional CPCs with and without a restricted exit Angle, to which solar cells are attached, are analyzed by the ray-tracing technique. Results show that, given an Acceptance Half–Angle ( a θ), for CPCs without a restricted exit Angle (CPC-1), radiation flux distribution on the base depends on the incidence Angle of solar rays (θ); whereas for CPCs with a restricted exit Angle (CPC-2), the flux distribution depends on θ and the restricted exit Angle ( e θ). For both CPC-1 and 2 with identical geometric concentration factor (Ct=2) and Acceptance Half–Angle ( aθ =20), the peak flux concentration ratio on the base of CPC-2 with e θ =6
Design and optical performance of CPC based compound plane concentratorsRenewable Energy, 2016Co-Authors: Feng Tang, Runsheng TangAbstract:
To simplify the fabrication of compound parabolic concentrators (CPC) with a one-sided 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 (CPC-A, in short). The design procedure of such concentrator as an alternative to CPCs is presented based on the edge-ray principle, and its optical performance and design optimization are theoretically investigated. Analysis shows that the effective Acceptance Half–Angle (θea) of CPC-A, dependent on plane mirror’s number (N) and geometry of CPC based on which CPC-A 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 CPC-A and CPC is almost identical for solar radiation withinθea. Results revealed that the annual collectible radiation of CPC-A oriented in the east-west 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 tilt-Angle. A further analysis indicates that CPC-A designed based on the edge-ray 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 non-tracking and novel types of tracking solar thermal collectors for process heat applications up to 300 °CSolar Energy, 2003Co-Authors: C. Grass, W. Schoelkopf, L. Staudacher, Z. HackerAbstract:
Abstract Evacuated CPC (compound parabolic concentrator) collectors with non-tracking reflectors are compared with two novel tracking collectors: a parabolic trough and an evacuated tube collector with integrated tracking reflector. Non-tracking 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 tube-collector with a trough-like concentrating mirror. Single-axis 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 non-tracking concentrating collectors. Ray-tracing 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 anti-reflective 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 tube-collector is compared by ray-tracing with non-tracking market available tube-collectors 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 cellsApplied Energy, 2015Co-Authors: Nianyong Liu, Runsheng TangAbstract:
Abstract To perform this comparison, the compound parabolic concentrator with a restricted exit Angle of 65° (CPC-65) and the one without exit Angle restriction (CPC-90) were fabricated and tested for concentrating radiation on multi-crystalline solar cells. Both CPC-65 and CPC-90 are identical in the Acceptance Half–Angle (20°) and geometrical concentration factor (2×). Theoretical calculations showed that CPC-90 based PV system (CPV-90) annually concentrated about 3–5% more radiation on solar cells as compared to CPC-65 based PV system (CPV-65). For CPV-65, all radiation would arrive on the solar cells at the incidence Angle less than 65°, but for CPV-90, 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 CPV-65 performed slightly better than CPV-90 in terms of short-circuit current and power output as the projection incidence Angle of solar rays on the cross-section of CPC-troughs (θp) less than the Acceptance Half–Angle, otherwise the CPV-90 did better. Compared to CPV-90, the power output at maximum power points from CPV-65 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 CPV-65 performed slightly but insignificantly better than the CPV-90 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 AngleRenewable Energy, 2014Co-Authors: 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 one-sided flat absorber can be employed for radiation concentration: one is the CPC without exit Angle restriction (CPC-1), and another is the CPC with a restricted exit Angle (CPC-2). In this work, the angular dependence of optical efficiency factor of both CPC-1 and CPC-2 for concentrating radiation on the RWARIA was derived, and a mathematical procedure to estimate daily radiation accepted by the RWARIA by using east-west oriented CPC-1 and CPC-2 was suggested based on the solar geometry and monthly horizontal radiation. Results by numerical calculations show that, for fixed full CPC-1 and CPC-2 with identical Acceptance Half–Angle (θa), the CPC-2 is slightly more efficient than CPC-1 for concentration radiation on the RWARIA except periods of about 30 days before and after both equinoxes; whereas for fixed truncated CPC-1 and CPC-2 with identical geometric concentration factor (Ct) and θa, the CPC-2 is always more efficient. Results also indicate that, for the case of the tilt-Angle of the aperture of CPCs being yearly adjusted four times at three tilts, full CPC-2 is less but truncated CPC-2 is more efficient than CPC-1 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 CPC-2 is more favorable and advisable for concentrating radiation on the RWARIA.