Two-dimensional Compound Parabolic Concentrator Research Articles

Multirod approach to enhance solar-to-laser conversion efficiency in the Odeillo solar furnace

A multirod solar laser station for the megawatt solar furnace (MWSF) in Odeillo, France, was conceptualized and numerically studied to improve the solar-to-laser power conversion efficiency. 18 heliostats from the 63-heliostat field were selected, and 347 kW of solar power was obtained at its focus. From there, a two-dimensional compound parabolic concentrator further concentrated and redistributed the solar rays toward 11 core-doped Nd:YAG rods, each fixed inside a fused silica flow tube. 11.40 kW of total multimode laser power was calculated, corresponding to a 3.29% solar-to-laser power conversion efficiency. This efficiency value represents an enhancement of 1.70 and 1.26 times over that attained from single-rod solar laser systems in side-pumping configuration tested in Odeillo, France, in which Nd:YAG rods were codoped with Cr3 + and Ce3 + ions, respectively. It was also 1.44 times higher than that obtained by a previously proposed side-pumping scheme with a solar flux homogenizer and 12 Nd:YAG rods for the same MWSF.

Design of a multibeam solar laser station for a megawatt solar furnace

A multirod solar side-pumping concept is proposed to study the feasibility of multirod/multibeam laser systems in large-sized solar furnaces. This scheme was based on the one-megawatt solar furnace (MWSF) in Odeillo, France, which collected and concentrated solar rays into an input face of a solar homogenizer placed at the focal zone. At its output face, 12 laser heads were positioned, each of which was composed of a two-dimensional compound parabolic concentrator that focused the uniform solar radiation from the homogenizer’s output to an Nd:YAG rod mounted inside a fused silica flow tube. Each laser rod was pumped by one-twelfth of the total concentrated solar power transmitted through the homogenizer, ensuring a good thermal performance under highly concentrated solar power. A 22.84-kW total multimode solar laser power, corresponding to 12.48-W / m2 collection efficiency and 2.28% solar-to-laser power conversion efficiency, was numerically determined. The latter represents an enhancement of 1.75 times over the previous numerically calculated value for a multirod/multibeam laser scheme based on another one-MWSF near Tashkent, Uzbekistan.

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 a Thermosiphon Solar Water Heater Based on a Compound Parabolic Concentrator (CPC) of Revolutions: Initial Tests

This research represents the initial steps in the development of a thermosiphon water heater based on the application of the compound parabolic concentrator (CPC) of revolutions. This application is based on the higher optical performance that the CPC presents in three dimensions compared to the two-dimensional CPC [1]. The article describes the construction and preliminary thermal testing of this model.

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.

Annular Compound Parabolic Concentrator

The annular compound parabolic concentrator (CPC) is a body of revolution consisting of two axisymmetric surfaces produced by rotating a classical two-dimensional CPC around an axis parallel to the CPCs axis. Its ability to further concentrate incoming radiation when used in tandem with a primary solar parabolic concentrator is analyzed by the Monte Carlo ray-tracing technique. Potential applications are found in capturing the annular portion of primary concentrated solar radiation and augmenting its power flux intensity.

A solar-pumped Nd:YAG laser in the high collection efficiency regime

Solar-pumped lasers can be used for space and terrestrial applications. We report on solar side-pumped Nd:YAG laser experiments, which included comprehensive beam quality measurements and demonstrated record collection efficiency and day long operation. A 6.75 m 2 segmented primary mirror was mounted on a commercial two-axis positioner and focused the solar radiation towards a stationary non-imaging-optics secondary concentrator, which illuminated a Nd:YAG laser rod. Solar side-pumped laser experiments were conducted in both the low and the high pumping density regimes. The low density system was composed of a 89 × 98-mm 2 aperture two-dimensional compound parabolic concentrator (CPC) and a 10-mm diameter 130-mm long Nd:YAG laser rod. The laser emitted up to 46 W and operated continuously for 5 h. The high density system was composed of a three-dimensional CPC with 98 mm entrance diameter and 24 mm exit diameter, followed by a two-dimensional CPC with a rectangular 24 × 33 mm 2 aperture. It pumped a 6-mm diameter 72 mm long Nd:YAG laser rod, which emitted up to 45 W. The results constitute a record collection efficiency of 6.7 W/m 2 of primary mirror. We compare the current results to previous solar side-pumped laser experiments, including experiments at higher pumping density but with low collection efficiency. Finally, we present a scaled up design for a 400 W laser pumped by a solar collection area of 60 m 2, incorporating simultaneously high collection efficiency and high pumping density.

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%.

Yearly distributed insolation model and optimum design of a two dimensional compound parabolic concentrator

Optimum acceptance angle of a compound parabolic concentrator (CPC) is studied by the use of an insolation model proposed in this paper. The insolation consists of two components; diffuse and direct. The direct radiation is supposed to be distributed in the field within ±23.5° of declination on the celestial hemisphere and the diffuse radiation is assumed to have uniform irradiance. This yearly insolation model suggests that the optimum half-acceptance angle at the two-dimensional CPC becomes 26° irrespective of the change of the diffuse radiation fraction. This result leads us to the conclusion that, almost all over the world, a common CPC could be used as an optimum concentration for many solar radiation collecting systems.

Analysis of the incidence angle of the beam radiation on CPC

Analytic expressions have been derived for the projected incidence angles ϑ l and ϑ t from a two-dimensional compound parabolic concentrator solar collector. For a CPC the fraction of the incident rays on the aperture at angle ϑ, which reaches the absorber, depends only on the ϑ l angle. In this paper, a mathematical expression for ϑ l and ϑ t has been calculated to determine the times at which acceptance of the sun's beam radiation begins and ceases for a CPC consisting of arbitrary orientation.

Truncation of CPC solar collectors and its effect on energy collection

Analytic expressions are derived for the angular acceptance function of two-dimensional compound parabolic concentrator solar collectors (CPC's) of arbitrary degree of truncation. Taking into account the effect of truncation on both optical and thermal losses in real collectors, we also evaluate the increase in monthly and yearly collectible energy. Prior analyses that have ignored the correct behavior of the angular acceptance function at large angles for truncated collectors are shown to be in error by 0–2% in calculations of yearly collectible energy for stationary collectors.