Inflatable divergent Fresnel lens and non-imaging concentrator based non-tracking solar concentrator

Abstract

An inflatable divergent Fresnel lens and non-imaging CPC based non-tracking high concentration ratio solar concentrator system comprises a flexible domed divergent Fresnel lens, and an inflatable non-imaging CPC concentrator with a domed transparent top cover and a flat transparent bottom cover. Where, the flexible domed divergent Fresnel lens is attached onto the said domed transparent cover of the said inflatable non-imaging CPC concentrator. When in operation, the oblique incident sunlight including beam light and diffuse light onto the domed divergent Fresnel lens, is deflected to change its direction, and consequently change its original incident angle relative to the said CPC concentrator from large to small, then eventually fall in the acceptance half-angle to be concentrated by the said CPC in large concentration ratio.

Claims

1. An inflatable divergent Fresnel lens and non-imaging CPC based non-tracking high concentration ratio solar concentrator system comprises a flexible domed divergent Fresnel lens, and an inflatable non-imaging CPC concentrator with a domed transparent top cover and a flat transparent bottom cover, the flexible domed divergent Fresnel lens is attached onto the domed transparent cover of the inflatable non-imaging CPC concentrator; wherein, when sunlight including beam light and diffuse light obliquely incident onto the domed divergent Fresnel lens, the oblique incident sunlight is deflected to change its direction, and consequently change its original incident angle relative to the CPC concentrator from large to small, then eventually falls in the acceptance half-angle of the CPC concentrator and to be concentrated by the CPC concentrator in large concentration ratio; wherein the flexible domed divergent Fresnel lens has a series of prisms with different sizes and apexes.

2. The inflatable divergent Fresnel lens and non-imaging CPC based non-tracking high concentration ratio solar concentrator system of claim 1, wherein the flexible divergent Fresnel lens is made of clear transparent materials such as silicon rubber, so that when it is attached onto the domed transparent cover of the inflatable non-imaging CPC concentrator, it will become into a domed divergent Fresnel lens.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

(2) FIG. 1 is the prior art of CPC indicated in a schematic drawing on construction of the CPC concentrator, which introduces some key concepts such as acceptance half-angle θ.sub.c, focus of each of the parabolas, concentrator aperture, receiver, and axis of parabola.

(3) FIG. 2 is the prior art of the truncated CPC with the labels of the concentrator structure variables.

(4) FIG. 3 is the schematic drawing illustrating the work principles of CPC concentrating both the beam light and the diffuse light.

(5) FIG. 4 is a schematic drawing of the inflatable non-imaging concentrator indicating the assembly of two clear membranes and a reflective membrane inflated into a CPC with a domed transparent cover on its top and a transparent cover at its bottom.

(6) FIG. 5 is a schematic drawing of the concentrating photovoltaic system with a photovoltaic receiver sealed into the inflatable non-imaging concentrator.

(7) FIG. 6 is a schematic drawing of the concentrating solar thermal system with a heat exchanger sealed into the inflatable non-imaging concentrator.

(8) FIG. 7 is the geometric diagram showing the refraction mechanism that changes the direction of the incident light through the domed divergent Fresnel lens during a diurnal day.

(9) FIG. 8 is the over view of the first stage of the divergent Fresnel lens and CPC based concentrating system.

(10) FIG. 9 is the cross-sectional view of the first stage of the divergent Fresnel lens and CPC based concentrating system.

(11) FIG. 10 is the schematic explanation on the general work principle of the divergent Fresnel lens and CPC based non-tracking non-imaging concentrating system with high concentration ratio.

DETAILED DESCRIPTION

(12) Reference will now be made in detail to the present exemplary embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

(13) Referring to FIG. 1, the prior art of the basic concepts of CPC is illustrated in the reference (FIG. 7.6.1 of John Duffle & William Beckman, Solar Engineering of Thermal Processes, 4th Edition, 2013, pp 337-344). Each side of the CPC is a parabola; the focuses and axis of parabola are indicated. Each parabola extends until its surface is parallel with the CPC axis. The angle between the axis of the CPC and the line connecting the focus of one of the parabolas with opposite edge of the aperture is the acceptance half-angle θ.sub.c. If the reflector is perfect, any radiation entering the aperture at angles between ±θ.sub.c will be reflected to a receiver at the base of the concentrator by spectacularly reflecting parabolic reflectors.

(14) Referring to FIG. 2, the prior art of the CPC is truncated to reduce its height from h to h′ with a resulting saving in reflector area but little sacrifice in performance. The truncated CPC is illustrated with the labels of structure variables.

(15) $f=a^{\prime }\left(1+\sin {\theta }_c\right)$$a=\frac{a^{\prime }}{\sin {\theta }_c}$$h=\frac{f\cos {\theta }_c}{{\sin }^2{\theta }_c}$$a_T=\frac{f\sin \left({\varphi }_T-{\theta }_c\right)}{{\sin }^2\left({\varphi }_T/2\right)}-a^{\prime }$$h_T=\frac{f\cos \left({\varphi }_T-{\theta }_c\right)}{{\sin }^2\left({\varphi }_T/2\right)}$$C_T=\frac{a_T}{a^{\prime }}$$C=1/\sin {\theta }_c$

(16) As shown in the above formula (FIG. 7.6.3 of John Duffle & William Beckman, Solar Engineering of Thermal Processes, 4th Edition, 2013, pp 337-344), where a′ is the half-size of receiver, f is the focal lengthy of the elemental parabola for CPC, θ.sub.c is acceptance half-angle, a is the half-size of aperture of the CPC, h is the height of CPC, a.sub.T is the half-size of the aperture of truncated CPC, h.sub.T is the height of truncated CPC, Φ.sub.T is the truncation angle, CT and C are concentration ratios of truncated CPC and full CPC respectively, the concentration ratio is a function of the acceptance half-angles and truncation fraction. The smaller the acceptance half-angle, the larger the concentration ratio. The concentration ratio varies from 1 to 11, as the acceptance half-angle varies from 36° to 5°. For acceptance half-angle 6°, as the height-aperture ratio raises from 1 to 3, the concentration ratio changes from about 4.4 to 8.7. However, small acceptance half-angle means small aperture of concentrator and small time interval with no need for tracking. It is contradict to have high concentration ratio and realize daylong stationary concentration for CPC.

(17) Referring to FIG. 3, the CPC is able to concentrate both the beam light I.sub.b and the diffuse light I.sub.d, as long as their incident angles relative to the CPC are smaller than the acceptance half-angle of the CPC.

(18) Referring to FIG. 4, two transparent membranes and one reflective membrane are sealed together into a pre-form. Then the pre-form is inflated into a balloon type CPC 100, with its top covered with a domed transparent cover 200 and its bottom covered with a flat transparent cover 300.

(19) Referring to FIG. 5, a photovoltaic receiver 500 is sealed into the inflatable non-imaging concentrator to form a concentrating photovoltaic system.

(20) Referring to FIG. 6, a heat exchanger 600 is sealed into the inflatable non-imaging concentrator to form a concentrating solar thermal system.

(21) Referring to FIG. 7, in the present invention, a flexible divergent Fresnel lens 400 is added on the domed transparent cover of the inflatable CPC 100 with small acceptance half-angle, so that the oblique incident light is refracted to fall in the small acceptance half-angle. During the diurnal day, the morning light with the original incident angle θ.sub.i relative to the CPC, is refracted by the left-hand side of the domed divergent Fresnel lens, and falls into the CPC with the changed incident angle θ.sub.2, where θ.sub.1>θ.sub.2, θ.sub.1>θ.sub.c, θ.sub.2<θ.sub.c, the afternoon light is refracted by the right-hand side of the domed divergent Fresnel lens, and the noon light is affected little.

(22) Referring to FIG. 8, a flexible divergent Fresnel lens 400 made of clear transparent materials such as silicon rubber is added onto the domed transparent top cover 200 of the inflatable CPC non-imaging concentrator 100. And the domed divergent Fresnel lens and the inflatable CPC non-imaging concentrator form a non-tracking close structure concentrator.

(23) Referring to FIG. 9, the overview of the domed divergent Fresnel lens and CPC based concentrating system is demonstrated in its cross-sectional view. In this design, the domed divergent Fresnel lens 400 only has one layer. It can be designed into multi-layer structure with multiple layers of domed divergent Fresnel lens.

(24) Referring to FIG. 10, the general work principle of the domed divergent Fresnel lens and CPC based non-tracking non-imaging concentrating system is elucidated. The incident light is firstly diverged by the divergent Fresnel lens 400, then is converged by the CPC non-imaging concentrator 100. When the input light obliquely incident, the domed divergent Fresnel lens firstly diverges the light to reduce the incident angles relative to the CPC, then the CPC with small acceptance half-angle concentrates the light in large concentration ratio.

(25) The work principle of the non-tracking concentrator structure is elucidated as the following. As the sun moving from east to west, the sunlight is refracted to change direction by various portion of the domed divergent Fresnel lens surrounding the CPC, so that the refracted sunlight falls into the relatively small acceptance half-angle of the CPC and is concentrated by it. The addition of the domed divergent Fresnel lens to the CPC enlarges the acceptance angle of the CPC, and therefore enables the stationary concentration with high concentration ratio.

(26) From the description above, a number of advantages of the solar concentrator become evident. The inflatable apparatus provides an approach to realize an ultra-light, exclusively cheap, extremely compact solar concentrator. The concentrator is able to concentrate both beam and diffuse light. The addition of the flexible divergent Fresnel lens onto the domed transparent top cover of the inflatable non-imaging CPC concentrator, eliminate the need of tracking system, reduce the cost, and raise the reliability of the concentrating system. The inflatable non-imaging balloon type concentrator has higher tolerance to shape distortion than imaging concentrator. The combination of the inflatable non-imaging balloon type concentrator and the photovoltaic receiver or heat exchanger makes super-light and extremely low cost concentrating photovoltaic system or solar thermal system. The close structure of the concentrator enables the filling of the lighter than air gases helium and hydrogen, and floating in the air.

(27) In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various other modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.

(28) Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.