KR100696283B1 - Concentration Enhanced Collector Designs that provide Uniform Energy Distribution on the Receiver Surface - Google Patents

Abstract

The present invention focuses sunlight using a reflector and the focused light is distributed on the light receiving surface with a uniform density, and at the acceptance angle defined by the Compound Parabolic Concentrator (CPC) reaching a thermodynamic limit. The present invention relates to a high-concentration light receiving density uniformity composite parabolic focusing device formed by extending a constitution surface of an original CPC (first stage) by increasing a limited concentration ratio by a 2nd stage CPC concept.

The high light receiving density uniforming composite parabolic focusing device according to the present invention uses a conventional light receiving density uniforming CPC focusing device as a first step CPC focusing device, and a second step CPC focusing device continuously under the two reflectors of the first step CPC focusing device. It extends to the position of the light-receiving surface is lowered so that the end light beam incident at the incident limit angle is reflected on the reflective surface once more to be received by the light-receiving surface.

Description

Concentration Enhanced Collector Designs that provide Uniform Energy Distribution on the Receiver Surface}

1 is a cross-sectional view of a parabolic structure and geometrical description of general optical properties

2 is a geometric cross-sectional view of the formed basic CPC collector

3 is an explanatory diagram of optical characteristics of a basic CPC

4 is a diagram illustrating an implementation process of an optical focusing device for uniforming light density on a light receiving surface

5 is an explanatory diagram of an implementation of a light density uniforming focusing device according to the present invention;

6 is an energy distribution diagram at the light receiving surface of the basic CPC device;

7 is an energy density distribution diagram of an energy uniformized high focusing device;

**** Description of the major symbols in the drawings ****

A, A ', B: Disadvantages of opening surface of CPC focusing device

F, F ', F: Parabolic focal point

J, J ': One point of the reflecting surface, the point where the end ray meets the reflecting surface

K, K ': lower end point of CPC reflecting surface

s, s': travel distance of the reflecting surface (left)

C, C ', C1, C2: Focus ratio

FF ': Width or exit surface of light receiving surface (heat absorbing surface) of CPC type focusing device

JJ ': Virtual light receiving surface (outlet surface) of the first stage focuser

KK '': Light receiving surface (outlet surface) of deformed CPC device

α is the incident limit half angle of the basic CPC device

(ρ, φ): Polar coordinate system of parabola

(x ', z'): Coordinate system of circular parabola

(x, z): Coordinate system of CPC type focusing device

The present invention provides an improved 1st stage light receiving density uniformity to solve the problems caused by uneven distribution of light density on the light receiving surface (or endothermic surface) of the basic composite parabolic surface (CPC) focusing apparatus for focusing sunlight. In order to increase the reduced focusing ratio of the composite parabolic surface (CPC) focusing device and the first stage device, a second stage CPC focusing device is formed by continuously extending the (lower) curved surface of the first stage CPC device. The present invention relates to an improved high-density ratio light receiving density uniformed composite parabolic surface (MCPC) focusing apparatus, which is formed by forming a pair of reflecting mirrors having a structure symmetrical with each other.

The solar focusing device using the compound parabolic plane (hereinafter referred to as CPC) increases the output of converting into electricity by increasing the density of solar energy reaching the light-receiving surface by the focusing ratio of the device, especially in the photovoltaic device. It is a useful device to reduce the

The basic CPC focusing device has been proven to be the ideal focusing device to reach the thermodynamic limits as an energy focusing device and allows the maximum incidence limit angle of any device for a given focusing ratio for solar-powered devices. Therefore, CPC has been applied to various applications (US Patent No. US 4,003,638, US Patent No. US 4,002,499, etc.).

In general, if the energy density reaching the light-receiving surface is not uniform for all incident angles, the efficiency of the device is reduced (see FIG. 6).

In particular, when the CPC device is used with a solar cell, a special problem occurs, i.e., the solar cell is locally irradiated, causing a shadow phenomenon, in which case the conversion efficiency is degraded or, in extreme cases, the sun Due to the unbalanced distribution of heat generated in the cell, thermal tension can occur and the solar cell can be damaged. (If the light-receiving surface is an endothermic surface, the endothermic surface is locally inefficiently heated and uniformly distributed.) That is, if a single solar cell is irradiated unevenly, the temperature and current of the cell are unevenly distributed as a result. Non-uniform irradiation affects the energy conversion efficiency and also results in a decrease in open voltage. Opening voltage and efficiency are significantly reduced as the irradiation contour is locally concentrated.

If a part of the PV cells constituting the module is partially or partially shaded, damaged, or if each cell constituting the module is not electrically matched with each other, the hot spots on the cell spots occur. This phenomenon causes thermal stress of the cell or module, and the voltage of the shaded cell can be reversed depending on the solar cell's power generation circuit, load, and shade level, dissipating power in the form of heat. Loss of a cell increases the temperature of the cell, causing overheating and damaging the cell. In addition, if high-density solar energy is concentrated on a part of the cell, the temperature of the cell may be locally increased, and the cell may be damaged. The performance loss of the shaded module is reduced in proportion to the loss of the shaded battery most. It also depends on the life of the module.

Applicant proposed a solution to the non-uniformity of the energy density distributed on the light receiving surface in the Korean Application No. 10-2004-44638 (application date 2004. 06.16), "light receiving density homogenous composite parabolic surface (CPC) focusing device" The model principle of the proposal described in the present invention is the focus of the focusing device (F, F) on the basic composite parabolic surface (CPC, see FIG. The light receiving surface (KK ') is placed in the middle of the light path gathered at the') area, and the reflected light is distributed on the surface of the light receiving surface (KK ') of the same size with a uniform density to the light receiving surface (KK'). This paper proposes a compound parabolic (CPC) solar energy concentrator with uniform light receiving density that increases efficiency, increases economic efficiency and extends life by increasing the electrical conversion efficiency (or temperature of endothermic surface) of installed solar cells.

However, the present invention has a disadvantage in that a substantially uniform energy density is distributed on the light-receiving surface as compared to the basic CPC apparatus, and the incident limit angle is maintained for a given focusing ratio, but the output ratio is reduced since the focusing ratio is smaller than that of the basic CPC.

An object of the present invention is to solve the problems caused by the non-uniform distribution by uniform distribution of light density in the light converging device using the above-described CPC, and to uniformize the "receiving density" It is characterized by a reflection curve that forms a pair of concentrators in which the output ratio is reduced by reducing the focusing ratio of the compound parabolic surface (CPC) focusing apparatus "(Domestic Application No. 10-2004-44638).

The present invention is a light-receiving surface of the composite parabolic surface (CPC) focusing device to focus the sunlight of the domestic application No. 10-2004-44638 (application date 2004. 06.16), "receiving density uniformized composite parabolic surface (CPC) focusing device" 2nd step (2nd) to increase the focusing ratio in the 1st stage light receiving density uniformity compound parabolic (CPC) focusing device, which is improved to solve the problem caused by the uneven distribution of light density on the (or endothermic surface). the CPC focusing device of the stage) is continuously extended to the lower end of the reflector of the CPC device of the first step to lower the position of the light-receiving surface so that the end-ray beam incident at the incident limit angle α is reflected once more on the reflecting surface. It is characterized in that it is formed to receive light on the light receiving surface to focus the collected light to increase the light receiving density.

The high-concentration light-receiving-density equalization device according to the present invention is a modification of the shape of the basic CPC, and when the focal point F is the origin of the coordinate system ρ, φ, the cross section shown in FIG. Focal length f is a relational expression

ρ = 2f / (1-cosφ) (1)

It consists of a light receiving surface (FF '= 2a') formed by connecting the right and left reflectors and the lower ends of the two reflectors satisfying the

The focal points F and F 'of the respective reflectors are formed at the lower end points of the opposite reflectors, and the axes of the reflectors are formed at an angle of ± α (incident limit half angle) opposite to each other with respect to the respective focal points, and the focusing ratio (C ') and focal length (f) are relational expressions

C '= 1 / sinα (2)

f = a '(1 + sinα) (3)

By improving the default CPC (Compund Parabolic Concentrator),

Relational expression for the selected limiting half-angle α

cosφ _{K '} = [1-2 (1 + sinα) * sinα] cosα + (1 + sinα) * (1-2sinα) Of

(cosα + sinα + 1) * (1-2sinα)²(4)

Determine the position of the point K 'determined by the value of the angle φ _K' satisfying

In determining the position of the point K which meets the line K'K and the line BF parallel to the device's abscissa (x-axis) at the point K ',

The left reflector AF is moved to the right along the device's transverse axis (x-axis) to the point where it meets point K. At the bottom of the right reflector BF as the left reflector AF moves to the right by s. The existing focus F 'is moved to the same distance at point F ",

In this state, the lower end of each reflector is cut with a line KK '(= 2a') to form a light receiving surface, and both ends of the light receiving surface are located apart from each focus of the left and right reflectors, and the received light density is uniformly distributed. The collector is formed. (See Fig. 4)

In the process of forming the concentrator, the structure of the reflector is the incident limit half angle (-α) and the light beam BF from the upper end point B of the right reflector to the focal point F of the right reflector is

* If you move the left reflection surface to reflect at one point J of the left reflection surface

* The reflected beam is directed towards the focal point F ", which is shifted the same distance as the left reflection surface.

* This beam (JF ") also meets at the bottom point K 'of the right reflective surface

* The length of the line segment KK 'formed by the line connecting the point K where the line parallel to the horizontal axis (x axis) meets the left reflection surface at the point K' is the width of the original light receiving surface (KK '= 2a')) With the position becoming equal

When formed by moving the left reflective surface by distance s'

* Width (2a ") of virtual light-receiving surface JJ 'is selected

f = a "(1 + sinα) (5)

To form a parabolic reflector characterized by a focal length f that satisfies

* A focusing device consists of a pair of parabolic mirrors that are symmetrical to each other.

The distribution of light density in the light receiving surface of the structure thus formed is formed in a pattern as shown in FIG. 7 in the virtual light receiving surface JJ 'and the light receiving surface KK'.

The focusing ratio is defined as C1 = A'B / JJ '> 1 for the first stage device, and the second stage device is defined as C2 = JJ' / FF '> 1, and the final focusing ratio (C) of the entire device is C = A'B / FF ', which is also expressed as the product of the focal ratios of the first and second stages. In other words

C = C1 * C2 = (A'B / JJ ') * (JJ' / FF ') = A'B / FF' (6)

Relationship is established.

In the selected CPC focusing device, the point J 'is calculated by the following relation in the parabola satisfying the relation (5).

cosφ _{J '} = [1-2 (1 + sinα) * sinα] cosα + (1 + sinα) * (1-2sinα) Of

(cosα + sinα + 1) * (1-2sinα)²(7)

The coordinate of point K '

ρ = 2f / (1-cosψ) (8)

Φ is in the range of 2α ≦ ψ ≦ π + α.

The final focusing ratio C by the above structure of the present invention is increased than the focusing ratio Ccpc of the basic CPC for a given incident limit half angle α.

Similar results can be obtained by replacing the reflector paraboloid cited in the present invention with an ellipsoid.

Alternatively, the first stage reflective surface may be composed of a parabolic surface, and the second stage parabolic surface may be a spherical surface, an elliptical surface, or a hyperbolic surface. In this case, the two curved surfaces should be connected at the junction J (or J ') continuously. That is, the slopes of each curved surface at the junction point J (or J ') must be equal.

Ordinary cone curves (circles, ellipses, parabolas, hyperbolas) are coordinate systems with the focal point as the origin.

in [(x ', z') or (ρ, φ)]

x ' ² + z' ² = e ² (d + z ') ² (9)

or

ρ = de / (1-e cosφ) (10)

Where d is the distance between the focal point and the directrix, e is the eccentricity, the parabola is e = 1, the ellipse is e <1, and the hyperbola is e> 1. Has a value.

The position of the point K '(x _k , z _k ) corresponding to the right end point of the light receiving surface is

x _{k '} = ρ _k' sin (φ _{k '} -α) (11)

z _{k '} = ρ _k' cos (φ _{k '} -α) (12)

It can be obtained from the relation of.

The present invention mitigates the shading of the light receiving surface (heat absorbing surface) due to the focusing of the solar energy collected at the focal point in the design of the conventional basic CPC, and at the same time reduces the high temperature phenomenon due to the energy focused on a part. It also increases the efficiency of the device (light-receiving or endothermic) due to the solar energy density distributed substantially uniformly at the exit surface of the device.

At the same time, the distribution of uniform light receiving density with increased focusing ratio than the basic CPC device can maximize the efficiency of the most ideal CPC type device in certain applications.

The focusing apparatus can reduce the area of the solar cell by the focusing ratio, thereby reducing the unit cost of the apparatus by reducing the use area of the solar cell, and also preserving the life of the solar cell with a uniform energy distribution.

Claims (3)

The cross section is parabolic, and the parabolic trajectory satisfies ρ = 2f / (1-cosφ) and the focal length f connects the right and left reflectors and the bottom of the two reflectors to satisfy f = a '(1 + sinα). Formed by a light-receiving surface having a 'width, Focus (F, F ') of each reflector is formed at the lower end of the reflecting mirror, In the basic CPC where the angle between the lines AF 'and BF connecting the focal point F and F' and the z axis and the z-axis is incident angle of ± α, Relational expression for the selected limiting half-angle α cosφ _{K '} = [1-2 (1 + sinα) * sinα] cosα + (1 + sinα) * (1-2sinα) / (cosα + sinα + 1) * (1-2sinα) ² Determine the position of the point K 'determined by the value of the angle φ _K'' satisfying Determine the location of the point K where the point K 'meets the line K'K parallel to the device's transverse axis (x-axis) and the line BF, The left first reflector AF is moved to the right by the distance s along the transverse axis (x-axis) of the device to the point where it meets point K. As the left reflector AF is moved to the right by s, the right reflector AF The bottom focus (F) is moved to point F ", In this state, the lower end of each reflecting mirror is cut by the line KK 'to form a light receiving surface, so that both ends of the light receiving surface are spaced apart from each focus of the left and right reflectors, so that the received light density is uniformly distributed. In density uniformizing CPC focusing apparatus, The light receiving density uniforming CPC focusing device is the first step CPC focusing device, and the second step CPC focusing device is continuously formed at the lower ends of the two reflectors of the first step CPC focusing device to lower the position of the light receiving surface to lower the incident angle ( High concentration and uniformity of light receiving density collected by collecting the end ray of light incident on α) once more from the reflecting surface to be received on the receiving surface According to claim 1, wherein the two reflecting mirrors of the second focusing device extending from the lower end of the first focusing device, the reflecting surface extends to the same curved surface as the reflecting surface of the first stage, the cross-section is parabolic The parabolic trajectory consists of the right and left reflectors satisfying ρ = 2f / (1-cosφ) and the light receiving surface formed by connecting the lower ends of the two reflectors. Focus (F, F ') of each reflector is formed at the lower end of the reflecting mirror, Right reflector (BF) of the basic CPC whose angle of incidence is α between the lines AF 'and BF connecting the focal point F and F' to the inlet-side ends A and B of the sunlight and the z axis. The light beam JF 'traveling from the upper end point B of') toward the focal point F of the right reflector reflects at one point J of the left reflector AF and proceeds toward the focal point F 'of the left reflector with the right reflecting surface. At the point K ', where the point is parallel to the device's abscissa (x-axis) and plots the position of point J' where cosφ _{J '} = [1-2 (1 + sinα) * sinα] cosα + (1 + sinα) * (1-2sinα) / (cosα + sinα + 1) * (1-2sinα) ² Determine the position of the point J 'determined by the value of the angle φ _J' satisfying At point K ', select the point K where the line drawn parallel to the abscissa meets the left reflector. Move the left reflector to the right along the horizontal axis so that the length between two points K and K 'is equal to the width of the selected light-receiving surface (KK' = a "), where the width of the virtual light-receiving surface (JJ '= a' ) Selects the focal length f that satisfies the relation f = a '(1 + sinα), and it is characterized by two paraboloids (AK, BK'). In this state, the lower part of each reflector is the line K, K The light receiving surface is cut to form a light receiving surface, and both ends of the light receiving surface are spaced apart from each focal point of the left and right reflecting mirrors so that the received light density is uniformly distributed and at the same time the focusing ratio of the focusing device (= A'B / KK '). = a / a ") is a high focusing, light-density uniformity focusing device which allows the same characteristic to be increased than the basic CPC. According to claim 1, wherein the two reflectors of the second stage focusing apparatus extending from the bottom of the first stage focusing apparatus has a reflecting surface is a two-dimensional curved surface (circle, ellipsoidal, hyperbolic surface) or polynomial curved surface (Cardioid, or multidimensional polynomial) A high focusing, light receiving density homogenizing device which is formed continuously along the original reflector formation trajectory at the lower end of the first stage focusing device to increase the light receiving density or increase the focusing ratio.

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