CN102540496A - Near-field light beam diffraction superposition method of light concentrating photovoltaic system - Google Patents

Abstract

The invention belongs to the field of solar light concentrating photovoltaic power generation, and in particular relates to a near-field light beam diffraction superposition method in a light concentrating photovoltaic power generation system by adopting a sub mirror array (sometimes called as an array lens, a fly's-eye lens or a fly lens), uniform light concentration with matched shapes are formed on a semiconductor solar battery by utilizing optical elements such as a traditional lens, a Fresnel lens, a reflection mirror, a wave band plate (sheet), a cylindrical lens or a cylindrical reflection mirror and an array thereof, so that efficient solar battery utilization and photoelectricity conversion efficiency is achieved. According to the invention, the incoming sunlight is resolved into a plurality of sub light beams in space by adopting the sub mirror array, and through near-field diffraction and transmission, the sub light beams are synthesized into uniform focusing light spots the shape and size of which are matched with the battery through incoherence superposition near the focal point of an convergence optical element, namely the position of the semiconductor solar battery. The near-field light beam diffraction superposition method of the light concentrating photovoltaic system has the advantages that the uniform focusing light spots the shape and size of which are matched with the battery can be realized by utilizing a simple optical system, the light concentration multiple can be regulated flexibly, and the near-field light beam diffraction superposition method of the concentrating photovoltaic system is suitable for a high-multiple concentrating photovoltaic system; and the required box body is small, the cost is low, and the influence by the system position deviation and nonuniform incoming sunlight is small.

Description

Near field beam diffraction stacking method in the concentration photovoltaic system

1. technical field

The invention belongs to the Application of Solar Energy field; Be specifically related at condensation photovoltaic (Concentrating Photovoltaic; CPV) adopt near field beam diffraction stacking method in the electricity generation system; Utilization lens, Fresnel lens, zone plate (sheet), catoptron, cylindrical lens or cylindrical mirror, and optical element such as array forms the uniform condensing that shape and size and semiconductor solar cell mate, to reach solar cell utilization efficiently and electricity conversion.

2. background skill

The tradition concentration photovoltaic system use one or more levels optical system usually, with sunlight on semiconductor solar cell.Because optically focused effect, the area of required semiconductor solar cell can be far smaller than the area of the incident sunshine of total system reception, thereby the material of saving solar cell greatly uses, and reduces the cost of concentration photovoltaic system.On this basis; Three or five (III-V) family many pn junction p ns solar cell (for example present existing gallium arsenide class three pn junction p n battery efficiencies have reached 41%) that can service efficiency is very high, cost is also higher relatively, thus the generating efficiency of concentration photovoltaic system improved.In addition, with respect to single times of solar irradiation, the mode of employing converge sunlight ability can also improve the energy conversion efficiency and the utilization factor of semiconductor solar cell itself.

Consider the cost of wafer cutting, semiconductor concentrating solar battery sheet is generally rectangle or square, but does not also get rid of other special shape.Optical design in the concentration photovoltaic system should make the solar light focusing hot spot of convergence and the shape and size of battery be complementary, and is radiated on the concentrator cell equably.Shape like focal beam spot and battery does not match, and can cause the waste of concentrator cell area or the part focused light spot energy can not be by effective reception; Inhomogeneous like focal beam spot, then can reduce corresponding concentrator cell efficient.

For the even focal beam spot of generation in concentration photovoltaic system and cell shapes and size match, rectangle prism array [list of references 1] is adopted in the optically focused design in a recent U.S. Patent application (application number: US 2008/0041441 A1).The sunshine that the sub-prism of each rectangle in the array all will shine respectively on it evenly is refracted on the rectangular concentrator cell.The size that a limitation of this method is each sub-prism need be followed the big or small similar of concentrator cell; That is to say; Assemble 500 times high power light concentrating photovoltaic system if adopt, this prism array needs 500 sub-prisms, causes the difficulty in the production and processing sharp expensive.Another limitation of the method is that higher numerical aperture can not be arranged, and causes the casing of concentrating photovoltaic assembly thicker.Another U.S. Patent application (application number: US 2007/0251568 A1) discloses an optical imagery convergence system [list of references 2] that similarly adopts sub-lens/sub-reflection mirror array.A limitation of this method is based on how much imaging stacks; Strict object-image relation requires sub-lens/sub-reflection mirror array is placed on 2 times of focal length places before the secondary optical element, causes whole optical system along optical axis direction 3 times of thickness more than the focal length of needs at least.Similar with previous patent, the method also requires the sub-mirror in the array similar with the concentrator cell size, is not suitable for high power light concentrating photovoltaic system equally.

The lens array past attempts is used for laser fusion and x-ray laser, is used for producing uniform laser field [list of references 3].The coherence of laser field is easy to produce the interference that brought by the array edge and strong diffraction, thus array can only be placed on primary mirror near.Main lens and sub-lens are circle lens in this technology, just focus on for uniform line, and sub-lens changes the post lens into.

Lens array also is called as lens-array, fly lens or fly's-eye lens sometimes.

The present invention adopts sub-lens/sub-reflection mirror array, utilizes the near field beam diffraction non-coherent addition method of sunshine to realize having the uniform condensing with the photovoltaic cell similar shape.

3. summary of the invention

The present invention uses array of optical elements such as lens/catoptron; First near field beam diffraction stacking method is used for concentration photovoltaic system, the near-incoherent property of utilizing sunshine is in the hope of obtaining to have (similar with the photovoltaic cell shape), the uniform optically focused of intensity of ideal form.And on condenser system, the design of a series of novelties has been proposed.

Because the existence of sub-lens array, the total system effective focal spot is positioned at the place ahead or the rear of main lens focus.For a desirable geometrical optics system (each optical element has paraboloidal); The beamlet that decomposes through sub-lens array has duplicate xsect on the focus of main lens, the stack of all beamlets on this focus can produce a uniform hot spot.Because the incoherentness and the near field diffraction pattern of sunshine, light spot shape is identical with sub-mirror in the array, and the size of hot spot is then determined by the focal length separately and the mutual alignment of primary mirror and sub-mirror.

Sub-mirror in the array that the present invention adopts can be convergence/divergence optical elements such as lens, Fresnel lens, zone plate (sheet), catoptron, Fresnel reflecting mirror; And the aspheric surface with paraboloidal or nearly parabolic is with eliminations/minimizing ball-shaped aberration, but some small sizes or grow burnt element and also can use sphere commonly used.Its shape should be identical with the photovoltaic cell shape.The one dimension condenser system can adopt the one dimension parabolic mirror usually.

The primary mirror that the present invention adopts can be convergence/divergence optical elements such as lens, Fresnel lens, zone plate, catoptron, Fresnel reflecting mirror, or their combination.And the aspheric surface with paraboloidal or nearly parabolic is with eliminations/minimizing ball-shaped aberration, but some small sizes or grow burnt element and also can use sphere commonly used.The one dimension condenser system can adopt the one dimension parabolic mirror usually.

Near field diffraction pattern makes the solar light focusing hot spot have the shape same with sub-mirror, and the diffraction stack of beamlet produces the optically focused that all even brightness is strengthened.Sub-lens/sub-reflection mirror array can be placed on any one-level of concentration photovoltaic system.As long as satisfy Near Field, array is apart from other optical elements regulated at will within the specific limits, thereby causes whole concentration photovoltaic system assembling casing to reduce, and cost reduces.Superiority of the present invention is:

1. produce the uniform condensing similar with the photovoltaic cell shape;

2. system cost is low, and casing is little;

3. down fixing at other element characteristics (focal length, the aperture of the diaphragm), light concentrating times also can be regulated through the distance of array and primary mirror, and flexible design is motor-driven, and is widely applicable;

4. receive the influence of relative sunshine position deviation of device and inhomogeneous incident sunshine smaller;

5. receive the position influence of photovoltaic cell on optical axis smaller.

4. description of drawings

For simplicity, unless stated otherwise, hereinafter without exception parabolic lens, Fresnel lens, sphere and non-spherical lens are referred to as lens, and are referred to as catoptron to parabolic reflector, Fresnel reflecting mirror, sphere and non-spherical reflector.In all figure, the Z coordinate is represented optical axis direction, and X, Y coordinate are represented the plane perpendicular to optical axis Z.

Fig. 1 is the first order optics design diagram of traditional concentration photovoltaic system.Among the figure, 11-incident sunshine, 12-front window, 13-main lens/concave mirror, 14-focused light spot and solar-energy photo-voltaic cell.

Fig. 2 is the two stage optical design diagram of traditional concentration photovoltaic system.Among the figure, 21-incident sunshine, 22-front window, 23-(first order) main lens/concave mirror, 24-(second level) lens/catoptron, 25-focused light spot and solar-energy photo-voltaic cell.

Fig. 3 is the one dimension that adopts near field beam diffraction stack, the optical design synoptic diagram of one-level concentration photovoltaic system.Among the figure, 31-incident sunshine, 32-front window, 33-cylindrical mirror array, 34-parabolic cylinder, 35-focused light spot and solar-energy photo-voltaic cell.

Fig. 4 is the two dimension that adopts near field beam diffraction stack, the optical design synoptic diagram of one-level concentration photovoltaic system, and sub-lens array is near front window.Among the figure, 41-incident sunshine, 42-front window; 43-lens/catoptron array, 43a-lens/catoptron array (front view), 44-parabolic primary mirror (convex lens or concave mirror); 45-focused light spot and solar-energy photo-voltaic cell; 45a-focused light spot and solar-energy photo-voltaic cell (front view), F-primary mirror focal length, Δ-array and primary mirror spacing.

Fig. 5 is the two dimension that adopts near field beam diffraction stack, the optical design synoptic diagram of two-stage concentration photovoltaic system, and sub-lens array is as the second level optical element behind the main lens.Among the figure, 51-incident sunshine, 52-front window; 53-parabolic primary mirror (convex lens or concave mirror), 54-lens/catoptron array, 54a-lens/catoptron array (front view); 55-focused light spot and solar-energy photo-voltaic cell; 55a-focused light spot and solar-energy photo-voltaic cell (front view), F-primary mirror focal length, Δ-array and primary mirror spacing.

Fig. 6 is the concentration photovoltaic system synoptic diagram of the influence of the offset of acceptor lens array or deviation not that show to adopt near field beam diffraction stack.Among the figure, 61-incident sunshine, 62-main lens/catoptron, the diaphragm that 63-departs from along the Y axle, 64-lens/catoptron array, 65-can form a complete hot spot from the light of different sub mirror complementary region.

Fig. 7 is the one dimension that adopts near field beam diffraction stack, the synoptic diagram of one-level concentration photovoltaic system.For illustrating conveniently, front window does not provide synoptic diagram.Among the figure, 71-incident sunshine, 72-are arranged in the catoptron array on the parabolic cylinder, 73-parabolic cylinder, 74-focused light spot and solar-energy photo-voltaic cell.

Fig. 8 is the one dimension that adopts near field beam diffraction stack, the synoptic diagram of two-stage concentration photovoltaic system, and sub-lens array position is near front window.Among the figure, 81-incident sunshine, 82-parabolic post lens array and front window, 83-principal reflection cylindrical mirror, 84-secondary reflex cylindrical mirror/level crossing, 85-focused light spot and solar-energy photo-voltaic cell.

Fig. 9 is the one dimension that adopts near field beam diffraction stack, the synoptic diagram of two-stage concentration photovoltaic system, and sub-lens array is as second level optical element.For illustrating conveniently, front window does not provide synoptic diagram.Among the figure, 91-incident sunshine, 92-principal reflection cylindrical mirror, 93-parabolic cylindrical mirror array, 94-focused light spot and solar-energy photo-voltaic cell.

Figure 10 is the two dimension that adopts near field beam diffraction stack, the synoptic diagram of two-stage concentration photovoltaic system, and sub-lens array position is near front window.Among the figure, 101-incident sunshine, 102-parabolic lens array and front window, 103-parabolic principal reflection mirror, 104-parabolic secondary reflex mirror, 105-focused light spot and solar-energy photo-voltaic cell.

Figure 11 is the two dimension that adopts near field beam diffraction stack, the synoptic diagram of two-stage concentration photovoltaic system, and sub-lens array is as second level optical element.For illustrating conveniently, front window does not provide synoptic diagram.Among the figure, 111-incident sunshine, 112-parabolic principal reflection mirror, 113-parabolic reflector array, 114-focused light spot and solar-energy photo-voltaic cell.

Figure 12 shows light path synoptic diagram in Figure 11 system.Among the figure, 121-incident sunshine, 122-parabolic principal reflection mirror, 123-parabolic reflector array, 124-focused light spot and solar-energy photo-voltaic cell.

Below in conjunction with accompanying drawing principle of work of the present invention is further specified.

The one-level light-gathering optics of tradition condensation photovoltaic only uses main convex lens or recessed catoptron to be used for optically focused (as shown in Figure 1).And in traditional concentration photovoltaic system two stage optical design of Fig. 2 signal, the utilization of primary and secondary two stage optical element makes that design is more flexible, and system can adopt accordion structure to reduce the integral thickness of plate.In actual the use, the front window that also adopts transparent material is with protection optical system and photovoltaic cell.

The incident sunshine is considered to the intensity substep evenly usually.And under actual conditions, the existence of system stop and optical element edge effect cause the focused light spot intensity distributions inhomogeneous because of stronger diffraction under high power concentrator.Which in the traditional high concentrating photovoltaic system is a serious problem Hen, particularly in the folded structure.In addition, because the out-of-shape property of the collective optics that the splicing of different concentrating components brings or the center details in a play not acted out on stage, but told through dialogues in the accordion structure all can make this problem even more serious.

The present invention adopts sub-lens array, and the equally distributed light of most intensity is through the sub-lens array projection primary mirror focal plane that is added to, and the light at diaphragm edge or (in the accordion structure) center details in a play not acted out on stage, but told through dialogues are also projected to the primary mirror focal plane by different sub-mirrors.From stack again behind the light focusing of different sub mirror, this has played certain " floating " effect, makes primary mirror focal plane optical field distribution than even with the direct optically focused of traditional condenser system.Because use parabolic or nearly aspheric imaging len of parabolic or catoptron, sunshine has identical xsect through the along at headprism or principal reflection mirror behind the diffracted beam of sub-lens array.Sunshine is a polychromatic light, all is far longer than under the situation of sunshine mean wavelength in the size of all optical elements, can think that also sunshine is an incoherent light.A plurality of light beams behind the sub-lens array diffraction of sunshine process are non-coherent addition directly, and can not interfere with each other, thereby on photovoltaic cell, produces the even focal beam spot similar with sub-mirror shape.

Key of the present invention is to utilize near field beam diffraction stack, and this satisfies the near field diffraction pattern condition with regard to the distance that requires sub-lens array and beam convergence stack face.Diffraction conditions can represent that near field diffraction pattern must satisfy Fresnel number more than or equal to one, that is: with Fresnel number

$F_{\#}=\frac{d^2}{L_e\mathrm{\λ}}\≥1$(stricter Near Field requires F_#＞10) (formula 1)

D is the size of single sub-mirror in the array in the formula 1, usually greater than 1 millimeter.λ is the mean wavelength of sunshine, generally is 0.5 to 1 micron.L_eBe the effective light path between sub-lens array and the light beam stack face, can be expressed as (A/B-1/R)^-1Wherein, A and B are sub-lens arrays to the light matrix unit of light beam stack face, and R is the radius-of-curvature of the convergence of rays that arrives sub-lens array/disperse.Simply, under the near field diffraction pattern condition, sunshine almost is the geometric projection according to a certain percentage of sub-mirror shape through each sub-mirror in the array at the diffraction pattern that stack face produces.

Satisfying under the near field diffraction pattern condition, sub-lens array can be placed near the front window of condenser system or separately as the first order or second level optical element.The schematic diagram of several frequently seen optical design such as Fig. 3 are shown in 4,5.Fig. 3 is the one dimension that adopts near field beam diffraction stack, the optical design synoptic diagram of one-level concentration photovoltaic system.Fig. 4 is the one dimension that adopts near field beam diffraction stack, the optical design synoptic diagram of two-stage concentration photovoltaic system, and its neutron lens array is as first order optical element near front window.Fig. 5 is the two dimension that adopts near field beam diffraction stack, the optical design synoptic diagram of two-stage concentration photovoltaic system, and its neutron lens array is as the second level optical element behind the main lens.Below in conjunction with Fig. 4 and Fig. 5, the near field beam diffraction stacking method in the concentration photovoltaic system is carried out quantitative test.The near field diffraction pattern transmission can be described with geometrical optics.In Fig. 4, sub-lens array is positioned at the front of main lens, and focal beam spot can be expressed as in the size of X and Y direction

$X=\left|\frac{F}{f}\right|\·d_x$And$Y=\left|\frac{F}{f}\right|\·d_y$(formula 2)

In Fig. 5, sub-lens array is positioned at the back of main lens, and focal beam spot can be expressed as in the size of X and Y direction

$X=\left|\frac{F-\mathrm{\Δ}}{f}\right|\·d_x$And$Y=\left|\frac{F-\mathrm{\Δ}}{f}\right|\·d_y$(formula 3)

Wherein f is the focal length of each sub-mirror in the array, and F is the focal length of main lens or principal reflection mirror, d_xAnd d_yBe the size of sub-mirror on X and Y direction in the array, Δ is the distance between sub-lens array and main lens or the principal reflection mirror.Can find out that from formula 2 and formula 3 size of focal beam spot can be regulated with a plurality of parameters.In the system of Fig. 4, the size of focal beam spot and Δ are irrelevant, thereby cause system simpler and stable.And the system of Fig. 5 is influenced by Δ, has also increased the dirigibility that system regulates simultaneously.

Fig. 6 is the concentration photovoltaic system synoptic diagram of the influence of the offset of acceptor lens array or deviation not that show to adopt near field beam diffraction stack.This also equivalence shown that design of the present invention receives alliance deviation and the uneven negative effect of incident sunshine to design little than the traditional optical in the concentration photovoltaic system.Skew in the optical system can be described with effective diaphragm, and sub-lens array does not receive the skew of X and Y direction and the influence of diaphragm error.As shown in Figure 6, when deviation appears in array position, just can be complementary from the sub-mirror diffraction spot of array top with the complementary or part of below, thus on photovoltaic cell, forming uniform optically focused, this is that single mirror institute is inaccessible.Realize that near field beam diffraction stack causes system not receive the influence of X and skew of Y direction or deviation so use sub-lens array.

In the present invention, if the position of photovoltaic cell on optical axis squint, as long as in Rayleigh scope (Rayleigh Range), can not exert an influence to condenser system.In fact, photovoltaic cell just in time is not placed on the focal position of main lens, but along the slightly inclined to one side certain distance of the effective focal spot direction that deviates from total system, the inhomogeneous far field construction spot that can avoid each sub-mirror edge and whole array edges to produce like this.

5. embodiment

Table one: the arrangements of components of one-level near field of light diffraction stack optically focused

Table two: the arrangements of components of two-stage near field of light diffraction stack optically focused

Table one and table two are listed the arrangements of components (part illustrates sample and is included in the Figure of description) that can realize one-level and two-stage near field beam diffraction stack optically focused respectively, and sub-lens array can be used on any one-level of the system that comprises front window, main lens/principal reflection mirror, inferior lens/secondary mirror.More complicated situation can further make up, and does not list fully in the table.Sub-mirror in the array can adopt two-dimentional parabolic or non-spherical lens/catoptron, Fresnel lens or zone plate (sheet).Specifically, cylindrical mirror is used for unidimensional system.Transparency window as front window can be flat glass or other transparent materials.Merit attention and be; Because parabolic or aspheric lens/or catoptron can eliminate ball-shaped aberration; The one dimension condenser system should adopt one dimension parabolic/aspheric lens pillar or catoptron, and two-dimentional condenser system should adopt two-dimentional parabolic/aspheric lens or catoptron.Fresnel lens or zone plate (sheet) also can be used for realizing similar system.

List of references

1.Z.Schwartzman，“Solar?concentrator?device?for?photovoltaic?energy?generator，”United?StatesPatent?Application?Publication，No.US?2008/0041441?A1

2.P.Y.Maeda，“Beam?integration?for?concentrating?solar?collector，”United?States?PatentApplication?Publication，No.US?2007/0251568?A1

3.X.Deng，X.Liang，Z.Chen，W.Yu，and?R.Ma，“Uniform?illumination?of?large?targets?usinga?lens?array，”Applied?Optics(ISSN?0003-6935)，vol.25，Feb.1，1986，page?377-381.

Claims (12)

1. in light gathering photovoltaic power generating system; The present invention adopts sub-lens array that sunshine is resolved into several beamlet; Through near field diffraction pattern and transmission; Near the focus of converging optical element, that is to say on the position of semiconductor solar cell, assemble the even focal beam spot that stack becomes shape and size and semiconductor solar cell coupling.The shape of focal beam spot is to be transmitted through near field diffraction pattern by the array neutron mirror, almost is the geometric projection by a certain percentage of sub-mirror shape.The light intensity uniformity of focal beam spot is to realize by whole light beam is divided into the process that beamlet carries out non-coherent addition again in the space.

2. in the claim 1, the condition that satisfies the near field diffraction pattern transmission is sub-lens array and beam convergence superposes between the face (being the photovoltaic cell position) pairing Fresnel number more than or equal to one, i.e. F_#=d²/ L_eλ>=1, (stricter Near Field requires F_#＞10), wherein d is the size of single sub-mirror in the array, and λ is the mean wavelength of sunshine, L_eIt is the effective light path between sub-lens array and the photovoltaic cell.Under this condition, the diffraction pattern that sunshine produces through each sub-mirror in the array is similar to the shape geometric projection by a certain percentage of sub-mirror.

3. in the claim 1, as long as satisfy the near field diffraction pattern transmission conditions, the distance of sub-lens array and converging optical element is regulated at will within the specific limits, thereby helps reducing of whole concentration photovoltaic system module case body thickness.

4. in the claim 1, concentration photovoltaic system can adopt one or more levels optical system.Therefore, converging optical element can be a main optical element, also can be the combination of main optical element and one or more secondary optics.Main optical element here and secondary optics can be single lens, catoptron, Fresnel lens, Fresnel reflecting mirror, zone plate (sheet) or their combination.Under the ideal state, optical element surface is paraboloidal to reduce the influence of spherical aberration.Also can adopt the aspherical optical element of nearly parabolic in the practice, even spherical optics element (but the spherical aberration that sphere brought can influence system performance).

5. for the one dimensional optical system, main optical element and secondary optics adopt cylindrical mirror in the claim 1 and 4, and it is parabola shaped that xsect is, and also can adopt nearly parabola shaped or circular arc in the practice.

6. in the claim 1, the array that sub-lens array is made up of the part of a plurality of identical unit optical elements or unit optical element, unit optical element wherein is called sub-mirror.Sub-mirror can adopt lens, catoptron, Fresnel lens, Fresnel reflecting mirror, zone plate (sheet) or their combination.Under the ideal state, sub-mirror surface is paraboloidal.Also can adopt the aspheric surface of nearly parabolic in the practice, even spherical optics element (but the spherical aberration that sphere brought can influence system performance).

7. for the one dimensional optical system, the sub-mirror in the claim 1 and 6 adopts cylindrical mirror, and it is parabola shaped that xsect is, and also can adopt nearly parabola shaped or circular arc in the practice.

8. claim 1,6, and the shape of the sub-mirror in 7 is rectangle or square normally, but does not also get rid of other special shape.Require identical with the shape of photovoltaic cell/similar.

9. claim 1; 6, if adopting, the sub-mirror in 7 disperses optical element, comprise concavees lens, convex mirror, disperse Fresnel lens or disperse Fresnel reflecting mirror/zone plate (sheet); Because of satisfying the condition of near field diffraction pattern transmission better, can accomplish the nearly geometric projection of sub-mirror shape better.

10. the focusing surface of the diffracted beam in the claim 1 promptly is the position of semiconductor solar cell.In real system, also can certain distance slightly be departed from along the direction that deviates from the condenser system equivalent focus in the position of solar cell near the focal position of converging optical element; Can avoid the far field construction of each sub-mirror edge and whole array edges generation like this, further improve the homogeneity of optically focused.

11. the sub-lens array in the claim 1 can be placed on any one-level in the concentration photovoltaic system.In practice, the position of sub-lens array can be: as front window or near front window, or near main optical element, or as second level optical element, or the like.In the various possible design that produces therefrom, claim 2,3,4,5,6,7,8,9,10 are suitable for.

12. (also can adopt the aspheric surface of nearly parabolic in the practice, even sphere) also can be arranged and be placed on the parabola to the sub-lens array in the claim 1.In reflecting system, should the parabola equivalence play the effect that lens are assembled, thereby constitute a kind of succinct design of claim 1.In this design, claim 2,3,4,5,6,7,8,9,10 are suitable for.

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