SOLAR CONCENTRATING SYSTEM

Abstract

A solar concentrating system and installation has a plurality of solar collectors configured for receiving, reflecting, and concentrating radiation in a focal point. The solar concentrating system and installation increases the efficiency of current solar concentrating systems, such as those based on linear Fresnel collectors, by reducing focal distances and increasing the effective surface of the system.

Claims

1. A solar concentrating system adapted for concentrating the energy coming from solar radiation in a plurality of focal points, comprising a plurality of collectors C configured for receiving, reflecting, and concentrating radiation in a focal point, wherein each collector C.sub.i, with i ∈ {1, . . ., n}, comprises: a plurality of m reflectors R, where each reflector R.sub.j,with j ∈ {1, . . ., m}, is flat or has a large radius of curvature compared to the other dimensions of the reflector, wherein each reflector R.sub.j comprises at least one substrate and one or more reflective surfaces, configured for reflecting solar radiation energy, each reflector has a substantially rectangular or square shape, having dimensions a, b, with a<b, and where b corresponds to the longitudinal direction, and each reflector R.sub.j is configured for rotating about a longitudinal axis L of the reflector R.sub.j, preferably about its longitudinal axis of symmetry; at least one receiver configured for receiving the solar radiation concentrated by the plurality of reflectors and conveying the energy by means of a thermal fluid; wherein the at least one receiver is positioned substantially in a focal point, and wherein the at least one receiver comprises a conduit adapted for the circulation of a thermal fluid, and a structural element adapted for supporting the conduit and positioning the conduit in the focal point; a support structure configured for positioning each reflector R.sub.j of the plurality of reflectors at a given height and distance for each reflector R.sub.j with respect to the at least one receiver, and configured for allowing each reflector R.sub.j to rotate an angle ϕ.sub.j with respect to the horizontal plane, wherein the angle ϕ.sub.j allows the reflector R.sub.j to reflect radiation in the focal point; wherein the system comprises an arrangement of the reflectors of each collector C.sub.i such that the reflectors are arranged at different heights and the longitudinal axes L.sub.ij about which the reflectors R.sub.ij rotate are arranged in parallel and contained on at least one surface the tangent of which in each longitudinal axis L.sub.ij forms an angle λ.sub.ij with respect to the horizontal plane, wherein each angle λ.sub.ij verifies that if ϑ is the angle of incidence of solar radiation, then the total annual solar irradiation time period is comprised between 1% and 50% of the total time
90°≥ϑ>90°−λ.sub.ij; i ∈ {1, . . . , n}; j ∈ {1, . . . , m}; and each collector C.sub.i is either separated from an adjacent collector C.sub.i±1 by a passageway free of obstacles for the solar radiation, or is separated from an obstacle at a height comparable to the collector by a passageway, wherein the passageway has a width of at least one distance D, measured at the narrowest point between the collectors, where
D>0 and wherein the plurality of m reflectors of each collector C.sub.i are grouped in two sections symmetrically arranged on either side of the at least one receiver.

2. The solar concentrating system according to claim 1, wherein an oblique plane containing at least the longitudinal axes of two reflectors of a collector C.sub.i is defined, said plane forms an angle ϵ.sub.i with the horizontal plane, and the total annual solar irradiation time period is comprised between 1% and 50% of the total time
90°≥ϑ>90°−ϵ.sub.i; i ∈ {1, . . . , n}.

3. The solar concentrating system according to claim 1, wherein the at least two longitudinal axes contained in the oblique plane correspond to at least two reflectors which are located at a greater height and at a lower height of the collector.

4. The solar concentrating system according to claim 1, wherein the reflectors are substantially aligned according to a North-South geographic orientation.

5. The solar concentrating system according to claim 1, wherein each reflector R.sub.ij of the plurality of n×m reflectors is arranged at a distance to the at least one receiver defined as
√{square root over (.sub.ij.sup.2+d.sub.ij.sup.2)} wherein the ratio between the distances to the at least one receiver of any two reflectors of the plurality of n×m reflectors is equal to a value comprised between 0.7 and 1.3.

6. The solar concentrating system according to claim 1, wherein the width D of the passageway substantially measures between 1 and 3 meters.

7. The solar concentrating system according to claim 1, wherein the width D of the passageway holds that $D=\frac{A_U}{2}$ where Au is the upper aperture a collector measured in parallel to the horizontal plane between its end points.

8. The solar concentrating according to claim 1, further comprising at least one actuation device to vary the angles ϕ.sub.ij of the reflector R.sub.ij, in which the movement of each reflector R.sub.ij can be either individual or synchronous with respect to the other reflectors.

9. The solar concentrating system according to claim 1, wherein the at least one receiver comprises a vacuum tube-type conduit, or a plurality of simple conduits.

10. The solar concentrating system according to claim 1, wherein each angle λ.sub.ij holds the following condition:
λ.sub.11=λ.sub.12= . . . =λ.sub.nm=λ; i ∈ {1, . . . , n}; j ∈ {1, . . . , m}.

11. The solar concentrating system according to claim 1, wherein the following condition is held:
λ=24°.

12. The solar concentrating system according to claim 1, wherein the surface on which the longitudinal axes about which the reflectors rotate are contained is a quadric surface, particularly a circular cylinder, a hyperbolic cylinder, a parabolic cylinder, or an elliptical cylindrical, or sections of the foregoing.

13. A concentrating installation comprising a solar concentrating system according to claim 1.

Description

DESCRIPTION OF THE DRAWINGS

[0067] These and other features and advantages of the invention will be better understood based on the following detailed description of a preferred embodiment given only by way of non-limiting illustrative example in reference to the attached drawings.

[0068] FIG. 1 shows a system with two collectors separated by a passageway, seen from the front.

[0069] FIG. 2 shows a perspective view of a system with two collectors separated by a passageway.

[0070] FIG. 3 shows the geometric relationships between the angle of incidence of solar radiation, the position of the reflectors, etc.

[0071] FIGS. 4a-4b show the geometric definition of the lateral aperture for two embodiments of the system.

DETAILED DESCRIPTION OF THE INVENTION

[0072] The present invention allows an improvement in solar concentrating systems with respect to conventional linear Fresnel concentrating systems, and with a lower cost than concentrating systems based on parabolic trough concentrators.

EMBODIMENT

[0073] In a specific embodiment, the concentrating system (1) is located close to the city of Seville, corresponding to a latitude of 37° 26′ 38″ North, and simply stated, it will be considered that the concentrating system (1) comprises only two collectors (10), with a passageway (14) between them as shown in FIG. 3. Advantageously, both collectors (10) are arranged in parallel and oriented according to a North-South axis to harness the greatest amount of energy possible. Each collector (10) comprises a set of twelve reflectors (12) with a small curvature having a radius between 6000 and 8000 mm, arranged following a symmetrical broken plane, which would be the equivalent of a V-shaped arrangement of the reflectors (12); some drawings only show a part of the reflectors for the sake of simplicity. The reflectors (12) would thereby be divided into two arms or branches in each collector (10); if the reflectors are numbered from left to right, looking at them from the South, the first branch or left branch would comprise reflectors 1 to 6, and the second branch or right branch would comprise reflectors 7 to 12, in each collector (10). This arrangement is particularly advantageous due to its simplicity, since the support structure (13) can be built in a conventional manner by means of straight beams or profiles. It thereby holds that the ratio between the distances to the receiver (11) of any two reflectors (12) is equal to a value comprised between 0.7 and 1.3, at least partly reducing distortions.

[0074] As shown in FIG. 2, each collector (10) comprises a linear receiver (11) measuring about 4 m in length, formed by a conduit (11.1) with a vacuum chamber, or evacuated tube, for conveying the thermal fluid, which is overheated water in this example. The receiver (11) is supported by means of a structural element (11.2), which is a simple structure attached to the support structure (13) and keeping the receiver (11) in a high position coinciding with the focal point (F) of the collector (10).

[0075] In this embodiment shown in FIGS. 1 and 3, each reflector (12) is formed by three flat mirrors measuring 1320 mm in length (b) by 529 mm in width (a), arranged one after the other parallel to the linear receiver (11), and is assembled on a frame capable of rotating about a longitudinal axis (12.3) of the mirrors an angle ϕ.sub.ij with respect to the horizontal plane; in this example the longitudinal axis (12.3) coincides with the axis of symmetry of the mirrors.

[0076] In each collector (10) the twelve reflectors (12) are grouped in two sections of six reflectors (12), with each section arranged on either side of the receiver (11). The reflectors (12) of one of the sections are arranged with their longitudinal axes (12.3) in parallel, and with their longitudinal axes (12.3) contained in an oblique plane with respect to the horizontal plane. In this example, the plane containing the longitudinal axes (12.3) of the reflectors (12) forms an angle λ=24° with the horizontal plane. Accordingly, the angles ϵ.sub.1, ϵ.sub.2, of each of the two collectors are equal to λ.

[0077] With an angle λ=24°, the reflectors of the ends, i.e., those which are at a greater height, are furthermore rendered accessible for an operator with relative ease, since they are at about 1.25 m from the lower level.

[0078] This angle depends on the latitude of Seville and corresponds to the value for which the angle of incidence of the sun (ϑ) holds that

90°≥ϑ>90°−λ.sub.ij; i ∈ {1, . . . , n}; j ∈ {1, . . . , m};

for a third (⅓) of the time in which there is solar radiation, or in other words a third (⅓) of the daytime hours. This relationship means that for 33.33% of the daytime hours of the year, solar radiation strikes below the plane containing the longitudinal axes (12.3) of the reflectors (12), or alternatively, the angle of incidence of the sun is ϑ>66°, which would corresponds to the first and to the last hours of the day.

[0079] Therefore, by taking a time of the day in which ϑ=70° (see FIGS. 3 and 4) the condition of lateral aperture is held, and for reflector R.sub.112 (i.e., the last reflector of the first collector: i=1; j=12) with its height and its distance to receiver h.sub.112=2042 mm; d.sub.112=2787 mm:

[00004]${\varphi }_{112}=\frac{\left(90°-\vartheta \right)-\arctan \left(\frac{2042\mathrm{mm}}{2787\mathrm{mm}}\right)}{2}=-8.115°$

which is the angle that holds the condition of reflection in the lateral aperture mode. Parameter B in this case measures B=2701 mm. In this case, the collector has a width of 6024 mm, and its upper aperture is:

A.sub.U=6024 m

so the width of the passageway D measures:

[00005]$D=\frac{6024\mathrm{mm}}{2}=3012\mathrm{mm}$$A_L=D.Math.\sin \left(\arctan \frac{B.Math.\sin {\mathrm{.Math.}}_1}{D+\cos {\mathrm{.Math.}}_1}\right)==3012\mathrm{mm}.Math.\sin \left(\arctan \frac{2701\mathrm{mm}.Math.\sin 24°}{3012\mathrm{mm}+2701\mathrm{mm}.Math.\cos 24°}\right)$$A_L=592.1\mathrm{mm}$

Tests

[0080] As discussed, the embodiment described above allows an improvement in optical output of 29.2% for the case of an isolated concentrator, and of 13.3% for the case of a collector surrounded by passageways measuring 3 m (D=3 m), according to the described solar concentrating system, for periods of time in which the angle of elevation of the sun is below 24° , compared to a concentrating system according to normal practice in the field of the art.

[0081] In the context of the present invention, optical output is understood as the ratio between radiation reaching the receiver and available radiation.

[0082] To arrive at these conclusions, the inventors performed a computational simulation of the calculation of optical output for a collector like the one described above (λ=24°), located at the same latitude as Seville, comprising a collector measuring 28 m in length and having 175.8 m.sup.2 of reflective surface, in three particular cases: a collector without a lateral aperture (equivalent to a collector without a passageway), an isolated collector, and a collector with passageways measuring 3 m on both sides.

[0083] The computational calculation was performed by means of Tonatiuh software, an open source program, and was launched by the Centro Nacional de Energias Renovables (CENER); version 2.2.4 of the software is available at http://iat-cener.github.io/tonatiuh/. Tonatiuh software allows the optical-energetic simulation of solar concentrating systems. It combines ray tracing with the Monte Carlo method to simulate the optical performance of a wide range of systems.

[0084] In addition to the design values set forth above, the following calculation parameters were considered:

TABLE-US-00001 Position of the sun Azimuth Az ϵ [0°, 180°] at intervals of 10° Elevation El ϵ [0°, 24°] at intervals of 3°

TABLE-US-00002 Radiation 10.sup.6 rays. Total square error (Sigma slope) σ.sub.Slope = 1.8 Sunshape “Buie” Circunsolar radiation CSR = 0.2 Irradiance 1000 W/m.sup.2

[0085] According to the preceding values, Tonatiuh software provided 171 results of optical output for each case, shown in the following three tables. The highlighted cells show the values that were physically possible for the indicated latitude (Seville).

Conclusions

[0086] For the cases corresponding to Tables 2 and 3, considering only the sum of the outputs that are physically possible for the indicated latitude, the sums of optical outputs were compared to the reference case, i.e., the case without a passageway (D=0 m), and the following was found:

[0087] For the case of an isolated collector (Table 2), the optical output improves by 29.2%.

[0088] For the case of a concentrating system with passageways measuring 3 m (Table 3), the optical output improves by 13.3%.