ES2262379A1 - Spherical mirror to reflect sun's rays at Stirling engine incorporates a blocking reflection ring directed at a plane - Google Patents

Abstract

A parabolic mirror reflects the sun's rays at e.g. a Stirling engine. The mirror has a spherical reflection surface with a blocking reflection ring whose median circumference (14) impinges on a plane (13).

Description

Optical concentration device

Object and field of application

The present invention relates to an optical device that allows, through a single reflection, to simultaneously obtain high concentrations (500-1000x) and uniform flow distributions, thereby increasing the efficiency and simplicity of optical concentration systems. Its use is in the field of solar energy, in applications of electrical energy production (photovoltaic or thermodynamic), heat generation in industrial processes, and thermochemical and photochemical processes.
Micos

Background of the invention

The search for a solar concentrator that presents a uniform flow distribution, with a flat profile, without requiring many reflections (which implies a loss of efficiency) represents an important challenge for most practical applications. In photovoltaic applications this is a critical issue since when the different cells are connected in series the maximum efficiency of the system is limited by the cell of lower performance. In thermal applications, non-uniform flows cause significant temperature gradients, which seriously affects the durability of solar boilers, their controllability and the reliability of
same.

On certain devices, such as the one described in US 2003075212 a secondary concentrator is used, which comprises a composite parabolic cylinder, which allows to obtain more flows soft, but that implies multiple reflections and therefore some significant losses of efficiency, in addition to a strong restriction in the vision factor.

In other cases, as in US 4,395,581 and US 4,999,059, the use of multiple facets, flat and small, is used to achieve a uniform flow distribution over the receiver; and while costs of these facets are low, the need for precise optical alignment equipment and requires skilled labor for installation "in situ" thereof.

Finally, some devices like the one described in US 5,153,780 they use Fresnel-type concentration systems, whose manufacturing complexity is notorious.

On the other hand, it is known that higher performance solar concentrators optical-geometric with image formation are the called parabolic discs. It is a disc with curvature parabolic that concentrate solar energy in a timely focus. With they can achieve high concentrations (Average values of 2000x with higher peaks). The parabolic disc gathers all the incident rays parallel to the optical axis at one point, the focus, what which leads to a fairly sharp flow distribution, producing important thermal gradients. This effect can be smoothing the receiver plane out of focus, but still The flow variations are considerable.

Consequently, it is an objective of the present invention getting an optical concentrator that using a single reflection produce the most uniform flow distribution possible.

It is another objective of the present invention the get an optical hub that, meeting the requirements Exposed technicians, can be manufactured and adjusted so Simple and economical.

Description of the invention

The proposed solution is based on using a spherical surface as a reflective element of the concentrator optical. The behavior of the sphere is only similar to that of the disk parabolic in its paraxial zone, that is, where its mathematical identification with the paraboloid is, for the purpose full practical. Outside the paraxial zone, any lightning incident parallel to the optical axis will not pass through the focus. But nevertheless, the path of the rays that symmetrically affect the axis optical will be symmetrical, that is, they will cut the optical axis in the same point. The optical axis of a spherical reflective surface represents the geometric place of convergence of ray families that affect it symmetrically with respect to the optical axis. This Effect is known as spherical aberration.

It is obvious that the concentration attainable with a spherical concentrator is always less than that attainable with a parabolic concentrator, since the spherical concentrators do not have a single focus; However, in many applications, and especially in those of solar energy, it is not necessary to form an image of our object to concentrate, in this case the sun, but it is about capturing its energy in the most effective and possible economic. In this line of work, non-image solar concentrators move. In our case and since we pursue a uniform flow distribution, we will enhance spherical aberration and work out of focus. It has been proven that in spherical concentrators this can be achieved by blocking the solar reflection in the geometric place of the sphere surface that focuses on the receiving plane. In the sphere, for each focal length there is a circumference whose reflected rays are focused on a single point. Consequently, if we block the reflection of the circumference that focuses on the receiving plane, we will have suppressed the flow peaks that give rise to an excessive thermal gradient. For practical reasons we will not only block the circumference in question, but we will extend the blockage to a band on each side of it, to form what we could call a reflection ring
blocked up.

Reflection blocking can be achieved easily by simply covering the surface of the concentrator with a poorly reflective painting; Black, for example.

The advantages of the optical concentrator with uniform flow distribution object of the invention are the following:

-

spherical reflective surface instead of parabolic, with the consequent reduction of the cost.

-

negligible thermal gradient over the receiving plane, eliminating dilatation problems differential and hot spots, which entails a reduction of Additional costs and improved reliability.

Brief description of the drawings

To complement the description above and in order to help a better understanding of the characteristics of the invention, a detailed description of a preferred embodiment, based on a set of drawings that accompany this descriptive report and where with character merely indicative and not limiting what has been represented next:

Figure 1 shows a disk device parabolic - Stirling engine for energy production electrical, according to the prior art.

Figure 2 shows the flow distribution on the receiver plane of the Stirling engine of the device Figure 1, depending on whether or not the receiving plane coincides with the plane focal.

Figure 3 is a schematic representation of the so-called spherical aberration.

Figure 4 shows the object optical concentrator of the invention.

Figure 5 shows the flow distribution produced on the receiving plane by a conventional spherical concentrator and by a spherical concentrator with a reflection ring locked according to the invention.
tion.

In the previous figures, the references Numeric correspond to the following parts and elements.

one.

Parabolic disc device - engine Stirling.

2.

Support structure.

3.

Parabolic Concentrator

Four.

Receiver.

5.

Sun.

6.

Flow distribution with concentrator parabolic.

7.

Flow distribution with concentrator Parabolic out of focus.

8.

Reflective surface spherical

9.

Reflection ring locked.

10.

Flow distribution with concentrator spherical.

eleven.

Flow distribution with concentrator spherical and reflection ring locked.

12.

Zone of flow reduction.

13.

Receiving plane

14.

Middle circumference of the ring blocked reflection (9).

Detailed description of a preferred embodiment

Figure 1 represents an installation of production of electricity from solar energy of the disk type parabolic - Stirling engine (1). In it, a support structure (2) properly orients a parabolic concentrator (3) that directs incident radiation from the sun (5) to a receiver (4), in this case a Stirling engine. These devices are known for years, although its commercial use is seen stopped by various problems among which the most important is the high cost In addition, one such solution, still getting high concentrations and consequently high efficiencies, presents a flow distribution with parabolic concentrator (6) on the very billy receiver (4), as can be seen in figure 2. The out of focus the receiver (4) leads to a distribution of flow with unfocused parabolic concentrator (7) more flattened. Yet thus, a non-negligible thermal gradient appears that introduces specific requests at the receiver (4).

For its part, a spherical reflective surface (8) as used in the optical concentrator of the invention it does not produce a single image but, as can be seen in the Figure 3, each circumference inscribed on the surface reflective focuses at a different point along the axis optical. For each focal point "d" there is only one radius circumference "r" whose reflected rays focus on that point This circumference constitutes the middle circumference (14) defining the locked reflection ring (9). See Figure Four.

The position of the receiving plane (13) can determined according to the expression:

d = R \ left (1 - \ frac {R} {2 \ sqrt {R 2} - r 2}} \ right)

in which "R" is the radius of the surface spherical

The optical concentrator, object of the invention, produces a flow distribution with spherical concentrator and reflection ring locked (11) considerably more uniform that the flow distribution with spherical concentrator (10) but without Reflection ring locked (9). As can be seen in Figure 5, The effect of the locked reflection ring (9) is to reduce strongly the peak of flow that occurs at the intersection of optical axis with the receiving plane (13), suppressing the power represented by the reduced flow zone (12) and improving considerably the uniformity of the flow distribution.

Claims (2)

1. Optical concentration device on a receiving plane (13), which uses a single reflection of the incident radiation, characterized by comprising a spherical reflective surface (8) having a locked reflection ring (9), whose average circumference (14 ) focus on the receiving plane (13); such that the distribution of the flow over the receiving plane (13) is substantially uniform. 2. Optical concentration device according to claim 1, characterized in that the incident radiation is from the sun.