WO2008017091A1

WO2008017091A1 - Solar collector for collecting solar radiation according to requirements

Info

Publication number: WO2008017091A1
Application number: PCT/AT2007/000381
Authority: WO
Inventors: Markus Birnhofer
Original assignee: Markus Birnhofer
Priority date: 2006-08-11
Filing date: 2007-08-08
Publication date: 2008-02-14

Abstract

The solar collector (1) comprises an absorber element (2), at least one reflector surface (3) above the absorber element (2) and at least one reflector surface (4) below the absorber element, the reflector being assembled from a lower, (4) central (13) and upper region (3) when viewed in cross-section. The alignment of the reflective surface of the lower reflector region (4) produces: a complete reflection of the light from the reflector when the incident angle of the solar radiation exceeds approximately 40°; and a complete reflection of the incident light rays onto the underside of the absorber (6), when the incident angle is less than approximately 25°, optionally using additional reflection via the central reflector region (13). The upper reflector region (3) causes the absorber (6) to be partially masked against the incident light when the incident angle of the solar radiation is greater than 30° and causes the incident light to be reflected onto the absorber when the incident angle is less than 30°.

Description

description

The present invention relates to a device for demand-adapted detection of solar radiation. It relates to the field of heating and energy conversion technology, in particular components of solar and photovoltaic systems.

This device is preferably used for hot water preparation, heating, cooling and, to a lesser extent, power supply. It can be mounted on walls and roofs, integrated in building structures or freely placed and has an efficiency that is optimally adaptable to the annual needs.

State of the art

Modern solar systems convert the solar irradiation with the help of flat collectors or vacuum tube collectors with CPC reflector (Compound Parabolic Concentrator) maximally into heat and thus warm water. Absorption and also reflection are exploited in such a way that a maximum amount of heat is released to the absorber for a certain irradiated area, even from different angles of incidence. In addition, alignment with the sun is optimized by means of automatically adjusting the inclination and horizontal orientation of the entire collector element from east to west. For rigid systems, or systems which do not allow movement of the entire collector surface for aesthetic reasons, specially shaped mirrors are used to increase the efficiency of certain angles.

DE 94 18 431 U discloses a special mirror which has a shape designated as "laxodrom" and which serves to compensate for seasonal fluctuations, an upper and a lower mirror and an absorber or a vacuum tube form the solar collector.

From DE 298 12 174 U a solar thermal mirror collector is known, in which a plurality of rotatably mounted plane mirror directing the solar radiation onto a long-cylindrical solar absorber. The mirrors can be optimally adjusted by motor and time control.

Finally, US Pat. No. 4,572,160 discloses a heliotropic solar heat collector system which has an east-west solar tracking system and allows the solar radiation to penetrate over a defined opening angle. This radiation is reflected by mirrors on two sides of a collector absorber, either the first reflection or two mirrors the second reflection reaches the absorber surface. The orientation is indirectly during the day always directly facing the sun. At the limit of the heat capacity optional photovoltaic elements can be folded as a panel over the solar window, which instead of heat, the light is converted into electricity.

A disadvantage of the above systems is the generation of excess energy, the need for permanent tracking of the elements with respect to the position of the sun and due to the moving parts high maintenance and susceptibility to errors. In addition, the

Discrepancy from high demand for heat and hot water with poor yield in winter and winter low demand with high yield in summer not eliminated. Most systems aim for the highest possible efficiency for a given solar area, although the costs of installation and maintenance are also of immanent importance.

Object of the invention

Based on this prior art, a device for demand-adapted detection of solar radiation has been sought. This should be possible inexpensively from standard components formable, have an ideal for the irradiated surface efficiency. It should be as compact as possible, be moldable in modules and be as rigid as possible in the structure. Moving parts are provided insofar that thereby the possibility for rapid adjustments or assembly or disassembly is possible, or a function change can be done for example on solar cooling. The recoverable energy intake in winter should be sufficient for heating, but in the summer still not exceed the maximum needs, or may be sufficient for solar cooling. Optionally, there should be the possibility of additional use as a photovoltaic power source and weather-related active losses can be corrected manually or automatically. In addition, diffuse scattered light and reflected light by snow should also be well absorbed.

The protection request

To solve this task, the subject solar collector for demand-adapted detection of solar radiation is proposed. This has an absorber element. Furthermore, a reflector is provided, which is constructed in cross section from a lower 4, a middle 13 and an upper portion 3.

At least one reflector surface above the absorber element serves to direct flat radiation with an angle of incidence below about 30 ° onto the absorber element. Steeper radiation from an angle of incidence of about 30 °, however, causes a partial shading of the absorber 6 from the incident light.

At least one reflector surface below the absorber element serves for the indirect irradiation of the side of the absorber element facing away from the sun. For this purpose, the reflector surfaces are aligned in heating mode such that at low sun, the reflected from the reflector surfaces solar radiation substantially falls on the collector surface. Thus, at shallow sunbeam angles of incidence up to 30 ° with respect to the horizon, as it is given in the morning and evening mornings and in the cold season by the ecliptic, much of the radiation is absorbed by the device and into heat or electrical energy transformed.

At high sunshine with steep sunbeam angles of incidence of up to 30 ° and more, relative to the horizontal plane, the orientation requires that little to no direct solar radiation is reflected by the reflector surfaces on the absorber surface.

From 40 °, the sunlight is thrown back from the lower reflector surface without impacting the absorber surface. This effect at Zenitstand (noon), especially in the warm season due to the ecliptic, prevents overheating of the heat carrier or avoids unwanted unnecessary energy absorption which could lead to damage.

At an angle of incidence of less than about 25 °, incident light beams are directed onto the underside of the absorber 6 directly via the lower reflector region 4 or optionally via a further reflection via the central reflector region 13.

Preferably, at least one of the reflector surfaces is constructed in several parts from plan mirror surfaces, whereby the structure can be easily, inexpensively and easily adapted to the geographical requirements.

For easy transport and easy installation on buildings, the invention has a cuboid flat light-introducing box as a housing and as a support for at least one absorber element and at least one reflector surface. As a result, similar prefabricated modules can be easily joined together and connected. Reflecting side walls also obliquely incident light over the reflector surfaces is optimally directed to the absorber elements.

Advantageously, an angle adjustment device can be provided for at least one reflector surface. The angles can be adjusted simultaneously by gear or belt in predetermined proportions to each other or each surface can also be individually adjustable. This also makes it possible to optimize for certain angles of inclination of roofs or walls on site. Also, the efficiency may be e.g. temporarily or permanently increased by a positioning lever for operation in the warm season, whereby cloudiness or local conditions such as shadows cast by trees can be taken into account. An adaptive angular adjustment by time-controlled electric motors or bimetal strips can be provided for further optimization.

In this context, a possible summer operation as an element for solar cooling, seen where the angle settings are different than for the heating operation.

As absorber element, a vacuum absorber tube can be used or it can absorber plate similar to those used in flat panels for heat absorption.

An angle adjustment device for the absorber surface can be provided for optimization. This is possible with flat plate collectors via hinge hinges between absorber plate and heat exchange tube.

For at least partial electrical use of the solar energy, at least one side of the absorber element can carry a photovoltaic cell. This can be arranged either in the stronger or in the less irradiated part of the surface of the absorber element depending on the need for hot water or electrical power.

This can advantageously be provided a pump for transporting the heat medium, which is operated by the solar power from the photovoltaic cell. This results in a radiation-dependent delivery rate. The invention will be described in detail with reference to the accompanying drawings. Show it:

An example of the device according to the invention in cross section with different solar irradiation angles

Figure 5 shows the effects of reflections within the device according to Example Figure 1 -4 at an angle of 5 ° to 30 ° _.

6 shows the section through a possible example of the device according to the invention with the determined optimum setting or bending angles for the reflector surface (s)

7 to 10 show different inner contours of the reflector surfaces with cover and the outer contour of the absorber in section.

Fig. L 1 and Fig.12 show the arrangement of several elements in a housing (cross-sectional view).

Fig. 13 and Fig. 14 shows the arrangement in inclined position (roof collector). Fig.l 5 is an example in a spatial representation.

In Fig.l the schematic internal structure of an example of the device 1 for detecting solar radiation is shown. The sun angle is here 5 ° with respect to the horizontal plane. The solar radiation falls through the cover 8 on the upper surface 5 of the absorber element 2, which here is a surface absorber 12 preferably made of aluminum or steel sheet with highly absorbent paint (black). In addition, the solar radiation falls on the reflector surface 3 above the absorber element 2 and on the reflector surface 4 below the absorber element 2 of where it is simply reflected. The central reflector surface 13 serves as a second reflection surface. At 5 °, part of the radiation is still reflected, whereby only about 60% of the radiation reaching through the cover falls onto the absorber element. Nevertheless, there is a higher temperature gradient compared to full-surface collectors, which enables better heat transfer.

2 shows the example of Fig.l with an angle of incidence of 10 ° relative to the horizontal plane. From this angle, all radiation falling through the cover 8 impinges on the surface 5, 6 of the absorber element 2 (100%). Due to the smaller area compared to the cover 8, the temperature increases more rapidly, since a certain beam overlay (bundling) takes place.

3 and 4 show the reflections at 40 ° and 50 °, respectively. Here only the directly certifiable surface 5 is reached by the radiation. Because of the positioning angle of the upper reflector surface 2 (in this case 30 °) is formed darübi ^• addition, shading a part of the upper Absorber element surface. This shading increases with increasing angle until at a (imaginary) direction of radiation of 90 ° no direct radiation falls on the absorber element. The scattered light is neglected here. The central reflector surface 13 is hit at these angles by no direct sunlight and no first reflection by the lower reflector plane 4.

Fig.5 is intended to illustrate the different efficiency of solar radiation as a function of the angle of incidence. The upper reflector surface 3 has a plane which can extend arbitrarily long in the direction normal to the plane of the drawing. The absorber element 2 is shown here symbolically as a flat collector 12 and forms with the upper part of the cover 8 and the reflector surface 3, a three-sided prism. The upper reflector surface here has an inclination of 30 °, which causes a shadow on the surface 5 for higher angles of incidence. Flat incident angles also impinge on the absorber element 2 via reflection via the upper reflector surface 3. Between 0 ° and 30 °, the radiation above the absorber element is almost completely absorbed. The lower area of the device is used for the indirect irradiation of the absorber element underside 6. A wavefront is created for each plane reflector section. An angle of incidence of 10 ° causes a double reflection of the wave front over the lowermost portion of the lower 4 and the uppermost portion of the middle 13 reflector region of the reflector surface. A simple reflection of the wavefront takes place at the second highest section of the lower reflector region. Here, an eight-sided prism is formed by the absorber element, the cover and the reflector surface (s). The angles of the reflector surfaces from bottom to top are chosen differently here. The lowest reflection area reflects solar radiation with a 10 ° angle of incidence on the highest reflection area near the absorber surface and from there on the same. Solar radiation with an incident angle of 20 ° is directed from the lowest reflection area directly onto the absorber surface. Incident angles above 20 ° are only deflected onto the absorber surface by a part of the lowest reflection plane, the rest exits from the cover 8. But possibly also a reflection in the cover can be done. Neglecting these reflections, only a quarter of the radiation in the lower region hits the absorber underside at 30 °. Following up to the lowest level reflection area further reflector surfaces follow. The next one has full alignment with the absorber surface at 10 ° and the next one at 5 °. This results in a dependent of the angle of incidence and the orientation of the reflector surfaces absorption. For 20 ° angle of incidence, the first reflection of the lowermost reflector section is already directed onto the absorber surface. However, the second reflector section only covers half the absorber surface underside.

The third reflector section reflects incident light up to about 25 ° on the absorber element.

Fig. 6 shows an example of a reflector surface arrangement. The course of the sun's position for a vertically oriented solar collector, eg for 47 degrees north latitude over the year, is adapted very well to the needs of the hot water, heat or solar energy consumers. 7 shows the contour of the cross section of a vertically mountable solar collector part with flat absorber element 12. FIG. 8 shows a contour of such a part with a vacuum tube absorber. Fig. 9 and Fig. 10 show further contours to the schematic representation for use in inclined roofs; here for 45 ° roof slopes and also as contour of a device with flat or with vacuum tube absorber version.

In Fig.l 1 and Fig. 12 it is shown how the individual devices 1 are integrated in an assembly with a box 7. So large areas can be covered. Fig. 13 and Fig. 14 sketch examples of boxes which are mounted on roof slopes.

LIST OF REFERENCE NUMBERS

1 solar collector device

2 absorber element

3 upper reflector area

4 lower reflector area

5 directly certifiable surface of the absorber element

6 indirectly bescheinbare surface of the absorber element

7 installation box (housing)

8 cover made of transparent material (glass, plastic)

9 Optical Compensation Layer

10 insulation material (insulation board)

11 vacuum absorber tube

12 flat absorber (absorber sheet)

13 middle reflector area

Claims

claims

1. Solar collector (1) for demand-adapted detection of solar radiation with an absorber element (2) and at least one reflector surface (3) above the absorber element (2) and at least one reflector surface (4) below the absorber element (2), characterized in that the reflector in cross-section of a lower (4), middle (13) and upper region (3) is constructed, wherein the orientation of the reflection surface of the lower reflector region (4)

^• • at an angle of incidence of solar radiation of about 40 ° to a complete

Reflection of the light from the reflector leads,

At an angle of incidence of less than about 25 ° leads to a complete reflection of the incident light rays, possibly via a further reflection via the central reflector region (13), to the underside of the absorber (6) and the upper reflector region (3)

At an angle of incidence of the solar radiation of more than about 30 ° causes a partial coverage of the absorber (6) from the incident light,

• and at an angle of incidence less than 30 ° leads to a reflection of the light falling on it on the absorber.

2. Device (1) according to claim 1, characterized in that at least one of the reflector surfaces (3,4,13) is constructed in several parts from plan mirror surfaces.

3. Device according to one of claims 1 to 2, characterized in that a cuboid flat light-introducing box (7) as a housing and support for at least one solar collector (1) is used, whose left and right inner wall surfaces have reflector surfaces.

4. Device (1) according to at least one of claims 1 to 3, characterized in that an angle adjustment device for at least one reflector surface (3,13,4) is provided.

5. Device (1) according to at least one of claims 1 to 4, characterized in that as the absorber element (2), a vacuum absorber tube (11) is used.

6. Device (1) according to at least one of claims 1 to 5, characterized in that the absorber element (2) is an absorber plate of a flat collector (12).

7. Device (1) according to claim 6, characterized in that an angle adjusting device for the absorber element (2) is provided.

8. Device (1) according to at least one of claims 1 to 8, characterized in that at least one side of at least one absorber element (2) carries a photovoltaic cell.

9. Device (1) according to spoke 8, characterized in that the pump is supplied to transport the heat medium via the photovoltaic cell with power.