DESCRIPTION

Technical Field

The present invention relates to a solar energy collec¬ tor and to a method for its manufacture, as defined in the preambles of respective independent Claims.

Background Art

Convention solar energy collectors are manufactured from a relatively large number of components made from expen¬ sive material, which renders the collectors both expen¬ sive and time-consuming to assemble. When several collectors are installed on one and the same site, complicated frame structures and other devices for supporting and mutually connecting the collectors are also required.

Disclosure of the Invention

An object of the present invention is to enable known solar energy collectors to be manufactured, mounted and installed in a simpler and less expensive manner than was possible hitherto. This object is fulfilled with an inventive solar energy collector and an inventive method having the characteristic features set forth in the characterizing clauses of respective independent Claims.

Brief Description of the Drawings

Figure 1 illustrates schematically and in perspective a plurality of solar energy collectors connected together

in accordance with a first embodiment of the invention;

Figure 2 is a cross-sectional view of two mutually connected collectors shown in Figure 1;

Figure 3 is a schematic top view of a plurality of collectors according to another embodiment of the inven¬ tion;

Figure 4 is a schematic sectional view taken on the line IV-IV in Figure 3;

Figure 5 is an enlarged view, partly in section, of elements included in the collector arrangement of Figure 3 and Figure 4; and

Figure 6 is a sectional view taken on the line VI-VI in Figure 5.

Description of Preferred Embodiments

Each solar energy collector of the mutually coupled collectors illustrated in Figures 1 and 2 is comprised of a casing 1, an absorber channel 2 and connections leading to a device 3 for recovery of the heat generated in the collector and to a vacuum pump 4 for evacuating air from the collector. The casing 1 is comprised partly of a hollow, elongated section 5 in the form of a tube of circular or generally circular cross-section, so as to give the casing the maximum radial strength and to ensure that it will not collapse as a result of the subpressure prevailing therein, and partly of two end closure devices in the form of circular caps 6 and 7 which are either glued or welded to the ends of the sections and which are preferably made of plastic material.

A hollow strip 8 which incorporates the channel 2, which consists of two part channels 2a, 2b and contains pig- mented absorber fluid (e.g. black fluid) is enclosed in the casing 1 and has the same axial extension as the casing and a radial extension which is almost equal to the radial extension of the casing. The band 8 is connected to the casing 1 by means of a strip 9, which also has the same axial extension as the casing. The bar 8 is mounted generally centrally in the casing 1 and is connected thereto solely by the strip 9, so as to maximize heat absorption and minimize heat losses.

Fitted to the outside of the casing 1 are elongated channel-like elements 10, 11 and 12 whose lengths are equal to the length of the casing. The function of these channel-like elements will be described further on.

The section 5, the band 8 and the strips 9-12 form an integral unit produced by the extrusion of transparent, plastic material, such as acryl or plexiglass, to form a profiled strand of considerable length, which is then cut into the lengths required. The profiled strand is flexible and can therefore be coiled onto a drum of large diameter, as the strand is discharged from the extrusion machine. The profiled strand can then be unwound from the drum and cut to desired lengths on the site at which the collectors are manufactured and/or constructed installed.

Prior to the constructions or installation of a plurali¬ ty of solar energy collectors, the profiled strand is cut into sections 5 of equal lengths, whereafter end covers 6 and 7 are attached to the ends of respective sections, so as to form an airtight casing 1 with the ends of the hollow band 8 closed. The casings 1 are

then placed adjacent one another on a supporting sur¬ face, for instance directly on the ground or on a roof structure (said sections then replacing the outer roof covering) and are mutually connected by means of the channel-like strips or elements 10, 11 and 12, in the manner illustrated in Figure 2, whereafter the collec¬ tors are mutually joined _v together and/or to the support¬ ing surface in some appropriate manner, not shown. The channel-like elements 12 also form elements for draining of rain water.

The connectors provided on each casing 1, preferably in the form of pipe connectors on the one end cover 6 , as shown in Figure 1, are then connected to pipes 13, 14 and 15 respectively. The pipe 13 is connected to the pump 4, which is started-up when necessary. The pump 4 is necessary because the plastic from which the casing 1 is made is not impervious to diffusion and therewith allows air to enter. Any air present in the casing will act as an insulator and therewith impair efficiency.

The pipes 14 and 15 are connected to the device 3, which may comprise a heat exchanger or some other heat utiliz¬ ing device. The connections coupled to the pipe 13 communicate with the inner volume of the casing 1, whereas the connections coupled to the pipes 14 and 15 communicate with the channel 2 provided in the band 8 and consisting of an inlet channel 2a and an outlet channel 2b, said channels communicating with one another in the vicinity of the end cover 7.

The embodiment of the inventive solar energy collector illustrated in Figures 3-6 comprises casings which consist of a plurality of mutually connected, shorter tubes 16 which together form long tubes. In the embodi- ment illustrated in Figures 3 and 4, the collector is comprised of four rows of mutually parallel casings,

although this number may be fewer or greater than four. Each row may be about 100 metres in length, and even longer, and is comprised of shorter tubes having lengths of between about 2 and 10 metres. The casings of each row rest on a frame, or stand, which is comprised of a plurality of mutually parallel bars 17 which rest hori¬ zontally on the ground and which are connected to posts 18 which, in turn, are connected to horizontal bars 19. The mutual spacing of the posts 18 corresponds to the distance between the rows of casings, and the bars 19 are located immediately beneath joins 20 between the mutually connected shorter tubes 16. The frame or stand structure 17-19 has a uniform height and may be made of concrete, wood or steel and is intended to be placed on flat ground, i.e. ground which does not slope. The left-hand row in the Figure 3 and 4 illustration is intended to be positioned so that its left side will face south when the solar energy collectors are install¬ ed in the northern hemisphere.

Each tube 16 is made of transparent glass or plastic and has a circular or oval cross-sectional shape. The ratio of the major and minor axes of the oval cross-section may be roughly 2:1, wherein the major axis may be about 190 mm and the minor axis about 90 mm. The oval cross- section has been found to be most advantageous, because of low material consumption, small reflection losses and good mechanical strength against externally applied pressure forces.

The advantage of using plastic material is that very long lengths of casings can be manufactured in one piece, for instance by extrusion, and because plastic is less fragile than glass and also because the plastic casing (strand) can be wound onto reels and transported in this state. The advantage with glass casings resides

in their high mechanical strength to atmospheric pres¬ sure, their resistance to aging (discolouration) and their low raw material price.

The casings are attached to the bars 19 in the regions of the joints 20 in an appropriate manner (not shown) , such that the major axes of the tube cross-section will form angles of about 80° to the bar 19 and to the ground surface. An absorber 21 is inserted into each casing. The absorber 21 is comprised of a rail or a band made of metal, such as steel, and having two channels 21a which accommodate absorber liquid. The channels 21a are mutually connected at the upper end of the casing in Figure 3. The absorber 21 is positioned along the major axes of the cross-sections of respective tubes and has a width which is slightly smaller than the width of said axes. The absorber 21 preferably extends along the whole length of the casing and is only connected to the casing at the lower end thereof, as shown in Figure 3, thereby enabling the absorber to expand in both its longitudinal direction and in a direction perpendicular thereto. The absorber 21 is held in place inside the casing solely by loose abutment with the joins 20 on the inner surface of the casing, roughly at the ends of the major axis.

The construction of the airtight joins 20 is shown in Figures 5 and 6. Mounted at the end of each tube 16 is a rectangular metal plate 22 which is provided with an oval hole 22a and which is attached with the aid of a suitable glue 23. The cross-sectional area of the hole 22a is much smaller than the internal cross-sectional area of the tubes 16. The plates 22 on two tubes 16 lie against one another through the intermediary of an 0- ring 24 and are mutually connected by means of four nuts and bolts 25.

As shown in Figure 3, both ends of each casing are sealed in an airtight fashion by means of a respective end cap 26 and 27. The end cap 27 is provided with holes through which lines 28 connected to the channels 21a extend. The channels 21a and the lines 28 form a closed system together with a heat exchanger 29, a circulation pump 30 and an absorber liquid container 31. The end cap 27 is also provided with holes for lines 32 which communicate with the interior of the casings and which are connected to a suction pump 33. This is because the casings are not completely airtight, espec¬ ially at the joins 20, and it is therefore desirable to maintain the casings under a pressure of about 1 milli- bar in order to create a so-called low vacuum therein.

As shown in Figures 3 and 4, the solar energy collector is provided with reflectors 34 which are constructed to ensure that the maximum amount of light will be deliv- ered to the absorbers 21. The reflectors 34 are suit¬ ably comprised of a plurality of steel plates of gener¬ ally triangular cross-section, with one side of the triangle straight and in abutment with and attached to the bars 19, and the two remaining sides of the triangle curved and dimensioned so that both diffuse and direct light will be reflected at a maximum onto the absorbers 21 and such that direct light will not be broken by adjacent reflectors, thereby enabling solar rays to be utilized effectively throughout the whole of the south- ern hemisphere.

Although the invention has been described solely with reference to two exemplifying embodiments thereof, it will be understood that the invention is not restricted to these embodiments and that the invention is restrict¬ ed solely by the scope of the following Claims.