WO2012067515A1

WO2012067515A1 - Arrangement for a solar collector plate, solar collector plate, solar collector module, and solar collector system

Info

Publication number: WO2012067515A1
Application number: PCT/NO2011/000314
Authority: WO
Inventors: John Rekstad
Original assignee: Aventa As
Priority date: 2010-11-16
Filing date: 2011-11-08
Publication date: 2012-05-24
Also published as: NO20101606A1

Abstract

The present invention relates to means for correcting a flow of heat carrier medium to be fed into a plurality of upstream conduits of a self-drainable solar collector plate. The invention further discloses a self-drainable solar collector plate comprising said flow correction means, as well as a system of self-drainable solar collector plates comprising flow correcting means.

Description

ARRANGEMENT FOR A SOLAR COLLECTOR PLATE, SOLAR COLLECTOR PLATE, SOLAR COLLECTOR MODULE, AND SOLAR COLLECTOR SYSTEM

Field of the invention

[0001] The present invention relates to a self-draining solar collector system for circulating a heat carrier medium. More particularly, the present invention relates to arrangements for correcting the upstream and downstream flow of heat carrier medium and for a heat carrier medium to be circulated in a plurality of solar collector plates, a solar collector plate, a solar collector module, and a solar collector system.

Background art

[0002] A solar collector is a device converting energy of solar radiation into heat within a usable range of temperatures. The energy conversion takes place in an absorber. This absorber is configured in such a manner that the radiation is absorbed and converted to thermal energy, and the energy is transferred to a heat carrier medium, a fluid, circulating within the absorber and transporting the heat away from the absorber of the solar collector plate to a heat storage, or to a means for immediate utilisation. The heat carrier medium may be a gas or a liquid, such as water. Generally the solar collector plate is insulated, with a sunlight transparent insulation, such as glass or transparent plastic, for example, commonly being used on the side of the absorber facing the sun and a mineral wool or some other solid, temperature resistant insulation commonly being used on the side of the plate facing away from the sun. A plane solar collector has a cover plate and usually a plane absorber, i.e. there is no focusing of the sunlight incident to the absorber. Plane solar collectors also exist which are not provided with a cover plate in front of the absorber.

[0003] Broadly speaking, three fundamentally different types of solar heat

systems comprising solar collectors exist, namely a self-driven (thermo- siphon) system (Fig. 1), a pressurised pump-driven solar heat system (Fig. 2), and a non-pressurised pump-driven drain-back system (Fig. 3). The thermo-siphon system is a so-called self-circulation system in which an accumulator is positioned above the solar collector, and the entire system is filled with water, or water containing a non-freeze solution if there is a risk of frost. The circulation is accomplished by heating the water in the solar collector to thereby reduce the density thereof. This results in a pumping action by which the heated water flows to the top of the

accumulator and is replaced by colder water from the accumulator bottom, which is then lead to the bottom of the solar collector.

In the pressurised pump-driven solar heat system of Fig. 2, the heat carrier (water with an added anti-freeze solution, or alternatively another liquid having an adequate thermal capacity) is contained under pressure in a separate circulation system containing a solar collector, heat exchanger, pump, and expansion tank. The heat from the solar collector is delivered to the accumulator tank via the heat exchanger. The systems shown in Figs. 1 and 2 differ significantly from the system shown in Fig. 3. The latter system is characterised in that the heat carrier, which in this case is pure water, is only present in the solar collector and its associated piping as long as the installation remains operative, i.e. delivers heat to the accumulator. When the incidence of solar rays ends, the circulation pump is stopped and the water drains back into the accumulator while air (water vapour) from the top of accumulator fills the solar collector and piping. The hydraulic conditions are entirely different for these three types of systems. In Fig. 1 and Fig. 2, the solar collector and accumulator tank are filled with liquid at all times. An overpressure exists in the solar collector, either in the form of the hydraulic overpressure established according to Fig. 2 or the hydrostatic pressure of the system shown in Fig. 1. The system shown in Fig. 3 is characterised in that both air and water are present in the system at the same time ~ i.e. a two-phase system. When the solar collector is filled with water, the pressure within the solar collector will be lower than the atmospheric pressure since the accumulator is at atmospheric pressure. This under pressure (gauge pressure) is maintained by keeping the liquid flow rate in the return conduit sufficient to prevent air from travelling against the liquid flow up into the solar collector. The under pressure results in the formation of a vapour pressure which is at its maximum at the highest temperature point, i.e. in the top of the solar collector. This vapour-air mixture must be transported with the water down into the accumulator tank. The solar collector design and assembly of solar collectors in a parallel-connected module system, therefore, involves several additional pressure conditions (dynamic pressure loss caused by the flow, static pressure from the liquid column, and air/vapour pressure due to temperature differences) than the systems shown in Fig. 1 and Fig. 2, in which only the dynamic pressure loss influences the flow pattern.

[0005] From U.S. 4,143,644 A, a so-called thermo-siphon system is known, i.e. a solar collector in which the accumulator is positioned above the solar collector itself and is filled with a heat carrier at all times. The circulation is effected by changes in the density of the heat carrier when it is heated within the accumulator. In the system of this publication, the circulation within the absorber will be self-adjusting in that should the water flow more slowly into one of the vertical flow conduits than the rest, then the heat carrier would be heated to a higher temperature in this conduit than in the others and hence have a higher density than the heat carrier in the other conduits. As a consequence, the flow velocity in this conduit will increase. In an application of this type, the homogenous flow through the absorber will not be an issue that needs to be taken into consideration.

[0006] Conventionally, solar collectors have been made using aluminium and copper for the absorber material and using glass or plastic for a

transparent cover plate. In absorbers made of aluminium, copper, and copper alloys, glycol-containing water is commonly used as the heat carrier medium to avoid frost damage. Alternatively, pure water may be used as heat carrier medium, but in this case, the water must be drained from the solar collector whenever there is a risk of frost.

[0007] Pure water has a thermal capacity that is about 30% higher than that of water containing glycol in a necessary concentration, and is hence more efficient as a heat carrier in a solar collector.

[0008] Instead of using metal, a solar collector absorber can be manufactured using a plastic material. Plastic solar collectors are often used for pool heating, in which case a transparent glass cover is omitted. With this, the temperature the absorber can possibly reach when exposed to sunlight is limited. Most plastic materials have a limited durability when exposed to sunlight and heat. The main argument for using plastic material for the absorber is the attractive mass production costs in comparison with metal absorbers. Production cost is a critical parameter, as the use of solar energy is primarily determined by its price competitiveness with the more conventional energy sources/carriers. Plastic materials able to meet the temperature requirements of a solar collector provided with a cover plate, however, are relatively expensive.

[0009] To be able to exploit the heat deposited in a solar collector, the heat must be transported from the solar collector to a heat storage or to a means for direct consumption. To this end, a fluid referred to as a heat carrier medium or liquid, is used which also circulates in the absorber of the solar collector. Filling the absorber with a circulating fluid is necessary due to the heat transfer, as the plastic material has a very small coefficient of thermal conductivity (I = 0.1 - 0.3 W/m degree). By bringing the liquid in direct contact with the underside of the thin plastic surface on which the radiation energy is deposited as heat, the heat transport path which must be followed through the plastic material is minimised.

[0010] In conventional metal solar collectors the heat carrier liquid normally has a gauge pressure, typically 1 -3 bars. Plastic materials are not very suited for the combination of high temperature and high pressure. The solar collector to which the invention relates, therefore, has a hydraulic system which is not pressurised, but in which the liquid drains from the solar collector back to a heat storage once the supply of fluid to the solar collector is stopped. The system is self-drainable, and therefore pure water can be used as the heat carrier, with no addition of glycol.

[0011 ] Thermal stress during stagnant conditions represents the greatest

challenge for a plastic absorber of a solar collector. When heat is not drawn from the solar collector and the collector is emptied for water, the temperature can reach about 160°C (in Spain, for example). A material must be found that is able to resist the thermal doses at the high

temperatures involved in normal use. So-called high performance polymers exist appearing to be good candidates for absorbers, of which a special variant of PPS (Poly-phenylene sulphide) seems particularly suited for absorber plates. This material exhibits excellent hydrolytic stability and temperature resistance properties. It maintains its shape, rigidity, and dimensional stability over time in conditions of large temperature

variations. A problem with these so-called high performance polymers, however, is that such polymers are difficult to process, e.g. by extrusion.

[00 2] In order to produce an absorber plate using such polymer materials an extrusion tool (die) must be provided. In order for the absorber plate to become as homogenous as possible, any conditions which may introduce stresses in the plate must be eliminated. This is particularly important with a solar collector absorber as the two sides thereof are heated to different temperatures when exposed to sunlight. Stress in the material means that the polymer has different orientations in different parts of the surface, with an appurtenant free volume. When the plate is unilaterally heated, the stress will result in a volume change and consequently a change of shape causing permanent deformation of the plate.

[0013] A need exists, therefore, for providing a process for the production of

absorber plates of so-called high performance polymers.

[0014] In order to achieve an optimum efficiency it is essential that the absorber plates ensures a good contact between the heated surface of the absorber and the heat carrier medium as the desired polymer materials exhibit poor thermal conductivity. It is therefore necessary to make sure the heat carrier fills the entire absorber volume, and that the circulation is

substantially the same in the entire absorber. If this is not the case, the temperature of parts of the absorber will become higher than necessary, with an associated increase in heat loss. Experience has shown that achieving a substantially equal circulation for an entire absorber plate is difficult.

[0015] Accordingly, it is a desire to develop an absorber plate design ensuring that the entire volume of the plates is filled with heat carrier medium and that the circulation of heat carrier medium is uniform for the absorber plate. [0016] In many cases, a solar collector plate having a single absorber plate will not meet a given thermal energy demand, and hence it is desirable to be able to connect several solar collectors. Two principles can be envisioned for connecting solar collector plates, either in series or in parallel. Serial connection will make sure all solar collectors have circulation, although the circulation is not necessarily the same internally in each individual absorber plate. Serial connection, however, entails a number of other disadvantages, such as that the inlet temperature of the absorber plates will increase successively in the direction of flow of the heat carrier medium. It is not ideal for the efficiency of the absorber plates that the inlet temperatures are additive in the direction of flow, and, moreover, it will of course bring along problems that absorbers receiving heat carrier medium at very high temperatures will be subjected to additional stress.

[0017] By connecting the modules in parallel, each module will receive water at the lowest temperature, which ensures the best efficiency for the solar collector. However, it is difficult to make sure that all solar collector plates of a parallel-connected system have substantially the same circulation.

[0018] Hence, it is a desire to provide a system for connecting solar collector plates in parallel which guarantees a good circulation through all solar collector plates.

Summary of the invention

According to the present invention, the problems indicated above are solved by an arrangement for a self-drainable solar collector plate for correcting a flow of heat carrier medium to be fed into a plurality of upstream conduits of a solar collector plate, wherein the arrangement is comprised of one or more guide elements within a lower end conduit adjacent and opposite to one or more supply orifices which cover a part of the cross-section of the end conduit.

[0019] According to an aspect of the arrangement, it includes a guide element located adjacent to a lateral surface of the end conduit and adjacent to one or more upstream conduits adjacent to the lateral surface for the solar collector plate. [0020] In a further aspect, the guide element can be located adjacent to a lateral surface of the end conduit and adjacent to one or more upstream conduits adjacent to the lateral surface for the solar collector plate, and on the opposite side of the downstream conduit of the end conduit.

[0021 ] The present invention also provides an arrangement for a self-drainable solar collector plate for correcting a flow of heat carrier medium to be circulated within a plurality of solar collector plates, wherein the

arrangement is comprised of at least one flow resistance element disposed in one or more downstream conduits of the solar collector plate. According to an aspect, the at least one flow resistance element may have the shape of a pipe section, the pipe section having a smaller minimum diameter than that of an adjacent downstream conduit.

[0022] Further, according to the present invention, the at least one flow

resistance element can be located within a portion of the at least one downstream conduit inside the end conduit. According to still another aspect of the invention, the arrangement may include a flow resistance element (49, r).

[0023] The present invention also provides an arrangement for a self-drainable solar collector plate for correcting a flow of heat carrier medium to be fed into one or more downstream conduits of a solar collector plate, wherein the arrangement is comprised of one or more guide elements in an upper end conduit, with each of the at least one guide element positioned adjacent to a downstream conduit.

[0024] In a further aspect of the invention, the arrangement includes a guide

element located adjacent to a downstream conduit of the upper end conduit.

[0025] According to the present invention, a self-drainable solar collector plate for circulating a heat carrier medium is also provided, wherein the solar collector plate is constructed with a first main part,

a) The first main part is shaped as a right-angled prism having rectangular end faces and two opposite rectangular lateral surfaces of length d defining a cavity with openings at to opposite ends and having an internal height h, internal width b, and depth d, where d > b > h. The first main part further includes several parallel upstream conduits extending in parallel with the lateral surfaces, and adjacent to at least one of the lateral surfaces at least one return conduit is provided extending in parallel with the upstream conduit.

5 b) The solar collector plate further includes an integrated inlet and outlet manifold having parallel inlet and outlet conduits, with the inlet conduit being provided with at least one opening for supplying heat carrier medium to the first main part and the outlet conduit being provided with at least one opening for receiving the heat carrier medium from the return conduit, the

10 integrated outlet and inlet manifold being engaged with the lower open end of the first main part so that the heat carrier medium from the inlet conduit is communicated to the parallel upstream conduits while the outlet conduit is put in communication with the at least one return conduit, c) An upper end conduit is provided at the opposite open end of the first i s main part, the end conduit comprising two second parallel lateral surfaces, a back surface perpendicular to the two parallel second lateral surfaces, as well as two second, plane congruent end faces so that the end conduit, when engaged with the first main part, forms a closed volume for circulation of the heat carrier medium.

20 [0026] In an aspect of the present invention, the inlet manifold is provided with an end conduit adjacent to said at least one opening, wherein the end conduit is located between the inlet conduit of the inlet manifold and the first main part, at least one first restriction/guide being disposed adjacent to said at least one opening and inside the end conduit, the at least one first

25 restriction/guide being disposed opposite or substantially opposite to the at least one first opening so that the heat carrier medium is given a velocity vector which is substantially perpendicular to the parallel conduits.

[0027] In a further aspect of the present invention, the solar collector plate is

characterised in that an imaginary rectilinear axis extending in parallel with 0 the upstream conduits and through the end conduit would pass through a centre line of the longitudinal direction of the inlet conduit and outlet conduit, and that the parallel inlet and outlet conduits are arranged adjacent to each other and in such a manner that one of the conduits is located adjacent to the end conduit.

[0028] In still another aspect of the present invention, the outlet-inlet conduit is provided with at least one tubular body communicating with the at least one return conduit guiding heat carrier medium out of the at least one return conduit and through the inlet conduit having an orifice into the outlet conduit.

[0029] In still another aspect of the present invention, the end conduit is provided with at least one second restriction for the heat carrier medium. The at least one second restriction (47) may be located adjacent to the at least one return conduit.

[0030] The solar collector plate according to the present invention may be made of a special variant of PPS.

[0031] According to the present invention a solar collector module comprising at least one solar collector plate is also provided. The solar collector plate may be configured as set forth above. The solar collector module may include:

a) A first transparent cover plate.

b) At least one solar collector plate disposed underneath the first transparent cover plate.

c) An insulating layer disposed adjacent to and underneath the at least one solar collector plate.

d) At least two attachment profiles for fixing the first transparent cover plate, with one of the attachment profiles being adapted for fixation onto a support.

[0032] According to an aspect of the present invention the first attachment profile has a length substantially equal to the length d of the solar collector plate, with the first attachment profile being further provided with a protruding lip for engagement with a complementary lip provided on the second attachment module so that the first and second attachment modules are configured for a snap connection.

[0033] In still another aspect of the present invention, the solar collector module further includes a top profile engaged with the upper end of the solar collector plate and the upper end of the transparent cover plate, and a bottom profile engaged with the lower end of the solar collector plate and the lower end of the transparent cover plate.

[0034] The present invention also provides a solar collector system comprising two or more solar collector modules, where the solar collector modules may be as set out above, connected in parallel and arranged in a side-by- side configuration wherein fluid communication between the modules is provided by way of manifold connectors, with a manifold connector being releasably mounted in each inlet conduit and outlet conduit, the two or more solar collector modules further being connected via the attachment means.

[0035] Further advantages of the present invention will be apparent from the

attached patent claims.

Brief description of the drawings

[0036] The present invention will be more easily understood with reference to the attached drawings, in which:

[0037] Fig. 1 shows a principle drawing of a self-driven solar collector system - a thermo-siphon system,

[0038] Fig. 2 shows a principle drawing of a pressurised pump-driven solar heat system,

[0039] Fig. 3 shows a principle drawing of a non-pressurised pump-driven solar heat system with drainage,

[0040] Fig. 4 shows an extrusion tool,

[0041] Fig. 5 shows an exemplary plate with three absorber elements,

[0042] Fig. 6 shows a cross-section of an exemplary embodiment of an absorber plate,

[0043] Fig. 7 shows a solar collector plate according to an embodiment of the present invention,

[0044] Fig. 8 shows a section of an absorber plate with an inlet-outlet manifold,

[0045] Fig. 9 shows a cross-section of a solar collector module,

[0046] Fig. 10 shows a section of an attachment for two solar collector modules, [0047] Fig. 11 shows exemplary top and bottom profiles of a solar collector module,

[0048] Fig. 12 shows exemplary manifold connectors,

[0049] Fig. 13 shows flow of heat carrier within two parallel solar collector plates, [0050] Fig. 14 shows flow conditions for parallel solar collector plates with no restrictions/guides,

[0051 ] Fig. 15 shows flow conditions for parallel solar collector plates with

restrictions/guides provided,

[0052] Fig. 16 shows a filling scenario for three parallel solar collectors, and

[0053] Fig. 17 shows a principle drawing of flow conditions for N parallel solar collectors.

Detailed description of the invention

[0054] The present invention will now be described in more detail with reference to the accompanying drawings. The invention relates to an absorber plate design for ensuring an optimum filling and circulation of such plates. The absorber plates are further constructed so as to be easily incorporable in a system of several solar collectors connected in parallel wherein each solar collector includes at least one absorber plate according to the present invention. Also disclosed are exemplary methods of producing absorber plates according to the present invention.

[0055] It is to be understood that in the following description, the terms absorber or absorber plate refer to elements in which radiant heat is absorbed and converted to thermal energy and the energy is transferred to a heat carrier medium circulating within the absorber plate.

[0056] A solar collector plate is understood to mean a construction component including at least one absorber plate, insulation against a support, and, in one embodiment, a transparent cover plate as well as attachment profiles keeping together the parts of the solar collector plate and providing possibility of attachment to an underlying support.

[0057] A solar collector system is understood to mean a system which includes several solar collector plates in which the heat carrier medium according to the present invention is connected in parallel.

[0058] According to the present invention, the heat carrier medium can be water, but other fluids may also be used.

[0059] In the following, the terms high performance polymers, polymer, PPS, or a "special variant of PPS" will be used interchangeably for the material from which the absorber plate of the present invention is made. It should be understood that when it comes to the principal solutions in relation to the circulation and distribution of heat carrier medium in an absorber plate or in a solar collector system, one or more parts may be made of another suitable material. As stated above, absorber plates can be made of a variety of materials, and when the description does not explicitly mention a specific material, all such known absorber plate materials are embraced by the terms "high performance polymers", PPS, or a "special variant of PPS." However, it has been a desire of the applicant to provide a well functioning extrusion process for a special variant of PPS (Poly-phenylene sulphide), and hence the production process often will make reference to PPS.

[0060] Thus, according to the invention, a system of absorbers made of plastic materials is provided, which plastic materials, according to the invention, necessitates that the system operates under conditions of limited pressure. The system pressure is largely determined by the pressure resulting from the liquid column present in conduits provided in the absorbers, as the system is self-draining (Fig. 1 ) and an accumulator tank containing a heat carrying medium will be at atmospheric pressure;

consequently the pressure will be limited, in particular as compared to those found in self-driven systems such as thermo-siphon systems (Fig. 1 ) or pressurised pump-driven systems (Fig. 2) with no drain-back.

[0061] An absorber made of a polymer material preferably has to operate with no overpressure (cf. Fig. 3) as the combination of high temperature and pressure causes the material to deform when the temperature becomes sufficiently high.

[0062] For two reasons it is desirable to use water with no added glycol or

another frost preventer, one being that water exhibits higher thermal capacity and consequently better heat transfer properties than other applicable carrier medias, and the other being that glycol or another frost preventer brings along both economical as well as environmental disadvantages. In order to prevent frost damage, therefore, the absorber must be emptied for water whenever there is a risk of frost.

[0063] These requirements results in a hydraulic system characterised in that the absorber is initially filled with air. When the solar collector is exposed to sunlight, a pump for lifting the water into the absorber is started. Thereby, the air is displaced from the absorber and carried back into the

accumulator tank located underneath the solar collector. The design of the conduit system of the absorber makes sure all air is removed. The absorber is hence similar to a siphon, so that the pumping energy needed for driving the water through the conduit system only has to overcome the pressure drop caused by the flow resistance of the conduits and piping.

[0064] When energy can no longer be extracted from the solar collector, the

circulation pump stops and air from the top of the accumulator tank will enter into the solar collector as the density of the air is significantly lower than that of water. The water then drains back into the accumulator tank, making the solar collector freeze-proof .

[0065] These particular requirements on the absorber and piping configuration present some additional problems which are solved by the present invention. Since the accumulator tank (Fig. 3) is located at a lower level than the absorber, the water circulating in the solar collector loop will seek the shortest (easiest) possible path back to the accumulator tank.

[0066] When several solar collectors are arranged in parallel, similarly, the water will seek the easiest possible path back to the accumulator tank, and this will happen basically in that circulation is established in one or a few of the parallel-connected absorbers. The reason for this is that as long as the absorber is filled with air, a hydrostatic back pressure will be present due to the water columns in the conduits of the absorber. Once the water reaches the top and fills the return channel, this hydrostatic pressure will disappear or become significantly reduced. If not all the absorbers are filled at the same time, the hydrostatic pressure will be reduced in the absorbers which have been filled but be maintained in those which have not been filled. This is the mechanism under which only a few of the absorbers get circulation, and consequently contributes to the capture of solar energy. According to the present invention, a solution to this problem is provided by incorporating a flow resistance in the outlet of each absorber, which flow resistance is configured in such a manner that when the water passes through the absorber at the appropriate (optimum) flow rate, the flow resistance will correspond to the hydrostatic back pressure in absorbers which have not been completely filled with water. In this manner all the absorbers are filled and the flow rate is approximately equal through each solar collector module. [0067] Hence, according to an aspect of the invention, a self-drainage will occur, meaning that all the water present must be able to evacuate from the absorbers driven by gravity. That is, no water traps of any kind exist, as opposed to metal solar collectors, for example, in which the heat carrier piping is commonly arranged in windings.

[0068] The draining occurs when the supply of heat carrying medium is stopped, after which air/vapour will emerge from a heat storage through the return pipe(s) from the solar collector to the heat storage. The air enters the return conduit(s) of the absorber plate and the water drains through a heat carrier supply pipe of the absorber. When this is emptied the residual water runs from the lower manifold pipe out through the at least one return pipe and back to the heat storage.

[0069] In the following, we will first describe the production of absorber plates having associated inlet and outlet conduits for the heat carrier medium made of a polymer, after which the absorber plate produced is described, and finally attention will be given to solar collector plates and entire solar collector systems.

Manufacturing absorber plates

[0070] If it is practically possible, an extrusion process will be well suited for the production of the main part of an absorber plate, i.e. the part in which the transfer of heat to the heat carrier medium takes place, which part usually constitutes a plane elongate, hollow body having a thickness of less than 5 cm which commonly is also provided with internal longitudinal conduits. Two important advantages of the extrusion process relative to other manufacturing processes is its ability to produce extremely complex cross- sections as well as to work with extremely brittle materials because the materials are only subjected to compression and shear stresses. The extrusion process may also be able to yield parts having an excellent surface finish.

[0071] Such a body will not be possible to cast in a single process, hence

necessitating a subsequent complex assembly process. [0072] Consequently, the applicant has put effort in trying to develop an extrusion process for suitable polymer materials having a desired design. Extruded PPS conduit plates having the dimensions necessary for a solar collector have never been produced. The applicant, in collaboration with other parties, has succeeded in producing plates by extrusion based on a design developed by the applicant.

[0073] To produce such a plate, an extrusion tool 10 (die) must be provided. In order for the plate to become as homogenous as possible, any conditions which may introduce stresses in the plate must be eliminated. This is particularly important with a solar collector absorber as the two sides thereof are heated to different temperatures when exposed to sunlight. Stress in the material means that the polymer has different orientations in different parts of the surface, with an appurtenant free volume. When the plate is unilaterally heated, the stress will lead to a volume change and consequently a change of shape causing permanent deformation of the plate.

[0074] Therefore, the configuration of the extrusion tool is critical.

[0075] The applicant has developed an extrusion tool, shown in Fig. 4, which

eliminates the so-called necking effects in the outermost regions of the plate which is the main cause of stress in the plate.

[0076] The extrusion tool includes a die 10 having an entrance 11 for feeding material such as PPS. The material is then fed from the die 10 through a constricted section 12 eliminating said necking effects, after which the material is run through a calibrator 13. Adjacent to the exit from the calibrator 13 four knives 14 are provided, all of which are arranged parallel to the direction of movement of the material discharged from the calibrator. In an embodiment, two knives are positioned so as to cut off the edges of the material discharged, while the remaining two knives 14 are positioned so that the distances between adjacent knives 14 are the same. This results in that three identical absorber plates are formed simultaneously in parallel. If it is desired to produce absorber plates of different widths, it will of course be possible to alter the individual distances between knives 4. However, according to an embodiment, the individual distances between the knives are adapted to common constructional standards so that, as mentioned, three equal absorber plates are output. According to an embodiment, the absorber plates are not symmetrical about a centre point along the horizontal axis, i.e. the width axis, in which case the distance between knives 14 cannot be straightforwardly altered to obtain absorber plates of different widths.

[0077] Extensive testing has been carried out of the absorber plates to make sure they are able to resist the temperature stresses encountered in a solar collector. The tests are based on accelerated aging at temperatures between 150°C and 200°C, and simulations of weather data from different climatic zones show that the operative life of the plates undergoing the temperature stresses is at least 20 years, even in southern Spain.

An absorber plate according to an embodiment

[0078] The efficiency of a solar collector, i.e. the portion of the radiation impinging on the solar collector being converted to useable heat, is given by the following approximate formula:

Π = Πθ - KT (Tabs - TambVIN - K₂ (Tabs ~ T_amb)² /I ,

(1 )

[0079] where: ηο is the efficiency when T_abs= T_amb,

Ki is the effective coefficient of heat loss,

K₂ is the effective coefficient of heat loss, and

I is the solar intensity.

[0080] r|o is determined by the transmission through the transparent cover plate, the absorptance of the absorber surface, and the heat transfer efficiency between the absorber and circulating heat carrier. The heat loss to the surroundings is of vital importance for the efficiency in the case of high working temperature and/or low solar intensity.

[0081 ] As polymer materials exhibit poor thermal conductivity, it is necessary to make sure the heat carrier fills the entire absorber volume, and that the circulation is substantially the same throughout the absorber and in the various connected modules. If this is not the case, the temperature in different parts of the absorber will become higher than necessary, resulting in an increased heat loss.

[0082] In order to achieve a substantially uniform flow-through in each absorber, the dimensions must be chosen with care. Moreover, it is a desire that the inner volume of the absorber plate is minimised so that the amount of heat carrier in the absorber plate is as small as possible. In this manner an optimum efficiency is ensured with a minimal emission of heat to the surroundings and a maximal transfer of heat to the heat carrier medium.

[0083] It is also a desire that an absorber plate shall be an integrated part of a solar collector plate, wherein the solar collector plate, in turn, is one of a plurality of such solar collector plates in a solar collector system. It is hence a desire that solar collector plates are connectable, and of course that the connection thereof is as easy as possible.

[0084] It is a further desire that the solar collector shall be configured as a

modular building component well suited for the working methods used in the construction industry. It shall allow for flexibility in shape and

dimensions so that it can be used/fill a space available on a building, and the connectors or manifold system of the solar collector shall be

configured so as to fit within the overall height (panel thickness) otherwise required for the solar collector.

[0085] An absorber plate generally includes a number of parallel conduits, and in one embodiment it comprises a significantly larger number of upstream conduits than downstream conduits. In another variant, an absorber plate is provided with a single downstream/return conduit. The heat carrier medium enters the absorber plate at a lower end thereof and is carried upstream through the conduits, and then returns through the downstream conduit(s) for utilisation.

[0086] The above restrictions suggest that it is desirable to have a thin-walled and thin (of small h) absorber plate having a width b adapted to common constructional standards. Building components are usually adapted to such standards in that they are made with a standard width or with a multiple of a standard width. In a constructional context, the height or length d is not equally critical. As indicated above, an absorber plate includes a main part, i.e. the part suited for extrusion, which part, in light of the above requirements, will be provided with a large number of upstream conduits and a small number of downstream/return conduits and also have a small internal thickness. According to an embodiment, the main parts are configured as indicated in Figs. 5 and 6. Fig. 5 shows a cross-section of three adjacent absorber plates 20 as they result from the parallel production of three absorber plate widths before separation thereof, with the conduits shown in section. Fig. 6 shows a section of an absorber plate according to one embodiment, or rather the main part 30 of an absorber plate. Main part 30 can be characterised by the following parameters: n: number of parallel upstream conduits 31 ,

m: number of downstream/return conduits 32, with only one being shown in Fig. 6,

b: width of a main part,

b₂: internal width of a downstream/return conduit as shown in fig 6, b₃: centre-to-centre conduit width for upstream conduits 31 , c: width of three parallel produced main parts as shown in Fig. 5, d: denotes the height or length of the main part, i.e. conduit lengths, h: internal height, i.e. distance between internal surfaces,

h₂: thickness of the main part 30 of an absorber plate,

ti: wall thickness of walls surrounding the downstream conduit 32, as well as all external walls, and

t₂: wall thickness between conduits.

In an embodiment adapted to a particular constructional standard, the parameters defined above for a main part 30 of an absorber plate according to an embodiment can be quantified as: n=55, m=1 , b= 560mm, b₂=7mm, b₃=10mm, c=1800mm, h=4.2mm, h₂=6mm, ti=0.9mm and t₂=0.4mm. The thickness if the main part is, as indicated in one

embodiment, h₂=6mm, which is the smallest conduit plate thickness that can be made of the special adapted PPS using the extrusion tool shown in Fig. 4. This gives an internal open volume of approx. 3.6 litres/m² of gross solar collector area. A thickness of 6mm is a very common thickness for building components adapted to the standard indicated above.

[0088] The main part 30 of an absorber plate must be connected to a system for the supply and return of heat carrier medium so that a complete absorber plate for a solar collector system with a circulating heat carrier is provided. In the following, an example of such heat carrier medium supply and return systems is described.

[0089] To obtain a compact absorber the main part 40,50 (see Figs. 7 and 8) is fitted with end conduits 43,53,48 and connected to a heat carrier (water) circulation manifold. Fig. 8 shows an example of how end conduits

43,53,48 having integrated manifolds 51 ,52,55 may be attached 57 to the main part 40,50. The result has been achieved through the development of a welding technique making it possible for obtain a tight connection between the cast end conduit 43,53 and the extruded main part 40,50. Due to their different production processes, these components may be comprised of slightly different types of material. Typically, the material of the end conduits may exhibit low viscosity in the liquid state, and have glass fibre added thereto, whereas the material of the extruded plates may exhibit significantly higher viscosity in the liquid state.

[0090] The welding can be performed through so-called hot plate welding, in

which the viscosities are corrected by keeping the heat plates at different temperatures towards the end conduits and towards the extruded plates. Alternatively, this can be accomplished by way of infrared melting, also in that case having different temperatures of the molten material. The welding process is particularly demanding because of the tiny dimensions of the walls to be welded together.

[0091] As mentioned, the lower end conduit 53,43 has an integrated manifold

51 ,52,55. In this example, the uppermost manifold pipe 51 is for supplying heat carrier. The heat carrier is introduced into the end conduit 43,53 through an opening 55 located down to the left in Fig. 8. The end conduit 43,53 distributes the heat carrier among the n parallel conduits in the longitudinal direction of the plate 40,50. When the heat carrier reaches the top, it is combined in an upper end conduit 48 and carried down and back to the return manifold pipe through a reinforced plate conduit on the right side (Fig 7). The reinforced return conduit is shown located on the right side, but it is of course possible to turn the absorber plate so that the return conduit is located on a left side, in which case opening 55 is located on the right side. Moreover, the mention of a single return conduit and the positioning thereof adjacent to three outer walls is only an exemplary embodiment. Preferably, m<n, but it is not an absolute requirement that only one return conduit is used and that this conduit is arranged as indicated herein. A multitude of upstream and downstream conduit configurations can be envisioned. It is also conceivable to experiment with one or more openings 55 as well as to experiment with the shape and size thereof.

[0092] An internal wall of lower end conduit 43,53 is welded together with the left wall of the return conduit of plate 40,50 so that it is separated from the remaining volume. A custom-made pipe 49 makes sure the return water passes the upper manifold pipe 51 and is delivered to the lower return pipe 52.

[0093] The end conduits 43,53,48 are welded onto the main part 40,50. Given the dimensions indicated for the main part 30,40,50 and end conduit 43,53,48, and with the small wall thickness, the welding process will be complicated.

[0094] It should be understood that the supply conduits/pipes and return

conduits/pipes may switch positions, or change shape. Additionally, the supply opening 55 and return pipe 49 may switch positions or change shape, and, if m>1 , it will be necessary to increase the number of return pipes 49. A solution is shown wherein the inlet and return manifold is made in one piece for engagement with a lower end of the main part 40,50. A particular solution could be that the return conduit 52 is disposed at an upper end of main part 40,50.

[0095] The design chosen, in which the end conduits and manifold are integrated into the absorber itself, imposes some dimensional limitations resulting in that a pure laminar flow is not achievable along parts of the flow path. So- called jet streams will occur in parts of the system so that a linear momentum becomes important for the pressure conditions. The jet streams have a fixed extent which is shorter than the length of the end conduit 43,53. In the lower end conduit 43,53, therefore, in an embodiment as illustrated in Figs. 7 or 8, the flow conditions will be significantly different between the left and right sides of this conduit 43,53. The arrows of Figs. 7 and 8 indicate the direction of flow of the heat carrier medium. It can be seen that the velocity vector of the heat carrier medium at the lower inlet conduit is perpendicular to the longitudinal direction of the upstream conduit, which is not a coincidence. As indicated above, it is a desire that the flow distribution within the upstream conduit is as uniform as possible. Had the velocity vector been parallel with the upstream conduits and the heat carrier medium was introduced through an opening 55 as indicated in Fig. 8, then a favourable flow/filling distribution of the heat carrier medium in the upstream conduit would not have been obtained. Hence, in order to counteract the impact of non-laminar effects, guides/restrictions 46,56,47 are introduced in the end conduits 43,53,48. At the opening 55 of lower end conduit 53, a stopper/restriction 46, 56 is provided adjacent and opposite to opening 55 which obstructs a portion of the cross-section of the end conduit 53 and makes sure the initial velocity component parallel with the upstream conduits are refracted and reflected so that a

dominating horizontal small-divergence velocity vector is obtained. The configuration of the restriction is a design matter and may be subject to experiments. The embodiment shown, therefore, is merely an example which has shown to be favourable for the configuration shown in Figs. 7 and 8.

According to an illustrated embodiment, the velocity vector in the lower end conduit 43,53 is directed to the right, and the outlet conduit having an opening in the upper end conduit 48 is located on the right side. Therefore, a biased distribution of the flow through the upstream conduits of the absorber plate with the greatest flow rate being on the right side will be natural both from an energy and impulse perspective. To correct for this biasing flow guides may be provided in the upper end conduit 48 so that parts of the water flowing upwards on the right side of the main part 40,50 of the absorber are directed to the left, i.e. against the dominant direction of flow in the upper end conduit 48. The flow guide can be configured variously, but the object is to limit the portion of the flow in the upper end conduit from the upstream conduits on the right side of the absorber plate 40,50 for the oppositely facing velocity vector. The configuration must also be chosen so that the mechanism operates satisfactorily with various flow velocities.

[0097] Fig. 7 shows a restriction 47 disposed in the upper end conduit 48,

wherein the restriction/guide is in the form of a tilted partition wall having its base adjacent to the return conduit. The restriction 47 has shown to be favourable for the flow conditions in the upper end conduit 48, with the heat carrier entering into the right, or left if the system is reversed, conduits being forced to move against the main flow some distance in the end conduit before the flow turns and is guided towards the outlet conduit. Without the arrangement 47, a disproportionately large portion of the water flow would occur in the higher part of the absorber. The effects are shown in the IR images of Figs. 14 and 15.

[0098] Figs. 14 and 15 show infrared photo grading of three absorbers. First, hot water is circulated (light colour), and then cold water (dark colour) is introduced. In this manner the water velocity distribution can be studied for the different conduits of the absorber plates. At the top, the cold water front is shown with no guide provided near the outlet of the upper end conduit. The bottom image shows the cold water front with the guide provided. The flow distribution in the lower image ensures an acceptable cooling and consequently high efficiency, whereas the flow distribution at the top is not acceptable.

[0099] If configurations other than the one shown in Fig. 7 are used, then other solutions for restrictions 47 are conceivable.

[00100] The vertical flow velocity in the upstream conduits of plate 40,50 is very low, in the order of 1 -2 cm/s, and therefore no pressure adjustment mechanism is necessary due to different flow resistances.

A solar collector plate according to an embodiment of the invention W

[00101] As indicated, the absorber plate must be adapted in an environment in some setting; hence the absorber must be provided with other elements so that a solar collector plate is obtained. Fig. 10 shows an exemplary solar collector plate. According to an embodiment, the width of the absorber 60 is chosen so that when it is assembled with aluminium profiles 63, 64 and covered with a transparent cover plate 62 (made of polycarbonate, for example), the overall width of the solar collector module will be 60 cm, which is a common constructional standard.

[00102] A separate attachment system has been developed, as shown in Figs. 10, 11 , and 12.

A solar collector system according to an embodiment of the present invention

[00103] A solar collector system is comprised of several modules or solar collector plates. These are positioned side by side and fastened as shown in Figs. 10-12. The manifolds may be connected using connectors 90 as shown in Fig. 12. The connectors 90 are pipe sockets which, according to an aspect of the invention, are provided with at least one o-ring packer for each end socket to be engaged with the upper 51 or lower 52 manifold pipes.

[00104] The circulation of heat carrier in a solar collector system consisting of two modules is shown in Fig. 13. By connecting the modules in parallel, each module will receive water at the lowest temperature, ensuring the best efficiency for the solar collector.

[00105] The solar collector is connected to a non-pressurised heat storage. Heat carrier medium is transported from the heat storage to one or more solar collectors, in which the fluid, via inlet manifold 101 and the lower end conduit, displaces the air initially present in the absorbers into the heat storage. When the circulation is stopped, air will flow back into the solar collectors from the heat storage and the water inside the solar collector and connection pipes 101 , 102 drains back to the heat storage.

[00106] It must be made sure that the circulation is substantially the same through all absorbers of a parallel-connected solar collector system. At power-up, when several modules are connected to the same manifold, there will be substantially uniform conditions due to the levelling effect of gravity. This is shown in Fig. 16. Once the water reaches the upper end conduit 48,108 and begins to flow back inside the return conduit, the static pressure will drop because the return conduit is filled. As all the modules have the same pressure in the lower end conduit 43,53, any delay in the filling of a module may result in that this module is never completely filled and remains passive.

[00107] According to the present invention, a method for making sure that

circulation is achieved in all solar collector modules is provided. In this relation, reference is made to Fig. 17, showing a schematic model of N solar collector modules mounted on the same manifold.

[00108] To make sure all absorbers participate a flow resistance 49, r is introduced at the bottom of the return conduit of each individual absorber. The flow resistance is provided by a pipe section having a small internal diameter. To the first order, the pressure drop across the restriction 49, r can be expressed as

Δρ = r v² (2)

[00109] where v is the flow rate through the solar collector module and r is a drag coefficient determined by the dimensions, geometry, roughness, and material of the obstruction.

[001 10] The total flow rate through all solar collector modules is V. If N modules have circulation, the flow rate of each module will be V/N as it is assumed that all modules are identical and that the pressure drop in the manifold pipes is negligible.

[001 1 1 ] Lifting the heat carrier fluid to the top of the solar collector module requires a minimum pressure of

[001 12] where H is the height of the solar collector module above the inlet pipe of the manifold, p is the liquid density, and g is the gravitational acceleration.

[001 13] When at least one of the modules is filled the pressure differential between the inlet and outlet, ρ,η - p_out is reduced to Δρ since the return conduit of the solar collector module is now filled with heat carrier. [001 14] If all solar collector modules is to achieve circulation, r must be chosen so that

Δρ = r (V/N)² = pgH (N-1 )²/N² (4)

[001 15] Hence, the resistance r is dependent both on the number of modules and on the total flow rate in the solar collector. According to an embodiment, the flow resistance is provided by a pipe section of length 5 cm having a small internal diameter. However, it is to be understood from the above expressions that r may assume different values, i.e. the length, internal diameter, and surface condition of the pipe section can be varied, among other things, according to the number of solar collector modules, N, and flow rate V.

[001 16] When one or more absorbers are passive, the flow velocity through the active absorbers will be correspondingly higher. The resistance of the pipe is chosen so that it is energetically advantageous to achieve a symmetric circulation in all the absorbers.

Claims

1. An arrangement for a self-drainable solar collector plate for correcting a flow of heat carrier medium to be fed into a plurality of upstream conduits of a solar collector plate,

characterised in that the arrangement is comprised of one or more guide elements (46,56) in a lower end conduit (43,53) adjacent and opposite to one or more supply openings (55) which covers a part of the cross-section of the end conduit (43,53).

2. The arrangement for a solar collector plate of claim 1 ,

characterised in that the arrangement comprises a guide element (46,56) disposed adjacent to a lateral surface of the end conduit (43,53) and adjacent to one or more upstream conduits adjacent to the lateral surface for the solar collector plate (40,50).

3. The arrangement for a solar collector plate of claims 1 or 2,

characterised in that the arrangement comprises a guide element (46,56) disposed adjacent to a lateral surface of the end conduit (43,53) and adjacent to one or more upstream conduits adjacent to the lateral surface for the solar collector plate (40,50) and on the opposite side of the downstream conduit of the end conduit (43,53).

4. An arrangement for a self-drainable solar collector plate for correcting a flow of heat carrier medium to be fed into one or more downstream conduits of a solar collector plate,

characterised in that the arrangement is comprised of one or more guide elements (47) in an upper end conduit (48), wherein each of the at least one guide element is positioned adjacent to a downstream conduit .

5. The arrangement for a solar collector plate of claim 4,

characterised in that the arrangement comprises a guide element (47) disposed adjacent to a downstream conduit of the upper end conduit (48).

6. An arrangement for a self-drainable solar collector plate for correcting a flow of heat carrier medium to be circulated in a plurality of solar collector plates, characterised in that the arrangement is comprised of at least one flow resistance element (49, r) disposed in one or more downstream conduits of the solar collector plate.

7. The arrangement for a solar collector plate of claim 6,

c h a r a c t e r i s e d i n that the at least one flow resistance element (49, r) is configured as a tubular section, the tubular section having a minimum diameter being smaller than an adjacent downstream conduit.

8. The arrangement for a solar collector plate of claims 6 or 7,

c h a r a c t e r i s e d i n that the at least one flow resistance element (49, r) is disposed in the portion of the at least one downstream conduit inside the end conduit (43,53).

9. The arrangement for a solar collector plate of claims 6 or 7,

c h a r a c t e r i s e d i n that the arrangement comprises a flow resistance element (49, r).

10. A self-drainable solar collector plate for circulating a heat carrier medium, the solar collector plate being configured with a first main part (30,40,50,100), wherein

a) the first main part (30,40,50,100) has the shape of a right-angled prism

having rectangular end faces and two opposite rectangular

lateral surfaces of length d defining a cavity having openings at two opposite ends, having an internal height h, an internal width b,

and a depth d, with d>b>h,

the first main part (30,40,50,100) further comprising several parallel upstream conduits extending in parallel with the lateral surfaces, with at least one return conduit, which is parallel with the upstream conduit, being arranged adjacent to at least one of the lateral surfaces,

b) the solar collector plate further comprises an integrated inlet and outlet manifold having parallel inlet and outlet conduits (51 ,101 ,52,102), the inlet conduit (51 ,101) being provided with at least one opening (45,55) for supplying heat carrier medium to the first main part (30,40,50,100), the outlet conduit (52,102) being provided with at least one opening for receiving the heat carrier medium from the return conduit, and the integrated outlet and inlet manifold being engaged (47) with the lower open end of the first main part (30,40,50,100) so that the heat carrier medium from the inlet conduit (51,101) is put in communication with the parallel upstream conduits while the outlet conduit (52,102) is put in communication with the at least one return conduit, c) an upper end conduit (48,108) is disposed at the opposite open end of the first main part (30,40,50,100), the end conduit (48,108) comprising two second parallel lateral surfaces, a back face perpendicular to the two parallel second lateral surfaces, and two second plane congruent end faces so that the end conduit (48,108), when engaged with the first main part (30,40,50,100), forms a closed volume for circulating the heat carrier medium.

11. The solar collector plate of claim 10,

characterised in that the inlet manifold is provided with an end conduit (43,53) adjacent to said at least one opening (45,55), the end conduit (43,53) being located between the inlet conduit (51 ,101) of the inlet manifold and the first main part (30,40,50,100), with at least one first restriction/guide (46,56) being disposed adjacent to said at least one opening (45,55) and within the end conduit (43,53), the at least one first restriction/guide (46,56) being disposed opposite or substantially opposite to the at least one first opening (45,55) so that the heat carrier medium assumes a velocity vector substantially perpendicular to the parallel conduits.

12. The solar collector plate of claim 11 ,

characterised in that an imaginary rectilinear axis extending in parallel with the upstream conduit and through the end conduit (43,53) will pass through a centre line in the longitudinal direction of the inlet conduit (51,101) and outlet conduit (52,102), and that the parallel inlet (51,101) and outlet conduits (52,102) are arranged adjacent to each other and in such a manner that one of said conduits is located adjacent to the end conduit (43,53).

13. The solar collector plate of claims 10 or 11 ,

characterised in that the outlet and inlet conduits (51,101,52,102) are provided with at least one tubular body (49) in fluid communication with the at least one return conduit which directs heat carrier medium out from the at least one return conduit and through the inlet conduit (51 ,101) with an orifice into the outlet conduit (52,102). 12/067515

30

14. The solar collector plate of claims 10-13,

characterised in that the end conduit (48,108) is provided with at least one second restriction (47) for the heat carrier medium.

15. The solar collector plate of claim 13,

characterised in that the at least one second restriction (47) is disposed adjacent to the at least one return conduit.

16. The solar collector plate of any one of claims 10-15,

characterised in that the solar collector plate is made of a special variant of PPS.

17. A solar collector module comprising at least one solar collector plate as

claimed in claims 10-16, the solar collector module comprising:

a) a first transparent cover plate (62,72),

b) at least one solar collector plate (60) positioned underneath the first transparent cover plate (62,72),

c) an insulating layer (61) disposed adjacent to and underneath the at least one solar collector plate (60), and

d) at least two attachment profiles (63,73,64,74) for fixing the first transparent cover plate (62,72), wherein one of the attachment profiles (63) is adapted for being fixed onto an underlying support.

18. The solar collector module of claim 17,

characterised in that the first attachment profile (63) has a length substantially equal to the length d of the solar collector plate (60), the first attachment profile (63,73) further being provided with a protruding lip (65) for engagement with a complementary lip (66) provided on the second attachment module (64,74), so that the first and second attachment modules (63,73,64,74) are adapted for a "snap connection".

19. The solar collector module of claims 17 or 18,

characterised in that the solar collector module further comprises a top profile engaged with the upper end of the solar collector plate (60) and the upper end of the transparent cover plate (62,72), and

a bottom profile engaged with the lower end of the solar collector plate (60) and the lower end of the transparent cover plate (62,72).

20. A solar collector system, comprising:

two or more solar collector modules as claimed in claims 17 - 19 connected in parallel and arranged in a side-by-side configuration, wherein fluid

communication between the modules is provided by manifold connectors (90), with a manifold connector (90) being releasably mounted in each inlet conduit

(51 ,101) and outlet conduit (52,102), the two or more solar collector modules further being connected via the attachment means (63,73,64,74).