WO2001096791A1

WO2001096791A1 - High temperature solar radiation heat converter

Info

Publication number: WO2001096791A1
Application number: PCT/IL2001/000540
Authority: WO
Inventors: Dan Sagie; Ido Anteby
Original assignee: Rotem Industries Ltd.
Priority date: 2000-06-13
Filing date: 2001-06-12
Publication date: 2001-12-20
Also published as: AU6628001A

Abstract

Method and apparatus for producing available thermal energy from the energy of the solar radiation. The solar radiation is concentrated to a sufficiently high intensity within a concentrator assembly (11). The concentrated radiation is caused to impinge on an absorber (14) capable of supporting high temperatures. The heat of the concentrated radiation is transferred by heat exchange to a fluid to reach high temperatures and flow rates, and the fluid is then used to actuate a generator of mechanical energy (33). The temperature which is created during the exchange of heat in the fluid may be of at least 400 °C. The pressure drop across the heat exchanger assembly may be selected to be low enough to facilitate turbo-compressor closed loop operation.

Description

HIGH TEMPERATURE SOLAR RADIATION HEAT

CONVERTER

Field of the Invention

The invention relates to a method and apparatus for collecting and using solar energy, more specifically, for producing, from the energy of the solar radiation, thermal energy, which can then be transformed into other forms of energy.

Background of the Invention

The collection and use of solar radiation for various purposes has received considerable attention in the art. One possible use of the solar radiation consists in heating gases, generally air, and then using the heated gases to heat buildings. For this purpose, a moderate gas temperature is required. The possible production of mechanical energy that can be transformed in other forms of energy, e.g., electrical energy, has also been considered. However, it requires high temperatures and concurrently high flow rates, two parameters that are to a certain extent contradictory.

William B. Stine and Richard B. Diver, in "A Compendium of Solar Dish/Stirring Technology", a paper prepared and released by Sandia National Laboratories, SAND93-7026 UC-236, describe a system for generating electric power by using a plurality of concave parabolic solar concentrators nicknamed dishes, a cavity receiver and a Stirling heat engine with an electric generator or alternator. A sun-tracking system controls the solar concentrator by rotation about two axes to keep itsoptical axis pointed directly towards the sun. The cavity receiver absorbs the concentrated solar energy and the thermal energy heats the working gas in the Stirling engine. The Stirling engine is considered an appropriate device for such a use. It is coupled to a separate electric generator or alternator to convert the mechanical power into electricity or an alternator may be integrated into the engine. The Stirling engine requires a working gas, which is to be heated, and the receiver of the apparatus, described in the aforesaid paper, has the function to transfer concentrated solar heat from the dish concentrator to the said working fluid.

The secondary concentrators for the collection of solar energy are typically nonimaging concentrators. Various types of such concentrators are described in W.T. Welford and R. Winston - High Collection Non-Imaging Optics, Academic Press, 1989. They are typically compound parabolic concentrators (hereinafter, briefly, CPC) which have been widely described in the literature. Such a concentrator has an exit aperture. The parabolic concentrator can thus be defined by rotating an arc of parabola about the axis of the concentrator (not the axis of the parabola), which passes through the exit aperture. A parabolic concentrator can be formed by means of a flexible sheath which is coupled to a suitable backbone frame and held against it, e.g., by the application of a vacuum on its outer surface, or can be made of a plurality of flat elements, so dimensioned and connected as to approach, as a whole, the parabolic shape. Such composite concentrators will be called hereinafter CPC concentrators.

USP 5,421,322 describes a central solar receiver comprising a housing with a frusto-conical window for the admission of instant concentrated solar radiation, a volumetric solar absorber within a housing surrounding the window, means for the injection of working fluid into contact with a volumetric solar absorber, and means for the withdrawal of heated working fluid. As further described and claimed in USP 5,323,764, the volumetric solar absorber of said receiver comprises a base body holding an array of absorber members spaced from each other and projecting from one face thereof, with their free ends facing a window of the receiver housing, means for the injection of working fluid into the volumetric solar absorber, in flow directions which intersect the absorber member, and means for the withdrawal of heated working fluid.

USP 5,245,986 discloses a solar receiver having a housing with a window for the admission of incident concentrated solar radiation, a volumetric solar absorber, working fluid injector means and means for withdrawing the hot working fluid, wherein the volumetric solar absorber has a base body holding an array of absorber members, each having two ends, one end fixed to the base body and the other end being free end spaced away from the base body, said absorber members being spaced from each other and projecting from one face of the base body, their free ends being turned towards the window, and the working fluid injector means injecting the working fluid into the volumetric solar absorber in flow directions which interest said absorber members and the incident solar radiation.

The devices of the above patents consist of a ceramic material for the absorbing matrix to survive the high temperatures involved. These construction materials enable operation at high temperature at the expense of cumbersome and expensive receiver.

USP 5,578,140 describes a dielectric mirror provided above a solar collector to reflect the concentrated solar radiation into a receiver. It also describes a plurality of nonimaging secondary concentrators arranged in consecutive zones intermediary between the dielectric mirror and the receiver.

Thomas W. Kerslake et al., in "Analysis of Solar Receiver Flux Distributions for U.S. /Russian Solar Dynamic System Demonstration of the MIR Space Station" in IECIC paper no. AP-136, ASME 1995, and Halj Strumpf et al. in "Design of the Heat Receiver for the U.S./Russian Solar Dynamic Power Joint Flight Demonstration" in IECIC paper no. AP-168, SMEE 1995, describe a solar dynamic system of flight demonstration on the Russian MIR space station, the said solar energy collector system comprising a concentrator and a receiver, the concentrator having a single parabolic facet, and the receiver having a configuration which comprises three functional components - the heat receiver, the heat exchanger, and a thermal storage device - into a single unit. It comprises a cylindrical receiver cavity, the walls of which are lined with a series of tubes running the length of the cavity. The working fluid flows through a finned annular region in the tubes. The receiver cavity walls consist of a metallic shelf with inner ceramic liner. The thermal storage includes a solid- to -liquid phase change material through which the heat is transferred to the working fluid.

Gideon Miron'et al., in "A Large Compound Parabolic Concentrator for 500 kW Solar Center Receiver System - Design and Evaluation", presented at the 9th SolarPACES International Symposium on Solar Thermal Concentrating Technologies, Font-Romeu, France, June 1998, describe a solar electricity generation plant which includes- a high temperature volumetric solar receiver integrated with a large compound parabolic secondary concentrator. A powerful solar radiation reflector reflects solar radiation into the secondary CPC, which is central and around which are arranged a number of peripheral CPCs. The central CPC is positioned at the top of a high temperature receiver. The peripheral CPCs are installed at the perimeter of the central CPC to collect the lower energy spillage of

the radiation. While the central secondary CPC transmits the solar energy to the high temperature receiver, the secondary CPCs transmit each to a preheater. The CPCs are constructed by assembling various modules of different sizes comprising aluminum frames, cast and machined to precise dimensions, and bolted to each other with special spacers. Each frame supports a flat reflecting element consisting of a glass mirror glued to an aluminum plate.

In spite of the extensive coverage in the prior art of the problem of producing available thermal energy and transforming it to mechanical and then to electrical energy, no efficient apparatus that satisfies these requirements, and particularly provides the high temperature and concurrently high flow rate required for such purposes, has been developed in the prior art. This invention is primarily directed to a method and an apparatus for producing available thermal energy from the energy of the solar radiation, from which thermal energy mechanical energy can be derived. Such an apparatus, in its entirety, has been called and will be called hereinafter 'receiver'" or "receiver assembly".

The conventional receivers are inherently limited to low fluxes and low temperatures, since only then the following conditions are valid:

- No significant re-radiation losses of energy;

- The temperature gradient over the conduct (tube) wall is not critical.

- Conventional materials are available for -the conducts (tubing) and for the selective coating (copper for the tubing with excellent fabrication and heat conduction properties, and epoxies paints for the selective coating).

It is therefore the main purpose of this invention to provide such a solar energy receiver or converter, wherein a working fluid is brought to extremely high temperature, up to 850°C and over, preferably 1000°C and over, at high flow rates. High fluxes produce a high specific power (power per unit volume or weight). It is another purpose of this invention to provide available thermal energy, which can be transformed into mechanical and then optionally into electrical energy directly from solar radiation, in a single solar energy receiver or converter.

It is a further purpose of the invention to provide a solar energy receiver or converter, which is suitable for constituting a preheater unit in a solar energy plant having a high temperature receiver.

It is a still further purpose of the invention to provide a solar energy receiver . or converter that is compact and hence cheap and easy to assemble and maintain in situ.

It is a still further purpose of this invention to provide a process and apparatus for producing thermal and/or mechanical and/or electrical energy from solar radiation with a high yield and efficiency.

It is a still further purpose of the invention to provide a solar energy receiver or converter that is reliable and not subject to malfunctions.

Other purposes and advantages of the invention will appear as the description proceeds.

Definitions:

For the sake of clarity, some terms used herein are defined as follows.

Insolation - Solar Electro -magnetic radiation.

Absorber - a device that absorbs insolation and converts the energy into thermal energy (heat). Collector - a device typically consisting of a frame and a glazing material that reflects incident insolation onto a desired target.

Concentrator - a reflective device (collector) that focuses incident insolation onto an area smaller than the reflective surface, resulting in an increased insolation at the point of focus. The concentrator is a special case of collector. Typical examples are a heliostat that reflects the insolation onto a central receiver, a trough that reflects the insolation onto a tube receiver, or a parabolic dish that reflects the insolation onto a heat engine located at the parabolic dish focus.

CPC - Compound Parabolic Concentrator - Non-imaging Optics device capable of high concentration of light radiation at the expense of losing the optical image. It is typically used where the original geometry (shape) of the light source is not important but only the energy delivered to the target.

Parabolic dish - A concentrator, generally bowl-shaped with a parabola contour cross-section, with two-axis tracking of the sun.

Receiver (Solar-) or Receiver Assembly- An assembly designed to receive solar electro-magnetic, radiation and convert it into thermal energy. Normally, a solar receiver includes a primary absorber with selective absorbing/radiation nature, together with a secondary absorbing medium (typically fluid) to absorb the thermal energy and deliver to the end-user. Some sort of heat exchange technology is applied to transfer the absorbed energy to the secondary medium. Structural elements together with flow circulating devices and insulation are essential components of the receiver assembly. Secondarv Concentrator - A reflective device that further concentrates an already concentrated insolation coming of the primary concentrator. The CPC is very frequently used as a secondary concentrator.

According to these definitions, a receiver might consist of absorber elements built in cavity-like geometry, all contained in a pressure vessel, and an appropriate fluid flow circulation device (conduits, pump, etc.). It may be called pre-heater, according to the specific application. The CPC may or may not be considered a part of the receiver assembly.

Summary of the Invention

One aspect of the invention is a method for producing thermal energy, that can be readily used as thermal or transformed into other forms of energy, from the electro-magnetic energy of the solar radiation which comprises the steps of:

1 - concentrating the solar radiation to a sufficiently high intensity;

2 - causing the concentrated radiation to impinge on an absorber capable of supporting high temperatures;

3 - transferring the heat of the concentrated radiation by heat exchange to a fluid at high temperatures and pressure;

4 - using the fluid to actuate a generator of mechanical energy.

In typical embodiments of the invention, the generator of mechanical energy is coupled to an electrical generator.

Preferably, the solar radiation is concentrated by using a CPC and the absorber is based on a cavity design that captures the radiation. The fluid is typically a gas, and reference will be made sometimes to a gas for purposes of description, though no limitation is intended by this. Preferably, the temperature which is created by the heat exchanger in the fluid is of at least 400°C and preferably at least 850°C and may exceed 1000°C. The flow rates of the fluid is adjusted to obtain the desired fluid temperature, and to eliminate local overheating of the absorber construction material. Preferably, the concentration of the solar radiation and its impingement on the receiver aperture reaches a flux level of 1000 to 4000 W per square meter of aperture.

According to another aspect thereof, the invention provides an apparatus for producing available thermal energy from the energy of the solar radiation, or "receiver assembly", which comprises a secondary concentrator of the radiation, hereinafter "the concentrator assembly", an absorber and heat exchanger assembly, and means for causing a fluid, which can be called the operating fluid, to flow into and out of the receiver assembly and come into heat exchange contact with said absorber. The remaining components of the receiver assembly, including a mechanical energy generator, as well as peripheral or auxiliary conduit means and accessories, may be such as known in the art and therefore need not be described. The mechanical energy generator typically actuates an electrical generator, coupled with or separate from it.

The concentration of the solar energy is preferably effected by diverting solar rays or causing them to enter into a space having reflective boundary surfaces, so as to create what can be defined as a secondary concentrator, said surfaces having a quasi-parabolic shape that focuses the radiation onto absorbing elements enclosed in a space defined as a cavity with close to black body characteristics (since most of the light beams are reflected back and forth within this cavity until completely absorbed). The cavity not only captures the incoming radiation but practically acts to average temperatures over the radiation incidence surface. The whole temperature field is thus more uniform, and dangerous local high temperature spots are eliminated. -

The absorber and heat exchanger assembly generally comprises a number of elements, each which will be called herein "absorber module".

Preferably, the pressure drop across the receiver assembly is low enough to facilitate turbo-compressor closed loop operation, with the receiver replacing, or operating in parallel to the combustion chamber. It may be desirable to circulate high pressure fluid, to provide improved heat transmission even with very thin heat conducting construction walls. The working pressure is dictated by the gas-turbine system and it may reach 20 or even 30 bars for large systems.

The invention is carried out by using techniques that are known in the art. These comprise the following:

1 - Means for tracking the sun to maintain the solar radiation incident into the receiver at its maximum energy during the days and the seasons.

2 - Means for diverting and directing the solar radiation to impinge on the quasi-parabolic concentrator (CPC) which is optically and mechanically tailor-made to couple to the receiver which is the subject of the invention. These means, which may be called "primary concentrators", may consist of hyperbolic mirrors or any other type of mirrors known in the art. In some cases, it might be possible to dispense from such primary concentrators and allow the solar radiation to impinge freely on the. quasi-parabolic concentrators of the invention. 3 - Choice of heat transmission fluid, also depending on the type of mechanical energy generating machine. Such means preferably include air or any gas compatible with the mechanical energy generating machine.

4 - Choice of mechanical energy generating machine and electrical energy production machine. These two machines may be independent, or integrated with one another. Known machines include Stirling engines, gas turbines, or any. heat engine that converts the energy of a fluid at high temperature and pressure into mechanical work.

The aforesaid elements that are known in the art need not be described herein.

According to a preferred embodiment of the invention, the receiver assembly is modular and each module consists of a plurality of heat absorbers and optionally at least one inner partition or intermediate plate parallel to said outer plates, and a system of undulations or zigzag fins

coupled to the outer plates. The partition, if such is present, is in heat-conducting contact with said undulations. Said undulations and said partition, if present, constitute heat exchange surfaces, which define fluid flow through passages along the absorber module.

Hereinafter, the fluid will be considered to be air, and the invention will be described with such an assumption, but this should not be interpreted as constituting any limitation of its scope. Preferably, the collector modules are rectangular. The lateral surfaces or internal front surfaces, the dimensions of which are the length and height of the absorber module, are opaque and made of preferably high temperature metal, e.g., chrome-nickel alloys such as Iconel, to have the best high temperature survival. The internal front surface is surface treated for controlling the ratio of absorbed to emitted radiation, for instance by an appropriate controlled oxidation and surface roughness. The outer plates or back surface are opaque and made of preferably high temperature metal, e.g., chrome-nickel alloys such as Iconel. They have a thickness of from 1 to 4 mm and do not need surface treatment. Preferably, the undulations or zigzag fins have cross-sections that are similar to laterally compressed sinusoids, have pitches that are comprised between 2 and 8 mm, have a ratio of height-to-pitch which is comprised from 4 to 10, and a thickness of the fins from 0.08 to 0.3 mm., but may have different shapes and dimensional features. The length and- width of the absorbing modules may vary widely from a few centimeters to a few tenths of centimeters, depending on the nominal total absorbing power and the required operating pressure and temperature.

The absorbers are placed within a space, called "cavity", similar to that of a black body, wherein the parabolic absorbers create a high concentration radiation. The elements of said absorbers are each associated with an inlet manifold and an exit manifold.

Brief Description of the Drawings

In the drawings:

Fig. 1 is a schematic vertical, axial cross-section of a receiver assembly according to an embodiment of the invention; Fig. 2 is a transverse cross-section of the same, taken on plane II-II of Fig. i;

Fig. 3 is a schematic illustration of the air flow in a concentrator assembly according to an embodiment of the invention;

Fig. 4 is a schematic illustration of the bottom structure of the assembly of Figs. 1 and- 2; Fig. 5 is a perspective cross-section of a collector module according to another embodiment of the invention;

Fig. 6 is a schematic illustration of a pre-heater receiver as integrated in a power generation solar plant; and

Fig. 7 is a schematic illustration of said receiver as integrated in a "solar dish" system.

Detailed Description of Preferred Embodiments

Fig. 1 is a schematic vertical, axial cross-section of a solar receiver assembly of a solar energy unit, according to an embodiment of the invention, and the Fig. 2 is a transverse cross-section through the receiver cavity. Said solar receiver assembly which comprises a concentrator assembly 11 and an absorption and heat exchange assembly generally indicated at 10. 13 are the quasi-parabolic concentrators elements, which are juxtaposed to one another and supported by an outer frame, not shown, to form the concentrator assembly 11, and together define the inner surface of said concentrator assembly, which reflects the radiation. Said absorption and heat exchange assembly 10 comprises a receiver body 15, connected to said concentrator assembly by coupling element 16, and consisting of a plurality of absorber modules 14, hereinafter described. 17 is a receiver cavity defined by said absorber modules 14 internal surface. Black body radiation exists in the space bounded by said inner surface of the cavity. 18 and 19 are the air inlet and the air outlet into and from said cavity 17.

As seen in Fig. 2, 14 are the absorber modules. Each of said modules, in this embodiment, is assumed to comprise only two outer plates 15'j between which the undulations or zig-zag fins 20 are arranged.

Fig. 3 schematically indicates how the air flow is directed in the absorption and heat exchange assembly 10. At the top of said assembly there is a manifold 21 which receives the air from tube 18 and distributes it in the absorber modules 14, only schematically indicated in Fig. 3, and which are vertically disposed in this embodiment. The air flows downwardly through the absorber .modules and is subjected to heat exchange with the inner surfaces thereof, particularly the fins 20, is directed at the bottom through triangular absorber modules 25, schematically illustrated in Fig. 4, and then flows through the exit pipe 19. The absorber modules function during the operation of the device, as heat exchanger modules as well. Pipe 19 leads the heated air to a mechanical energy generator, such as a gas turbine, not illustrated, as it may be conventional. The finned structure of the bottom may be as shown in Fig. 4, or as desired. It is preferably identical to that of the peripheral plates, except for the triangular rather than rectangular external shape.

In the embodiment illustrated, the absorber modules are five, but they could be in any desired number (3 and above). Triangular gaps exist between the sides of adjacent modules, and if desired, they may be filled in to provide light-sealed structures, not shown in Fig. 1. A specific embodiment of absorber module is shown, only as a particular example, in perspective cross-section in Fig. 5. The module consists of two plates 15', which, with reference to Fig. 1, may be called the front and the back plates, but in some circumstances might in fact be equal and interchangeable. In this embodiment, differently from that of Figs. 1 and 2, an intermediate partition 30 is provided.

It will be understood that metal structures that may reach temperatures above 1000°C are subject to severe thermal strains and consequent stresses. Nevertheless, their component elements cannot be allowed to expand and contract independently of one another, because they are in mutual heat-conducting relationship. It is a feature of the invention that they are so made as to permit fully efficient heat transmission and to assure structural stability in spite of the thermally originated stresses. Deflection/deformation with minimal stress of the single absorber elements is achieved through the described structure, in which flexibility is assured by the corrugated fin, structure that bends and finds automatically by itself the point of balance. The inner and outer plates are stiff relatively to the fins, so that all temperature gradients are expressed by deformation of the fins with only minor deformations of the plates. When assembled, each of the plates will deform independently, and only to a very small extent, so that there are no relevant light leaks at the elements interface. This elastic behavior is one of the advantages of the invention.

The use for the production of energy, rom solar radiation of an absorber module, as herein described, is also an aspect of the invention.

The dominant heat fluxes through the front surface exposed to the concentrated solar radiation. The high temperature involved dictates unique alloys with relatively low heat conduction coefficient. Thick wall means high temperature gradient over the wall thickness. In conventional high temperature heat exchangers this is the limiting effect that dictates the maximum allowable flux and results in large (and expensive) transmission area per kW absorbed. In this invention the fine corrugation provides extensive support to the internal front surface of the absorber. This allows this wall to be very thin with low temperature gradient. The corrugation can be fine because the fluid flows on both sides at the same pressure, and balance the forces.

The amount of energy provided by a solar energy unit, comprising a radiation collecting and heat exchange assembly 10 as described herein, depends, among other things, on the direct solar radiation at the moment of use. The 'summer equinox (March 21st) is traditionally taken to represent average radiation data, while maximum radiation is assumed. For example only, in a specific installation according to an embodiment of the invention, the average incident power at the CPC inlet aperture was 50 kW, with 42.5 kW reaching the cavity, and 39 kW (92% thereof) were transmitted to air flowing therethrough at such a flow rate as to bring said air to a temperature of 680° C. At higher radiation, the incident power reached 68 kW, resulting in 53 kW absorbed, permitting to increase the temperature and/or the flow rate of the air. The above data are of course only an example, and very different data may apply to other installations, depending on their location, the season and the weather.

The receiver assembly of the invention can also be used as a preheater in an apparatus for generating mechanical energy from solar radiation. Such a use in illustrated schematically in Fig. 6.

Fig. 6 is a schematic illustration of a solar combined cycle power plan The tower reflector 40 reflects the solar radiation collected by the hehostats' field (not shown) to incident into the secondary concentrators (CPCs) 42 and 43. The concentrated radiation then heats the air flowing through the receiver 45, which here serves as a pre-heater. The heated air is then further heated in the high temperature receiver 41, before expanding in the gas-turbine assembly 33. Its compressor supplies the compressed air for both the pre-heater and the fuel operated combustion chamber.

The net mechanical power generated by the gas-turbine drives an electrical generator 34 to supply customer's load 35. The power plant typically uses the gas-turbine waste heat for bottoming steam electrical generation 32, according to a concept called combined cycle power plant. Fig. 7 is a schematic illustration of a solar dish system. The dish 46 concentrates solar radiation onto the secondary concentrator (CPC) 47. The concentrated radiation then heats the air flowing through the receiver 48 to be used either directly as heat or to drive a heat engine 49 to generate electrical power. This is illustrated in the detail A of Fig.7.

While embodiments of the invention have been described for purposes of illustration, it will be understood that the invention can be carried out with many modifications, variations and adaptations, without exceeding the scope of the claims.

Claims

1. Method for producing available thermal, energy from the energy of the solar radiation, which comprises the steps of: concentrating the solar radiation to a sufficiently high intensity; causing the concentrated radiation to impinge on an absorber capable of supporting high temperatures, transferring the heat of the concentrated radiation by heat exchange to a fluid to reach high temperatures and flow rates and using the fluid to actuate a generator of mechanical energy.

2. Method according to claim 1, wherein the temperature which is created the exchange of heat in the fluid is of at least 400°C.

3. Method according to claim 1, wherein the pressure drop across the heat exchanger assembly is low enough to facilitate turbo-compressor closed loop operation.

4. Method according to claim 1, wherein the concentration of the solar radiation and its impingement on the receiver aperture reaches a flux level of 1000 to 4000 KW per square meter of aperture.

5. Method according to claim 1, wherein high pressure fluid can be handled, to provide improved heat transmission even with very thin heat conducting construction walls.

6. Method according to claim 1, comprising concentrating the solar radiation by diverting solar rays or causing them to enter into a space having absorbing boundary surfaces, so as to create a black body cavity, said surfaces having a quasi-parabolic shape that focuses the radiation onto an absorbing surface enclosed in said space.

7. Apparatus for producing available thermal energy from the energy of the solar radiation, which comprises a collector system including a concentrator of the radiation, an absorber and heat exchanger, and means for causing the heat exchange fluid to flow into and out of the collector and come into heat exchange contact with said absorber and heat exchanger.

8. Apparatus according to claim 7, wherein the absorber and heat exchanger comprises a plurality of flat modules.

9. Apparatus according to claim 8, wherein each module comprises at least two main outer plates and a system of undulations coupled to the outer plates in heat-conducting contact and constituting heat exchange surfaces, which define fluid flow through passages along the module.

I 10. Apparatus according to claim 9, wherein each module further comprises at least one inner partition parallel to the outer plates, coupled in heat-conducting contact with the undulations.

11. Apparatus according to claim 9, wherein the modules are rectangular.

12. Apparatus according to claim 9, wherein the radiation absorbing plates are opaque and made of heat conducting material.

13. Apparatus according to claim 9, wherein the outer plates are made of metal and are surface treated, for controlling the ratio of absorbed to emitted radiation.

14. Apparatus according to claim 9, wherein the undulations have pitches from 2 and 8 mm and a ratio of height-to-pitch from 4 andlO.

15. Apparatus according to claim 9, wherein the undulations have a thickness from 0.08 to 0.3 mm

16. Apparatus according to claim 8, wherein the absorber and heat exchanger is provided with an inlet manifold and an exit conduit.

17. Use of an absorber module, which comprises at least two main outer plates and a system of undulations coupled to the outer plates in heat-conducting contact and constituting heat exchange surfaces, which define fluid flow through passages along the module, for the production of energy from the solar radiation.

18. Use according to claim 17, wherein the module has at least one of the following characteristics: a) it further comprises at least one inner partition parallel to the outer plates, coupled in heat-conducting contact with the undulations; b) is rectangular; c) the radiation absorbing plates are opaque and made of heat conducting material;, d) the radiation absorbing plates are made of metal and are surface treated, for controlling the ratio of absorbed to emitted radiation; e) the undulations have pitches from 2 and 8 mm and a ratio of height-to-pitch from 4 andlO; f) the undulations have a thickness from 0.08 to 0.3 mm

19. Method for producing thermal energy from the energy of the solar radiation, substantially as described and illustrated.

20. Apparatus for producing thermal energy from the energy of the solar radiation, substantially as described and illustrated.