WO2011048584A2

WO2011048584A2 - A solar energy conversion system and method

Info

Publication number: WO2011048584A2
Application number: PCT/IE2010/000062
Authority: WO
Inventors: Richard Mark Blackburn; Sean Aida Hayes
Original assignee: Artemis Energy Limited
Priority date: 2009-10-21
Filing date: 2010-10-21
Publication date: 2011-04-28
Also published as: WO2011048584A3

Abstract

A solar energy conversion system comprises a plurality of mirrors (8) arranged on the ground in arrays (7) for collecting and directing solar radiation towards a heat exchanger (6) of a Stirling engine (3) for heating a working fluid, namely, helium for the Stirling engine 3. The Stirling engine (3) is mounted on a platform (19) on the top of a mast (5) and is coupled to an electricity generator (20) for producing electricity. The Stirling engine is operated in accordance with an alpha Stirling cycle. The mirrors (8) are pivotally mounted about respective perpendicular axes for following the trajectory of the sun as it traverses from east to west across the sky. The Stirling engine (3) together with the heat exchanger (6) is also pivotally mounted about respective perpendicular axes for facilitating alignment of the heat exchanger (6) with the mirrors (8) as the mirrors (8) are pivoted to follow the trajectory of the sun across the sky as it traverses from east to west.

Description

"A solar energy conversion system and method"

The present invention relates to a solar energy conversion system and method, and in particular, to a solar energy conversion system and method for converting solar energy to usable energy, for example, mechanical energy, electrical energy, and the like.

Solar energy provides a vast source of energy, which is largely under-utilised. While solar panels are provided for converting solar energy to usable energy, for example, to electrical energy, in the case of solar panels comprising photovoltaic cells, and to heat energy in the case of solar panels through which water or other suitable heat exchange medium is circulated between relatively closely spaced apart panels, or through relatively small bore tubes. However, such solar panels, in general, have limited applications, and typically, are suitable for mounting on the roofs of buildings, such as houses, offices, industrial premises and the like, and in general, are suitable only for supplementing the energy requirements of such buildings. In general, such solar panels are unsuitable for converting solar energy to usable energy on a relatively large scale, for example, on a scale which would be required by an energy utility provider, such as an electricity utility provider.

There is therefore a need for a solar energy conversion system, and a method for converting solar energy to usable energy on a relatively large scale.

The present invention is directed towards providing such a system and method.

According to the invention there is provided a solar energy conversion system comprising a Stirling engine operable in a Stirling cycle, a heat exchanger for heating a working fluid for powering the Stirling engine, and a collecting means for collecting and directing solar radiation from the sun at the heat exchanger for heating the working fluid therein.

In one embodiment of the invention the collecting means comprises a plurality of collecting elements. Preferably, the collecting elements are arranged in an array for directing the solar radiation at the heat exchanger. Advantageously, at least two arrays of collecting elements are provided on respective opposite sides of the heat exchanger. In one embodiment of the invention a first one of the arrays of collecting elements is directed for receiving solar radiation when the sun is in an eastern half of the sky, and a second one of the arrays of collecting elements is directed for receiving solar radiation when the sun is in a westerly half of the sky. Preferably, a plurality of the collecting elements are provided in a third array which is directed in a generally southerly direction and the heat exchanger is adapted to receive solar radiation from the collecting elements of the third array simultaneously as solar energy is being received from the collecting elements of one of the first and second arrays.

In another embodiment of the invention each collecting element is selectively orientable in order to track at least a portion of the trajectory of the sun in the sky as the earth rotates relative to the sun. Preferably, each collecting element is pivotal about at least one pivot axis. Advantageously, each collecting element is pivotal about a pair of pivot axes. Ideally, the respective pivot axes about which each collecting element is pivotal are disposed substantially perpendicularly to each other.

Preferably, a first one of the pivot axes about which each collecting element is pivotal is a horizontal pivot axis for tracking the elevation of the sun in the sky.

Advantageously, a second one of the pivot axes about which each collecting element is pivotal is disposed for tracking the east to west trajectory of the sun through the sky. Preferably, each collecting element is pivotal about the second pivot axis for tracking the sun in the azimuth plane.

In one embodiment of the invention the angle of the second pivot axis of each collecting element relative to the ground varies as the elevation of the sun varies in the sky. Preferably, the angle which the second pivot axis of each collecting element makes with the ground varies as the orientation of the collecting element varies about the corresponding first horizontal pivot axis. In another embodiment of the invention each collecting element is shaped in order to track at least a portion of the trajectory of the sun.

In a further embodiment of the invention each collecting element is arranged and controlled to collect and reflect the solar radiation in an optimum manner depending on any one or more of the time of day, the time of year and the latitude at which the solar energy converting system is located.

In another embodiment of the invention each collecting element comprises a reflecting means. Preferably, each reflecting means is of a reflectance index of not less than 85%.

In another embodiment of the invention each reflecting means comprises a reflector. In a further embodiment of the invention each reflecting means comprises a plurality of reflecting elements.

Preferably, each reflecting element is one of coated and shielded with one of a translucent protective medium, a glass or other translucent protective medium.

Advantageously, each reflecting element comprises a reflective material. Preferably, the reflective material comprises a foil material. Advantageously, the reflective material comprises a reflective coating comprising metal particles embedded in a flexible material.

In one embodiment of the invention each reflecting element comprises a flat lite.

Preferably, each reflecting element is of a construction of one of spherical, parabolic and other curved shapes.

In one embodiment of the invention each reflecting means is secured to the support substrate. Preferably, the support substrate comprises one of a metal material, a plastics material and a polymer material. Advantageously, the support substrate is of one of spherical, parabolic and other curved shape, and the reflecting means is formed onto the support substrate to be of the one of the spherical, parabolic and other curved shape. In one embodiment of the invention each reflecting means comprises a heliostat mirror.

Preferably, the collecting means is located spaced apart from the heat exchanger. Preferably, the collecting means is located adjacent the ground.

In one embodiment of the invention the heat exchanger is located at a level above the level of the collecting means, and the collecting means is adapted for directing the solar radiation in a generally upwardly direction to the heat exchanger.

Preferably, the heat exchanger is mounted on a support means. Advantageously, the support means comprises one of a mast, a tower and a framework.

Alternatively, the heat exchanger is located at a level substantially similar to the level of the collecting means. In another alternative embodiment of the invention the heat exchanger is located at a level below the collecting means.

In a further embodiment of the invention the solar radiation is directed by the collecting means to an intermediate directing means which directs the solar energy received from the collecting means to the heat exchanger. Preferably, the intermediate directing means is located at a level above the collecting means and the heat exchanger. Advantageously, the intermediate directing means comprises an intermediate reflecting means. Ideally, the intermediate reflecting means comprises a reflector of one of a parabolic, a spherical and other curved shape.

In one embodiment of the invention one of the orientation and the position of the intermediate directing means is moveable for facilitating aligning of the intermediate directing means with the collecting means for receiving the reflected solar radiation. Preferably, the intermediate directing means is pivotal about a pair of pivot axes at an angle to each other. Advantageously, the pivot axes about which the

intermediate directing means is pivotal extend perpendicularly to each other.

Preferably, a first one of the pivot axes of the intermediate directing means extends in a general horizontal direction. Advantageously, the intermediate directing means is pivotal about the first one and a second one of the pivot axes about which the intermediate directing means is pivotal for receiving solar radiation from the collecting means as the sun travels along its trajectory from east to west.

In another embodiment of the invention the height of the intermediate directing means relative to the collecting means is variable. In a further embodiment of the invention one of the orientation and the position of the heat exchanger is moveable for facilitating aligning the heat exchanger with the collecting means for receiving reflected solar radiation therefrom.

In another embodiment of the invention the heat exchanger is pivotal about a pair of pivot axes at an angle to each other. Preferably, the pivot axes about which the heat exchanger is pivotal extend perpendicularly to each other. Advantageously, a first one of the pivot axes of the heat exchanger extends in a general vertical direction. Ideally, the heat exchanger is pivotal about the first vertical axis for selectively and sequentially receiving solar radiation from the respective first and second arrays of the collecting elements as the sun travels along its trajectory from the east to the west.

In another embodiment of the invention the height of the heat exchanger relative to the collecting means is variable.

In another embodiment of the invention the heat exchanger is integral with the Stirling engine. Preferably, a protective shield is located for protecting the Stirling engine from solar radiation directed towards the heat exchanger.

Advantageously, the Stirling engine comprises at least one pair of cylinders, one cylinder of each pair of cylinders having a power piston operable therein and the other cylinder of each pair of cylinders having a displacer piston operable therein. Preferably, the pistons of each pair of cylinders are configured so that the power and displacer pistons operate out of phase with each other by approximately 90° in accordance with the Stirling cycle. Ideally, each pair of cylinders is configured in a V-configuration.

Preferably, the cylinders of each pair are configured so that a geometrical central axis defined by the respective cylinders extend at substantially 90° to each other. In one embodiment of the invention each pair of cylinders is provided with a corresponding heat exchanger. Advantageously, each pair of cylinders is provided with a corresponding regenerator.

In another embodiment of the invention a plurality of pairs of cylinders are provided, the pistons of the respective pairs of cylinders being coupled to a common crank shaft.

In a further embodiment of the invention a plurality of heat exchangers are provided. In one embodiment of the invention a plurality of Stirling engines are provided.

In another embodiment of the invention one heat exchanger is provided for each Stirling engine. In another embodiment of the invention a plurality of heat exchangers are provided for each Stirling engine.

In a further embodiment of the invention one heat exchanger is provided for a plurality of Stirling engines.

In a further embodiment of the invention at least some of the collecting elements are adapted to direct solar radiation to more than one Stirling engine. Preferably, the at least some of the collecting elements are adapted to direct the solar radiation to more than one Stirling engine sequentially.

In another embodiment of the invention one of the heat exchanger and the Stirling engine is adapted to receive energy from an energy source other than the sun in order to maintain the system operational in the absence of solar radiation or sufficient solar radiation to maintain the system operational. Preferably, the energy source is a heat source, and the heat exchanger is adapted to receive heat from a heat exchange medium heated by the heat source. Advantageously, the heat exchanger is adapted to accommodate the heat exchange medium therethrough.

In one embodiment of the invention the energy source other than the sun is a boiler.

In another embodiment of the invention the energy source other than the sun is a source of stored energy.

Preferably, each Stirling engine is adapted to power an electrical generator.

Advantageously, each Stirling engine is adapted to power a permanent magnet generator. In one embodiment of the invention each Stirling engine is coupled to the electrical generator.

In another embodiment of the invention each Stirling engine is coupled to the electrical generator through a drive transmission means.

The invention also provides in combination a system according to the invention further comprising an electrical generator coupled directly or indirectly to the Stirling engine, and driven by the Stirling engine. Additionally, the invention provides a method for converting solar energy to usable energy, the method comprising providing a Stirling engine operable in a Stirling cycle, providing a heat exchanger for heating a working fluid for powering the Stirling engine, and providing a collecting means for collecting and directing solar radiation from the sun at the heat exchanger for heating the working fluid therein, the method further comprising operating the collecting means for directing and concentrating the solar radiation onto the heat exchanger for heating the working fluid of the Stirling engine for in turn powering the Stirling engine.

The advantages of the invention are many. A particularly important advantage of the invention is that it provides a solar energy system which can produce usable energy on a relatively large scale, and typically, on a scale required by a utility provider, such as, for example, an electricity utility provider. The collecting means according to the invention when provided by arrays of collecting elements provides an efficient system whereby solar radiation which is collected over a relatively wide area is concentrated into a relatively small area, for example, the relatively small area of a heat exchanger. Accordingly, the system and method according to the invention produces a production density of solar radiation which is significantly higher than solar energy conversion systems and methods known heretofore. By facilitating movement of the heat exchanger, the area of the heat exchanger exposed to the solar radiation received from the collecting means can be maximised as the sun travels across the sky in its east to west trajectory. Additionally, providing the collecting means to be moveable optimises the solar radiation collected by the collecting means as the sun travels across the sky in its east to west trajectory.

Adapting the heat exchanger to receive heat from a source other than the sun allows the system to operate continuously even in the absence of solar energy, or where the level of solar energy is insufficient to operate the system at its maximum capacity or at a required capacity. Thus, by so adapting the heat exchanger, the system can operate efficiently throughout the day as well as throughout the night when solar energy is absent. The heat source other than the sun may be any suitable heat source, and indeed, it is envisaged that the heat source may be a source of stored energy. Such stored energy may be stored from any suitable system capable of providing and storing energy, and it is envisaged that the stored energy may be energy which has been stored from the system according to the invention. Such energy could be stored from the system during periods where the supply of energy provided by the system exceeded the demand for energy from the system.

Accordingly, with the heat exchanger adapted to receive heat from a source other than the sun, the system can provide dispatchable power continuously throughout the day and night with a ride-through feature capable of withstanding intermittent variation in both solar radiation availability and demand requirement for energy from the system. A further advantage of the invention is that the system can be produced in modular form and is suitable for applications in the form of a single unit small plant as a distributed energy product or in large scale multi-unit format in utility application.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, which are given by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a top plan view of a solar energy conversion system according to the invention,

Fig. 2 is a schematic end elevational view of a portion of the solar energy conversion system of Fig. 1 ,

Fig. 3 is a schematic side elevational view of a detail of the solar energy conversion system of Fig. 1 ,

Fig. 4 is a diagrammatic end elevational view of a Stirling engine of the solar energy conversion system of Fig. 1 , Fig. 5 is a perspective view of a mounting arrangement of the Stirling engine of the solar energy conversion system of Fig. 1 ,

Fig. 6 is a perspective view of a detail of a portion of the system of Fig. 1 , Figs. 7(a) to (d) are diagrammatic views of alternative constructions of another detail of the solar energy conversion system of Fig. 1 , Fig. 8 is a view similar to Fig. 1 of a solar energy conversion system according to another embodiment of the invention,

Fig. 9 is an elevational view of a portion of a solar energy conversion system according to another embodiment of the invention, and

Fig. 10 is a view similar to that of Fig. 3 of a similar detail to that of Fig. 3 of a solar energy conversion system according to a further embodiment of the invention. Referring to the drawings and initially to Figs. 1 to 6, there is illustrated a solar energy conversion system according to the invention, indicated generally by the reference numeral 1 , for converting solar energy to usable energy, in this embodiment of the invention the solar energy conversion system 1 is adapted for converting solar energy to electrical energy as will be described below. The solar energy conversion system 1 comprises a plurality of Stirling engines 3, in this embodiment of the invention nine Stirling engines 3 mounted on top of

corresponding masts 5. The Stirling engines 3 are each operable with a working fluid, which in this embodiment of the invention is a gas, namely, helium, and each Stirling engine 3 is provided with a heat exchanger 6 within which the helium working fluid of the corresponding Stirling engine 3 is heated for operating the Stirling engine 3. The Stirling engines 3 and the heat exchangers 6 are illustrated in block representation in Figs. 1 and 2. Each Stirling engine 3 in this embodiment of the invention operates in accordance with the scientifically termed alpha Stirling cycle. A collecting means, which in this embodiment of the invention is provided by a plurality of arrays 7 of respective collecting elements, which in this case are reflectors provided by mirrors 8 for collecting and directing solar radiation from the sun to the heat exchanger 6 of a corresponding one of the Stirling engines 3. In this embodiment of the invention the mirrors 8 of .each array 7 are arranged in arcuate sub-arrays 9 such that the arcuate arrangement of the mirrors 8 of each sub-array 9 define a centre of radius which substantially coincides with a corresponding one of the masts 5 on which the Stirling engines 3 and the heat exchangers 6 are located.

The mirrors 8 are heliostat mirrors and are pivotal about first and second pivot axes 10 and 11 to facilitate tracking of the sun by the mirrors 8 as the elevation of the sun in the sky varies and the sun tracks from east to west. In this embodiment of the invention each first pivot axis 10 is a horizontal pivot axis defined by a first shaft 12, see Fig. 6, for facilitating pivoting of the corresponding mirror 8 to track the elevation of the sun in the sky. The second pivot axis 1 1 of each mirror 8 is perpendicular to the first pivot axis 10 and is defined by a second shaft 13 which is rigidly secured to the mirror 8, and is pivotally mounted on the first shaft 12 by a pivot mounting 2. Pivoting of the second shaft 13 about the second pivot axis 11 accommodates pivoting of the corresponding mirror 8 to facilitate tracking of the sun in the azimuth phase as the sun tracks from east to west across the sky. Mounting brackets 4 adapted for mounting on the ground pivotally carry the first pivot shaft 2 about the first pivot axis 10. A pair of servomotors (not shown) or other suitable drive means are provided for each mirror 8 for pivoting the mirror 8 about the first and second pivot axes 10 and 11 as the sun tracks across the sky.

Each mirror 8 is of parabolic shape for directing and concentrating the solar radiation collected by the mirrors 8 onto the heat exchanger 6 of the corresponding Stirling engine 3. Each mirror 8 comprises a plurality of lites which are mounted on a support in order to form the mirror 8 as a parabolic mirror, and the reflectance index of each mirror is preferably not less than 85%.

The second pivot axis 11 about which each mirror 8 is pivotal for tracking the sun as the sun moves from east to west, as discussed above, extends perpendicularly from the first pivot axis 10, and accordingly, the second pivot axis of each mirror 8 forms an angle with the ground which varies in accordance with the angle which the corresponding mirror 8 makes with the ground about the first pivot axis 10 as the mirror 8 is being pivoted about the first pivot axis 10 for tracking the elevation of the sun in the sky.

Each Stirling engine 3 comprises a plurality of pairs of cylinders, namely, a hot expansion cylinder 14 and a cold compression cylinder 15. The cylinders 14 and 15 of each pair are configured into a V-configuration with the geometrical central axes 21 and 22 of the cylinders 14 and 15, respectively, extending at an angle of approximately 90° relative to each other. The hot expansion cylinder 14 of each pair of cylinders 14 and 15 comprises a power piston 23 operable therein, and the cold compression cylinder 15 of each pair comprises a displacer piston 24. The pistons 23 and 24 of the pairs of cylinders 14 and 15, respectively, are coupled by respective connecting rods to a common crank shaft 16 of the Stirling engine. The crank shaft 16 is illustrated in block representation in Fig. 4. The power and displacer pistons 23 and 24 are coupled to the crank shaft 16 to be approximately 90° out of phase with each other. In this embodiment of the invention each Stirling engine 3 comprises four pairs of cylinders 14 and 15 and four pairs of corresponding pistons 23 and 24. Although, it will be readily apparent to those skilled in the art that any number of pairs of cylinders 14 and 15 and corresponding pairs of pistons 23 and 24 may be provided in each Stirling engine 3. The heat exchanger 6 of each Stirling engine 3 heats the working fluid, namely, helium, which is delivered into the hot expansion cylinder 14 from the heat exchanger 6 for urging the power piston 23 therein downwardly. With the 90° phase difference the displacer piston 24 in the corresponding cold compression cylinder 15 of the pair of cylinders is urged upwardly for displacing the cold working fluid cooled in a gas cooler 25, for delivering to a regenerator 17 of the Stirling engine 3 for in turn delivering to the heat exchanger 6 for heating thereof.

Each Stirling engine 3 is mounted on a platform 19 on top of the corresponding mast 5 with the heat exchanger 6 directed in a generally downwardly direction for receiving solar energy directed to the heat exchanger 6 by the mirrors 8. A protective shield 8, in this embodiment of the invention of ceramics material located behind the heat exchanger 6 protects the Stirling engine 3 and the regenerator 7 from solar radiation reflected by the mirrors 8. The platform 19 of each mast 5 is mounted on the corresponding mast 5 about a first pivot axis 26 and a second pivot axis 27 perpendicular to the first pivot axis 26. The first pivot axis 26 extends vertically for facilitating pivoting of the corresponding Stirling engine 3 through 360° for facilitating aligning the corresponding heat exchanger 6 with one or more of the arrays 7 of the mirrors 8 for selectively receiving solar energy from the aligned one or more of the arrays 7 of the mirrors 8 as will be described below. The second pivot axis 27, which is perpendicular to the first pivot axis 26, facilitates aligning the heat exchanger 6 with the mirrors 8 of the one or more arrays 7 for receiving solar radiation therefrom, as the sun traverses along its trajectory across the sky. The mounting arrangement of the platform 19 of each mast 5 to be pivotal about the first and second axes 26 and 27 is substantially similar to that of the pivot mounting of the mirrors 8, but of a more robust construction. Two pivot shafts (not shown) pivotal relative to each other are provided to define the first and second axes 26 and 27, one of the shafts which defines the first pivot axis 26 extends vertically and is pivotal relative to the mast to define the first pivot axis 26, and the other shaft extends perpendicularly from the vertical pivot shaft and is pivotally mounted to the vertical pivot shaft by a pivot mounting similar to the pivot mounting 2 in order to define the second pivot axis 27. Servomotors (not shown) for pivoting the corresponding platform 19 about the first and second pivot axes 26 and 27, for in turn orienting the Stirling engine 3 and the corresponding heat exchanger 6 to receive solar energy from the mirrors 8 of the corresponding arrays 7. Alternatively, instead of servomotors for pivoting the platform 19 about the first and second pivot axes 26 and 27, electrical, hydraulic or pneumatic rotational or linear motors may be provided. An electrical generator 20, which in this embodiment of the invention is a permanent magnet generator is also mounted on each platform 19, and is driven by the corresponding Stirling engine 3 for generating electricity. Electrically conductive cables (not shown) from the generator 20 extend down the corresponding mast 5 for carrying the generated electricity therefrom.

As mentioned above, a plurality of arrays 7 of mirrors 8 are provided, and in this embodiment of the invention six arrays 7 of mirrors 8 are provided. For

convenience, the six arrays 7 are identified by the reference letters 7a to 7f. Additionally, in this embodiment of the invention nine Stirling engines 3 mounted on respective masts 5 are provided for receiving solar radiation from the mirrors 8. The nine Stirling engines 3 are identified by the reference letters 3a to 3i in Fig. 1. In this embodiment of the invention, the arrays 7 are mounted on the ground and the sub arrays 9a and 9b of arrays 7a and 7b are located on the northern side of the corresponding masts 5 of engines 3a and 3b, for collecting solar radiation while the sun is in the southern half of the sky. In this embodiment of the invention, the arrays 7c and 7d are located on the easterly side of the corresponding masts 5 for collecting solar radiation while the sun is in the western half of the sky.

In this embodiment of the invention, the sub arrays 9 of the arrays 7e and 7f are shown in various orientations required to enable the corresponding Stirling engines 3 to receive solar radiation from the mirrors 8 as the position of the sun changes throughout the day. Thus, while the sun is in the southern half of the sky, the platforms 19 of the masts 5 of the respective Stirling engines 3a and 3b are oriented so that the heat exchangers 6 thereof face the sub arrays 9 of the arrays 7a and 7b of the mirrors 8. As can be seen, sub-arrays 9a of the arrays 7a and 7b are arranged for directing solar radiation at the heat exchanger 6 of the Stirling engine 3a, while the sub-arrays 9b of the arrays 7a and 7b are arranged for directing solar radiation at the heat exchanger 6 of the Stirling engine 3b. The arrays 7c and 7d are arranged to direct solar radiation at the heat exchangers 6 of the Stirling engines 3c and 3d, respectively, when the sun is in the western half of the sky. However, by virtue of the fact that the mirrors 8 of the arrays 7c and 7d are pivotal about the respective first and second pivot axes 10 and 11 , the mirrors 8 of the array 7c are orientable in order to collect solar radiation when the sun is in the eastern half of the sky for direction at the heat exchanger 6 of the corresponding Stirling engine 3d. It will be appreciated that in this embodiment of the invention the heat exchanger 6 of the Stirling engine 3c may receive solar radiation from the mirrors 8 of the arrays 7c and 7d, simultaneously, while the heat exchanger 6 of the Stirling engine 3d will, in general, only receive, optimum solar radiation from the mirrors 8 of the array 7d.

The heat exchangers 6 of the Stirling engines 3e, 3f and 3g are arranged to receive solar radiation from the mirrors 8 of sub arrays 9 within the arrays 7e and 7f. The mirrors 8 of the arrays 7e and 7f are arranged in a plurality of sub-arrays 9, variously in accordance with the position of the sun, in order to appropriately collect and direct solar radiation to the heat exchangers 6 of the Stirling engines 3e, 3f and 3g.

Similarly, the heat exchangers of the Stirling engines 3h and 3i are located to receive solar radiation from the mirrors 8 of the arrays 7e and 7f. The heat exchanger 6 of the Stirling engine 3f simultaneously receives solar radiation from the mirrors 8 of the arrays 7e and 7f, while the heat exchanger 6 of the Stirling engine 3e in general receives solar radiation from some of the mirrors 8 of the arrays 7e only, and the heat exchanger 6 of the Stirling engine 3g, in general, receives solar radiation primarily from the mirrors 8 of the array 7f. In this embodiment of the invention the heat exchanger 6 of the Stirling engine 3h receives solar radiation from some of the mirrors 8 of the array 7e only, while the heat exchanger 6 of the Stirling engine 3i, in general, receives solar energy from the mirrors 8 of the array 7f only. In use, as the sun rises in the east, the mirrors 8 of the respective arrays 7 are oriented by their respective servomotors (not shown) to direct solar radiation to the heat exchangers 6 of the corresponding Stirling engines 3. The servomotors (not shown) which operate the platforms 19 of the respective Stirling engines 3 are similarly operated to align the heat exchangers 6 of the Stirling engines 3 to receive the solar radiation from the mirrors 8 of the corresponding arrays 9. As the sun traverses along its trajectory across the sky from east to west, the servomotors (not shown) of the mirrors 8 of the arrays 7 substantially continuously orient the mirrors 8 in order to track the trajectory of the sun. The orientation of the mirrors 8 to track the trajectory of the sun require corresponding alteration to the orientation of the heat exchangers 6 of the respective Stirling engines 3 in order that the solar radiation continues to be directed on the respective heat exchangers 6.

Referring now to Fig. 7, there is illustrated four configurations of heat exchange tubes 28 which may be used in the heat exchanger 6 of the Stirling engine 3.

Referring now to Fig. 8, there is illustrated a portion of a solar energy conversion system according to another embodiment of the invention, indicated generally by the reference numeral 30. The solar energy conversion system 30 in this embodiment of the invention is substantially similar to the solar energy conversion system 1 described with reference to Figs. 1 to 5, and similar components are identified by the same reference numerals. The solar energy system 30 comprises a plurality of arrays 7 of mirrors 8, only one array 7 being illustrated in Fig. 7 for collecting and directing solar radiation at heat exchangers (not shown) of a plurality of Stirling engines 3 located relative to the arrays 7. In this embodiment of the invention only one Stirling engine is illustrated in block representation and indicated by the reference numeral 3. However, in this embodiment of the invention the Stirling engines 3 are mounted on the ground at a similar level to that at which the mirrors 8 are mounted. An intermediate directing means, namely, an intermediate parabolic mirror 31 is mounted relative to each Stirling engine 3 for directing the solar radiation from the mirrors 8 of the corresponding array 7 onto the heat exchanger (not shown) of the corresponding Stirling engine 3. In this embodiment of the invention the intermediate mirror 31 for each Stirling engine 3 is mounted on a mast 32, and is pivotal about a first horizontal axis 34 perpendicular to the plane of the page in the direction of the arrows A and B, respectively, and also about a second vertical axis 35 perpendicular to the first horizontal axis 34 for accommodating pivoting of the intermediate mirror 31 for maintaining the intermediate mirror 31 in alignment with the corresponding mirrors 8 of the corresponding array 7 as the mirrors 8 of the corresponding array 7 are pivoted about their respective first and second axes 10 and 11 for tracking the trajectory of the sun across the sky, and also for maintaining the intermediate mirror 31 in alignment with the heat exchanger of the Stirling engine 3. The intermediate mirror 31 corresponding to each Stirling engine 3 comprises a heat resistant, reflective material of reflectance index of not less than 85%, which may be coated with a glass or other translucent protective medium.

! Otherwise, the solar energy conversion system 30 is similar to the solar energy conversion system 1.

Referring now to Fig. 9, there is illustrated a plurality of heat exchangers which are arranged in an array to optimise the transfer of energy from an array of mirrors to a Stirling engine, for example, for optimising the transfer of energy from the array 7 of mirrors 8 to the Stirling engine 3.

Referring now to Fig. 10, there is illustrated a portion of a solar energy conversion system 40 according to another embodiment of the invention. The solar energy conversion system 40 is substantially similar to the solar energy conversion system 1 , and similar components are identified by the same reference numerals. In this embodiment of the invention the heat exchanger 6 as well as being adapted for receiving solar radiation from the arrays 7 of mirrors 8, neither of which are illustrated in Fig. 10, is also adapted to receive heat from a heat source 41 other than the sun. The heat source 41 is illustrated in block representation, may be a source adjacent to or remote from the heat exchanger 6, and in this embodiment of the invention comprises a remotely located boiler 41 for heating a heat exchange medium. The heat exchanger 6 in this embodiment of the invention comprises an indirect heat exchanger which is suitable for receiving the heated heat exchange medium from the boiler 41 and for transferring the heat from the heat exchange medium to the Stirling engine 3. Flow and return pipes 42 and 43, respectively, transfer the heat exchange medium between the boiler 41 and the heat exchanger 6. Typically, the boiler 41 would be a steam generating boiler which would generate steam at an appropriate temperature which would be delivered through the flow pipe 42 to the heat exchanger 6, and returned through the return pipe 43, and condensed in a suitable condenser (not shown) prior to being returned to the boiler 41.

Needless to say, any other suitable heat exchange media may be used besides steam, for example, heated gases or the like.

It is also envisaged that the source 41 , instead of being a boiler, may be a stored source of energy which would be transferred to the heat exchanger 6. The stored energy could be stored from any suitable source, and it is envisaged that the stored energy could be stored from energy produced, by the system 40 according to the invention.

In use, the system 40 operates and is powered by solar radiation during periods while the sun is in the sky, and during periods where there is sufficient solar radiation in order to produce the power requirement from the system 40. In the absence of solar radiation, or in the absence of sufficient solar radiation to operate the system to produce the required power output, the boiler 41 is activated to produce heated steam in order to provide heat to the heat exchanger 6 so that the system 40 can continue to operate in the absence of solar energy, or when there is insufficient solar energy available to operate the system to produce the required power output.

Where the source 41 , instead of being provided by a boiler, is provided as stored energy, and when the stored energy is to be derived from the system 40 according to the invention, it is envisaged that during periods when the power output produced by the system 40 exceeds the demand for power from the system 40, the excess energy produced by the system 40 would be stored in the energy store, and subsequently transferred to the heat exchanger 6 when required. The stored energy could be stored in any convenient form, and converted to an appropriate form for supply to the heat exchanger. It is also envisaged that the stored energy in an appropriate form could in certain circumstances be delivered to the Stirling engine instead of to the heat exchanger.

While the mirrors 8 have been described in particular arrays, the mirrors 8 may be provided in any other array configuration, and while the sub-array configurations are essentially of arcuate configuration, this, while it is preferable, is not essential.

While the mirrors have been described as being parabolic mirrors, the mirrors may be of any other geometrical shape, and in certain cases, it is envisaged that the mirrors may be provided as plain planar mirrors.

While the intermediate directing means has been described as being provided by a parabolic mirror, any other suitable intermediate directing means for directing and concentrating solar radiation from the mirrors pf the array of mirrors to the heat exchanger of the corresponding Stirling engine may be used. It is also envisaged that the intermediate directing means may be moveable upwardly and downwardly along the mast 5.

In the embodiment of the invention of Fig. 8 it is envisaged that the parabolic mirror 31 will be located at a height of approximately 2 metres to 40 metres above the ground. While the heat exchangers and Stirling engines have been described as being mounted on a mast, the Stirling engines and heat exchangers may be mounted on any other suitable support means, for example, a support structure, such as a tower, a building, a structural framework, which may, for example, be a steel framework. Additionally, it is envisaged that one support means may be provided for each Stirling engine, or a plurality of Stirling engines may be supported on the one support means. It is also envisaged that where more than one Stirling engine is mounted on a single support structure, the heat exchangers thereof may face in different directions. While the Stirling engines have been described as being adapted to operate on the alpha cycle, the Stirling engines may be adapted to operate on any suitable Stirling cycle.

While the working fluid has been described as being helium, any other suitable working fluid may be provided, for example, hydrogen or nitrogen gas, and the working fluid may be a liquid or a gas.

It is also envisaged that each Stirling engine may comprise a plurality of cylinders whereby each cylinder contains a single double acting piston which is urged to move by having a temperature and pressure differential between a hot end and a cold end thereof, which typically, would correspond with the top and bottom, respectively of each piston. The cylinders may be configured into a V-configuration with the geometrical central axis of the respective cylinders extending at an angle of approximately 90° relative to each other, or at any other suitable angle. In general, it is envisaged that an individual heat exchanger will be provided for each cylinder of each Stirling engine, and the working fluid would be expanded in the cylinder for urging the piston downwardly therein. It is also envisaged that the Stirling engine may be adapted to operate on what is termed scientifically as the beta cycle or a gamma cycle. In a further embodiment of the invention the Stirling engine may be adapted to operate in a double acting arrangement, whereby each Stirling engine would comprise a multiple of four cylinders whereby each cylinder would contain one double acting piston which is urged to move by having a temperature and pressure differential between the hot and cold ends of the top and bottom, respectively, of each piston. The cylinders may be configured into a parallel configuration relative to each other, and in which case, individual heat exchangers of each individual cylinder of the Stirling engine would heat the working fluid which would be expanded into the cylinder for urging the piston therein downwardly.

It is also envisaged that a plurality of heat exchangers may be provided for each Stirling engine, whereby the heat exchangers would be disposed in order to optimise receipt of the reflected solar radiation from the respective arrays of the collecting elements as the sun travels along its trajectory from the east to the west. During that period a plurality of collecting elements may be provided in a number of arrays to direct solar energy towards different ones of the heat exchangers as the sun traverses its east west trajectory.

It is also envisaged that in the absence of solar energy, for example, at night time, other suitable heating means may be provided for heating the working fluid in the heat exchanger, for example, such heating of the working fluid may be carried out by attaching a gas or an oil fired burner to each heat exchanger for heating the working fluid therein. It is also envisaged that a plurality of Stirling engines may be provided on each mast, and the Stirling engines would be located on the mast with their respective heat exchangers oriented to optimise reception of solar radiation from the reflecting elements.

Claims

1. A solar energy conversion system comprising a Stirling engine operable in a Stirling cycle, a heat exchanger for heating a working fluid for powering the Stirling engine, and a collecting means for collecting and directing solar radiation from the sun at the heat exchanger for heating the working fluid therein.

2. A system as claimed in Claim 1 in which the collecting means comprises a plurality of collecting elements. 3. A system as claimed in Claim 2 in which the collecting elements are arranged in an array for directing the solar radiation at the heat exchanger.

4. A system as claimed in Claim 3 in which at least two arrays of collecting elements are provided on respective opposite sides of the heat exchanger.

5. A system as claimed in Claim 4 in which a first one of the arrays of collecting elements is directed for receiving solar radiation when the sun is in an eastern half of the sky, and a second one of the arrays of collecting elements is directed for receiving solar radiation when the sun is in a westerly half of the sky.

6. A system as claimed in Claim 4 in which a plurality of the collecting elements are provided in a third array which is directed in a generally southerly direction and the heat exchanger is adapted to receive solar radiation from the collecting elements of the third array simultaneously as solar energy is being received from the collecting elements of one of the first and second arrays.

7. A system as claimed in any of Claims 2 to 6 in which each collecting element is selectively orientable in order to track at least a portion of the trajectory of the sun in the sky as the earth rotates relative to the sun.

8. A system as claimed in any of Claims 2 to 7 in which each collecting element is pivotal about at least one pivot axis.

9. A system as claimed in Claim 8 in which each collecting element is pivotal about a pair of pivot axes.

10. A system as claimed in Claim 9 in which the respective pivot axes about which each collecting element is pivotal are disposed substantially perpendicularly to each other.

11. A system as claimed in Claim 9 or 10 in which a first one of the pivot axes about which each collecting element is pivotal is a horizontal pivot axis for tracking the elevation of the sun in the sky.

12. A system as claimed in Claim 11 in which a second one of the pivot axes about which each collecting element is pivotal is disposed for tracking the east to west trajectory of the sun through the sky.

13. A system as claimed in Claim 12 in which each collecting element is pivotal about the second pivot axis for tracking the sun in the azimuth plane.

14. A system as claimed in Claim 12 or 13 in which the angle of the second pivot axis of each collecting element relative to the ground varies as the elevation of the sun varies in the sky.

15. A system as claimed in any of Claims 12 to 14 in which the angle which the second pivot axis of each collecting element makes with the ground varies as the orientation of the collecting element varies about the corresponding first horizontal pivot axis. 6. A system as claimed in any of Claims 2 to 15 in which each collecting element is shaped in order to track at least a portion of the trajectory of the sun.

17. A system as claimed in any of Claims 2 to 16 in which each collecting element is arranged and controlled to collect and reflect the solar radiation in an optimum manner depending on any one or more of the time of day, the time of year and the latitude at which the solar energy converting system is located.

18. A system as claimed in any of Claims 2 to 17 in which each collecting element comprises a reflecting means.

19. A system as claimed in Claim 18 in which each reflecting means is of a reflectance index of not less than 85%.

20. A system as claimed in Claim 18 or 19 in which each reflecting means comprises a reflector.

21. A system as claimed in any of Claims 18 to 20 in which each reflecting means comprises a plurality of reflecting elements. 22. A system as claimed in Claim 21 in which each reflecting element is one of coated and shielded with one of a translucent protective medium, a glass or other translucent protective medium.

23. A system as claimed in Claim 21 or 22 in which each reflecting element comprises a reflective material.

24. A system as claimed in Claim 23 in which the reflective material comprises a foil material. 25. A system as claimed in Claim 23 or 24 in which the reflective material comprises a reflective coating comprising metal particles embedded in a flexible material.

26. A system as claimed in any of Claims 21 to 25 in which each reflecting element comprises a flat lite.

27. A system as claimed in any of Claims 21 to 26 in which each reflecting element is of a construction of one of spherical, parabolic and other curved shapes.

28. A system as claimed in any of Claims 18 to 27 in which each reflecting means is secured to the support substrate. 29. A system as claimed in Claim 28 in which the support substrate comprises -one of a metal material, a plastics material and a polymer material.

30. A system as claimed in Claim 28 or 29 in which the support substrate is of one of spherical, parabolic and other curved shape, and the reflecting means is formed onto the support substrate to be of the one of the spherical, parabolic and other curved shape.

31. A system as claimed in any of Claims 18 to 30 in which each reflecting means comprises a heliostat mirror.

32. A system as claimed in any preceding claim in which the collecting means is located spaced apart from the heat exchanger.

33. A system as claimed in any preceding claim in which the collecting means is located adjacent the ground.

34. A system as claimed in any preceding claim in which the heat exchanger is located at a level above the level of the collecting means, and the collecting means is adapted for directing the solar radiation in a generally upwardly direction to the heat exchanger.

35. A system as claimed in Claim 34 in which the heat exchanger is mounted on a support means. 36. A system as claimed in Claim 35 in which the support means comprises one of a mast, a tower and a framework.

37. A system as claimed in any of Claims 1 to 33 in which the heat exchanger is located at a level substantially similar to the level of the collecting means.

38. A system as claimed in any of Claims 1 to 33 in which the heat exchanger is located at a level below the collecting means.

39. A system as claimed in Claim 37 or 38 in which the solar radiation is directed by the collecting means to an intermediate directing means which directs the solar energy received from the collecting means to the heat exchanger. 40. A system as claimed in Claim 39 in which the intermediate directing means is located at a level above the collecting means and the heat exchanger.

41. A system as claimed in Claim 39 or 40 in which the intermediate directing means comprises an intermediate reflecting means.

42. A system as claimed in any of Claims 39 to 41 in which the intermediate reflecting means comprises a reflector of one of a parabolic, a spherical and other curved shape. 43. A system as claimed in any of Claims 39 to 42 in which one of the orientation and the position of the intermediate directing means is moveable for facilitating aligning of the intermediate directing means with the collecting means for receiving the reflected solar radiation. 44. A system as claimed in Claim 43 in which the intermediate directing means is pivotal about a pair of pivot axes at an angle to each other.

45. A system as claimed in Claim 44 in which the pivot axes about which the intermediate directing means is pivotal extend perpendicularly to each other.

46. A system as claimed in Claim 44 or 45 in which a first one of the pivot axes of the intermediate directing means extends in a general horizontal direction.

47. A system as claimed in any of Claims 44 to 46 in which the intermediate directing means is pivotal about the first one and a second one of the pivot axes about which the intermediate directing means is pivotal for receiving solar radiation from the collecting means as the sun travels along its trajectory from east to west.

48. A system as claimed in any of Claims 43 to 47 in which the height of the intermediate directing means relative to the collecting means is variable.

49. A system as claimed in any preceding claim in which one of the orientation and the position of the heat exchanger is moveable for facilitating aligning the heat exchanger with the collecting means for receiving reflected solar radiation therefrom.

50. A system as claimed in Claim 49 in which the heat exchanger is pivotal about a pair of pivot axes at an angle to each other.

51. A system as claimed in Claim 50 in which the pivot axes about which the heat exchanger is pivotal extend perpendicularly to each other.

52. A system as claimed in Claim 50 or 51 in which a first one of the pivot axes of the heat exchanger extends in a general vertical direction.

53. A system as claimed in any of Claims 50 to 52 in which the heat exchanger is pivotal about the first vertical axis for selectively and sequentially receiving solar radiation from the respective first and second arrays of the collecting elements as the sun travels along its trajectory from the east to the west.

54. A system as claimed in any of Claims 49 to 53 in which the height of the heat exchanger relative to the collecting means is variable.

55. A system as claimed in any preceding claim in which the heat exchanger is integral with the Stirling engine.

56. A system as claimed in any preceding claim in which a protective shield is located for protecting the Stirling engine from.solar radiation directed towards the heat exchanger.

57. A system as claimed in any preceding claim in which the Stirling engine comprises at least one pair of cylinders, one cylinder of each pair of cylinders having a power piston operable therein and the other cylinder of each pair of cylinders having a displacer piston operable therein.

58. A system as claimed in Claim 57 in which the pistons of each pair of cylinders are configured so that the power and displacer pistons operate out of phase with each other by approximately 90° in accordance with the Stirling cycle.

59. A system as claimed in Claim 57 or 58 in which each pair of cylinders is configured in a V-configuration.

60. A system as claimed in any of Claims 57 to 59 in which the cylinders of each pair are configured so that a geometrical central axis defined by the respective cylinders extend at substantially 90° to each other. 61. A system as claimed in any of Claims 57 to 60 in which each pair of cylinders is provided with a corresponding heat exchanger.

62. A system as claimed in any of Claims 57 to 61 in which each pair of cylinders is provided with a corresponding regenerator.

63. A system as claimed in any of Claims 57 to 62 in which a plurality of pairs of cylinders are provided, the pistons of the respective pairs of cylinders being coupled to a common crank shaft. 64. A system as claimed in any preceding claim in which a plurality of heat exchangers are provided.

65. A system as claimed in any preceding claim in which a plurality of Stirling engines are provided.

66. A system as claimed in any preceding claim in which one heat exchanger is provided for each Stirling engine.

67. A system as claimed in any of Claims 1 to 65 in which a plurality of heat exchangers are provided for each Stirling engine.

68. A system as claimed in any of Claims 1 to 65 in which one heat exchanger is provided for a plurality of Stirling engines.

69. A system as claimed in any preceding claim in which at least some of the collecting elements are adapted to direct solar radiation to more than one Stirling engine.

70. A system as claimed in Claim 69 in which the at least some of the collecting elements are adapted to direct the solar radiation to more than one Stirling engine sequentially. 71. A system as claimed in any preceding claim in which one of the heat exchanger and the Stirling engine is adapted to receive energy from an energy source other than the sun in order to maintain the system operational in the absence of solar radiation or sufficient solar radiation to maintain the system operational. 72. A system as claimed in Claim 71 in which the energy source is a heat source, and the heat exchanger is adapted to receive heat from a heat exchange medium heated by the heat source.

73. A system as claimed in Claim 72 in which the heat exchanger is adapted to accommodate the heat exchange medium therethrough.

74. A system as claimed in any of Claims 71 to 73 in which the energy source other than the sun is a boiler.

75. A system as claimed in any of Claims 71 to 74 in which the energy source other than the sun is a source of stored energy. 76. A system as claimed in any preceding claim in which each Stirling engine is adapted to power an electrical generator.

77. A system as claimed in Claim 76 in which each Stirling engine is adapted to power a permanent magnet generator.

78. A system as claimed in Claim 76 or 77 in which each Stirling engine is coupled to the electrical generator.

79. A system as claimed in any of Claims 76 to 78 in which each Stirling engine is coupled to the electrical generator through a drive transmission means.

80. In combination a system as claimed in any preceding claim further comprising an electrical generator coupled directly or indirectly to the Stirling engine and driven by the Stirling engine.

81. A method for converting solar energy to usable energy, the method comprising providing a Stirling engine operable in a Stirling cycle, providing a heat exchanger for heating a working fluid for powering the Stirling engine, and providing a collecting means for collecting and directing solar radiation from the sun at the heat exchanger for heating the working fluid therein, the method further comprising operating the collecting means for directing and concentrating the solar radiation onto the heat exchanger for heating the working fluid of the Stirling engine for in turn powering the Stirling engine. 82. A method as claimed in Claim 81 in which the collecting means is provided by a plurality of collecting elements.

83. A method as claimed in Claim 82 in which the collecting elements are arranged in an array for directing the solar radiation at the heat exchanger.

84. A method as claimed in Claim 83 in which at least two arrays of collecting elements are provided on respective opposite sides of the heat exchanger.

85. A method as claimed in Claim 84 in which a first one of the arrays of collecting elements is directed for receiving solar radiation when the sun is in an eastern half of the sky, and a second one of the arrays of collecting elements is directed for receiving solar radiation when the sun is in a westerly half of the sky.

86. A method as claimed in any of Claims 83 to 85 in which a plurality of the collecting elements are provided in a third array which is directed in a generally southerly direction and the heat exchanger is adapted to receive solar radiation from the collecting elements of the third array simultaneously as solar energy is being received from the collecting elements of one of the first and second arrays.

87. A method as claimed in any of Claims 82 to 86 in which each collecting element is selectively orientable in order to track at least a portion of the trajectory of the sun in the sky as the earth rotates relative to the sun.

88. A method as claimed in any of Claims 82 to 87 in which each collecting element is pivotal about at least one pivot axis.

89. A method as claimed in any of Claims 82 to 88 in which each collecting element is pivotal about a pair of pivot axes.

90. A method as claimed in Claim 89 in which the respective pivot axes about which each collecting element is pivotal are disposed substantially perpendicularly to each other.

91. A method as claimed in Claim 89 or 90 in which a first one of the pivot axes about which each collecting element is pivotal is a horizontal pivot axis for tracking the elevation of the sun in the sky.

92. A method as claimed in any of Claims 89 to 91 in which a second one of the pivot axes about which each collecting element is pivotal is disposed for tracking the east to west trajectory of the sun through the sky.

93. A method as claimed in any of Claims 89 to 92 in which each collecting element is pivotal about the second pivot axis for tracking the sun in the azimuth plane. 94. A method as claimed in any of Claims 89 to 93 in which the angle of the second pivot axis of each collecting element relative to the ground varies as the elevation of the sun varies in the sky.

95. A method as claimed in any of Claims 89 to 94 in which the angle which the second pivot axis of each collecting element makes with the ground varies as the orientation of the collecting element varies about the corresponding first horizontal pivot axis.

96. A method as claimed in any of Claims 89 to 95 in which each collecting element is shaped in order to track at least a portion of the trajectory of the sun.

97. A method as claimed in any of Claims 82 to 96 in which each collecting element is arranged and controlled to collect and reflect the solar radiation in an optimum manner depending on any one or more of the time of day, the time of year and the latitude at which the solar energy converting system is located.

98. A method as claimed in any of Claims 82 to 97 in which each collecting element comprises a reflecting means.

99. A method as claimed in Claim 98 in which each reflecting means comprises a reflector.

100. A method as claimed in Claim 98 or 99 in which each reflecting means comprises a plurality of reflecting elements. .

101. A method as claimed in any of Claims 99 to 100 in which each reflecting element is of a reflectance index of not less than 85%.

102. A method as claimed in any of Claims 98 to 101 in which each reflecting means comprises a heliostat mirror.

103. A method as claimed in any of Claims 81 to 102 in which the collecting means is located spaced apart from the heat exchanger.

104. A method as claimed in any of Claims 81 to 103 in which the collecting means is located adjacent the ground. 105. A method as claimed in any of Claims 81 to 104 in which the heat exchanger is located at a level above the level of the collecting means, and the collecting means is adapted for directing the solar radiation in a generally upwardly direction to the heat exchanger. 106. A method as claimed in any of Claims 81 to 104 in which the heat exchanger is located at a level below the collecting means.

107. A method as claimed in any of Claims 81 to 104 in which the heat exchanger is located at a level substantially similar to the level of the collecting means. 08. A method as claimed in Claim 106 to 107 in which the solar radiation is directed by the collecting means to an intermediate directing means which directs the solar energy received from the collecting means to the heat exchanger. 109. A method as claimed in Claim 108 in which the intermediate directing means is located at a level above the collecting means and the heat exchanger.

1 10. A method as claimed in Claim 108 or 109 in which the intermediate directing means comprises an intermediate reflecting means.

111. A method as claimed in any of Claims 108 to 110 in which the intermediate reflecting means comprises a reflector of one of a parabolic, a spherical or other curved shape.

112. A method as claimed in any of Claims 108 to 111 in which one of the orientation and the position of the intermediate directing means is moveable for facilitating aligning of the intermediate directing means with the collecting means for receiving the reflected solar radiation.

113. A method as claimed in any of Claims 108 to 112 in which the intermediate directing means is pivotal about a pair of pivot axes at an angle to each other. 114. A method as claimed in Claim 113 in which the pivot axes about which the intermediate directing means is pivotal extend perpendicularly to each other.

115. A method as claimed in Claim 1 13 or 114 in which a first one of the pivot axes of the intermediate directing means extends in a general horizontal direction.

116. A method as claimed in any of Claims 113 to 115 in which the intermediate directing means is pivotal about the first one and a second one of the pivot axes about which the intermediate directing means is pivotal for receiving solar radiation from the collecting means as the sun travels along its trajectory from east to west.

1 17. A method as claimed in any of Claims 108 to 116 in which the height of the intermediate directing means relative to the collecting means is variable.

118. A method as claimed in any of Claims 81 to 117 in which one of the orientation and the position of the heat exchanger is selectively moveable for facilitating aligning the heat exchanger with the at least one reflecting element for receiving reflected solar radiation therefrom.

119. A method as claimed in any of Claims 81 to 118 in which the heat exchanger is pivotal about a pair of pivot axes at an angle to each other.

120. A method as claimed in Claim 119 in which the pivot axes about which the heat exchanger is pivotal extend perpendicularly to each other.

121. A method as claimed in Claim 119 or 120 in which a first one of the pivot axes of the heat exchanger extends in a general vertical direction. 122. A method as claimed in any of Claims 119 to 121 in which the heat exchanger is pivotal about the first vertical axis for selectively and sequentially receiving solar radiation from the respective first and second arrays of the collecting elements as the sun travels along its trajectory from the east to the west. 123. A method as claimed in any of Claims 118 to 122 in which the height of the heat exchanger relative to the collecting means is variable.

124. A method as claimed in any of Claims 81 to 123 in which a plurality of Stirling engines are provided.

125. A method as claimed in Claim 124 in which at least some of the collecting elements are adapted to direct solar radiation to more than one Stirling engine.

126. A method as claimed in Claim 125 in which the at least some of the collecting elements are adapted to direct the solar radiation to more than one Stirling engine sequentially.

127. A method as claimed in any of Claims 81 to 126 in which one of the heat exchanger and the Stirling engine is adapted to receive energy from an energy source other than the sun in order to maintain the system operational in the absence of solar radiation or sufficient solar radiation to maintain the system operational.

128. A method as claimed in Claim 127 in which the energy source is a heat source, and the heat exchanger is adapted to receive heat from a heat exchange medium heated by the heat source.

129. A method as claimed in Claim 128 in which the heat exchanger is adapted to accommodate the heat exchange medium therethrough.

130. A method as claimed in any of Claims 127 to 129 in which the energy source other than the sun is a boiler. 131. A method as claimed in any of Claims 127 to 130 in which the energy source other than the sun is a source of stored energy.