WO2021019198A1

WO2021019198A1 - Solar heating system

Info

Publication number: WO2021019198A1
Application number: PCT/GB2019/052749
Authority: WO
Inventors: John Squire; Karl HICK
Original assignee: Larkfleet Limited
Priority date: 2019-08-01
Filing date: 2019-09-27
Publication date: 2021-02-04
Also published as: GB2589670B; WO2021019251A1; GB2618930B; GB2618930A; GB2586062A; GB201910997D0; GB202312959D0; GB2586062B; EP4007872A1; GB2589670A; GB202011917D0

Abstract

A solar heating system (1), including: a lens array (3) including at least one lens assembly (9), the lens assembly including a supporting substrate (11) and a film (13) applied to a surface of the supporting substrate, the film (13) having at least one lens (9) formed therein; a tubular receiver (5) adapted to carry fluid and located at a focal point of the at least one lens assembly; a frame (17, 19) for supporting the lens array (3) and adapted for pivoting movement about a first axis (Z-Z) arranged coaxial with the tubular receiver (5) and a second axis arranged perpendicular to the tubular receiver (5).

Description

SOLAR HEATING SYSTEM

TECHNICAL FIELD

The present invention relates to a solar heating system, and a steam generation plant, a desalination plant, a waste treatment plant, an electrical generator plant, a water treatment plant, and a cooling system, each of which include a solar system according to the invention. In particular, the solar heating system includes a lens array, such as a Fresnel lens array, that is arranged to heat fluid in a tubular receiver.

BACKGROUND TO THE INVENTION

The utilisation of thermal radiation from the sun, referred to herein as solar radiation, for heating water in a tube for the purposes of producing steam and, subsequently used in various processes is generally known. For example, WO2010097637 (Boyle) discloses an apparatus with a Fresnel lens mounted on a frame for selectively directing solar radiation onto a thermosensitive member and a generator means for converting the resulting thermal expansion/contraction into electrical power. While expansion/contraction of the thermosensitive member is the main drive means for the generator, this document also describes an embodiment where sunlight is focussed through an array of Fresnel lenses onto a tube carrying water for the purposes of producing steam capable of powering an electrical generator, and also for utilisation as a desalination process. A pictorial representation of this apparatus is provided as Figure 1 in the attached drawings.

In particular, the prior art embodiment of Figure 1 describes a rod 402, a water source 406, a pair of steam accumulators 408, 408', a pair of steam "engine rooms" 410, 410', a corresponding motor 412, 412' and a plurality of condensing areas 414. The rod 402 is supported by a frame and, in turn, is used as a pivot axis for a Fresnel lens (not seen) with a focal line centred on the rod. Water is injected into the rod 402 at a central location such that, by the time it reaches the respective ends of rod 402, it has turned to steam for collection by the steam accumulators 408/408' whereupon the high pressure is used for power generation.

SUMMARY OF THE INVENTION

The present invention seeks to improve upon the basic principles outlined in the prior art for the purposes of producing a solar heating system, that has many potential applications.

According to one aspect of the invention there is provided a solar heating system according to claim 1. The invention is arranged to produce steam and/or hot water in an efficient and cost-effective manner. The invention can be arranged to produce high temperature steam, for example at greater than or equal to 200°C, or hot water, for example at around at greater than or equal to 70°C, and preferably greater than or equal to 90°C. The steam and/or hot water produced can be used for many different applications, for example many industrial and commercial uses such as in dairies for pasteurisation processes, in the food industry for steam cooking, in agriculture for the treatment of waste water, in hotels for hot water and water treatment. Many other applications are also envisaged such as desalination of water, general treatment of wastewater, cooling systems, and electricity generation.

According to another aspect of the invention there is provided a solar heating system.

The solar heating system can include a lens array having at least one lens assembly. The lens assembly can comprise a Fresnel lens assembly. The lens assembly can include a supporting substrate. The lens assembly can include a film applied to a surface of the supporting substrate. The film can have at least one lens formed therein, and preferably at least one Fresnel lens formed therein.

The solar heating system can include a tubular receiver adapted to carry fluid. The tubular receiver can be located at a focal point of the at least one lens assembly.

The solar heating system can include a frame arranged to support the lens array. The frame can be adapted for pivoting movement about a first axis arranged coaxial with the tubular receiver. The frame can be adapted for pivoting movement about as second axis arranged perpendicular to the tubular receiver. The first axis can be a generally horizontal axis, and is sometimes referred to as a roll axis. The second axis can be a generally vertical axis, and is sometimes referred to as a yaw axis. In use, the lens assembly directs light to the tubular receiver. The light heats a fluid in the tubular receiver to increase the temperature of the fluid, and in some instances to change the state of the fluid, for example from a liquid to a gas.

The film can comprise a plastics material, and preferably a thermoplastic material such as Polymethyl methacrylate (PMMA). The film can have a maximum thickness that is greater than or equal to 30 microns. The film can have a maximum thickness that is less than or equal to 250 microns.

The lens can be formed in the film by a casting drum.

The supporting substrate can comprise a plastic material, and preferably a thermoplastic material such as Polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), polyethylene terephthalate (PET) and/or polycarbonates (PC).

The at least one lens can have a focal length that is greater than or equal to 1 m. The at least one lens can have a focal length that is less than or equal to 2m. Preferably the at least one lens can have a focal length in the range 1.2m to 1.8m, and is preferably around 1.65m.

The lens array can include a plurality of lens assemblies, and preferably a plurality of Fresnel lens assemblies. Each lens assembly can include a supporting substrate. Each lens can include a film applied to at least one surface of the supporting substrate. Each film can have a lens formed therein, and preferably a Fresnel lens formed therein. Each lens assembly can be arranged according to any configuration described herein.

The lens array can be planar. A plurality of lens assemblies can be arranged in an array. For example, the array can include at least one row of Fresnel lens assemblies, and preferably a plurality of rows of Fresnel lens assemblies. The tubular receiver can include a tubular absorber. The tubular absorber can be metallic, and is preferably made from steel. The tubular absorber can be coated with an absorber coating to minimise heat loss, for example infrared heat loss. The coating can comprise a nano-coating. Nano-coatings are particularly effective at reducing heat loss. The coating can be a dark colour, such as black. The tubular receiver can include an optically transparent casing housing at least part of the tubular absorber. This provides a very efficient arrangement. A receiver arranged in this manner has been found to have an efficiency of around 98.4%. The optically transparent casing helps to prevent light escaping. The optically transparent casing can be coaxial with the tubular absorber. The casing can be made from glass. The casing can have an antireflective coating to increase solar transmittance.

The tubular receiver can be arranged to include a space between the optically transparent casing and the tubular absorber. Air can be evacuated from said space to create a vacuum. The vacuum reduces or prevents gas heat conduction between the transparent casing and the tubular receiver, which can improve performance.

The tubular receiver can include an annular member mounted on the tubular absorber co-axially therewith. The annular member can be arranged to support a first end of the optically transparent casing. The annual member can include a first annular part sealably attached to the tubular absorber. The annual member can include a second annular part sealably attached to the optically transparent casing. The tubular receiver can include an expandable flexible member folded in a concertina arrangement. The expandable flexible member is attached to the first annular part and the second annular part. The expandable member accounts for differences in thermal expansion between the tubular receiver and the optically transparent casing. The expandable flexible member can be sealed to the first annular part. The expandable flexible member can be sealed to the second annular part.

The tubular receiver can include a second annular member mounted on the tubular receiver co-axially therewith. The second annular member can be arranged to support a second end of the optically transparent casing. The second annual member can include a first annular part sealably attached to the tubular absorber. The second annual member can include a second annular part sealably attached to the optically transparent casing. The tubular receiver can include an expandable flexible member folded in a concertina arrangement. The system can include an elongate reflector mounted parallel with the tubular receiver on a side of the tubular receiver that is opposite to the side facing towards the lens array. The reflector redirects light towards the tubular receiver.

The frame can include first and second parts.

The second part can be arranged to support the tubular receiver. The second part can be arranged to pivot about the second axis.

The first part can support the lens array. The first part can be arranged to pivot relative to the second part about the first axis. The tubular receiver can be arranged co-axially with the first axis. Thus the lens array can be pivoted about the tubular receiver. The system can include a linear actuator. The linear actuator can be arranged to pivot the first part of the frame relative to the second part of the frame. The first part of the frame can be arranged to pivot through an angle of approximately 90 degrees. The first part of the frame can be arranged to pivot between a first position wherein the lens assembly is in a horizontal orientation and a second position wherein the lens assembly is in a vertical orientation. The first part of the frame can be arranged to move to a least one intermediate position that is intermediate between the first and second positions.

The system can include a slew ring drive that is arranged to pivot the second part of the frame about the second axis. Since the first part of the frame is mounted on the second part of the frame, the first part of the frame is also pivoted about the second axis. The second part of the frame can be mounted on casters and/or rollers. The system can include a track, for example a circular track or an arcuate track. The casters and/or rollers can be mounted on the track. The casters and/or rollers move along the track as the slew ring drives the frame to pivot about the axis that is perpendicular to a longitudinal axis of the tubular receiver.

The system can include a tracking system arranged to automatically adjust the orientation of the lens array. The tracking system can be arranged to automatically adjust the orientation of the lens array to keep the lenses facing towards the sun. This helps to maximise the amount of light focused on the tubular receiver. The tracking system can comprise an open-loop arrangement.

The tracking system can include an astronomical algorithm and a real-time clock to control the orientation of the lens array. The astronomical algorithm can be arranged to calculate the correct position of the sun in the sky at any given point in time. The real-time clock can be used to determine the calendar date and time of day. The tracking system can be arranged to use an output signal from the real time clock to enable the astronomical algorithm to determine the correct position of the sun in the sky for the date and time indicated by the output signal from the real-time clock.

The tracking system can be arranged to automatically adjust the orientation of the lens array about the first axis. The tracking system can be arranged to automatically adjust the orientation of the lens array about the second axis.

The tracking system can be arranged to automatically adjust at least one of the linear actuator and the slew ring to adjust the orientation of the lens array. The tracking system can be arranged to automatically operate at least one of the linear actuator and the slew ring to keep the lens array facing towards the sun. The tracking system can be arranged to automatically adjust at least one of the linear actuator and the slew ring to adjust the orientation of the lens array in response to the tracking system calculating at least one of the solar azimuth and zenith angles of the sun. The system can include at least one limit switch arranged to limit movement of the linear actuator; and/or at least one limit switch arranged to limit movement of the slew ring.

The tracking system can include a wind protection mode. The tracking system can include wind speed measurement means and the processor is arranged to receive signals from the wind speed measurement means. The tracking system can be arranged to move the lens assembly to a safe orientation in response to receiving a signal from the wind speed measurement means that indicates that the wind speed is greater than or equal to a threshold value. Typically the safe orientation is a horizontal orientation. When the lens assembly is in the horizontal orientation, typically the first part of the frame is in a vertical orientation.

The system can include a fluid supply system. The fluid supply system supplies a thermal transfer fluid to the tubular receiver.

The fluid supply system can be arranged to supply the fluid in a liquid state to the tubular receiver. The lens array can be arranged to heat the tubular receiver to a sufficiently high temperature to generate gas from the liquid.

The fluid supply system can include a header tank. The header tank can be arranged to store fluid in a liquid state.

The fluid supply system can include a condenser arranged to condense gas to liquid. The liquid can be recycled back to the header tank. In general, if water is not used for other purposes (e.g. drinking water) then water from the system is recyclable back to the header tank.

The fluid supply system can include a de-ionizer arranged to de-ionize the fluid, such as water. The fluid system can include at least one pump. The fluid system can include at least one pump arranged to pump the fluid into the tubular receiver. Typically, the pump can be arranged to pump a liquid into the tubular receiver. The fluid supply system can include at least one pump arranged to pump fluid to the header tank.

The fluid supply system can include a blowdown tank. The blowdown tank is arranged to store the fluid in gaseous form.

The fluid supply system can include an energy storage tank. The energy storage tank is a larger and/or lower pressure vessel than the blowdown tank and is arranged to store a larger volume of fluid in liquid and/or gaseous form. The energy storage tank can include an output, for example an output pipe, that supplies the second fluid, such as hot water and/or steam, to a downstream process or user. The output pipe can include at least one valve to control the flow of the second fluid from the energy storage tank.

The fluid supply system can include an absorption chiller. The absorption chiller can be a lithium bromide absorption chiller. The absorption chiller includes a refrigeration system that is driven by heat taken from the fluid. The fluid is typically supplied to the absorption chiller at a temperature in excess of 60°C.

The fluid supply system can include at least one filter arranged to filter fluid in the system. The fluid supply system can include a plurality of filters, the arrangement being such that one of the filters can be changed without having to shut down the solar heating system. The fluid supply system can include at least one additional tank for storing the thermal transfer fluid.

The system can include at least one temperature sensor arranged to monitor a fluid temperature in the fluid supply system. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the header tank, for example at an output side of the header tank. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the tubular receiver, for example at an output side of the tubular receiver. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the heat exchanger, for example at an output side of the heat exchanger. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the blowdown tank, for example at an input side of the blowdown tank. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the condensate tank, for example at an input side of the condensate tank. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the energy storage tank, for example at an input side of the energy store tank. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the absorption chiller, for example at an input side of the absorption chiller.

The system can include a controller arranged to receive signals from at least one temperature sensor.

The controller can be arranged to send a control signal to the tracking system to adjust the position of the lens array in response to receipt of a signal from at least one temperature sensor, for example a signal indicating that the temperature has reached a threshold value. The tracking system can be arranged to adjust the position of the lens array in response to receipt of the control signal from the controller. For example, the tracking system can be arranged to move the lens array to a position that decreases the amount of solar energy directed on to the receiver. In one embodiment the tracking system can be arranged to move the lens array to a position wherein the solar array faces away from the sun. This provides the solar heating system with a safety arrangement to prevent components from overheating. The tracking system can be arranged to move the lens array to a position that increases the amount of solar energy directed on to the receiver. The fluid supply system can include at least one flow meter.

The fluid supply system can include a primary circuit having a first thermal transfer fluid. The primary circuit can include the tubular receiver.

The fluid supply system can include a secondary circuit having a second thermal transfer fluid. Typically the second thermal transfer fluid is different from the first thermal transfer fluid.

The fluid supply system can include a heat exchanger arranged to transfer heat from the first thermal transfer fluid to the second thermal transfer fluid. The heat exchanger can be part of the primary and secondary circuits.

The primary circuit can include a header tank. The header tank can store the first fluid, typically in a liquid state.

The primary circuit can include the tubular receiver.

The header tank, tubular receiver and heat exchanger can be arranged in series. The primary circuit can be a closed loop circuit. The primary circuit can include a first filter system. Preferably the second filter system includes first and second filters. The first filter system can be located between the heat exchanger and the header tank.

The primary circuit can include at least one pump. At least one pump can be arranged to pump the first fluid to the to the tubular receiver. The first fluid is typically in a liquid state went it enters the tubular receiver. The at least one pump can be arranged to pump the first fluid to the header tank.

The primary circuit can include at least one valve. A check valve can be located between the header tank and the receiver tube. A check valve can be located between the heat exchanger and the header tank.

The primary circuit can include at least one temperature sensor, and preferably a plurality of temperature sensors, arranged to measure the temperature of the first fluid. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the header tank, for example at output side of the header tank. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the tubular receiver, for example at an output side of the tubular receiver. A temperature sensor can be arranged to monitor the fluid temperature in and/or adjacent the heat exchanger.

The primary circuit can include at least one flow meter. A flow meter can be located between the header tank and the receiver tube.

The secondary circuit can include a header tank. The header tank is arranged to store the second fluid, preferably in a liquid state.

The secondary circuit can include the blowdown tank. The blowdown tank is arranged to store the second fluid in gaseous form. The blowdown tank can be a steam tank. The secondary circuit can include the condenser. The condenser is arranged to condense the second fluid from a gaseous state to a liquid state.

The secondary circuit can include the energy storage tank.

The secondary circuit can include the absorption chiller. The secondary circuit can include a second filter system. Preferably the second filter system includes first and second filters. The filter system can be located between the blowdown tank and the condenser.

The secondary circuit can be a closed loop circuit.

In the secondary circuit, the header tank, heat exchanger, blowdown tank and condenser can be arranged in series. In the secondary circuit, the header tank, heat exchanger, blowdown tank, and absorption chiller can be arranged in series.

The energy storage tank can be arranged in parallel with the absorption chiller.

The secondary circuit can include at least one pump. At least one pump can be arranged to pump the second fluid in a liquid state from the header tank to the heat exchanger. At least one pump can be arranged to pump the second fluid in a liquid state to the header tank.

The secondary circuit can include at least one valve. A check valve can be located between the header tank and the heat exchanger. A check valve can be located between the condenser and the absorption chiller. A diverter valve can be located between the blowdown tank and the condensate tank. The diverter valve can be arranged to control the flow of fluid from the blowdown tank to the condensate tank. The diverter valve can redirect the output from the blown tank to the energy storage tank. The secondary circuit can include at least one temperature sensor, and preferably a plurality of temperature sensors, arranged to measure the temperature of the second fluid. A temperature sensor can be arranged to monitor the fluid temperature in the header tank, at an input side of the header tank and/or an output side of the header tank. A temperature sensor can be arranged to monitor the fluid temperature in the heat exchanger, at an input side of the heat exchanger and/or an output side of the heat exchanger. A temperature sensor can be arranged to monitor the fluid temperature in the blowdown tank, at an input side of the blowdown tank and/or an output side of the blowdown tank. A temperature sensor can be arranged to monitor the fluid temperature in the condenser, at an input side of the condenser and/or an output side of the condenser. A temperature sensor can be arranged to monitor the fluid temperature in the energy store, at an input side of the energy store and/or an output side of the energy store. A temperature sensor can be arranged to monitor the fluid temperature in the absorption chiller, at an input to the absorption chiller and/or an output to the absorption chiller.

The secondary circuit can include at least one flow meter. A flow meter can be located between the header tank and the heat exchanger.

According to another aspect of the invention there is provided a steam generator plant, including a solar heating system according to any configuration described herein. The steam, or other gas, generated by the solar heating system can be used for any suitable purpose.

According to another aspect of the invention there is provided a desalination plant, including a solar heating system according to any configuration described herein. The steam, or other gas, generated by the solar heating system can be used in a desalination process. According to another aspect of the invention there is provided a waste treatment plant including a solar heating system according to any configuration described herein. The steam, or other gas, generated by the solar heating system can be used in a waste treatment process. According to another aspect of the invention there is provided an electrical generator plant including a solar heating system according to any configuration described herein. The steam, or other gas, generated by the solar heating system can be used in an electrical generator plant to generate electricity. For example, the steam, or other gas, can be used to drive turbine to generate electricity. According to another aspect of the invention there is provided a water treatment plant including a solar heating system according to any configuration described herein.

According to another aspect of the invention there is provided a cooling system, including a solar heating system according to any configuration described herein. The cooling system can include an absorption chiller unit.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described with reference to the following drawings by way of example only:

Figure 1 illustrates a view of a prior art system relating to the present invention; Figure 2 is an isometric view of a solar heater system according to the present invention;

Figures 3 to 5 are side views of the solar heating system of Figure 2, in different orientations; Figure 6 is a diagrammatic view of a tracking system used in the embodiment of Figure 2;

Figure 7 is a plan view of a linear actuator used in the tracking system of Figure 6;

Figure 8 is a plan view of a slew ring used in the tracking system of Figure 6;

Figure 9 provides diagrammatic views illustrating varying operating positions of a solar panel assembly included in the embodiment of Figure 2;

Figure 10 is a cross-sectional detailed view of end part of a tubular receiver included in the embodiment of Figure 2;

Figure 1 1 is an enlarged isometric view of an end part of the tubular receiver of Figure 10;

Figure 12 is an enlarged diagrammatic view of a part of a lens included in the embodiment of Figure 2; Figure 13 is a schematic view of a lens arrangement in the embodiment of

Figure 2;

Figures 14 to 16 are examples of circuits including the tubular receiver of Figure 10. DETAILED DESCRIPTION OF THE INVENTION

Figures 2-13 illustrate the main components of a solar heating system 1 according to an embodiment of the invention. The solar heating system 1 includes a lens array 3, a tubular receiver 5 arranged to receive solar energy from the lens array 3 and a frame 7.

The lens array 3 includes a plurality of lenses, such as Fresnel lens 9. Typically the lens array 3 includes four to twenty lenses 9. In Figure 2, the arrangement has twelve lenses 9. The number of lenses is selected according to the heating requirements. Each Fresnel lens 9 includes a substrate 1 1 and a film 13. The substrate 1 1 provides support for the film 13. The substrate typically comprises a panel, and preferably a planar panel. Typically the panel is rectangular in plan view. The panel is typically made from a plastic material, and preferably a thermoplastic material, such as polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), polyethylene terephthalate (PET) or polycarbonates (PC). The substrate 1 1 preferably comprises a PMMA panel.

The film 13 includes an arrangement of lens elements 15 formed therein. Each lens element 15 typically comprises a micro-prism. The overall arrangement of the lens elements 15 produces the Fresnel lens 9. The film 13 typically has a thickness in the range 30-250 microns. The film 13 is typically made from polymethyl methacrylate (PMMA). The film 13 is applied to a major surface of the substrate 1 1. The film 13 is preferably bonded to the substrate 1 1, for example by a solvent such as methyl chloride.

The film 13 is produced by forming a lens pattern into a curved surface of a casting drum. The casting drum can be made from copper or high phosphorus nickel, the lens pattern is typically cut into the drum using diamond cutters that are computer controlled according to a program arranged to provide a lens with a specific focal length. The casting drum is mounted in a roll to roll UV casting machine. A web of film material is fed over the casting drum and the lens pattern on the casting drum forms the arrangement of lens elements 15 in the web of film material. The film 13 is then cut to size and each film portion is mounted on to a respective substrate 1 1. Each Fresnel lens is approximately 1.2m long 0.7m wide. Each lens has a specific focal length, which is typically in the range 1 m to 2m, preferably 1.2m to 1.8m, and is preferably around 1.65m. Optionally, a transparent wear film or coating can be applied to the film 13 to protect the optical surfaces.

The Fresnel lenses 9 are mounted in the frame 7. The frame 7 includes a first and second parts 17,19. The first part 17 is pivotally attached to the second part 19. For example, the first part 17 can be pivotally attached to the second part in a manner that enables the first part 17 to pivot relative to the second part 19 about a generally horizontal axis Z-Z. The first part 17 supports the Fresnel lenses 9. This enables the orientation of the Fresnel lenses 9 to be adjusted along an arcuate path about the generally horizontal axis Z-Z (see Figures 3 to 5). Typically the Fresnel lenses 9 are arranged to move through an arc of around 90 degrees, for example while tracking the sun. Starting at a first orientation at 0 degrees of rotation, wherein the Fresnel lenses 9 are arranged in a generally vertical plane, the Fresnel lenses 9 are able to pivot along the arcuate path to a final orientation at 90 degrees of rotation wherein the Fresnel lenses are in a generally horizontal plane (see Figure 9). The Fresnel lenses 9 are arranged to move along the arcuate path in both directions. The Fresnel lens 9 are mounted in the first part 17 of the frame in a 2 x 6 array. Each Fresnel lens 9 is arranged in a common plane. The first part 17 of the frame includes an arrangement of frame members 21a-c,23a-g that engage and support edges of the Fresnel lenses 9. The first part 17 of the frame includes a trestle 25, which supports the frame members 21a-c,23a-g and the array of Fresnel lens 9. The trestle 25 includes a first pair of frame members 27a-b that are inclined to one another at a first end of the first part 17 and a second pair of frame members 29a- b that are inclined to one another at a second end of the first part 17. The frame members 27a-b flare outwards in the direction of their distal ends where they connect with frame members 23a, 21 a, 21c, and taper inwards in the direction of their proximal ends. The frame members 29a-b flare outwards in the direction of their distal ends where they connect with frame members 23g,21a,21c, and taper inwards in the direction of their proximal ends. This provides the first part of the frame 17 with a space frame having a generally triangular prismatic arrangement. A counterweight 31 is located at an apex of the trestle 21. The counterweight 31 provides a means of balancing the Fresnel lens 9 about its pivot axis Z-Z to reduce the torque on any pivoting connection, which may be mechanised to enable raising and lowering of the Fresnel lenses 9 in an arc about the pivot axis Z-Z. The counterweight 31 extends between the first pair of frame members 27a-b and the second pair of frame members 29a-b. The counterweight 31 comprises an elongate member, and preferably is comprises an elongate cylindrical member. The counterweight 31 is arranged generally parallel with frame member 21 b, which is arranged along a longitudinal centre line of the Fresnel lenses 9. The counterweight 31 is attached to the trestle 25 by first and second end plates 33,35. The first end plate 33 is attached to the first pair of frame members 27a-b. The second end plate 35 is attached to the second pair of frame members 29a-b. The first and second end plates 33,35 have a triangular shape. The second part 19 of the frame is arranged to support the first part of the frame 17 and the lenses 9 mounted on the first part 17 of the frame. The second part 19 of the frame is arranged to pivot about a generally vertical axis, which enables the orientation of the Fresnel lenses 9 to be adjusted about the vertical axis. The generally vertical axis is arranged centrally relative to the second part 19 of the frame. This enables the orientation of the Fresnel lenses 9 to be adjusted along a second arcuate path about the vertical axis (see Figures 3 to 5). Typically the Fresnel lenses 9 are arranged to move through an arc of up to 180 degrees. For example, when located in-situ, the second part 19 of the frame can have a starting orientation (0 degrees) wherein the Fresnel lenses 9 face in a generally easterly direction and can be rotated slowly about the vertical axis while tracking the sun to a final orientation (180 degrees) wherein the Fresnel lenses face in a generally westerly direction (see Figure 9, which shows the second part of the frame at 45 degrees). The second part 19 of the frame preferably comprises a carriage having casters, wheels or rollers 36. The casters, wheels or rollers 36 are preferably located on a circular track 37. The casters, wheels or rollers 36 enable the second part 19 of the frame to rotate about the generally vertical axis along an arc of a circular path.

The first part 17 frame is pivotally attached to the second part 19 of the frame by bearings 40. Typically the bearings 40 are attached to end portions of the first and second frames 17,19. For example, the second part 19 of the frame can include third and fourth end plates 43,45. One of the bearings 40 can be attached to each of the respective third and fourth end plates 43,45.

The system 1 includes a slew ring 39 (see Figures 6 and 8). The slew ring 39 is arranged to drive the second part 19 of the frame to rotate about the generally vertical axis. The slew ring 39 is mounted on the second part 19 of the frame (see Figures 3 to 5).

The system 1 includes a linear actuator 41 (see Figures 6 and 7). The linear actuator 41 is arranged to pivot the first part 17 of the frame relative to the second part 19 of the frame about the generally horizontal axis. The linear actuator 41 is mounted on the second part of the frame (see Figures 3 to 5).

The tubular receiver 5 is mounted on the second part 19 of the frame. The tubular receiver 5 is elongate. The tubular receiver 5 is centrally located on the second part 19 of the frame. A central longitudinal axis of the tubular receiver 5 is co-axial with the generally horizontal axis Z-Z which the first part 17 of the frame pivots about relative to the second part 19 of the frame. The tubular receiver 5 is located at a focal line of the Fresnel lenses 9. In use, the lenses 9 focus solar energy onto the tubular receiver 5 to heat a fluid stored therein. R Figure 13 illustrates diagrammatically the lenses 9 focusing light towards the tubular receiver 5.

The tubular receiver 5 comprises a thermally conductive absorber tube 49, which is typically made from metal, such as steel (see Figure 10). The absorber tube 49 has a transparent outer casing 51, which is typically made from glass. The outer casing 51 is arranged co-axially with the absorber tube 49. The outer casing 51 has a larger diameter that the absorber tube 49 such that the inner surface of the outer casing 51 is spaced apart from the outer surface of the absorber tube 49. The space between the outer casing 51 and the absorber tube 49 is evacuated to create a vacuum. The vacuum supresses gas heat conduction, and convection within the space. Each end of the tubular receiver 5 has end assembly 53. The end assembly 53 includes a ring assembly 55, which separates the outer casing 51 from the absorber tube 49 and a bellows assembly 57 which allows for differences in the rates of thermal expansion and contraction between the absorber tube 49 and the outer casing 51. The ring assembly 55 comprises a first part 55a sealed to the absorber tube 49. The metal ring 55 includes a second part 55b sealed to the outer casing 51. The bellows assembly 57 is sealed to both the first and second parts of the ring. The receiver 5 can include getter material in order to maintain the vacuum in the receiver. The getter material is arranged to absorb free gases in the space between the outer casing 51 and the absorber tube 49. In use, the absorber tube 49 carries a fluid, such as water or an oil, which is heated up by the solar energy directed on to it by the Fresnel lenses 9. The heat generated can be sufficient for the fluid to change state, for example the fluid can be inserted into the absorber tube 49 in the form of a liquid and can change state to a gas. For example, liquid water can be changed to steam.

Pipe portions 47 are attached to each of the third and fourth end plates 43,45 and are arranged co-axially with the tubular receiver 5. Each pipe portion 47 is connected to a respective end of the absorber tube 49 and is in fluid communication therewith. The pipe portions 47 connect the tubular receiver 5 to a fluid circuit, such as a steam circuit (see Figures 14 and 15).

The outer diameter of the outer casing 51 is typically around 100mm to 150mm and is preferably around 125mm. The outer diameter of the tubular absorber is typically in the range 50mm to 100mm, and is preferably around 70mm. The absorber is typically between 3m and 5m long, and is preferably around 4.00m long. The tubular receiver is very efficient at converting solar energy to heat the fluid. The arrangement has an efficiency of 98.4%.

The absorber tube 49 can include a coating to promote heat absorption. For example, the absorber tube 49 can include a coating of nanoparticles to promote heat absorption. The outer casing 51 can include an anti-reflective coating to reduce the amount of light reflected by the casing 51. A reflector 52 is shown in Figure 1 1 which is in the form of a semi-cylindrical element coaxial with the receiver, providing a reflective surface to direct light and heat energy back upon tubular receiver 5.

The system 1 includes a solar tracking system 59. The tracking system 59 is arranged to automatically adjust the orientation of the Fresnel lenses 9 to track the position of the sun, thereby increasing the amount of solar energy directed to the tubular receiver 5. The tracking system 59 includes memory and at least one processor. Preferably the tracking system 59 has an open-loop control arrangement. The tracking system 59 is preferably includes a real-time clock and is programmed with an algorithm that enables the processor to calculate the solar azimuth and zenith angles of the sun. These angles are then used by the processor for positioning the Linear Fresnel Lenses to point toward the sun. The algorithm is mathematical based on astronomical data instead of utilizing real-time light- intensity readings. Data specific to the location is stored in the memory, so the mathematical calculations are performed accurately. The data includes values relating to the Timezone (TZ), Longitude and Latitude of the desired location. The processor also receives input from the real-time clock to determine the time of day, and optionally the date. The time and/or date information is used to calculate the solar azimuth and zenith angles of the sun. The tracking system 59 controls operation of the linear actuator 41 and the slew drive 39, in accordance with the calculated solar azimuth and zenith angles of the sun. The tracking system 59 operates a slew drive motor 61 in order to rotate the Fresnel lenses about the vertical axis. The tracking system 59 operates a linear actuator motor 63 in order to rotate the Fresnel lenses 9 about the horizontal axis. The tracking system 59 moves the Fresnel lenses 9 to face the sun at the optimum angles. Due to the two axes of movement of the Fresnel lenses 9, the lenses 9 may track the movement of the sun during daylight hours in both elevation and from East to West.

The tracking system 59 can include a limit switch that limits movement of the linear actuator 41. The tracking system 59 can include a limit switch that limits movement of the slew ring 39.

Optionally, the tracking system 59 can include a wind protection system that is arranged to move the lens array 3 into a safe orientation in the event of high winds. The tracking system 59 can include a wind speed measurement device, or at least be arranged to receive an input from a separate device. The tracking system is arranged to monitor the wind speed. When the tracking system 59 determines that the wind speed is greater than or equal to a threshold value, in response the tracking system moves the lens array 3 into a safe orientation, for example by actuating at least on the linear actuator 41 and the slew ring 39. A safe orientation is when the lens array 3 is in a generally horizontal orientation.

The solar heating system 1 can include a fluid supply system that is arranged to supply fluid to the receiver 5. The fluid supply system can include a fluid supply circuit. Figures 14 and 15 are examples of such circuits.

Figure 14 shows a fluid supply system that can be used for generating high temperature steam, for example at 200C + and/or hot water, for example at 90C. The arrangement is capable of providing high temperature steam for example for the treatment of wastewater, brackish water, saline water, industrial and commercial uses, textiles, chemicals, agriculture, dairies for water treatment and pasteurisation, food-steam cooking, agriculture, and hospitals. Alternatively the arrangement is cable of providing hot water for lower temperature applications, for example for use in various industrial facilities, such as factories, and commercial facilities, such as hotels, and other organisations such as hospitals, schools, etc. The fluid supply system includes a first water tank 65, a second water tank 67 (also referred to as a steam condenser), a heat radiator 69, a steam tank 71 and the receiver tube 5. The fluid supply system can include several valves V1 -V12, such as ball valves, and check valves. The fluid supply system can include one or more pumps MT1 - MT4. The table in Figure 14 illustrates how the state of the valves (open/closed) and operation of the pumps can effect circuit functions, for example to fill the second water (condenser) tank 67, recirculation for steam generation, agitation between tanks for temperature equalization, download to the first water tank 65, and closing the radiator 69.

Water fed to the receiver tube 5 is heated to a sufficiently high temperature by the solar gain from the Fresnel lenses 9 to generate the required steam. The steam generated can be used for any application requiring steam and/or hot water.

Optionally, the solar heating system 1 can include at least one sensor, and preferably a plurality of sensors. For example, the solar heating system 1 can include one or more temperature sensors T1...Tn arranged to monitor a fluid temperature in the fluid supply system. The solar heating system 1 can include a controller 73 that is arranged to receive signals from the temperatures sensors T1...Tn (see Figure 6). If at least one of the temperature sensors T1...Tn reaches a threshold value, the controller 73 is arranged to send a control signal to the tracking system 59 to adjust the position of the Fresnel lenses 9, for example to decrease the solar energy directed on to the receiver 5. The tracking system 59 can be arranged to move the Fresnel lenses 9 to a position where they no longer face towards the sun, thereby reducing the solar energy falling on the receiver 5. This provides a safety system to prevent components in the solar heating system 1 from overheating.

Optionally, the fluid supply system can include at least one filter arranged to filter a fluid, such as water, in the fluid supply system. Preferably the fluid supply system includes a duplex filter system. The duplex filter system allows one of the filters to be exchanged with a new filter without having to shut down the solar heating system 1.

Optionally, the circuit can include a de-ionizer.

It is envisaged that the invention can be used for the purpose of solar thermal irrigation, tea plantations, horticulture, and solar thermal cooling by integrating an "absorption chiller" system.

Figure 15 relates to a power generation circuit. A preferred form of the system will include temperate and pressure gauges to monitor operation at critical points of the system. Furthermore, condensate can be returned to the header tank. In the circuit of Figure 15 air vents may be fitted at any high points in the circuit as required. Likewise, drain points (e.g. DN15) may be fitted at low points. If a temperature gauge 26 on header tank 28 is not easily visible to an operator, a temperature transmitter can be considered, to be received by a control unit (not seen).

Preferably water is drawn from a low level of the tank 28 by a pump 30, passed through a strainer 32 and ultimately returned via line DN32 to a higher level. Referring to Figure 15, any power generation apparatus would be located downstream of receiver tube 5, e.g. within line DN32. A plurality of valves 34, 32 may be installed for control of flow through the circuit. Similarly, thermocouples may activate an emergency shut down in the event that operating parameters are exceeded.

Lagging/insulation of pipe work may not be required, particularly since it is desirable that the steam, after power generation, should return to a liquid state before return to header tank 28, or as use for purified drinking water etc.

Unlike the prior art system (Figure 1) it is intended to introduce liquid water at one end of tubular receiver 5, where it will be turned to steam and pressurised as it travels along tubular absorber 49. However, alternative configurations are possible, such as a central or multiple injection points. The Fresnel lenses 9 are designed to focus solar radiation onto a line that is substantially coaxial with the tubular receiver 5 or its wall surface.

Figure 16 is an example of a system having a primary circuit 100 and a secondary circuit 200. The primary circuit 100 is connected to the secondary circuit 200 by means of a heat exchanger 300. The primary 100 circuit includes a header tank 165 that stores a thermal transfer fluid in a liquid state. The thermal transfer fluid is preferably an organic thermal transfer fluid such as a thermal oil. For example, Marlotherm^® XC can be used as the thermal transfer fluid. It has a suitable operating temperature range for pressurised systems of: -90°C to 300°C. The thermal transfer fluid enables the primary circuit 100 to operate at higher temperatures than a water circuit normally would. For example, the thermal transfer fluid can be heated to around 220°C to 240°C. The header tank 165 includes a low-level meter 166. A temperature sensor 168 measures the temperature of the thermal transfer fluid on an output side of the header tank 165. An output side of the header tank 165 is connected to an input side of the receiver tube 5. A check valve 101 and a flow meter 102 are located between the header tank 165 and the receiver tube 5. A pump 103 is arranged to pump the thermal transfer fluid from the header tank 165 through the tubular receiver 5. An output side of the receiver tube 5 is connected to an input side of the heat exchanger 300. An output side of the heat exchanger 300 is connected to an input side of the header tank 165. A check valve 105 is located between the heat exchanger 300 and the header tank 165. A pump 107 is arranged to pump the thermal transfer fluid back to the header tank 165. A filter 108 is located between the heat exchanger 300 and the header tank 165 to filter the thermal transfer fluid. The header tank 165, tubular receiver 5 and heat exchanger are preferably arranged in series.

A temperature sensor 1 1 1 measures the temperature of the thermal transfer fluid at an output side of the tubular receiver 105. A control system monitors output signals from the temperature sensors 168,1 1 1 and can control the position of the lens array 3 in response to the output signals thereby adjusting the amount of solar energy directed to the tubular receiver 5. For example, if at least one of the temperature sensors 168,1 1 1 indicates that the temperature of the thermal transfer fluid exceeds at threshold value, and therefore is too high, the control system controls operation of the linear actuator 49 and/or slew ring 31 to adjust the position of the lens array 3 to reduce the amount of solar energy falling on the tubular receiver 5, for example by orienting it away from the sun.

The secondary circuit 200 includes the heat exchanger 300, a blowdown tank 271, a condensate tank 250, a header tank 265 and a filtration system 260. The header tank 265 typically stores water. The header tank 265 includes a low-level meter

266. The header tank 265 is connected to an input side of the heat exchanger 300 and supplies liquid water thereto. The water supplied to the input side of the heat exchanger is typically at a temperature of around 6C to 20C. A pump 201 pumps water from an output side of the header tank 265 to an input side of the heat exchanger 300. A check valve 203 and flow meter 204 are located between the header tank 265 and the heat exchanger 300. The blowdown tank 271 is connected to an output side of the heat exchanger 300. A temperature sensor 21 1 measures the temperature of the water at an output side of the heat exchanger 300 / input side of the blowdown tank 271. Typically, the water is in the form of steam or very hot liquid water as it exits the heat exchanger 300 and enters the blowdown tank 271. Typically, the water temperate is in the range 90C to 120C. An output side of the blowdown tank 271 is connected to a diverter valve 272. The diverter valve 272 is arranged to direct hot liquid water / steam to at least one of an energy storage tank 270 (sometimes referred to as an energy store) and a condensate tank 250, according to the setting of the diverter valve 272. The diverter valve 272 can be manually operated or can be controlled by a control system. The energy storage tank 270 is arranged to store hot liquid water / steam until required for a useful purpose. An output side of the energy storage tank is connected to a gate valve 274, typically via a gate valve 276. A user or a process can extract hot liquid water / steam from the energy storage tank 271 via gate valve 276. The condensate tank 250 is arranged to cool hot liquid water / steam received from the blowdown tank 271, typically to around 60C to 90C. The filter system 260 is located between the blowdown tank 271 and the condensate tank 250. A pump 262 is arranged to transfer water from the blowdown tank 271 to the condensate tank 250. An output side of the condensate tank 250 can be connected to an absorption chiller 280. The absorption chiller 280 can be used in a cooling process, for example as an air-conditioning unit. An output side of the absorption chiller 280 is connected to an input side of the header tank 265. A valve 205 is located between the condensate tank 250 and the absorption chiller 280. Preferably the header tank 265, filtration system 260, heat exchanger 300, blowdown tank 271 and condensate tank 250 are arranged in series. The absorption chiller 280 can be a lithium bromide absorption chiller 280. Water supplied from the condensate tank 250C to the absorption chiller 280 is typically at a temperature in the range 60C to 90C. The absorption chiller 280 uses the hot water to drive a refrigeration process and, as a consequence, removes heat from the water. For example, water leaving an output side of the absorption chiller 280 can have a temperature of around 6°C to 20°C. Water leaving the absorption chiller 280 is returned to the header tank 265. Preferably the condensate tank 250, absorption chiller 280 and header tank 265 are arranged in series.

A temperature sensor 209 measures the temperature of the water at an output side of the header tank 265. A temperature sensor 21 1 measures the temperature of the water at an output side of the heat exchanger 300 and/or an input side of the blowdown tank 271. A temperature sensor 213 measures the temperature of the water at an input side of the energy storage tank 270. A temperature sensor 215 measures the temperature of the water at an input side of the condensate tank 215. The control system monitors output signals from the temperature sensors 209,21 1,213,215 and is arranged to control the position of the lens array 3 in response to the output signals thereby adjusting the amount of solar energy directed to the solar array. For example, if at least one of the temperature sensors indicates that the temperature of the water exceeds at threshold value, and therefore is too high, the control system controls operation of the linear actuator 49 and/or slew ring 31 to adjust the position of the lens array 3 to reduce the amount of solar energy falling on the tubular receiver 5, for example by orienting it away from the sun.

Preferably at least one of the filters 108,260 comprises a double filter system. The double filter system allows one of the filters to be exchanged with a new filter without having to shut down the solar heating system 1. In use, the lens array 3 directs solar energy onto the tubular receiver 5, which heats the thermal transfer fluid to a temperature around 220°C to 240°C and turns it into a vapour and/or gas. The receiver tube 5 is connected to the heat exchanger 300. The vapour and/or gas passes through the heat exchanger 300 and condenses back to a liquid thereby providing heat to the secondary circuit 200. The heat exchanger 300 receives liquid water from the header tank 265. Heat provided from the primary circuit 100 causes the liquid water to turn to steam, which is supplied to the blowdown tank 271. Hot liquid water / steam can be supplied from the blowdown tank 271 to energy store 270 for later use by a process or user. For example, the hot liquid water/steam can be used for sterilization purposes, for cleaning, washing, etc. Hot liquid water / steam can be supplied from the blowdown tank 271 to the condensate tank 250 and then to the absorption chiller 280 to drive the refrigeration process. The refrigeration process can be used for many purposes, such as air conditioning, chilling food, chilling medical products, etc.

It will be appreciated that the above examples can be modified while still falling within the scope of the invention. For example, a different number of Fresnel lenses 9 can be included in the array. The lenses 9 can have a different focal length. The lens panels can have a different size and/or shape.

Claims

CLAIMS:

1. A solar heating system, including: a lens array including at least one lens assembly, the lens assembly including a supporting substrate and a film applied to a surface of the supporting substrate, the film having at least one lens formed therein; a tubular receiver adapted to carry fluid and located at a focal point of the at least one lens assembly; a frame for supporting the lens array and adapted for pivoting movement about a first axis arranged coaxial with the tubular receiver and a second axis arranged perpendicular to the tubular receiver.

2. The system of claim 1, wherein the film includes a plastics material, and preferably a thermoplastic such as polymethyl methacrylate (PMMA).

3. The system of claim 1 or 2, wherein the film has a thickness in the range 30 to 250 microns.

4. The system of any one of the preceding claims, wherein the lens is formed in the film by a casting drum.

5. The system of any one of the preceding claims, wherein the supporting substrate comprises a plastic material, and preferably a thermoplastic such as polymethyl methacrylate (PMMA), thermoplastic polyurethane (TPU), polyethylene terephthalate (PET) or polycarbonates (PC).

6. The system of any one of the preceding claims, wherein the lens has a focal length in the range 1 m to 2m, preferably 1.2m to 1.9m, and more preferably still 1.4m to 1.8m.

7. The system of any one of the preceding claims, wherein the lens array includes a plurality of lens assemblies, each lens assembly including a supporting substrate and a film applied to at least one surface of the supporting substrate, the film having a lens formed therein.

8. The system of any one of the preceding claims, wherein the at least one lens assembly comprises a Fresnel lens assembly, the film having at least one Fresnel lens formed therein.

9. The system of any one of the preceding claims, wherein the lens array is planar.

10. The system of any one of the preceding claims, wherein the tubular receiver includes a tubular absorber.

1 1. The system of claim 10, wherein the tubular receiver includes an optically transparent casing housing at least part of the tubular absorber.

12. The system of claim 1 1, including a space between the optically transparent casing and the tubular absorber, wherein air is evacuated from said space to create a vacuum.

13. The system of claim 1 1 or 12, including an annular member mounted on the tubular absorber co-axially therewith, the annular member is arranged to support a first end of the optically transparent casing.

14. The system of claim 13, wherein the annual member includes a first annular part sealably attached to the tubular absorber, a second annular part sealably attached to the optically transparent casing, and an expandable member sealably attached to the first and second annular parts.

15. The system of any one of the preceding claims, including an elongate reflector mounted parallel with the tubular receiver to redirect light towards the tubular receiver.

16. The system of any one of the preceding claims, wherein the frame includes first and second parts, the second part supports the tubular receiver and is arranged to pivot about the second axis, the first part supports the lens array and the first part is arranged to pivot relative to the first part about the first axis.

17. The system of claim 16, including a linear actuator arranged to pivot the first part of the frame relative to the second part of the frame.

18. The system of claim 16 or 17, including a slew ring drive that is arranged to pivot the frame about the second axis.

19. The system of any one of the preceding claims, including a tracking system arranged to automatically adjust the orientation of the lens array.

20. The system of claim 19, wherein the tracking system comprises an open- loop arrangement.

21. The system of claim 19 or 20, wherein the tracking system includes an astronomical algorithm and a real-time clock to control the orientation of the lens array.

22. The system of any one of claims 19 to 21, when dependent on claim 16 or 17, wherein the tracking system is arranged to automatically adjust at least one of the linear actuator and the slew ring to adjust the orientation of the lens array.

23. The system of claim 22, including at least one limit switch arranged to limit movement of the linear actuator; and/or at least one limit switch arranged to limit movement of the slew ring.

24. The system of any one of claims 19 to 23, wherein the tracking system includes a wind protection mode.

25. The system of claim 24, wherein the tracking system includes wind speed measurement means, and is arranged to move the lens assembly to a horizontal orientation in response to an output signal from wind speed measurement means.

26. The system of any one of the preceding claims, including a fluid supply system arranged to supply fluid to the tubular receiver.

27. The system of claim 26, wherein the fluid supply system is arranged to supply liquid to the tubular receiver, wherein the lens array is arranged to heat the tubular receiver to a sufficiently high temperature in daylight conditions to generate at least some gas from the liquid.

28. The system of claim 27, wherein the fluid supply system includes a header tank for storing the liquid.

29. The system of claim 28, wherein the fluid supply system includes a condenser arranged to condense gas to liquid, wherein the liquid is recycled back to the header tank.

30. The system of any one of claims 26 to 29, wherein the fluid supply system includes a de-ionizer.

31. The system of any one of claims 26 to 30, wherein the fluid supply system includes at least one pump arranged to pump the fluid into the tubular receiver.

32. The system according to any one of claims 26 to 31, including at least one temperature sensor arranged to monitor a fluid temperature in the fluid supply system, and a controller arranged to receive signals from the at least one temperature sensor.

33. The system according to claim 32 when dependent on any of claims 19 to 25, wherein the controller is arranged to send a control signal to the tracking system to adjust the position of the lens array in response to receipt of a signal from the at least one of the temperature sensor indicating that the temperature has reached a threshold value.

34. The system according to claim 33, wherein the tracking system is arranged to adjust the position of the lens array in response to receipt of the control signal from the controller.

35. The system according to claim 34, wherein the tracking system is arranged to move the lens array to a position that decreases the amount of solar energy directed on to the receiver.

36. The system according to claim 35, wherein the tracking system is arranged to move the lens array to a position wherein the solar array faces away from the sun.

37. The system of any one of claims 26 to 36, wherein the fluid supply system includes a primary circuit having a first thermal transfer fluid and the tubular receiver, a secondary circuit having a second thermal transfer fluid and a heat exchanger arranged to transfer heat from the first fluid to the second fluid.

38. The system of claim 37, wherein the first fluid is an organic fluid, such as an oil; and/or the second fluid comprises water.

39. The system of any one of claims 26 to 38, wherein the fluid supply system includes an absorption chiller.

40. The system of any one of claims 26 to 39, wherein the fluid supply system includes a blowdown tank.

41. The system of any one of claims 26 to 40, wherein the fluid supply system includes an energy storage tank.

42. The system any one of claims 26 to 41, wherein the fluid supply system includes at least one filter arranged to filter fluid in the system.

43. The system according to claim 42, including a plurality of filters, the arrangement being such that one of the filters can be changed without having to shut down the solar heating system.

44. A desalination plant, including a solar heating system of any one of the preceding claims.

45. A waste treatment plant, including a solar heating system of any one of claims 1 to 43.

46. An electrical generator plant, including a solar heating system of any one of claims 1 to 43.

47. A water treatment plant, including a solar heating system of any one of claims 1 to 43.

48. A cooling system, including a solar heating system of any one of claims 1 to 43.