Field

[0001] The present invention relates to an improved system for collecting solar energy. Priority

[0002] This application claims priority from Australian Provisional Patent Application No.

2015904533, the entire contents of which are incorporated herein by cross-reference.

Background

[0003] There is an increased focus worldwide on harnessing the energy of the sun as a renewable energy source to reduce the amount of fossil fuels consumed in energy production.

[0004] The present inventors have previously described a solar energy collection device comprising a solar collector and an array of solar reflectors in WO 2010/034071, the entire contents of which are incorporated herein by cross-reference. This device comprises reflectors surrounding a tower target, resulting in high cosine losses in certain instances. Also, it has been found that minor inaccuracies in ali gnment of the solar reflectors can have a significant effect on the efficiency of the system. Accordingly, there is a need for an improved solar energy collection device which at least partially ameliorates one or both of these problems.

Summary of Invention

[0005] Disclosed herein is a solar collector comprising: a heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in themial contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy.

[0006] According to a first aspect of the present invention, there is provided a solar energy collection system comprising: - a solar collector which comprises: a heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy; and

- at least one solar reflector disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjuster for adjusting the orientation of the solar reflector and wherein the or each solar reflector is a toroidal heliostat; and

- a control system for controlling the operation of the solar collection system.

[0007] The following options may be used in conjunction with the first aspect, either individually or in any suitable combination.

[0008] The position detector may comprise at least one solar panel. It may comprise a thermal detector. It may comprise a calibration target portion and a detector portion. The calibration target portion may comprise, or may be coupled to, the detector portion. The calibration target portion may comprise a diffuse reflector. The detector portion may comprise a camera. The camera may be capable of detecting one or more of visible, infra-red and ultraviolet light impacting on the calibration target portion.

[0009] At least a portion of the posi tion detector, commonly the calibration target porti on, may be coupled to the solar collector. It may be coupled to the housing. It may be rigidly coupled to the housing. It may project from the housing. It may project horizontally from the housing. It may be mounted such that it is substantially coplanar with a lower surface of the housing.

[00010] The position detector may be coupled to the adjustor(s) and/or to the module controller so as to send a control signal thereto. The position detector may be coupled directly to the adjustor(s) or it may be coupled to the control system which sends a control signal to the adjusters .

[0001 1 ] The aperture may be positioned off-center relative to the geometric center of a surface of the heat regulating medium. Additionally or alternatively, the cavity may be positioned off- center relati ve to the geometric center of a surface of the heat regulating medium. The aperture and/or the cavity is positioned towards a side of the housing to which at least a portion of the position detector is coupled.

[00012] The aperture of the solar collector may be directed downwards. The reflectors may be located at a lower height than the aperture. They may be located to the side of the solar collector. They may be located to the side of the solar collector at a lower height than the solar collector.

[00013] The heat regulating medium may be a solid. The heat regulating medium may define a rectangular prism. It may be a cube or a rectangular parallelepiped.

[00014] The heat regulating medium may comprise graphite, graphite particles embedded in a thermally conductive matrix, pure carbon or a mixture of any two or more of these. The thermally conductive matrix may comprise copper, gold, aluminium or silver, or a mixture or alloy of any two or more of these. If a mixture or alloy is used, it may be in any desired proportion of components. The heat regulating medium may comprise graphite which is at least about 95% pure. The graphite heat regulating medium may be a synthetic graphite heat regulating medium or it may be a non-synthetic graphite heat regulating medium. The synthetic graphite heat regulating medium may be made from petroleum coke. A thickness of the heat regulating medium may be between about 10 and about 1500mm.

[00015] The energy collection device may be in physical contact with the heat regulating medium. The energy collection device may be metallic. The energy collection device may comprise stainless steel or other metal or alloy suitable for use at high temperatures, for example suitable for use at the operating temperature of the device. It may be, or may be in the form of, a layer, e.g. a layer having a thickness of about 1 to about 10mm. The layer may cover

substantially all of the inner surface of the cavity. The energy collection device may be capable of absorbing solar energy and converting it into heat. It may be capable of transferring the heat to the heat regulating medium. The energy collection device may form part of an enclosure in which the heat regulating medium is disposed. The enclosure may be gas tight or it may be substantially gas tight. It may be pressure regulated. It may have a protective atmosphere.

[00016] The solar collector may comprise a protective layer on a surface of the energy collection device abutting the cavity. The protective layer may cover a portion of the surface of the energy collection device, or it may cover substantially the entire surface thereof. It may comprise any high temperature resistant surface coating. The protective layer may be about 1 to about 200 microns thick. The protective layer may comprise metal and/or ceramic. It may comprise aluminium metal. It may comprise alumina. The protective layer may protect the energy collection device from damage e.g. physical damage or oxidative damage.

[00017] The solar collector may additionally comprise a heat exchanger in thermal contact with the heat regulating medium. The heat exchanger may comprise heat exchange tubing capable of accepting a heat transfer fluid. The heat exchange tubing may be at least partly embedded in the heat regulating medium. It may be at least about 50mm from the energy collection layer.

Di fferent porti ons of the heat exchange tubing may be embedded in the heat regulating medium at different distances from the energy collection device. Portions of the heat exchanger may be distributed substantially evenly throughout the thickness of the heat regulating medium. The heat regulating medium may be formed from a plurality of adjoining heat regulator slabs. At least some of said portions may have grooves therein. In this case, the heat exchanger tubing may be disposed within said grooves.

[00018] The heat exchange tubing may be coupled to a source of water or other suitable heat exchange fluid. In use, the heat exchanger tubing may be capable of withstanding an internal steam pressure (or pressure of other heated heat exchange fluid, e.g. liquid water) of up to a pressure between about 10 and about 200 bar (e.g. up to about 10 bar, or up to about 20, 30, 40, 50, 60, 70, 80, 90, 100, 120, 140, 160, 180 or 200 bar). The heat regulating medium may be formed from a plurality of adjoining heat regulator slabs. At least some of said portions may have grooves therein, whereby the heat exchanger tubing is disposed within said grooves.

[00019] The solar collector may additionally comprise a thermally insulating layer at least partially surrounding the heat regulating medium. The insulating layer may comprise a thermally insulating solid having pores and/or voids. The pores and/or voids may have an inert or non- oxidizing gas therein. The thermally insulating layer may comprise fibrous, granular or particulate insulation. The insulating layer may be coupled to a source of inert gas or it may be coupled to a source of non-oxidizing gas. The source of inert or non-oxidizing gas may be regulated or controlled. The source of inert or non-oxidizing gas may comprise a pressure control device for controlling a pressure of the inert or non-oxidizing gas in the insulating layer. The pressure control device may for example be capable of controlling the pressure of the inert or non-oxidizing gas in the insulating layer to slightly above atmospheric pressure. This may ensure that no oxygen or air is drawn into the insulating layer. The solar collector may therefore comprise an inert or non-oxidizing gas supply system coupled to the insulating layer for supplying the inert or non-oxidizing gas thereto. A suitable inert or non-oxidizing gas supply system comprises a source of inert or non-oxidizing gas coupled to the insulating layer, a controllable valve for controlling flow of the inert or non-oxidizing gas to the insulating layer and a gas pressure detector coupled to the insulating layer for detecting a pressure of gas therein, said detector being coupled to the controllable valve for controlling said valve.

[00020] The thermally insulating layer may be maintained under vacuum. It may be maintained at an absolute pressure of less than about 0.1 atmosphere. The thermally insulating layer may be maintained at a pressure above atmospheric pressure. The thermally insulating layer may have an inert or non-oxidizing gas therein. This gas may be maintained at a pressure above atmospheric pressure.

[00021] The aperture of the solar collector may be surrounded by a lip comprising a high temperature lip material, i.e. a material which will withstand very high temperatures. This may be regarded as a high temperature resistant lip material. The aperture may be lined by a high temperature aperture ceramic lining material. The high temperature lip material may be a high temperature ceramic lip material, i.e. it may be suitable for withstanding very high temperature operations. The high temperature lip material or lining material may be, or may comprise, silicon carbide, alumina, zirconia, zircon, silica, magnesium silicate, calcium silicate, aluminosilicate (each independently being optionally in a fibrous or foamed form) or a mixture of any two or more of these.

[00022] The heat regulating medium may be located on a thermally insulating support. The thermally insulating support may comprise a ceramic material.

[00023] The housing may be constructed from steel or some other suitable material. The housing may be sealed against the energy collection device so as to form a substantially gas tight enclosure surrounding the heat regulating medium and, if present, the thermally insulating layer.

[00024] The solar collector may comprise a shield disposed below the housing for protecting a lower portion of the housing from damage. The shield may have a shield aperture for allowing solar energy to pass through the shield into the cavity. A gap may be present between the housing and the shield. This may serve to allow heat to escape from the shield. The shield may comprise a plurality of ribs for improving the structural strength and for radiating heat from said shield. The ribs may extend radially from the shield aperture. The shield may be at least partially covered with ceramic insulation fibres to protect the surface of the shield. The shield may comprise stainless steel, aluminised stainless steel, aluminised mild steel or some other material. The shield may not only be disposed to protect the lower portion of the housing but also may be disposed to shield fire bricks facing into the cavity.

[00025] The solar collector may comprise a removable cover for inhibiting reirradiation from the cavity. The cover may be disposed to cover the aperture or, if present, the shield aperture. The cover may be a plug. The plug may be disposed to be inserted into the aperture. Alternatively, it may be disposed to be inserted into the shield aperture. The cover may be a flap. The flap may be a hinged flap or it may be a sliding flap. The cover may be disposed to close across the aperture. Alternatively, it may be disposed to close across the shield aperture. The cover may restrict flow of a gas into and/or out of the cavity. The cover may be opaque to solar energy. It may be thermally insulating. It may be for example constructed from steel, stainless steel or aluminised steel or some other material, optionally coated or partially coated with a thermally insulating material, for example a ceramic such as ceramic cloth. The cover may be disposed and/or shaped so as to be capable of being inserted into or closing across the aperture or, if present, the shield aperture. It may for example be circular, square, triangular, pentagonal, oval or some other suitable shape. The solar collector may comprise a mechanism for covering and uncovering the aperture or shield aperture. Alternatively, the cover may be manually positioned into or closed across the aperture or shield aperture. The mechanism for covering the aperture or shield aperture may be manually operable or may be automatically operable. It may comprise for example a scissor lift type mechanism, a screw jack, a pneumatic ram or a hydraulic ram for raising the cover into place when required. The mechanism for covering and uncovering the aperture may be coupled to a control system. The control system may be capable (e.g. may be programmed so as to be capable) of controlling the closing of the aperture or shield aperture at times when solar energy ceases to be directed to the aperture and to remove the cover at times shortly before solar energy commences to be directed to the aperture. This enables solar energy to enter the cavity when required. The cover may restrict convective loss from the cavity when there is no solar energy input and/or serves to restrict re-irradiation of heat energy from the cavity at such times. This in turn serves to maintain the heat regulating medium and the cavity at a higher temperature for a longer time than would be the case without the cover. [00026] The solar collector may comprise at least one thermocouple for determining a temperature within the solar collector. Commonly the collector has between about 10 and about 40 thermocouples, or 10 to 30, 10 to 20, 20 to 30, 30 to 40 or 25 to 35 thermocouples, e.g. about 10, 12, 14, 16, 18, 20, 30, 40 or 50 thermocouples. These may be arranged symmetrically or may be arranged asymmetrically in the collector. The thermocouple, or at least one of the

thermocouples, may be disposed in a location near or adjacent a position on the energy collection device which is capable of directly receiving solar energy from outside the cavity. It/they may be disposed in a lower portion of the solar collector. At least one thermocouple may be in contact with the energy collection device for measuring a temperature thereof. At least one thermocouple may be disposed in the heat regulating medium for determining a temperature thereof. There may be thermocouples disposed at different depths within the heat regulating medium. The thermocouple, or each thermocouple independently, may be disposed so as to be capable of measuring the temperature in a location selected from in the energy collection device, in the body of the heat regulating medium, on the outside of heat exchange tubing (if present) and in the thermally insulating layer (if present). Throughout this specification, it should be recognised that appropriate temperature measuring devices other than thermocouples may be used wherever thermocouples are indicated for use. Such suitable devices include non-contact thermometers and infra-red thermometers.

[00027] The solar energy collection system may comprise a solar reflector or may comprise a plurality of solar reflectors. The or each solar reflector may be a mirror. The or each solar reflector may comprise a heliostat. The heliostat may be a toroidal heliostat. It may be a concave heliostat. It may be a parabolic heliostat.

[00028] The solar energy collection system may comprise a support structure on which the solar collector is mounted. The solar collector may be mounted on the support structure such that solar energy reflected from the solar reflectors to the aperture does not impinge on the support structure. This serves to prevent damage to the support structure from the solar energy reflected from the solar refiector(s). The solar collector may be cantilevered from the support structure. The solar collector may be mounted at a height of about 5 to about 20 m, or about 5 to about 30m, above the ground. It may be mounted at a height of at least about 15m above ground. It may comprise a support structure, e.g. a tower, on which the solar collector is mounted. The support structure may comprise a tower. The solar collector may be mounted on said tower by means of at least three, optionally four, substantially vertical poles. The vertical poles may be splayed to provide additional stability. The support structure may be at least partially surrounded by a protector so as to protect said poles from damage from the concentrated solar energy from the array of reflectors. The protector may comprise a thermal insulator. Alternatively or additionally the structure may be at least partially treated or coated so as to protect the poles from damage from the concentrated solar energy.

[00029] The aperture and/or the cavity may be positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure if the system is located in the northern hemisphere. To achieve this arrangement, the heat regulating medium may be cantilevered from the support structure. It may be cantilevered from the support structure in a supporting cradle. The cradle may be any suitable structure for attaching the heat regulating medium to the support structure. It may be rigidly attached to the support structure or may represent a portion of the support structure. It may attach the heat regulating medium rigidly to the support structure in the desired orientation (as described elsewhere herein). It may comprise one or more rigid struts for supporting the heat regulating medium. The position detector, or the calibration target portion thereof, may be mechanically coupled, commonly rigidly mechanically coupled, to the cradle, or it may be mechanically coupled (e.g. rigidly) to the support structure or to the heat regulating medium or to more than one of these. Additionally or alternatively, the aperture and/or the cavity may be positioned off-center relati ve to the geometric center of a surface of the heat regulating in order to achieve the desired arrangement.

[00030] The solar energy collection system may comprise an array of solar reflectors. The array being positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north si de of the support structure if the system is located in the northern hemisphere. The array may be positioned such that the majority of the solar reflectors in the array are positioned south of a parallel of latitude passing through the support structure if the system is located in the southern hemisphere or north of a parallel of latitude passing through the support structure if the system is located in the northern hemisphere.

[00031] The control system may be capable of controlling the movement of each solar reflector independently. It may be capable of controlling at least one of: (i) movement of the solar collection system so as to direct the concentrated solar energy through the aperture of the solar collector and into the cavity if required, or so as to place the solar collection system, or at least one reflector of said solar collection system, in a non-collecting orientation if required; (ii) opening or closing of a cover (if present) on the aperture or on a shield aperture (if present); (iii) water inflow into the collector; and (iv) hot water or steam outflow from the collector.

[00032] The solar collector of the system may comprise at least one thermocouple for determining a temperature within the solar collector. The thermocouples may be configured to provide a temperature related signal to the control system for controlling the operation of the solar collection device. Suitable thermocouples have been described above.

[00033] The solar energy collection system may comprise a heat exchanger in thermal contact, optionally in direct contact, with the heat regulating medium. The heat exchanger may be coupled to an electricity generator which is capable of being powered by a heated heat transfer fluid, so that, in use, solar energy incident on the aperture of the collector is transmitted in the form of heat to a heat transfer fluid in the heat exchanger, which heat exchange fluid is transferred to the electricity generator so as to generate electricity. Alternatively, if industrial steam and/or hot water applications are required, the heat exchange fluid may be transferred to a location so that it may be used, for example in a boiler. In this specification the terms "heat exchange fluid" and "heat transfer fluid" may be used interchangeably and should be taken to encompass the same range of materials.

[00034] Using a heat exchanger, the steam or hot water may be used to preheat boiler water but a more common use is for generating process steam. A heat exchanger may be used to produce steam for heating or drying products.

[00035] The solar energy collection system may comprise a heat transfer fluid circuit comprising a first heat exchanger in thermal contact with the heat regulating medium and a second heat exchanger external to the heat regulating medium. The second heat exchanger may be configured such that, in use, heat transfer fluid passes from an outlet of the first heat exchanger to an inlet of the second heat exchanger. The second heat exchanger may be configured such that, in use, the heat transfer fluid passes from an outlet of the second heat exchanger to an inlet of the first heat exchanger, whereby the heat transfer fluid circuit is a closed loop system. The second heat exchanger may be designed for generating steam.

[00036] The heat transfer fluid may be water, which, in use, may be heated to a high temperature and/or converted to steam as it passes through the first heat exchanger. The steam may be condensed to form water prior to reentering the first heat exchanger. The solar energy collection system may comprise a water purifier, e.g. a reverse osmosis system and/or a deioniser, for purifying the water prior to said water entering the first heat exchanger. The water purifier may be capable of purifying the water to a purity of at least about 99%, or at least about 99.9% on a weight/volume basis, in some cases to a purity of 99.99999%). Typically a reverse osmosis system will remove up to about 99.9999%) of dissolved solids. If this is followed by a deioniser (ion exchanger) the water may be improved to < 50 ppb dissolved solids.

[00037] The second heat exchanger may be coupled to either an electricity generator or a boiler for generating steam, and in the case in which high temperature water is produced may be coupled to a device which regulates the temperature and pressure of said water for use in industrial applications. It may be designed for generating steam. This may be accomplished by passing water through a tube of the second heat exchanger.

[00038] The said second heat exchanger system may or may not use water which has not been purified as described above.

[00039] The solar energy collection system may be capable of providing an energy output which drops by no more than 5% when solar energy incident on the solar energy collector is blocked for no more than 1 minute. It may be capable of providing an energy output which drops by no more than 10% when solar energy incident on the solar energy collector is blocked for no more than about 16 hours. The thickness of the heat regulating medium and/or the heat capacity of the heat regulating medium may be such that the above criteria are met. The system may be used to regulate the time that the solar energy can be used to generate electricity or to produce steam or high temperature hot water for industrial or other purposes.

[00040] In an embodiment the solar collector of the system comprises: a graphite heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultravi olet light impacting on the calibration target portion.

[00041 ] In another embodiment the solar collector of the system comprises: a graphite heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet light; and wherein the solar collector comprises a shield disposed below the housing for protecting a lower portion of the housing from damage, said shield having a shield aperture for allowing solar energy to pass through the shield into the cavity, said calibration target portion being substantially coplanar with the shield aperture.

[00042] In another embodiment the solar collector of the system comprises: a graphite heat regulating medium in the form of a rectangular parallelepiped disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture, wherein the aperture is positioned off-center relative to the geometric center of a lower surface of the heat regulating medium; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector porti on in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet light; and wherein the solar collector comprises a shield disposed below the housing for protecting a lower portion of the housing from damage, said shield having a shield aperture for allowing solar energy to pass through the shield into the cavity, said calibration target portion being substantially coplanar with the shield aperture. [00043] In another embodiment the solar collector of the system comprises: a graphite heat regulating medium in the form of a rectangular parallelepiped disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture, wherein the aperture is positioned off-center relative to the geometric center of a lower surface of the heat regulating medium; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector is rigidly coupled to the housing, said position detector comprising at least one solar panel.

[00044] In another embodiment of the first aspect of the invention, there is provided a solar energy collection system comprising: a solar collector comprising: a graphite heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet light; an array of solar reflectors disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjuster for adjusting the orientation of the solar reflector; and a control system for controlling the operation of the solar collection system; and wherein the solar collector is mounted on a support structure, and b) operating at least one of the adjustors so that solar energy incident on at least one solar reflector is directed into the cavity.

[00045] In another embodiment of the first aspect of the invention, there is provided a solar energy collection system comprising: a solar collector comprising: a graphite heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the posi tion detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet light; and wherein the solar collector comprises a shield disposed below the housing for protecting a lower portion of the housing from damage, said shield having a shield aperture for allowing solar energy to pass through the shield into the cavity, said calibration target portion being substantially coplanar with the shield aperture; an array of solar reflectors disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjuster for adjusting the orientation of the solar reflector; and a module controller for controlling the operation of the solar collection system; wherein the solar collector is mounted on a support structure and said array is positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure if the system is located in the northern hemisphere.

[00046] In another embodiment of the first aspect of the invention, there is provided a solar energy collection system comprising: a solar collector comprising: a graphite heat regulating medium in the form of a rectangular parallelepiped disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture, wherein the aperture is positioned off-center relative to the geometric center of a lower surface of the heat regulating medium; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet li ght; and wherein the solar col lector comprises a shield disposed below the housing for protecting a lower portion of the housing from damage, said shield having a shield aperture for allowing solar energy to pass through the shield into the cavity, said calibration target portion being substantially coplanar with the shield aperture; an array of solar reflectors disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjustor for adjusting the orientation of the solar reflector; and a control system for controlling the operation of the solar collection system ; wherein the solar collector is mounted on a support structure; wh erein th e aperture is positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure if the system is located in the northern hemisphere and said array is positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure if the system is located in the northern hemisphere.

[00047] According to a second aspect of the present invention, there is provided a method for collecting and regulating solar energy, said method comprising: a) providing a solar energy collection system according to the first aspect of the invention; and b) operating at least one of the adjusters so that solar energy incident on at least one solar reflector is directed into the cavity.

[00048] The following options may be used in conjunction with the second aspect, either individually or in any suitable combination.

[00049] The method may further comprise c) operating one of the adjustors to adjust the orientation of an active solar reflector by a fixed angle so that solar energy incident on the solar reflector is directed onto the position detector; d) detecting a position of solar energy incident on the position detector and, if not in a desired position, adjusting the orientation of the solar reflector such that the solar energy incident on the position detector is in the desired position; and e) adjusting the orientation of the solar reflector by said fixed angle so that solar energy incident on the solar reflector is directed into the cavity. Steps c) to e) may be carried out sequentially for each active solar reflector. Steps c) to e) may be carried out for each active solar reflector in constant rotation during times when the solar energy collector is receiving solar energy into the cavity. Each active solar reflector may be calibrated at least once a day, for example, each active solar reflector may be calibrated 1 time a day or it may be calibrated 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23 or 24 times a day. Each active solar reflector in the array may be calibrated in constant rotation during times when the solar energy collector is receiving solar energy into the cavity.

[00050] The solar energy collection system may comprise an array of solar reflectors. Step b) may further comprise detecting a temperature at a position within the solar energy collector. If said temperature exceeds a predetermined limit, it may comprise orienting at least one of said solar reflectors to a non-collecting orientation. A temperature related signal may be passed from one or more thermocouples disposed in the solar energy collector to a control system. A control signal may be generated in said control system. The control signal (if generated) may be sent to one or more adjusters, each adjuster being coupled to one of the solar reflectors, so as to control the orientation of said solar reflector( s).

[00051] The method may additionally comprise controlling the solar reflector(s) so that said reflector(s) is (are) in a non-collecting orientation and closing the aperture or shield aperture so as to restrict loss of heat from the cavity of the solar energy collector when it is desired not to collect solar energy. In the case where the solar energy collection system comprises a plurality of reflectors, the non-concentrating orientation may be one in which said reflectors are in a substantially horizontal orientation. This minimises the chance of damage to the reflectors from high wind gusts when they are not in use. The cover may at least partially, optionally

substantially fully, close the aperture of the solar energy collector or into the shield aperture in the shield (if present).

[00052] The method may additionally comprise removing the cover so as to allow concentrated thermal energy to enter the cavity through the aperture and controlling the solar energy reflectors so that at least one reflector is in a collecting orientation in which it directs concentrated solar energy through the aperture into the cavity, when it is again desired to collect solar energy.

[00053] The method may comprise passing a heat transfer fluid through heat exchanger tubing disposed within the heat regulating medium so as to heat said heat transfer fluid. The heat transfer fluid may be water. This may be converted to steam as it passes through the heat exchanger tubing. It may be condensed to liquid water prior to being returned to the heat exchanger tubing. The method may comprise controlling the solar energy collection system so as to generate steam of substantially constant temperature and pressure.

[00054] The solar energy collection system may be controlled so as to generate steam or high temperature hot water of substantially constant temperature, pressure and flow rate.

[00055] The heat exchanger tubing and second heat exchanger may form parts of a closed loop whereby the heat transfer fluid is returned from the second heat exchanger to the heat exchanger tubing. The heat transfer fluid may be water. In this case the water may be converted to steam as it passes through the heat exchanger tubing and is condensed to liquid water prior to being returned to the heat exchanger tubing. The heat transfer fluid may be purified before it is returned to the heat exchanger tubing. The purification may be for example by means of ion exchange etc. The heat regulating medium may be maintained in an atmosphere of inert or non- oxidizing gas. The inert or non-oxidizing gas may be maintained at a pressure slightly above atmospheric pressure. The method may comprise detecting a pressure in the solar energy collector and, if necessary, adjusting the pressure of the inert or non-oxidizing gas in said collector in order to maintain the pressure in said collector within a predetermined pressure range. In an example, the method comprises passing a pressure related signal from a pressure sensor in the solar energy collector to a control system, if necessary generating a control signal in response to the pressure related signal and passing the control signal (if generated) to a controllable valve in a gas line leading from a reservoir of the inert or non-oxidizing gas to the solar energy collector so as to cause said valve to open for sufficient time for the pressure in the solar energy collector to return to the predetermined pressure range.

[00056] In an embodiment of the second aspect of the invention, there is provided a method for collecting and regulating solar energy, said method comprising: a) providing a solar energy collection system comprising: a solar collector comprising: a graphite heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet light; an array of solar reflectors disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjustor for adjusting the orientation of the solar reflector; and a module controller for controlling the operation of the solar collection system; and wherein the solar collector is mounted on a support structure; b) operating at least one of the adjustors so that solar energy incident on at least one solar reflector is directed into the cavity; c) operating one of the adjustors to adjust the orientation of an active solar reflector by a fixed angle so that solar energy incident on the solar reflector is directed onto the calibration target portion; d) detecting a position of solar energy incident on the calibration target portion and, if not in a desired position, adjusting the orientation of the solar reflector such that the solar energy incident on the calibration target is in the desired position ; and e) adjusting the orientation of the solar reflector by said fixed angle so that solar energy incident on the solar reflector is directed into the cavity, wherein steps c) to e) are be carried out sequentially for each active solar reflector.

[00057] In another embodiment of the second aspect of the invention, there is provided a method for collecting and regulating solar energy, said method comprising: a) providing a solar energy collection system comprising: a solar collector comprising: a graphite heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy, wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet light; and wherein the solar collector comprises a shield disposed below the housing for protecting a lower portion of the housing from damage, said shield having a shield aperture for allowing solar energy to pass through the shield into the cavity, said calibration target portion being substantially coplanar with the shield aperture; an array of solar reflectors disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjuster for adjusting the orientation of the solar reflector; and a module controller for controlling the operation of the solar collection system; wherein the solar collector is mounted on a support structure and said array is positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure if the system is located in the northern hemisphere; b) operating at least one of the adjustors so that solar energy incident on at least one solar reflector is directed into the cavity; c) operating one of the adjustors to adjust the orientation of an active solar reflector by a fixed angle so that solar energy incident on the solar reflector is directed onto the calibration target portion; d) detecting a position of solar energy incident on the calibration target and, if not in a desired position, adjusting the orientation of the solar reflector such that the solar energy incident on the calibration target portion is in the desired position; and e) adjusting the orientation of the solar reflector by said fixed angle so that solar energy incident on the solar reflector is directed into the cavity. [00058] In another embodiment of the second aspect of the invention, there is provided a method for collecting and regulating solar energy, said method comprising: a) providing a solar energy collection system comprising: a solar collector comprising: a graphite heat regulating medium in the form of a rectangular parallelepiped disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture, wherein the aperture is positioned off-center relative to the geometric center of a lower surface of the heat regulating medium; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector for detecting a position of incident solar energy so as to enable focusing of said energy , wherein the position detector comprises a calibration target portion in the form of a diffuse reflector rigidly coupled to said housing, and a detector portion in the form of a camera which is capable of detecting one or more of visible, infrared or ultraviolet light; and wherein the solar collector comprises a shield disposed below the housing for protecting a lower portion of the housing from damage, said shield having a shield aperture for allowing solar energy to pass through the shield into the cavity, said calibration target portion being substantially coplanar with the shield aperture; an array of solar reflectors disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjuster for adjusting the orientation of the solar reflector; and a module controller for controlling the operation of the solar collection system; wherein the solar collector is mounted on a support structure; wherein the aperture is positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure if the system is located in the northern hemisphere and said array is positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure i f the system is located in the northern hemisphere; b) operating at least one of the adjustors so that solar energy incident on at least one solar reflector is directed into the cavity; c) operating one of the adjustors to adjust the orientation of an active solar reflector by a fixed angle so that solar energy incident on the solar reflector is directed onto the calibration target; d) detecting a position of solar energy incident on the calibration target and, if not in a desired position, adjusting the orientation of the solar reflector such that the solar energy incident on the calibration target is in the desired position; and e) adjusting the orientation of the solar reflector by said fixed angle so that solar energy incident on the solar reflector is directed into the cavity, wherein steps c) to e) are be carried out sequentially for each active solar reflector. [00059] According to a third aspect of the present invention, there is provided a solar collector comprising: a heat regulating medium disposed within a housing, said heat regulating medium defining a cavity therein and having an aperture in communication with the cavity for allowing solar energy to enter the cavity through the aperture; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and wherein the aperture is positioned off-center relative to the geometric center of a surface of the heat regulating medium.

Brief Description of Drawings

[00060] A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein:

[00061 ] Figure 1 is a photograph of a solar energy collection system as described herein.

[00062] Figure 2 is a diagrammatic representation of a plan view of a solar energy collection system as described herein and shown in Figure 1.

[00063] Figure 3a is a 3D diagrammatic representation of a back view of a solar collector as described herein, wherein the solar collector is cantilevered from a support structure.

[00064] Figure 3b is a 3D diagrammatic representation of a front view of a solar collector as described herein, wherein the solar collector is cantilevered from a support structure.

[00065] Figure 3c is a 3D diagrammatic representation of a plan view of a solar collector as described herein, wherein the solar collector is cantilevered from a support structure.

[00066] Figure 4 is a photograph of a solar collector as described herein comprising a calibration target portion of a position detector mounted substantially coplanar with a lower surface of the housing, and wherein the solar collector is cantilevered from a support structure.

Description of Embodiments

[00067] The present invention relates to a solar collector, a solar energy collection system comprising a solar collector, at least one solar reflector and a control system, and a method of collecting solar energy. In particular the present invention relates to collecting concentrated solar thermal energy and controlling the time of transfer of that thermal energy to a heat exchanger system prior to its extraction for subsequent use. The solar reflector and the collector may be disposed so that solar energy impinging on the solar reflector is concentrated on a collection region of the collector. The energy so collected may then be transferred from the heat transfer material in the collector to a heat transfer fluid in the heat exchanger.

[00068] The solar collector according to the present invention comprises a heat regulating medium. The heat regulating medium may be a solid. Suitable heat regulating solids commonly have a high carbon content. Suitable materials include for example graphite, graphite particles embedded in a thermally conductive matrix such as a metallic matrix (e.g. copper, gold, aluminium, silver, mixtures or alloys of any two or more of these etc.) or a mixture of any two or more of these. The graphite may be of high purity, e.g. at least about 95%, or at least about 96, 97, 98, 99, 99.5, 99.9, 99.95 or 99.99, or about 95 to about 99.99% or about 95 to 99.9, 95 to 99, 99 to 99.99, 99.9 to 99.99, 99 to 99.9 or 99 to 99.5 e.g. about 95, 96, 97, 98, 99, 99.1 , 99.2, 99.3, 99.4, 99.5, 99.6, 99.7, 99.8, 99.9, 99.91, 99.92, 99.93, 99.94, 99.95, 99.96, 99.97, 99.98 or 99.99%). It may have a low ash content. The ash content may be less than about 3%, or less than about 2, 1.5, 1 , 0.5, 0.1 or 0.05%>. The graphite heat regulating medium may be a synthetic graphite heat regulating medium or it may be a non-synthetic graphite heat regulating medium. The synthetic graphite heat regulating medium may be made by any suitable means, for example it may be made from petroleum coke.

[00069] The heat regulating medium should have a high heat capacity, e.g. above about lJ.cm ^{" 3} .K ^_1 , or at least about 1.1 , 1.2, 1.3, 1.4 or l .SJ.cm^.K ^"1 , or about 1 to 5, 1 to 3, 1.5 to 5 or 1.5 to 3J.cm ^~~ .K ^"1 , e.g. about 1.1 , 1.2, 1.3, 1.4 or 1.5J .cm ^"3 .K ^_1 . It should also have a high thermal conductivity, e.g. at least about lOOW/m. , or at least about 150 or 200W/m.K, or about 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190 or 200 W/m.K. It should also be capable of withstanding high temperatures, such as those present in use in the system, without substantial degradation or vapourisation, optionally without melting or fracturing. It should be capable of withstanding temperatures of at least about 1000°C, or at least about 1500 or 2000°C, e.g.

capable of withstanding a temperature of about 1000, 1 100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100 or 2200°C without substantial degradation or vapourisation, optionally without melting or fracturing. In some instances, the heat regulating medium may be in the form of a meltable substance, e.g. a metal, encapsulated within a non-meltable substance, e.g. graphite. In this case, energy may be absorbed by the melting of the meltable substance, whilst retaining the resulting molten material within a solid matrix. The heat regulating medium may be in the form of a layer. The layer may be about 10 to about 1500mm thick, or about 10 to 1000, 10 to 500, 10 to 250, 10 to 100, 10 to 50, 10 to 20, 20 to 500, 100 to 500, 200 to 500, 50 to 200, 50 to 100, 500 to 1500, 1000 to 1500, 500 to 100 or 100 to 200mm thick, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1 100, 1200, 1300, 1400 or 1500mm thick. The heat regulating medium may have variable thickness. The thickness may vary from about 10 to 1500mm thick, or about 10 to 1000, 10 to 500, 10 to 250, 10 to 100, 10 to 50, 10 to 20, 20 to 500, 100 to 500, 200 to 500, 50 to 200, 50 to 100, 500 to 1500, 1000 to 1500, 500 to 100 or 100 to 200mm thick. The thickness of the heat regulating medium may depend on the intended use of the collection system. The heat regulating medium in a single collector may be about 2 to about 20 tonnes or more, or about 2 to 10, 2 to 5, 5 to 20, 10 to 20 or 5 to 15 tonnes, e.g. about 2, 3, 4, 5, 10, 15 or 20 tonnes. In some cases, particularly where the collector is not on a tower, collectors may have more than 20 tonnes of heat regulating medium, e.g. 25, 30, 35, 40, 45, 50, 60, 70, 80, 90 or 100 tonnes. The total weight of the collector may be about 10 to about 30 tonnes, or about 10 to 20, 20 to 30 or 10 to 15 tonnes, e.g. about 10, 15, 20, 25 or 30 tonnes. For larger heat regulating media, the total weight will be correspondingly greater. A tower and its footings which support the collector should be sufficient to support the weight of the collector, even under high wind load.

[00070] The heat regulating medium in the present invention defines a cavity or chamber.

Otherwise expressed, the solar collector comprises a heat regulator which defines a cavity, wherein the heat regulator comprises, or consists essentially of, the heat regulating medium. The heat regulator has an aperture in communication with the cavity so that solar energy enters the cavity through the aperture. In this way the solar energy is able to heat the heat regulator. Solar radiation which enters the cavity may be partially absorbed so as to heat the heat regulator and partially reflected. The reflected portion may be reflected so as to impact a different part of the heat regulator, and again may be partially absorbed and partially reflected. Thus multiple reflections result in the effective absorption of the majority of the incident solar energy, so that only a smal l portion will escape through the aperture. Less than about 20% of the incident energy may escape, or less than about 10 or 5%. The remainder will be absorbed so as to heat the heat regulator. In some cases the solar collector may have a plurality of apertures. Each aperture may communicate with a cavity in the heat regulating medium so as to allow solar energy incident on the aperture to enter the cavity through the aperture. In some cases, each aperture communicates with a different cavity in the heat regulating medium.

[00071 ] The heat regulating medium may be provided in a single portion or monolith, or may be provided in more than one section. These sections may be in at least partial thermal contact with each other. This may facilitate heat transfer between the sections. The sections may be disposed so as to al low for thermal expansion thereof without causing physical damage to the solar collector. In some embodiments in which the heat regulating medium is in the shape of a rectangular prism, the heat regulating medium may comprise a number of trapezoidal sections which fit together to form the overall cubic shape (optionally together with other shaped sections for example square sections). The heat regulating medium may be in layers. This may facilitate construction of the solar collector (or of the heat regulator). Thus it may be convenient to transport the heat regulating medium and other portions of the solar collector to the site at which the system is to be located and fit them together on site to form the heat regulator. The provision of the heat regulating medium in layers (or portions of layers) may also facilitate fabrication, in particular it may facilitate the fitting of the heat exchanger into the solar collector. Thus heat exchange tubes, or portions thereof, may be fitted around a layer of heat regulating medium, or portion of a layer, and these layers or portions may be then fitted together when constructing the solar collector such that the heat exchange tubes are at least partially embedded in the heat regulating medium so as to facilitate efficient heat exchange between the heat regulating medium and a heat exchange fluid in the heat exchange tubes. In particular, the heat regulating medium may be in the form of a plurality of slabs. These slabs may be about 20 to about 200 mm thick, or about 20 to 150, 20 to 100, 50 to 200, 100 to 200, 50 to 150 or 50 to 100mm thick, e.g. about 20, 30, 40, 50, 60, 70, 75, 80, 90, 100, 120, 140, 160, 180 or 200mm thick. In this context the thickness represents the vertical dimension when the slabs are assembled. Each slab may weigh about 50 to about 200kg, or about 50 to 100, 100 to 200, 100 to 150, 70 to 130, 50 to 80, 70 to 100 or 60 to 80kg, e.g. about 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190 or 200kg. The slabs may have grooves in their upper and/or lower faces into which the heat exchange tubing may be fitted. The grooves may be semicircular, square, rectangular, trapezoidal, triangular or some other shape in cross section. In preferred

embodiments they are semicircular, and are disposed so that, when assembled in the solar collector, a groove on a face of one slab together with a corresponding groove on a face of an adjoining slab form a groove with circular cross section suitable for fitting a cylindrical portion of heat exchange tubing. The slabs may have a depth of about 10 to about 1500mm thick, or about 10 to 1000, 10 to 500, 10 to 250, 10 to 100, 10 to 50, 10 to 20, 20 to 500, 100 to 500, 200 to 500, 50 to 200, 50 to 100, 500 to 1500, 1000 to 1500, 500 to 100 or 100 to 200mm thick, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1 100, 1200, 1300, 1400 or 1500mm thick. This dimension represents the thickness of the heat regulating medi um (i.e. the distance from the energy collection device to the outside of the heat regulating medium) when the slabs are assembled. The grooves may extend along the length of the slabs, and may extend to opposing edges thereof. This facilitates construction of the collector, as it enables slabs to be slid in from the side so as to fit them into a pre-existing heat exchange tubing.

[00072] The heat regulating medium may have an overall shape of a rectangular prism, for example, it may be a cube or a rectangular parallelepiped. In some embodiments in which the heat regulating medium i s provided in a single portion or monolith, the dimensions of the heat regulating medium may be such that it is suitable for transportation by standard shipping container handling equipment. It may be dimensioned such that is fits on standard shipping "flat rack". In other embodiments the heat regulating medium may be a cylinder or a sphere or a polyhedron (e.g. dodecahedron, icosahedron, icosidodecahedron, triacontahedron etc.) or some other shape. It may have a cross-section that is round, square, rectangular, pentagonal, hexagonal or some other suitable shape. It may have a constant cross-section over its height, or it may have a variable cross-section with height. The aperture may be round, square, rectangular, pentagonal, hexagonal or some other suitable shape. The aperture may be positioned in the geometric center of a surface of the heat regulating medium, or it may be positioned off-center relative to the geometric center of a surface of the heat regulating medium. The aperture may be positioned towards a side of the housing to which the detector, or a portion thereof, is coupled. In some embodiments in which the heat regulating medium has an overall shape of a rectangular prism, the aperture may be positioned on a lower face of the heat regulating medium. In embodiments in which the aperture is positioned off-center relative to the geometric center of a surface of the heat regulating medium having the form of a rectangular prism, the ratio of the distance from the center point of the aperture to an edge of the surface of the heat regulating medium furthest from the aperture to the distance from the center point of the aperture to the opposing edge of the surface of the heat regulating medium is in the range of about 1.2: 1 to about 5: 1. For example, the ratio may be in the range of about 1.2: 1 to about 4: 1, about 1.5: 1 to about 5: 1 , about 2: 1 to about 5: 1, about 2: 1 to about 4: 1, about 1.5: 1 to about 3: 1, or about 1.5: 1 to about 2.5: 1 , e.g. about 1.2: 1 , 1.5: 1 , 2: 1. 2.5: 1 , 3: 1 , 3.5: 1 , 4: 1 , 4.5: 1 or 5: 1 . An off-center arrangement of the aperture may all ow the aperture to be positioned on the side of the solar collector nearest to which an array of solar reflectors is positioned, thereby improving the efficiency of solar energy collection. The cavity may be in the shape of a cube, or a rectangular parallelepiped or a cylinder or a sphere or a polyhedron or some other shape. It may have a cross-section that is round, oval, square, rectangular, pentagonal, hexagonal or some other suitable shape. It may have a constant cross-section over its height, or it may have a variable cross-section with height. The cavity may be positioned off-center relative to the geometric center of a surface of the heat regulating medium. It may be positi oned towards a side of the housing to which the detector, or a portion thereof, is coupled. When the cavity is positioned off-center, the ratio of the distance from the center point of the cavity to an edge of the heat regulating medium furthest from the cavity to the distance from the center point of the cavity to the opposing edge of the heat regulating medium is in the range of about 1.2: 1 to about 5:1. For example, the ratio may be in the range of about 1.2: 1 to about 4: 1 , about 1.5: 1 to about 5: 1, about 2: 1 to about 5: 1, about 2: 1 to about 4: 1, about 1.5: 1 to about 3: 1 , or about 1.5: 1 to about 2.5: 1 , e.g. about 1.2: 1 , 1.5: 1 , 2: 1. 2.5: 1, 3: 1, 3.5: 1, 4: 1, 4.5: 1 or 5: 1. Positioning the cavity off-center relative to the geometric center of a surface of the heat regulating medium may result in improved efficiency of solar energy collection as it may enable more heat energy to impact on a surface adjacent to the majority of the mass of the graphite, thereby requiring less transfer of heat and/or reflection of solar energy to store the same amount of heat energy as in the case where the cavity is positioned in the center of the heat regulating medium. In some embodiments, the aperture and the cavity may be off-set by the same distance and in the same direction. In one embodiment, the center line of the cavity and the center of the aperture are co-incident.

[00073] The heat regulating medium may have a single cavity therein, or it may have more than one cavity therein, e.g. 2, 3, 4, 5, 6, 7, 8, 9 or 10 or more than 10 cavities. In the event that more than one cavity is present, each may be separated from the others by the heat regulating medium, or by some other form of separation material. Alternatively at least two of the caviti es may be connected internally to the collector by a connecting passage. The connecting passage may have air therein, or may have an inert or non-oxidizing gas, for example nitrogen, helium, neon, argon, carbon dioxide or some other inert or non-oxidizing gas. In the present context, the term "inert" refers to the feature that the gas does not react substantially with the heat regulating medium at the maximum operating temperature of the solar collector, and the term "non-oxidizing" refers to the feature that the gas does not cause oxidation of the heat regulating medi um at the maximum operating temperature of the solar collector. In some embodiments, the cavity (or each cavity) has a single aperture communicating therewith allowing solar energy incident on the aperture to enter the cavity through the aperture. In other embodiments the cavity (or at least one of the cavities) has more than one aperture (e.g. 2, 3, 4, 5 or more than 5) apertures communicating therewith allowing solar energy incident on the apertures to enter the cavity through the apertures. Commonly, although not necessarily, the aperture(s) and cavity(s) are oriented so as to reduce or minimise convective heat loss from the solar collector. For that reason it is common that the apertures do not communicate with the upper surface of the heat regulating medium, since hot air rising from an aperture on an upper surface would facilitate heat loss. An aperture may communicate with a side surface. It may communicate with a lower surface. It may communicate with a lower edge and/or corner of the heat regulating medium. An aperture in a side surface may communicate with a cavity which extends upwards so as to partially trap heated gas and restrict loss of heat by means of heated gases flowing out of the cavity. A cavity may have a reflective surface angled so as to restrict or prevent reirradiation of solar energy which enters the cavity.

[00074] The aperture of the collector may be surrounded by a lip comprising a high temperature lip material. This material serves to protect and contain the heat transfer material. It should be capable of withstanding the high operating temperatures of the system, and is preferably a thermal insulator. Suitable materials include silicon carbide, silica, calcium silicate, magnesium silicate, alumina, zirconia, zircon, aluminosilicate, optionally in fibrous or foamed form, and mixtures of any two or more of these.

[00075] The solar collector of the invention compri ses an energy collection device in the internal cavity so as to enhance the collection of solar energy. The energy collection device may comprise stainless steel or some other suitable thermally conductive substance which is capable of tolerating (i.e. not degrading chemically or physically, or melting or vapourising) at the operating temperature of the device, e.g. up to about 1000°C, or up to about 1500 °C, e.g. about 1000, 1 100, 1200, 1300, 1400 or 1500°C. The energy collection device may be about 1 to 10mm thick, or about 1 to 5, 1 to 2, 2 to 10, 5 to 10, 2 to 8 or 4 to 7mm thick, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10mm thick. It may be in the form of a layer of the thermally conductive substance on the wall of the cavity. It may cover a portion of the wall of the cavity, or it may cover substantially the entire wall of the cavity. It may cover at least about 50% of the area of the cavity, or at least about 60, 70, 80, 90 or 95% thereof. There may be a protective layer between the energy collection device and the internal cavity. The protective layer may be on the surface of the energy collection device. It may cover a portion of the surface of the energy collection device, or it may cover substantially the entire surface thereof. It may cover at least about 50% of the surface of the energy collection device, or at least about 60, 70, 80, 90 or 95% thereof. It may be about 1 to 200 microns thick, or about 1 to 100, 1 to 50, 1 to 20, 10 to 200, 50 to 200, 100 to 200, 50 to 100, 5 to 20, 50 to 150 or 100 to 150 microns thick, e.g. about 1, 2, 3, 4, 5, 6, 7, 8, 9,

10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 1 10, 120, 130, 140, 150, 160, 170, 180, 190 or 200 microns thick. Suitable materials for a surface coating (protective layer) on the energy collection device include any high temperature resistant surface coating. The energy collection device is commonly in contact, thermal and/or physical, with the heat regulating medium. The surface coating may be any thermal, flame or plasma applied material such as a metal (e.g. aluminium, chromium, cobalt, nickel or an alloy of any of these), an oxide (e.g. alumina, chromia, zirconia or a combination of any two or more such materials), a carbide or nitride (e.g. silicon nitride, silicon carbide, tungsten carbide or a combination of any two or more of these). The surface coating may comprise combination of any two or more of the above classes of materials. It may comprise metals, ceramics and/or cermets (a composite comprising ceramic and metal). The surface coating may have a single layer or may have multiple layers (e.g. 2, 3, 4 or 5 layers). Each layer may, independently, be as described above.

[00076] The energy collection device may have an energy absorbing surface or coating. The coating or surface may be black. It may be profiled. It may comprise a plurality of projections shaped and disposed so as to reduce reflection of radiation so as to increase absorption of incident solar radiation. The projections may be microprojections. They may be about 0.1 to 20 microns in length, or about 0.5 to 20, 1 to 20, 5 to 20, 0.1 to 10, 0.1 to 5, 0.1 to 1, 0.5 to 5, 1 to 5 or 1 to 10 microns, e.g. about 0.1 , 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,

1 1, 12, 13, 14, 15, 16, 17, 18, 19 or 20 microns.

[00077] Thus in an embodiment, the collector is in the form of a layered shell surrounding a cavity, said cavity communicating to the outside through an aperture. The layer adjacent the cavity can be a high temperature resistant surface coating or protective layer. Behind the surface coating, and in physical and thermal communication therewith, is an energy collection layer. Behind the energy collection layer, and in thermal and physical communication therewith, is a heat regulating medium. Commonly the bulk (i.e. greater than 50% of the volume) of the collector will be the heat regulating medium. Surrounding the heat regulating medium is commonly an insulating layer. [00078] The solar collector of the present invention comprises a position detector. In some embodiments, the position detector may comprise a calibration target portion and a detector portion. The position detector may be used to calibrate the solar reflector(s) so that the efficiency of solar energy collection is maintained or improved. At least a portion of the position detector may be mounted such that it is substantially coplanar with the aperture. Alternatively, it may be mounted such that it is substantially coplanar with the shield aperture. In some embodiments, at least a portion of the position detector may be mounted such that it is substantially coplanar with a lower surface of the housing, for exampl e, if the posi tion detector comprises a calibration target portion, said calibration target portion may be positioned such that it is substantially coplanar with a lower surface of the housing. The position detector may be any device that is suitable for detecting solar energy. For example, it may be an array of solar detectors or of thermal energy detectors, or it may be an optical camera or a solar imaging camera. The position detector or a portion thereof may comprise a flat surface or calibrating surface which is positi oned

substantially coplanar with the aperture, or, if present, the shield aperture. The position detector or a portion thereof may be coupled to the solar collector, for example, it may be coupled to the housing of the heat regulating medium. In some embodiments, the position detector or a portion thereof is rigidly coupled to the housing. In embodiments in which the detector comprises a calibration target portion and a detector portion, the calibration target portion may be rigidly coupled to the housing. In some embodiments, the calibrating surface is parallel to the ground and the detector is located on the ground beneath the calibrating surface. However, the calibration target portion and the detector portion may be arranged in any suitable configuration to allow solar energy incident on the calibration target portion to be detected by the detector portion. In some embodiments, the calibration target portion comprises a diffuse reflector, for example, it may be inorganically bound fibre ceramic board capable of withstanding

temperatures of at least 1 100°C. The detector portion may comprise a camera or any instrument suitable for detecting the position of the solar energy incident on the calibration target. The camera may be capable of detecting visible light, infrared light or ultraviolet light. At least a portion of the position detector should be capable of withstanding the high temperatures of the concentrated solar energy directed onto the detector from the solar reflector(s). The detector, or at least a portion of the detector which is coupled to the housing, should also be capable of withstanding strong weather conditions, e.g. wind.

[00079] The solar collector of the present invention comprises a housing, which surrounds the heat regulating material. The housing may be sealed against the energy collection device so as to form an encl osure surrounding the heat regulating medium and, if present, the thermally insulating layer. The enclosure may be at least substantially gas tight. It should be understood that in practice, the housing (which is disposed around the outside of the solar collector) in combination with the energy collection device (which commonly coats the inner surface of the aperture and cavity) will not form a completely sealed system, and minor leaks may occur. It is for that reason that an inert or non-oxidizing gas system may be used to maintain the inert or non-oxidizing gas within the housing/energy collection device enclosure at slightly above atmospheric pressure, so that any leaks occur out of the enclosure rather than into the enclosure. If air were to leak into the enclosure, this may come in contact with the heat regulating medium. In the event that this comprises carbon, or a carbonaceous material (e.g. graphite) this could cause oxidation at the operating temperature of the collector, leading to loss and/or degradation of the heat regulating medium. Other suitable heat regulating media, such as silicon carbide, may equally require protection from oxygen. Thus in a commonly used arrangement, when a pressure below a preset threshold is detected in the enclosure, a valve to the source of inert or non- oxidizing gas is opened so as to produce a brief burst of inert or non-oxidizing gas flow into the enclosure. This is sufficient to raise the pressure above the preset threshold, at which stage the valve is closed again. An alternative, though less preferred, procedure is to maintain a very low constant flow of inert or non-oxidizing gas into the enclosure sufficient to maintain the pressure therein within a desired range.

[00080] There may be a separate shield below the housing in order to protect the lower surface of the housing from thermal energy. This may be useful in cases where focusing of the solar radiation from the solar reflector is not sufficient to direct all of the solar energy into the aperture. The shield should have a shield aperture which is the same size as, or smaller in size than, the aperture leading to the cavity and aligned therewith, so as to allow the concentrated solar energy to enter the cavity. The distance between the shield and the lower portion of the housing may be about 2 to about 50cm at its closest point, or about 2 to 20, 2 to 10, 2 to 5, 5 to 10, 5 to 20, 20 to 50 or 10 to 40 cm, e.g. about 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50cm. It may be sufficiently large to allow reasonable airflow between the housing and the shield so as to prevent overheating of the housing. It may be sufficiently small so as to not substantially interfere with the focusing of solar energy into the aperture. It may have ribs. These assist in strengthening the shield. They may also serve to improve heat loss from the shield so as to maintain it at as low a temperature as possible. The shield may be made for example from steel, e.g. mild steel. It may have thermal insulation thereon. The thermal insulation may be for example a ceramic fibre insulation or some other suitable insulation. It may be about 10 to about 100mm thick (or about 10 to 50, 10 to 20, 50 to 100 or 40 to 80mm, e.g. about 10, 20, 30, 40, 50, 60, 70, 80, 90 or 100mm), or thicker if required.

[00081] In some cases there may be an inner shield extending to about the upper level of a support which supports the heat regulating medium. The heat regulating medium may be supported for example on ceramic bricks. It is preferable that solar energy does not impact the energy collection device adjacent these bricks. Thus an inner shield can shield the energy collection device in this region. The inner shield may be for example stainless steel or aluminised steel. It may have thermal insulation thereon. The thermal insulation may be for example as described above on the shield. There may be a space between the inner shield and the energy collection device. The space may be about 2 to about 50cm at its closest point, or about 2 to 20, 2 to 10, 2 to 5, 5 to 10, 5 to 20, 20 to 50 or 10 to 40 cm, e.g. about 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45 or 50cm. This allows for air movement between the inner shield and the energy collection device to reduce heating of the energy collection device in this region. The inner shield may be angled inwards towards its lower portion. In some cases the inner shield is contiguous with the shield below the aperture, to form a single shield which protects both the lower portion of the collector and a lower portion of the energy collection device.

[00082] The solar collector of the invention may comprise a heat exchanger. The heat exchanger may comprise heat exchange tubing, which may be in the form of one or more heat exchange tubes. The heat exchange tubing is in thermal contact with, optionally embedded in, the heat regulating medium. The internal diameter of the tubing shoul d be sized so that it is capable of the desired heat transfer. It may be between about 0.5 and about 5 cm internal diameter or about 0.5 to 2, 0.5 to 1, 1 to 5, 2 to 5 or 1 to 3cm internal diameter. The tubing should be made of a material that does not degrade, soften or melt at the operating temperature of the device. The tubing should be at least about 10mm from the surface that receives the solar energy from the solar reflector, or at least about 20, 30, 40, 50, 60, 70, 80, 90 or 100mm therefrom. This ensures that sufficient heat transfer material is present between the heat transfer tubing and the receiving surface (protective layer and/or energy collection device) to provide the required buffering effect. Thus the greater the energy buffering that is required (see above) the greater distance should be allowed between the heat transfer tubing and the receiving surface. The tubing should have a heat transfer fluid therein. Suitable heat transfer fluids are thermally stable to the operating temperature of the device, and preferably have a high heat capacity. Commonly the heat transfer fluid used in the present invention is water. In operation the water is heated and may volatilise to form steam, which may be used as an energy source for example in an electricity generator. In the event that water is used as a heat transfer fluid, it may be high purity water, so as to minimise deposition of scale when it volatilises. It may be at least about 99% pure, or at least about 99.5, 99.9, 99.95, 99.99, 99.995 or 99.99999% pure. It may be purified prior to entering the heat exchanger. Common purification techniques such as reverse osmosis, ultrafiltration, microfiltration, ion exchange etc. are well known. Other suitable heat transfer fluids include any organic or inorganic fluid capable of withstanding the required operating temperatures. Examples include biphenyl, biphenyl oxide (diphenyl ether), silicone fluid (e.g. polydimethylsiloxane), partially hydrogenated terphenyls, dibenzyl toluene fluids,

alkylbenzenes, diaryl alkyl diphenylethane, alkylated aromatics, diaryl ethers and triaryl methanes as well as similar or related fluid compounds or combinations of any two or more of the above. Particular examples are: modified terphenyl, synthetic hydrocarbon mixture, alkyl substituted aromatic, isopropyl biphenyl mixture, a mixture of synthetic aromatics,

terphenyl/quaterphenyl, phenylcyclohexane/bicyclohexyl 90: 10 mixture, and biphenyl diphenyl oxide (DPO) eutectic mixture. Many of these are commercially available, and other similar products may also be used in this application.

[00083] It is preferred that a thennally insulating layer at least partially surrounds the heat regulating medium. This reduces thermal losses from the collector during operation. The insulating layer may comprise a thermally insulating solid having pores and/or voids. Preferably the pores and/or voids have an inert or non-oxidizing gas therein, such as nitrogen, helium, argon, neon, or a mixture of any two or more of these. The presence of such a gas serves to reduce high temperature oxidation of the heat transfer device, the heat transfer tubes, the insulating material etc. Suitable insulating materials are capable of withstanding the operating temperatures of the device. They include any fibrous or porous or particulate ceramic materials. There may be tubing and valves so as to supply the gas to the insulation and optionally to remove the gas from the insulation. Thus the gas may flow through the insulation. Alternatively it may be sealed in the insulation. In some embodiments the thennally insulating layer comprises an at least partial vacuum in order to insulate the heat regulating medium. In this event it may be maintained at an absolute pressure of less than about 0.1 atmosphere, or less than about 0.05, 0.02, 0.01 , 0.005, 0.002 or 0.001 atmosphere. The atmosphere of the containment (i.e. in the thennally insulating layer) may be maintained at a pressure slightly above atmospheric pressure so that a failure in the containment seal results in an outflow of the containment atmosphere gas rather than an inflow of air. The exclusion of oxygen protects the high temperature components of the solar collector from corrosion. The solar collector i s provided with an input valve to allow entry of the protective gas and an exhaust valve to discharge the gas if the containment pressure rises above design limits. The balance between admission of the protective gas and the exhaust of the containment atmosphere may be achieved by monitoring the containment pressure and utilising this signal to allow the control system to set the inlet and exhaust valve positions. The protective (i.e. inert) gas may be maintained in the insulating layer and also optionally in the heat regulating medium, optionally also in the thermal collection device.

[00084] The solar energy collection system according to the present invention comprises at least one solar reflector disposed so as to be capable of directing solar energy through the aperture of the solar collector and into the cavity, the or each solar reflector being coupled to an adjuster for adjusting the orientation of the solar reflector. The solar reflector may comprise a lens. It may comprise a reflector. It may comprise a plurality of lenses. It may comprise a plurality of reflectors. It may comprise an array of reflectors. In the event that the solar reflector comprises a plurality of reflectors or a plurality of lenses, these may all have approximately the same focal point, or may be disposed so as to reflect and/or focus light towards the same area. They may be disposed so as to reflect and/or focus light towards the cavity of the collector. The, or each, reflector may be a fiat mirror, or may be a concave reflector. It (each independently) may be, for example, a spherical or a parabolic concave reflector. The solar reflector(s) may comprise a heliostat. In some embodiments, the heliostat is a toroidal heliostat. The use of toroidal heliostats may improve the efficiency of collection of the sun's energy as spherical and parabolic mirrors suffer from the optical effect "astigmatism", whereby the image of the sun i s distorted in the morning and afternoon, resulting in energy being dissipated around the aperture. The solar energy collection system may comprise an array of solar reflectors. In some embodiments in which the solar collector is mounted on a support structure, the array of solar reflectors may be positioned substantially on a south side of the support structure if the system is located in the southern hemisphere or substantially on a north side of the support structure if the system is located in the northern hemisphere. This configuration may result in the angle subtended by the solar energy incident on the reflector and the solar energy reflected therefrom being acute for the majority of the solar reflectors in the array for most of the time during which solar radiation impinges on them. The efficiency of any solar concentration system which reflects the sun is governed by a number of factors. One of these factors is called the "cosine effect", which relates to the angle of incidence of the sun on the reflector. The most efficient reflection of the sun's energy from a reflector occurs when the angle subtended by the solar energy incident on the reflector and the solar energy reflected therefrom is acute (< 90°). If the angle is obtuse (> 90°), then there are losses referred to as "cosine" losses. A reflector field subject to high cosine effects is less efficient.

[00085] The array of solar reflectors being positioned substantially on a south side of the support structure refers to the majority of the solar reflectors in the array being located south of a parallel of latitude passing through the support structure. In some embodiments, all of the solar reflectors will be located south of a parallel of latitude passing through the support structure. Similarly, the array of solar reflectors being positioned substantially on a north side of the support structure refers to the majority of the solar reflectors in the array being located north of a parallel of latitude passing through the support structure. In some embodiments, all of the solar reflectors will be located north of a parallel of latitude passing through the support structure. This serves to reduce cosine losses relative to a situation in which the support structure (and hence the solar collector) is surrounded by reflectors. Figure 1 shows a solar energy collection system according to the present invention which is mounted on a support structure located in the southern hemisphere, the array of solar reflectors positioned substantially on a south side of the support structure. Figure 2 shows a diagrammatic plan view of a solar energy collection system as represented in Figure 1.

[00086] In embodiments in which the aperture and/or the cavity is positioned off-center relative to the geometric center of a surface of the heat regulating medium, the aperture and/or the cavity may be positioned substantially on a south side of the support structure if the system is located in the southern hemisphere, or substantially on a south side of the support structure if the system is located in the northern hemisphere. This orientation of the aperture and/or the cavity may also be achieved by positioning the heat regulating medium such that it is positioned asymmetrically on the support structure, for example, by cantilevering the heat regulating medium from the support structure (as shown in Figure 3), and may help to reduce the amount of concentrated solar energy impinging on the support structure. The aperture and/or the cavity being positioned substantially on a south side of the heat regulating medium refers to the geometri c center of the aperture and/or the cavity being located south of a parallel of latitude passing through the support structure. Similarly, the aperture and/or the cavity being positioned substantially on a north side of the support structure refers to the geometric center of the aperture and/or the ca vity being located north of a parallel of latitude passing through the geometri c center of the support structure.

[00087] The collector may be mounted above the ground. It may be mounted at a height of about 5 to about 50 m above the ground, or at least about 15m or at least about 20m above the ground, or about 5 to 10, 5 to 7, 7 to 20, 10 to 20, 15 to 20, 10 to 15, 8 to 12, 5 to 30, 10 to 30, 20 to 30, 5 to 40, 10 to 40, 20 to 40, 30 to 40, 10 to 50, 20 to 50, 30 to 50, or 40 to 50m above the ground, e.g. about 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45 or 50m above the ground. This is particularly convenient in cases where the solar reflector comprises reflectors. In this event the reflectors may be located near the ground, and the collector may be mounted at a sufficient height that reflected solar energy from all reflectors can efficiently be directed towards the collector, in particular without one or more solar reflectors shadowing one or more other solar reflectors. The solar energy collection system may comprise a support structure on which the collector is mounted. The support structure may be a tower, or a stand, pole or post. It should be sufficiently strong to support the weight of the collector, including under strong wind conditions.

[00088] With reference to Figure 4, in one embodiment the solar energy collection device of the present invention may comprise a solar collector comprising a graphite heat regulating medium disposed within a housing 1 and a shield 2 disposed below the housing for protecting a lower portion of the housing from damage, said shield having a shield aperture 3 for allowing solar energy to pass through the shield into the cavity; an energy collection device disposed in the cavity and in thermal contact with the heat regulating medium to collect solar energy entering the cavity; and a position detector in the form of a calibration target portion 4, which is rigidly coupled to the housing 1 and mounted substantially coplanar with a lower surface of the housing 1 and shield aperture 3, and a detector portion (not shown) for detecting a position of incident solar energy 5 so as to enable focusing of said energy into the aperture or, if present, the shield aperture. The solar collector may be cantilevered from a support structure 6, such that the aperture 3 is positioned substantially on a south side of support structure 6 when the system is located in the southern hemisphere or substantially on a north side of support structure 6 when the system is located in the northern hemisphere.

[00089] The or each solar reflector in the present invention is coupled to an adjuster, e.g. a motor, for adjusting the orientation of the solar reflector. The or each solar reflector and its adjuster may be coupled to a control system (or tracking device) for controlling the operation of the solar collection system. The solar reflector(s) fields may be started to track progressively. The heliostats in the west of the field may be started in the morning, in order to cope with the low angle of the sun. The heliostats in the east of the field may be started once the sun has risen to sufficient elevation that the images produced by these heliostats can be captured in the receiver cavity. The heliostats in the west of the field are commonly the first ones to be parked late in the day as the angle between the sun, the heliostat and the receiver cavity becomes too great. The heliostats in the east of the field are commonly the last ones to be parked late in the day, as the sun is at an advantageous elevation for these.

[00090] The module controller may be coupled to the adjustor(s) to control the movement of the solar reflector(s). The control system may be capable of controlling the movement (or tracking) of each solar reflector independently. The control system is capable of moving the solar reflector so as to provide concentrated solar energy to the collector and to the calibration target. Such tracking devices are known. Since the sun changes position during the course of the day, it is advantageous for the solar reflector to move correspondingly, so that whenever solar energy is incident on the solar reflector is directed towards the collector that solar energy is directed to the collector. The tracking device may comprise a detector for detecting an angle of the sun. It may comprise one or more adjusters, e.g. motors, for moving the solar reflector. It may comprise a processor for determining from the angl e of the sun detected by the detector the angle(s) required for the solar reflector to direct the solar energy to the collector (i.e. into the aperture thereof). The processor may generate one or more signals dependent on said determined angle(s) of the solar reflector and send said signal(s) to the adjustor(s) so as to cause the adjustor(s) to move the solar reflector so as to direct the solar energy into the aperture of the collector.

[00091] In some embodiments, the tracking device (or module controller) may move the solar reflector to a position suitable to deliver the concentrated solar energy to the receiver aperture, by employing predetermined calculations based on the predicted sun position. In such embodiments the tracking device control system may comprise a processor (e.g. a computer) for calculating from a predicted position of the sun (including at sun rise each day), the required position of the solar reflector. The processor may also be capable of predicting the position of the sun so as to calculate the required position of the solar reflector. The processor may also be capable of measuring the insolation rate from day to day and from that data calculating the number of solar reflectors required to be acti ve from day to day to achieve the desired energy output needs of a system. Such calculations would take into account seasonal variations in insolation rates.

[00092] The mirror position may be adjusted on the basis of an algorithm that predicts the position of the sun at a gi ven time of day for the particular geographic position. Each heliostat, or sun tracking mirror, has its own individual path. This tracking path may be programmed into the controller on each heliostat post. The control system may instruct the heliostats to track at the start of their operating cycle and to park (i.e. return to a non-collecting orientation) at the end of the operating cycle. The heliostat tracking path for each heliostat may alternatively be embedded in the control system with the control instructions issued centrally.

[00093] The control system also may instruct the heliostats to park, e.g. move to a near horizontal position, if the wind velocity increases above a preset level. This prevents damage to the heliostats in the event of high wind velocities.

[00094] To compensate for differences in the summer and winter solar resource at any site, the field of solar reflectors may have more daily energy collection capability in summer than the storage medium can absorb. Therefore, particularly in summer periods, it is advantageous to provide a mechanism to direct the incidence radiation from some reflectors away from the aperture to prevent the solar collector overheating. The heliostats target the center of the at least one aperture present in the surface of the heat regulating medium, commonly in the base, and deliver the solar energy into the cavity. The temperature of the interface between the cavity and the heat regulating medium may be measured by means of a number of thermocouples, which may be inserted through the heat regulating medium to the surface of the energy collection device on the cavity wall. If the temperature of the heat regulating medium increases above the design level (for example about 800°C) then the control system may instruct a number of the heliostats (for example, in increments of around 10% of the heliostat field) to track so as to focus to a point (e.g. in the sky) away from the solar collector. If the temperature continues to rise then the control system may instruct more heliostats to likewise track away from the solar collector. The control system may repeat this cycle until control is achieved and the temperature stops rising. An advantage of sending the heliostats to track so as to focus on a position in the sky, as opposed to park, is that they can be quickly brought back into operation if the need arises. [00095] The control system may be capable of predicting (or may be programmed with) sunrise and/or sunset times. This enables the control system to signal some or all of the heliostats to be prepared for the commencement of insolation at sunrise, or to commence collection of solar energy once the sun has reached a suitable elevation, e.g. about 1 hour after sunrise, or when the insolation rate is sufficiently great. It may also enable the control system to signal the heliostats to return to non-collecting orientations when insolation decreases during the day, for example due to cloud activity, or ceases at sunset.

[00096] At least one solar energy reflector is provided to focus solar energy into the aperture of the solar collector. The solar energy as it enters the aperture should have a maximum beam focal point diameter which is no wider than the aperture, preferably narrower. The or each solar reflector may focus the solar energy beam focal point at or near the aperture. The focal point may be within about 300mm of the aperture, or within about 250, 200, 150 or 100mm of the aperture, and may be either inside the cavity or outside the cavity. Typically, since the solar energy enters from an angle in the form of a circular beam, it will cast an elliptical beam cross- section at the aperture. It may have an aspect ratio of about 1.5 to about 3, or about 1.5 to 2, 2 to 3 or 1.8 to 2.5, commonly about 2.

[00097] The present invention provides a method for collecting and regulating solar energy comprising operating at least one of the adjusters so that solar incident on a solar reflector is directed into the cavity of the heat regulating medium. In some embodiments, the active solar reflector(s) may be calibrated to ensure that solar energy entering the cavity through the aperture is maximized. An active solar reflector refers to a reflector which is operating to direct solar energy incident on the reflector into the cavity of the heat regulating medium. A suitable method for calibrating a solar reflector involves adjusting the orientation of the active solar reflector by a fixed angle so that solar energy incident on the solar reflector is directed onto at least a portion of the position detector. The position detector may detect the position of the solar energy incident on at least a portion of the position detector and provide feedback to the control system to determine if the solar energy incident on at least a portion of the position detector is in the desired position. Alternatively, the position detector may provide feedback directly to the adjustor coupled to the solar reflector being calibrated. The desired position refers to the position of incidence on at least a portion of the position detector such that when the solar reflector is adjusted by said fixed angle in an opposite direction to direct solar energy directed from the solar reflector into the cavity, the solar energy is focused on the center of the aperture. The desired position may be determined on the basis of an algorithm, and taking into account the fixed angle by which the solar reflector has been adjusted, that predicts the optimum position of the solar energy incident on the aperture, based on the position of the sun at a given time of day for the particular geographic position, to provide maximum solar energy incident on the aperture. If the solar energy incident on at least a portion of the position detector is not in the desired position, the control system may adjust the orientation of the solar reflector such that the solar energy incident on at least a portion of the position detector is in the desired position. Once the desired position has been achieved, the control system may adjust the orientation of the solar reflector by the fixed angle by which the solar reflector was originally adjusted in the opposite direction so that solar energy incident on the solar reflector is once again directed into the cavity. Each active solar reflector may be calibrated individually. Each active solar reflector in an array may be calibrated sequentially. Each active solar reflector may be calibrated at least once a day, for example, each active solar reflector may be calibrated 1 time a day or it may be calibrated 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 times a day. Each active solar reflector in the array may be calibrated in constant rotation during times when the solar energy collector is receiving solar energy into the cavity.

[00098] In certain embodiments of the invention the solar collector has facil ity for absorbing energy from sources other than solar energy. For example, it may be heated by resistive heating by means of one or more resistor embedded in the heat regulating medium. The resistor(s) may be electrically insulated from the heat regulating medium, particularly in cases where said medium is thermally conductive (e.g. graphite, metals or combinations thereof). The electric current to the resistor may be obtained from a renewable source such as wind energy. Thus a wind turbine, e.g. located on top of the solar collector, may be sufficient to heat, or at least partially heat, the heat regulating medium in the absence of solar energy input. The wind turbine may for example provide up to 10-500kW of energy or more, depending on design of the turbine and on wind speed and direction. This option enables energy input to the solar collector to be continued at times when there is insufficient solar energy flux, for example on overcast days or at night. The non-solar input may be controlled by a control system for the solar collector. This may reduce the non-solar input if necessary to prevent overheating of the heat regulating medium.

[00099] The heat regulating medium may be in the form of a shell. It defines an internal cavity and the cavity communicates to the outside through an aperture. The aperture and/or the cavity may, independently, have an energy transmitting substance therein. Suitable energy transmitting substances may be gases, e.g. air, nitrogen, argon, helium, carbon dioxide or mixtures of these. Additionally or alternatively solid and/or liquid energy transmitting substances, e.g. quartz, may also be present in some embodiments. For example a quartz window may be present in the aperture. This may be useful in cases where it is desired to maintain an inert or non-oxidizing gas (e.g. nitrogen) in the cavity. The window may be in the form of a lens. In this case, solar energy incident on the lens from the solar reflector may be distributed by the lens so as to impact a larger portion of the solar energy collector inside the cavity. It may be a convex lens. It may be a planoconvex lens. It may be some other suitable shape. In the event that a window or lens is present in the aperture, it may seal the aperture or may not seal the aperture. Sealing has the advantage of maintaining the atmosphere within the cavity, however a lack of sealing prevents pressure buildup due to thermal expansion of gases in the cavity. However in many embodiments the cavity and aperture contain air and are open to the atmosphere.

[000100] The heat regulating medium serves to buffer the solar energy input so that short reductions or interruptions in the supply of solar energy to the system can be tolerated with little or no drop in the energy output from the system. In some embodiments such interruptions are of the order of seconds or minutes, for example due to a cloud passing between the sun and the solar reflector. In other embodiments such interruptions are of the order of hours, for example extended storms, or night time. The sol ar energy collection system may be capable of providing an energy output which drops by no more than about 20%, or no more than about 10, 5, 2 or 1 %, when solar energy incident on the solar reflector is blocked for no more than about 1 minute, or no more than about 2, 3, 4, 5, 6, 7, 8, 9 or 10 minutes. It may be capable of providing an energy output which drops by no more than about 25%, or no more than about 20, 15, 10 or 5% when solar energy incident on the solar reflector is blocked for no more than about 2 hours, or no more than about 5, 10, 12, 14, 16, 18 or 20 hours. The thicker the heat regulating medium, the greater its thermal mass, and consequently the longer the system can withstand interruption in energy input without suffering a large interruption in energy output. The blockage of energy input may represent for example night time (which represents an extended blockage) or it may represent the passage of a cloud or other obstacle between the sun and the solar reflector or a portion thereof, representing a blockage of shorter duration. In the latter case solar energy may still reach the solar reflector, but may be incapable of being focused on the collector due to the diffuse (non- directional) nature thereof. A typical installation may comprise multiple heliostat modules (solar energy reflectors) and regulator modules (solar collectors) so that the time that the overall energy collection system may be operated is increased while maintaining the required output. Thus the heat regulating medium, and the solar collector, and the solar energy collection system, and the solar energy collection installation, are capable of regulating the time that solar energy can be used to generate electricity or to generate steam.

[000101 ] The invention also provides a method for collecting and regulating solar energy. Thus either a single collection system or an installation of collection systems comprising a number of such systems is set up so as to be capable of receiving solar energy. Solar energy is then allowed to impinge on the solar reflector(s) of the system. This energy is then concentrated and/or focused by the solar reflector(s) and the concentrated/focused energy is directed to the collector(s). In particular it is directed into the aperture(s) of the collectors) so as to collect the concentrated solar energy by way of the protective and collection layers. These layers do not hold substantial amounts of thermal energy, however are capable of collecting and transmitting the energy so as to heat the heat regulating medium. The heated heat regulating medium can then transfer the heat to a heat transfer fluid in the heat exchanger, thereby enabling the energy to be transferred when it is required.

[000102] An important aspect of the invention is the fact that the large thermal mass of the heat regulating medium enables fluctuations in the incident solar energy to be evened out so as to generate a relatively constant output of heated heat transfer fluid if required. Such fluctuations may be short term, for example a cloud passing in front of the sun, or they may longer term, such as night time. The ability of the system to absorb and even out such fluctuations depends on the thermal mass of heat regulating medium. Thus the larger the thermal mass of the heat transfer fluid (i.e. the larger its mass and the higher its heat capacity) and the lower the removal rate of heat (i.e. the lower the flow rate of heat transfer fluid) the greater the ability of the device/system will be to absorb sharper and/or longer fluctuations in incident solar energy.

[000103] The present invention is designed to address the disadvantages of solar energy only being available in daylight hours and also the problem of variations in output quality (as clouds pass over for example), and to provide improved efficiency compared to existing solar energy collection devices. The invention relates to solar thermal power generation. It relates to the regulation of solar energy conversion so as to ensure that the converted energy is produced at a consistent quality and also enabling it to be produced at any time on demand.