The present invention relates to a device for collecting electromagnetic radiation, and more specifically, but not limited to, solar radiation. It further relates to a heating system utilising a solar collector device, and also a method of utilising such a solar collector device to heat a heat-transfer fluid, which can be, for instance, salt water within a desalination system.

Energy conservation is becoming a highly important topic as climate change and the usage of fossil fuels continues. Experts claim that many of the Earth's finite resources are being depleted at ever increasing rates, with some even believing that the availability of crude oil, the base resource from which we obtain fuels such as petrol and diesel, is likely to run out within the next 40 years.

The imminent removal of this scarce resource from the global market has led to a surge of interest in so-called 'green' technologies, which aim to find environmentally-friendly solutions to problems which are currently solved in environmentally-damaging ways. Particularly of interest are methods of reducing our reliance on electricity, by either developing increasingly efficient devices or methods, or by utilising alternative energy sources to negate the need for electricity completely.

In the developing world, the interest in low- or no-power solutions is particularly important. Technologies are required which can help with such tasks as increasing food production or even just providing clean water to populations. In many areas of the developing world, access to electricity is limited, unreliable, or simply non-existent, and therefore the provision of non-electrical equipment is both desirable and necessary. Nevertheless, such equipment requires power in some form or another.

Given that many countries in the developing world lie within the tropics, a favoured method of harnessing power is by use of solar radiation. Generating electricity by way of photo-voltaic cells tends to be expensive due to the materials involved in production, along with the necessary repair and maintenance work throughout their working life. Along with this, the efficiency of conversion of solar radiation to electrical energy is physically limited to around 30%, with the use of current technology. By creating a solar collector that converts solar radiation to thermal energy rather than electrical energy, this physical limit can be avoided. Thermal energy, whilst typically not having as many uses as electricity, can be used in the generation of clean water or running of heating systems, and is therefore still very useful, especially in the developing world. However, such solar collectors inherently have their own problems, such as finding materials which can efficiently absorb as large a portion of the electromagnetic spectrum as possible. Preferably, such a material will not be damaged in the process, so that repair and maintenance costs can be limited.

It is an object of the present invention to provide a solar collector which is capable of removing or limiting the above-mentioned problems in order to provide improved thermal efficiency and lower ongoing maintenance costs than its competitors.

According to a first aspect of the invention there is provided a solar collector device for converting solar radiation into thermal energy, comprising: a heat exchange element; a transparent cover forming at least part of an outer surface of the solar collector device; and a solar-energy absorption element, interposed between the heat exchange element and the transparent cover; the solar-energy absorption element having at least a primary absorption layer which preferably comprises a resin in which carbon nanoelements are contained, and a secondary absorption layer which preferably comprises a carbon fibre twill, the secondary absorption layer being positioned between the primary absorption layer and the heat exchange element for the absorption of at least a portion of the radiation transmitted by the primary absorption layer, the secondary absorption layer is preferably in thermal contact with the resin of the primary absorption layer; and a UV-protection layer may be on or adjacent to the solar-energy absorption element, for protecting at least the primary absorption layer from UV-related damage. The term 'carbon nanoelements', as used herein and throughout, refers particularly, but not necessarily exclusively, to carbon nanotubes and/or carbon nanoparticles. The term can also refer to and include or comprise either alone or in combination molecules such as iiillerenes or other similar allotropes of carbon or graphene- based materials.

The use of a bi-layered solar-energy absorption element allows the solar collector device to operate in a more thermally efficient manner. The carbon nanoelements within the primary absorption layer absorb the majority of the incident solar radiation. A further percentage of the radiation which passes through this layer is then absorbed by the secondary absorption layer, resulting in more efficient absorption of the solar collector device as a whole. Carbon fibre is not only a good absorber of solar radiation, but also has good heat conduction properties, making it an efficient conduit between the heat-absorbing layers and the heat exchange element.

The resin holds the carbon nanoelements in place and also enables enhanced heat conduction between the carbon nanoelements and the secondary absorption layer. Beneficially, the resin is preferably transparent. However, the resin may only be partially transparent, translucent or possibly opaque providing the incident solar radiation can be appropriately absorbed. As the resin and/or carbon nanoelements may be damaged by UV-radiation from the Sun, it is advantageous to provide protection against harmful degrading UV-rays. The UV-protection layer may provide protection against the entire ultraviolet region of the electromagnetic spectrum or may only protect against specific damaging frequencies.

In a preferable configuration, the primary absorption layer may include carbon nanotubes and/or carbon nanoparticles. Carbon nanotubes and carbon nanoparticles offer extensive absorption of solar radiation of a variety of different wavelengths, and can thus be used to enhance the absorption characteristics of the solar collector device.

Beneficially, the UV-protection layer may be formed as part of the transparent cover. Thus, assembly of the solar collector device may be simplified due to one less component being required.

In an optional arrangement, the heat exchange element may further comprise at least a further absorption layer. Further absorption layers allow a higher proportion of the solar radiation to be absorbed, thus improving the efficiency of the solar collector device. A percentage of the solar radiation transmitted through each absorption layer will be absorbed the absorption layer below, thus improving the efficiency of the solar collector device with every additional layer. Each further absorption layer may be formed from the same or different material from the or each other absorption layer.

Preferably, the heat exchange element may include at least one thermally-conductive baffle, disposed on a lower surface of the heat exchange element. The addition of thermally-conductive baffles provides extra surface area for heat exchange. It would be advantageous for the or each thermally-conductive baffle to extend into a heat -transfer fluid. Optionally, the heat-transfer fluid may be one of brackish water, salt water, or fresh water.

By extending the or each thermally-conductive baffle into the heat-transfer fluid, heat exchange can be maximised. The use of brackish water, salt water, or fresh water as the heat-transfer fluid allows the solar collector to take advantage of the relatively high specific heat capacity of water. Additionally, heated brackish water or salt water can be evaporated, and further condensed into fresh water, which can then be consumed.

Preferably, at least the heat exchange element, solar-energy absorption element, and transparent cover may be in a laminated arrangement. Such an arrangement allows good thermal conduction between the layers, enhancing the efficiency of the solar collector device.

According to a second aspect of the invention, there is provided a heating system comprising: a solar collector device, preferably in accordance with the first aspect of the invention; and a circulation system containing a heat-transfer fluid; the circulation system being in communication with at least a portion of the heat exchange element of the solar collector device for transferring heat from the heat exchange element to the heat-transfer fluid of the circulation system.

A heating system formed in this manner allows energy to be harvested from solar radiation and used to heat water, or another fluid, which can then be used for many different purposes.

In a beneficial arrangement, the heating system may further comprise an enclosure, within which at least a portion of the solar collector device is contained. By holding at least a portion of the solar collector device within an enclosure, the system may be made more portable, and/or protected from damage. Preferably, the enclosure may be insulated. Insulation reduces the re-emission of absorbed energy, making the heating system more efficient.

Preferably, the heating system may form part of a desalination system, such that the heat absorbed by the heating system may be utilised for the creation of potable water.

According to a third aspect of the invention there is provided a method of heating a heat-transfer fluid, preferably using a solar collector device according to the first aspect of the invention, comprising the steps of: a] having the solar collector device in the path of solar-radiation; and b] the solar collector device transferring absorbed thermal energy to said heat-transfer fluid in communication with the heat-exchange element of the solar collector device.

Use of a solar collector device as described above allows a high proportion of incident solar radiation to be absorbed as thermal energy and then passed onto the heat -transfer fluid. This thermal energy can then be usefully utilised by other parts of a system. According to a fourth aspect of the invention there is provided a method of absorbing solar radiation, preferably using a solar collector device according to the first aspect of the invention, the method comprising the step of providing a primary solar-radiation absorption element including carbon nanoelements and a secondary solar-radiation absorption element which is in communication with and different to the primary solar-radiation absorption element.

Providing at least two absorption layers increases the efficiency of the solar radiation absorption as a percentage of the solar radiation transmitted through the primary absorption element, which would otherwise be wasted, will be absorbed by the secondary absorption element. According to a fifth aspect of the invention, there is provided a solar collector device for converting solar radiation into thermal energy, comprising: a heat exchange element; a light-transmissible, and preferably transparent, cover forming at least part of an outer surface of the solar collector device; and a solar-energy absorption element, interposed between the heat exchange element and the cover; the solar-energy absorption element having at least a primary absorption layer, including carbon nanoelements, and a secondary absorption layer being positioned between the primary absorption layer and the heat exchange element for the absorption of at least a portion of the radiation transmitted by the primary absorption element. According to a sixth aspect of the invention, there is provided a method of improving the thermal stability of a solar-energy absorption element of a solar collector device, the method comprising the steps of: a] providing a heat exchange element of the solar collector; b] providing a secondary absorption layer on top of the heat exchange element, wherein the secondary absorption layer includes, preferably flexible, carbon fibres; and c] providing a primary absorption layer on top of the secondary absorption layer, the primary absorption layer comprising a resin in which carbon nanoelements are contained, the secondary absorption layer physically separating the primary absorption layer and the heat exchange element.

The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a cross-sectional view of an embodiment of a solar collector device, in accordance with the first aspect of the invention; and

Figure 2 shows a perspective view of an embodiment of a heating system, in accordance with the second aspect of the invention. Referring firstly to Figure 1 of the drawings, there is shown a solar collector device 10. The outer surfaces 12 of the solar collector device 10 are defined by an enclosure 14 comprising a base portion 16 and side portions 18, and a transparent cover 20 which is positioned at the top of the side portions 18. The transparent cover 20 seals the top of the enclosure 14. Whilst being depicted as being transparent in the present embodiment, it will be apparent to the skilled person that the cover 20 need only be light-transmissible, and a translucent cover could alternatively be provided.

Underneath the transparent cover 20 is situated a heat-absorption element 22. The heat-absorption element 22 includes two distinct layers 24. The primary absorption layer 24a is preferably at least in part formed of a transparent resin containing or encasing nanoelements which in this embodiment is a mixture of carbon nanoparticles and carbon nanotubes. The carbon nanoparticles and nanotubes are adept at absorbing solar radiation of a variety of wavelengths. Although preferably a mixture of carbon nanoparticles and carbon nanotubes, one may be dispensed with in preference to the other. However, the mixture is beneficial in terms of trapping and absorbing solar radiation, whereby the nanoparticles naturally locate in space or voids between the nanotubes, thereby providing a more complete electromagnetic radiation absorbing surface.

Although preferably transparent, the resin or other suitable holding material, may be translucent or even opaque providing the incident solar radiation can be adequately absorbed by one or both primary and secondary heat -absorption layers.

Disposed immediately beneath the primary absorption layer 24a of the heat-absorption element 22 is a secondary absorption layer 24b which is formed from a different material to that of the primary absorption layer 24a. This secondary absorption layer 24b preferably comprises of at least carbon fibre, which in this case is carbon fibre twill. The carbon fibre twill is preferably formed as a flexible carbon fibre material having a fabric pattern which has a surface of diagonal parallel ridges. This can ensure that the secondary absorption layer 24b can be readily shaped so as to fit to the heat-absorption element 22 in a manner in which a rigid carbon fibre plate would not be able, since the weave of the twill can improve the ability of the secondary absorption layer 24b to drape over other objects.

The secondary absorption layer 24b is designed to absorb as high a proportion as possible of the incident solar radiation which is transmitted through the primary absorption layer 24a without being absorbed. The secondary absorption layer 24b also provides a thermally-conductive path for the transmission of the absorbed thermal energy from the solar-energy absorption element 22 to a heat-exchange element 26, which is positioned immediately below the secondary absorption layer 24b. The secondary absorption layer 24b may be positioned so as to be in contact with both the primary absorption layer 24a and the heat-exchange element 26, so as to facilitate heat transfer therebetween, thereby forming a layered structure from the heat exchange element 26, to the secondary absorption layer 24b, up to the primary absorption layer 24a.

The resin of the primary absorption layer 24a may act as a means of providing thermal exchange and physical support for the carbon fibre of the secondary absorption layer 24b. Furthermore, the carbon fibre of the secondary absorption layer can act as a buffer against the thermal expansion characteristics associated with the heat exchange element 26 which, if in direct contact with the primary absorption layer 24a, would lead to degradation of or damage to the resin thereof. As the heat exchange element 26, which is typically formed from metal, resin affixed thereto would ordinarily crack or delaminate; however, the presence of the secondary absorption layer 24b, having the form of carbon fibres, acts as a buffer between the heat exchange element 26 and the primary absorption layer 24a.

A UV-protection layer 28 is provided for protecting primarily the resin, but potentially also the carbon nanoparticles of the solar-energy absorption element 22 from harmful frequencies of ultra-violet radiation which form portion of the incident solar radiation. In this embodiment, the UV-protection layer 28 is formed of a UV-resistant film 30 and is interposed between the primary absorption layer 24a of the solar-energy absorption element 22 and the transparent cover 20. The UV-protection layer 28 provides a means of limiting degradation of the resin of the primary absorption layer 24a and/or unstable nanoelements therein, if applicable. Alternatively, the UV-protection layer could be formed from a different UV-protective material such as soda-lime glass or titanium dioxide. It could also be incorporated into another element, such as the transparent cover, in order that the overall number of components is reduced. A reduction in this manner will inevitably make assembly of the solar collector device easier. An air space or vacuum void may also be provided interposed between the cover 20 and/or the UV-protection layer 28 and the heat-absorption element 22.

The heat-exchange element 26 occupies the remaining space within the confines of the enclosure 12 and transparent cover 20. Direct contact between the secondary absorption layer 24b of the solar-energy absorption element 22 and the heat-exchange element 26 ensures that maximum conduction is enabled. However, it is also possible that a further solar energy absorption layer or layers could be interposed if desired. The heat-exchange element 26 itself comprises a hollow structure with a plurality of thermally-conductive baffles 32 interconnecting the top and bottom surfaces 34a, 34b of the heat-exchange element 26.

Whilst the heat-exchange element 26 in the preferred embodiment is hollow and comprises a plurality of baffles, the heat exchange element could also be planar, undulating, or any other shape, dependent on space requirements and the required surface area for heat-exchange. Additionally, thermally-conductive baffles may or may not be required, and therefore may be omitted, without detracting from the overall invention.

Adjacent thermally-conductive baffles 32 extend from opposing sides of the heat-exchange element 26, which are not visible on the cross-sectional view in Figure 1 , and extend the majority of the way across the breadth of the heat-exchange element 26. In this way, they define a tortuous flow-path for the flow of a heat -transfer fluid 36 within the heat-exchange element 26. The heat-transfer fluid 36 can thus enter into the heat-exchange element 26 through an inlet 38, located at one end of the heat-exchange element, and exits through an outlet 40, located at the other end of the heat-exchange element 26, which are visible in Figure 2. By utilising thermally-conductive baffles 32 along the flow-path the amount of energy conducted from the heat-exchange element 26 to the heat-transfer fluid 36 can be maximised.

The inlet 38 and outlet 40 are located dependent on the design of the heat-exchange element 26, and therefore, if the heat-exchange element 26, or any other part of the solar-collector device 10, should be redesigned, the inlet 38 and outlet 40 can be relocated accordingly. Whilst it is preferable for the inlet 38 and outlet 40 to be positioned at extreme ends of the heat-exchange element 26, so as to maximise the surface area that the heat-transfer fluid contacts, in some instances this may not be necessary.

Whilst the thermally-conductive baffles 32 in this embodiment extend from one side to an opposing side in a simple, parallel fashion, the thermally-conductive baffles could also extend diagonally or along curved paths, dependent solely on manufacturing capability and the individual design of the heat-exchange element.

The enclosure 14 which, together with the transparent cover 20, surrounds the remaining components in this embodiment may instead be utilised to enclose only one or more sides of the solar collector device so as to leave the heat exchange element exposed if desired. Alternatively, the enclosure could be disposed of altogether, if there is no need for additional protection against external phenomena such as wind, rain, or dust.

The heat-transfer fluid could be a gas or a liquid. For example, argon gas could be circulated past the heat-exchange element, or more preferably, brackish water, salt water, or fresh water could be utilised due to its high specific heat capacity.

Four of the solar collector devices 10 depicted in Figure 1 are depicted in Figure 2, as part of a heating system 42. The solar collector devices 10 are disposed in a grid formation on a solar collector frame 44. Three of the solar collector devices 10a, 10b, 10c are shown in a fully assembled arrangement, whilst the fourth solar collector device l Od is shown with a horizontal cross-section exposing the plurality of thermally-conductive baffles 32 within the heat exchange element 26, arranged as described in reference to Figure 1 . For brevity, features described in detail in relation to Figure 1 have been omitted from further explanation.

In the present embodiment, four solar collector devices 10 are positioned in a grid formation. A greater or lesser number of solar collector devices 10 could also be used for the creation of a heating system, dependent on space and heating requirements of an individual installation. Furthermore, the solar collector devices 10 could be installed in a row, grid, or circular formation, again dependent on design choice.

Each solar collector device 10 additionally comprises the inlet 38 at one end of the flow-path defined by the thermally-conductive baffles 32, and the outlet 40 at the opposing end of said flow-path. Therefore, water, oil, or another heat-transfer fluid 36 can be admitted to one end of the heat exchange element 26 of a solar collector device 10 and rejected at the other end, having been heated by the absorbed thermal energy. Three connection conduits 46 are used to connect the four solar collector devices 10. The connection conduits 46 conjoin a said outlet 40 of one solar collector device to the inlet 38 of another, in order that the heat-transfer fluid 36 running through the heating system 42 can pass through each solar collector device 10 in turn. Thus, the fluid absorbs heat from each solar collector device, before exiting the heating system.

Whilst in this preferred embodiment the solar collector devices 10 are connected in series, it would also be possible for the heating system to comprise multiple heating circuits, whereby the heat-transfer fluid of the heating system is split into multiple parts and each part is fed through only one solar collector device for heating, which can be described as the solar collector devices being connected in parallel. Alternatively, each heating circuit could comprise two or more solar collector devices. Any such arrangement of solar collector devices is possible without departing from the scope of the present invention.

The solar collector frame is supported, in this example, by two frame legs 48, situated centrally towards first and second sides 50a, 50b of the solar collector frame 44. A proximal end 52 of each frame leg 48 is connected to the solar collector frame 44 by way of a rotatable joint 54 which allows relative rotational motion of the frame leg 48 and solar collector frame 44. A distal end 56 of each frame leg 48 can then be placed on the ground or other supporting surface, in order to support the solar collector frame 44. Adjacent to a third side 50c of the solar collector frame 44 is a frame base element 58. The frame base element 58 is a rectangular panel with one longitudinal edge 60a in contact with the ground or other supporting surface. The opposing longitudinal edge 60b is connected to a tilting element 62, which in this case is a scissor lift 64 but which may be any other suitable height-adjustment or rotational mechanism, such as a jacking mechanism and/or electric motor drive unit.

The scissor lift 64 is interposed between the frame base element 58 and the third side 50c of the solar collector frame 44. As such, extension and retraction of the scissor lift 64 results in the third side 50c of the solar collector frame 44 rising and falling, respectively. Due to the rotational connection between the solar collector frame 44 and the frame leg 48, the movement of the third side 50c results in a change in orientation of the solar collector frame 44.

As a result of this change in orientation, the heating system 42 can be positioned by a user to allow optimal absorption of solar radiation. For instance, the solar collector frame 44 could be automatically or manually reoriented to face the Sun throughout the day to maximise the incident radiation on each solar collector device 10.

In order to enable automatic reorientation of the solar collector frame or solar collector devices, motors could be used, together with sensors for detecting the direction of incident light. A controller could be provided to utilise the sensed information and position to the solar collector devices in the optimal position. Alternatively, predetermined data about solar position could be used in place of sensors. Other methods of automatically reorientating the solar collector devices will be obvious to those skilled in the art.

Whilst a scissor lift 64 has been utilised in this embodiment, other methods of reorientation in addition to those mentioned could be used such as a screw or hydraulic ram. A ball joint or similar feature could also be utilised to allow a full range of pitch, roll, and yaw motions to be utilised with only one joint. These features could be provided in one or more locations on the heating system in order to enable single- or multiple-axis reorientation. Similarly, each solar collector device 10 could be orientated individually by any of the above-mentioned or similar methods in order to ensure maximum incident solar radiation on each device.

With different methods of orientating the heating system, it is clear that the frame leg need not necessarily be as described in this embodiment, and could, in fact, be omitted completely in some cases. Similarly, if no reorientation of the solar collector frame is required, more frame legs could be added to enhance the support for the solar collector frame. Joints connecting the frame legs to the solar collector frame could be any type of joint, such as a ball, hinge, or even a fixed joint, if no relative motion of the parts is required.

The outlet 40 of the third solar collector device 10c is preferably connected to a heating conduit 66. The heating conduit 66 connects the solar connector devices to a pump 68 and at least one radiator 70 before completing the heating system 42 by connecting to the inlet 38 of the fourth solar collector device l Od.

The pump 68 is configured to circulate the heat-transfer fluid 36 around the heating system 42. The pump 68 could take the form of any sort of pumping device, or, if the heating system is adapted to be a desalination system, the pump could be removed completely if the salt or brackish water was pushed through the system by another means, such as gravity. The pump may be driven via electricity supplied through a photovoltaic panel and/or from a mains electricity supply, as required.

The radiator 70 is in this embodiment a convection radiator, but could also take the form of a forced-convection radiator, underfloor heating system, or other heat transfer device. Alternatively, in the case of a desalination system, the radiator could be replaced by an evaporation chamber, condenser and/or other necessary desalination equipment. Additionally, a vacuum pump could be added to the evaporation chamber to decrease the pressure and assist evaporation. Clearly, if the heating system were to be converted to a desalination system, the desalination equipment would not be reconnected to the solar heating system and there would instead be a tap, pipe, or other exit through which clean water could flow or be discharged in a controlled manner.

Whilst throughout the description the invention has been described with reference to solar radiation, it is entirely possible for the described device and system to be used with other sources of electromagnetic radiation such as other visible light sources or thermal radiation emitters like molten rock or other forms of geothermal energy. As such, the description of certain features as the "solar collector device" or "solar-energy absorption element" are described as such due to their intended use in the described embodiment and are not intended to be limiting to their possible uses.

It is therefore possible to provide a solar collector device comprising at least a two-layer solar-energy absorption element which enabling higher efficiency of energy absorption than an otherwise designed device. It is also possible to provide a heating system which utilises such a solar collector device to transfer the absorbed thermal energy to a heat-transfer fluid, in order that the heat can then be used.

The words 'comprises/comprising' and the words 'having/ including' when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components, but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

The embodiments described above are provided by way of examples only, and various other modifications will be apparent to persons skilled in the field without departing from the scope of the invention herein described and defined.