Solar light collector

Abstract

EA collector 100 for collecting electromagnetic radiation from the sun has a plurality of cells 110i-110n. Each cell has an optical arrangement 112i-112n and an optical fibre 111i-111n. The optical arrangement couples any incoming radiation into the optical fibre, and the optical fibres are combined in a cable 120. Each cell can include a top plate 610, a middle plate 620, a bottom plate 630, a lens 611 and a coupling channel 641, the coupling channel facilitating coupling of the lens to the optical fibre 621, and the internal surface of the coupling channels may be coated with a reflective coating. The middle plate functions to couple and support the interface between the coupling channel and the optical fibre. The arrangement finds use in a heating system (1300 Figure 13), and the cell can be part of an optical heating system. The cell can be part of an optical heating element and the heater element is located in a tank for increasing the temperature of the fluid stored in it. For instance, the tank may be a water tank. The arrangement provides increased flexibility in the use of solar heating of water with solar energy collected remotely and easily transported to the point of use.

Description

Technical Field The present disclosure relates to a collector for collecting electromagnetic radiation from the sun. The disclosure also relates to a system comprising such a collector, for example a heating system. Background Solar energy can be used in various types of buildings including private housing or industrial plants. Various system for collecting solar power have been reported including WO2006 / 049560 and WO2010051595A1. These systems can be relatively thick, bulky and heavy, protruding outwards, and are relatively complex to implement or lack efficiency. There is a need for an efficient solar light collector that can be implemented and deployed easily. Summary According to a first aspect of the disclosure there is provided a collector for collecting electromagnetic radiations from the sun, the collector comprising a plurality of cells, wherein each cell comprises an optical arrangement and an optical fibre, the optical arrangement being adapted to couple an incoming radiation into the optical fibre; and wherein the optical fibres are combined in a cable. The cable may be an umbilical cable. The plurality of cells may form a collecting surface. The collecting surface may be flat. Alternatively, the collecting surface may be curved. Optionally, the collector comprises a connector formed of a plurality of optical fibre combiners. Optionally, wherein each optical fibre combiner has an input for receiving a plurality of optical fibres from a single cell, and an output provided with a single output optical fibre; and wherein the output optical fibres of each optical fibre combiner are combined in the cable. Optionally, wherein each cell is orientable, so that an outer surface of the cell projects along a desired direction. Optionally, the collector comprises a mechanical arrangement adapted to adjust an orientation of one or more cells. For instance, the cells may be arranged in a plurality of linear arrays mounted on a rotatable platform, wherein each linear array is rotatable around a longitudinal axis of the linear array. Optionally, wherein one or more cells comprise an actuator configured to adjust a position of the optical fibre or a position of an optical steerer in the cell. Optionally, the collector comprises a controller configured to generate one or more control signals to control at least one of the mechanical arrangement and the actuator. Optionally, the collector comprises one or more sensors coupled to the controller. For instance, the one or more sensors may comprise at least one of a camera, a photodiode, a photoresistance, and a phototransistor. Optionally, wherein the controller is configured to receive sensor data from the sensor, and to generate the one or more control signals based on the sensor data. For example the controller may comprise a processor adapted to execute an algorithm for generating the one or more control signals. Optionally, wherein the controller comprises a safety module configured to generate a safety signal upon detection of a malfunction. For instance, the safety signal may be configured to deactivate the collector. For example the safety signal may be configured to close a mechanical or electrical shutter to reduce or prevent illumination of the cells. Alternatively the safety signal may be configured to change an orientation of the cells to reduce illumination of the cells. Optionally, wherein the optical arrangement is configured to focus the incoming radiation into the optical fibre. Optionally, wherein the optical arrangement comprises one or more lenses. Optionally, wherein the optical arrangement comprises an array of lenses or an array of microlenses. For instance, the lenses may have a hexagonal shape. The array of microlenses may form a lenslet array. Optionally, wherein each lens is coupled to the optical fibre via a coupling channel. For instance, the coupling channel may be coated with a reflective coating. Optionally, wherein the coupling channel has a conical shape. Optionally, wherein one or more cells comprise a set of secondary lenses, wherein a secondary lens is located at an input end of each optical fibre. Optionally, wherein the cells comprise a frame having a first mount holding the optical arrangement and a second mound holding the optical fibres. For instance, the first mount and the second mount may be separated by a distance defined by a focal length of the optical arrangement. Optionally, wherein the second mount is movable along a translation axis with respect to the first mount. Optionally, the collector comprises a plurality of optical steerers provided between the optical arrangement and the optical fibres. Optionally, the cable comprises one or more electric wires. For instance the one or more electric wires may be configured to carry an electric signal. The controller may be configured to receive the electric signal as part of a safety mechanism. One or more electric wires may be thermal conductors configured to break above a predefined threshold temperature. According to a second aspect of the disclosure, there is provided a system comprising a collector according to the first aspect, coupled to an external element. Optionally, wherein the external element comprises an optical heater. Optionally, the optical heater comprises a housing adapted to receive the cable; and a fastening means configured to attach the optical heater to a chamber for receiving a liquid or substance to be heated. The housing may have an elongated shape. For instance the housing may have an elongated tubular shape. The housing may also be sealed to prevent ingress of the liquid or substance into the housing. For instance, the housing may be waterproof. The optical heater may also comprise a heating target provided within the housing and configured to receive optical power via the cable. Optionally, the system comprises a chamber for receiving a liquid or substance to be heated, and wherein the optical heater is located in the chamber to heat the liquid or substance. Description of the drawings The disclosure is described in further detail below by way of example and with reference to the accompanying drawings, in which: figure 1A is a collector for collecting electromagnetic radiations; figure IB is a diagram of an array of cells mounted on a turntable; figure IC is an exemplary implementation of a controller for use with the collector of figure 1A; figure 2A is another collector for collecting electromagnetic radiations; figure 2B is a diagram of a single cell connected to a fibre connector; figure 2C is a diagram of a microlens; figure 3A is a perspective view of an array of circular microlenses; figure 3B is a side view of the array of microlenses of figure 3A; figure 3C is a top view of a hexagonal lens; figure 3D is a top view of an array of hexagonal lenses; figure 4 is a cross section of a first exemplary cell; figure 5 is a cross section of a second exemplary cell; figure 6 is a cross section of a third exemplary cell; figure 7 is a cross section of a fourth exemplary cell; figure 8 is a cross section of a fifth exemplary celt- figure 9 is a cross section of a sixth exemplary cell; figure 10 is a cross section of an umbilical; figure 11 is an example implementation of a sun-tracking architecture for use with the collector of figure 1 or 2; figure 12 is a diagram of a steering structure for steering a lens; figure 13 is a diagram of a heating system; figure 14 is a diagram of the collector of figure 2A coupled to an optical heating element or optical heater; figure 15 is a diagram of an optical heater. Description Figure 1A illustrates a collector for collecting electromagnetic radiations from the sun. Electromagnetic radiation from the sun, or “sunlight”, includes infrared, visible, and ultraviolet light. In the context of this application the electromagnetic radiations refer to a flux of photons emitted by the sun. The collector 100 includes a plurality of cells labelled 1101 -llOn forming a collecting surface 110, and a cable 120 also referred to as optical fibre bundle 120, or umbilical cable. Each cell is provided with an optical arrangement 112i-112n and an optical fibre llli-llln. For each cell the optical arrangement and optical fibre are optically coupled so that an incoming radiation (photons emitted by the sun) received by the cell is coupled into the optical fibre. The optical fibres are combined in the cable 120 also referred to as umbilical or umbilical cable. The collector 100 may be provided with a mechanical arrangement (not shown) adapted to orientate one or more cells. For instance the mechanical arrangement may be designed to adjust the orientation of the whole panel 110. Alternatively, the mechanical arrangement may be designed to adjust the orientation of each individual cell , or of a set of cells. By tilting the surface of one or more cells to be directed towards the sun, the collection efficiency can be improved. The mechanical arrangement may be adapted to move the optical arrangements, for instance the lenses 112i-112n, simultaneously so that they point in a same direction. For example a rotating turntable with a single axis tilt may be used. Figure IB is a diagram of an array of cells mounted on a rotatable platform also referred to as turntable. In this example the plurality of cells labelled 1 lOi -llOn are mounted on a turntable 170. The turntable is rotatable around a rotational axis 105. The cells are arranged in four linear arrays Al-A4. Each linear array is rotatable around a respective longitudinal axis. For instance the linear array A4 is rotatable around the longitudinal axis R4. The linear arrays may be controlled to rotate or tilt in unison so as to face incoming sunlight. The turntable 170 provides a panning function, while the linear arrays provide a tilting function. The arrangement of figure IB permit the implementation of a relatively thin panel 110. Alternatively, or in combination, one or more cells may be provided with an actuator configured to adjust a position of the optical fibre or a position of an optical steerer in the cell. By adjusting a position of the optical fibre in relation to the optical arrangement, the optical coupling can be adjusted and optimized. The cells may be mounted on a platform . The design of the platform may differ depending on the form factor of the collector. A controller 190 may be provided to send one or more control signals Sc to control the mechanical arrangement. The controller 190 may generate the control signal (or set of control signals) based on sensing data. For example a sensor 180 may be provided to sense a direction of incoming radiation. Such a tracking system may be used to track the sun and improve collection efficiency. The direction of the panel may be monitored and updated at regular intervals for instance every 2 minutes to keep the spot within the diameter of the optical fibre. The collector 100 may be installed on a building, for instance on a roof. The collector 100 may be used to send optical power to one or more devices via the umbilical 120. For instance, the umbilical may be connected to one or more illuminators for providing daylight internal illumination. In another application the collector 100 may be coupled to a heater for providing hot water heating. When considered as an energy source, the technology has wide application potential: to concentrate sunlight onto photovoltaic cells or solar thermal tubes, the next generation of high concentrator perovskite, 11-V or GaN semiconductors photovoltaic cells, solid-state batteries, direct heat exchangers, ancillary buffer tanks and super heaters for air or ground heat pumps or as an energy source for hydrogen fuel cell hydrogen generation. In figure 1A, the collecting surface 110 is represented as a flat surface or panel. It will be appreciated that the cells may be arranged to form a collecting surface 110 having a curved shape or another form factor. For instance the cells may be arranged to form a sphere and the collecting surface being spherical, for instance a whole sphere, or half a sphere. The cells may also be arranged to form other shapes including a dome or a tube or a square shape, to name a few. The modular nature of the cells means that many different shapes can be envisaged depending on the application. Figure IC is an exemplary implementation of a controller for use with the collector of figure 1A. The controller may include one or more of a sun tracker module, a safety module, a metrics module, a user display module, and a power management module. The sun tracker module is configured to receive data from the sensor 180 and to control the inclination of the cells in a feedback loop. The safety module is configured to sense a potential malfunction of the collector and if necessary, shut it down. This may be implemented using a safety loop running between the collector and an external element connected at the other end of the umbilical; for instance a heating element. The metric unit is configured to monitor various parameters of the collector which could include optical power received by the cells, among others. The user display is configured to provide a user interface allowing the user to set up the collector, and display data. Figure 2A illustrates another collector for collecting electromagnetic radiations. The collector 200 includes a plurality of N cells labelled 2lOi -210n (of which only 5 are shown) forming a panel 210, and an optical fibre bundle or umbilical 220. In this case the panel 210 is coupled to the umbilical 220 via a panel connector 230. The panel connector 230 includes N optical fibre combiners labelled 231-23N. So in this example each cell is provided with a dedicated fibre combiners. For example the fibre combiner 23N has an input that receives a number Z of optical fibres from the cell 210n and an output provided with a single output optical fibre. The output optical fibres of each fibre combiner are then combined into the umbilical cable 220. By merging the optical fibres from each cell into a fibre combiner, it becomes easier to combine many fibres combiners into the umbilical cable 220. This provides a fast and convenient way of installing the collector. Using this approach relatively thin cells can be used. Figure 2B shows a single cell connected to a fibre combiner. The cell 2lOi is provided an optical arrangement 212i implemented as an array of lenses covering a portion of the surface of the cell. In this example the array is an array of microlenses. Each microlens pL is coupled to an optical fibre Fb. The optical fibre combiner 23i couples the plurality of optical fibres Fb to a single output fibre 220i, also referred to fibre core. In this example the microlenses are arranged in a tessellated fashion, however it will be appreciated that different geometries may be considered. The cells may be relatively small in size, for example each cell may be a square of about 100mm x 100mm containing about 100 micro lenses. The optical fibres may be silica MM fibres of relatively small size. The size of the optical fibres Fb will depend on the design of the cell. For example assuming a cell with 100 lenses, optical fibers fb may be chosen with a diameter of 0.1mm, and the output fiber / fiber core 220i with an area of 1mm2. The optical fibres Fb and 22Oi may be multimode fibers. The optical fibres Fb and 220i may have a relatively high numerical aperture (NA). For instance, a numerical aperture of about 0.5 may be selected. The optical fibers may be made of different materials. For instance, the fibers may be silica fibers. Alternatively the fibres may be plastic fibres including polymethyl methacrylate (PMMA) polystyrene, polycarbonate, cyclic olefin polymers (COP) and polyester. The umbilical may be a plastic MM Fiber having a 1.5mm core. As another alternative the fibres may be hollow-core fibres. Figure 2C is a diagram of a microlens focusing optical rays into a corresponding optical fibre. The lenses may have different outer shapes and sizes. They may also be selected as convex or piano convex lenses. The lenses may be single layer or multilayer lenses. Figure 3A is a perspective view of an array of circular microlenses. Figure 3B is a side view of the array of microlenses of figure 3A. Figure 3C is a top view of a hexagonal lens sometimes also referred to as cookie cut hexagonal lens. Figure 3D is a top view of an array of hexagonal lenses. To achieve maximum density of fiber and lenses, and therefore maximum efficiency, it is preferable the lenses be in a hexagonal shape as shown in Figures 3C and 3D. The arrays of lenses as shown in figures 3A, and 3D may be referred to as a fly’s eye lens arrays or lenslet arrays. The cells of the collector may be designed to butt up together with minimal dead space between each other. For instance, the space may be just large enough to allow the tilt mechanism of the sun tracking feature to function so that cells do not interfere with each other's motion. The cells of the collector can be implemented in different fashions. Below are some examples of cells for use in the collector of figure 1 or figure 2. Figure 4 is a cross section of a first exemplary cell. In this example the cell 400 has a top plate 410 provided with separate individual lenses, a middle plate 420, and a bottom plate 430 also referred to as bot plate. The middle plate 420 is designed to hold a plurality of optical fibres (one for each lens). The middle plate 420 is parallel to the top plate 410 and positioned at a distance D defined by the focal lens of the arrays of lenses. The fibres are arranged so that each lens is optically aligned with its corresponding optical fibre. For instance, the lens 411 is optically aligned with the optical fibre 421, so that an electromagnetic radiation received by the lens 411 is focused into the optical fibre 421. The plates 410, 420 and 430 are held together via members Ml, M2, M3 and M4. Together the plates 410,420 and 430 and the members Ml, M2 and M3 form a mounting frame. Figure 5 is a cross section of a second exemplary cell. The cell 500 is similar to the cell 400 of figure 4, except that in this embodiment the array of lenses is integrally formed into the top plate 510. The middle plate 520 and the bottom plate 530 are the same as the plates 420 and 430 of figure 4. Figure 6 is a cross section of a third exemplary cell. The cell 600 is similar to the cell 400 of figure 4, however in this embodiment each lens is coupled to its corresponding optical fibre via a coupling channel. For instance, the lens 611 is coupled to the optical fibre 621 via the coupling channel 641. The internal surface of the coupling channels may be coated with a reflective coating. In this example the coupling channels have a conical shape, the tip of which being attached to middle plate 620. Figure 7 is a cross section of a fourth exemplary cell. The cell 700 is similar to the cell 400 of figure 4, however in this embodiment the cell includes a set of secondary lenses, also referred to as input lenses. An input lens is located at the input end of each optical fibre. The input lens may be used to obtain a smaller focal point, to improve optical concentration and optical coupling into the optical fibre. For instance, the input of the optical fibre 721 is provided with the input lens 751. The input lenses may be attached onto the surface of the middle pate 720. The incoming light changes direction during the course of the day. The cells may also be modified in order to adjust the optical coupling to maintain the desired optical coupling. Below are some examples of cells provided with an optical steering functionality. Figure 8 is a cross section of a fifth exemplary cell. The cell 800 is similar to the cell 600 of figure 6, however in this embodiment the middle plate 820 is provided with a set of actuators 822 and 824 adapted to translate the plate along to translation axis 805 in the plane of the middle plate 820. The plates 810, 820 and 830 are attached together via flexible members Ml',M2’,M3’, M4’ so that during translation of the plate 820, the top and bottom plates 810 and 830 remain fixed. The actuators may be controlled by the controller 190 described in figure 1. Figure 9 is a cross section of a sixth exemplary cell. The cell 900 is similar to the cell 400 of figure 4, however in this embodiment a plurality of optical steerers is provided between the array of lenses and the optical fibers. For instance, the optical steerer 941 is provided between the lens 911 and the optical fiber 921. A single steerer is shown for clarity but multiple steerer would be provided. The optical steerer may be an optical element such as a lens or a mirror. In operation the optical steerer may be adjusted to improve optical coupling depending on the orientation of the incoming radiation on the array of lenses. The adjustment would depend on the nature of the optical steerer. For instance, if the optical steerer is a lens this may include moving a position of the lens, for instance translating the lens to improve optical coupling. Figure 10 is a cross section of an umbilical cable. The umbilical 1000 contains a plurality of optical fibers also referred to as fiber cores. In this example the fibers are arranged in a hexagonal configuration. It will be appreciated that other layouts may be considered. The fibres include the optical fibres coming from each cell and carrying an optical beam / signal. The umbilical may also include electrical wires for carrying an electrical signal. When provided, the electrical wires can be used to implement some safety features. The number of optical fibres in the umbilical may vary. In this example the umbilical 1000 includes 100 optical fibres labelled 1010 and 10 electrical wires labelled 1020. The umbilical 1000 also includes an outer sheath or conduit 1030. The outer sheath may be armored or reinforced. This can be achieved using Kevlar. The umbilical may be provided with connectors at either end to allow easy connection between the pane connector and the external element (for instance optical heater). The size of the optical fibres may be selected based on the size of the cells making the whole panel. In the above example a panel having a surface of Im2 is considered. The panel is made of 100 lOmmxlOmm cells, each with 100 micro-concentrators. Each cell has a collimator or manifold to terminate in 100 separate optical fibres gathered inside the umbilical. Each fiber in the umbilical gets supplied by its own separate cell. Each optical fibre will carry on optical power that will depend on the size of the cell, for instance 10W. Having many separate optical fibers (for instance a 100 or more) has the benefit of mechanical flexibility, as fibers can then slide over each other in the bundle when the umbilical is bent or twisted. This also increases robustness, provides a level of redundancy and increases pulling strength. Maximum fiber bend radius is an important parameter for fiber, as if bent too much light can escape, hence heavily impacting efficiency, or in extreme cases cause a safety hazard. The bend radius as defined by the American National Standards Institute (ANSI), will depend on various factors including the wavelength of light, pulling tension, tensile load, cladding material, type of fiber, cables outside diameter. The length of the umbilical will depend on the application. For installing the system on a house, the umbilical may have a length of at least 10 meters, for instance a length ranging between about 10m to about 50m. This would allow the umbilical fibre to extend from the roof of a building to a cylinder water tank on a ground floor. Alternatively, the umbilical maybe shorter, as desirable if the tank can be placed near the roof, or an external wall, when the panel can be wall mounted, this is the situation more likely when the system is used to heat a buffer tank for air source heat pumps or a pre-heater for warming water before it enters the main cylinder tank. Figure 11 is an example implementation of a sun-tracking architecture for use with the collector of figure 1 or 2. The electro-mechanical system 1100 includes a sensor / detector 1180 coupled to the controller 1190 and two actuator 1105a, 1105b implemented in a feedback loop. The actuators may be implemented as a pair of servomotors for controlling a position of the cell along a vertical axis (up / down position of the cell) and a position of the cell along a horizontal axis (left / right position of the cell). In operation, the sensor / detector 1180 detects a signal indicative of the direction of illumination from the sun. The controller 1190 includes a processor configured to run an algorithm that receives data from the detector 1180 and provides control signals to the servomotors. Each cell may be controlled individually. Alternatively, several cells, or all the cells may be controlled at once. The detector / sensor may be an optical sensor mounted on the panel and used as a target. For instance, the detector / sensor 1180 may be a photosensor with four quadrants QI, Q2, Q3 and Q4 used as a target for adjusting the inclination of the cells. In this implementation, when the light received by the detector is split equally between the four quadrants, then the detector and the cells are considered aligned in the best position, hence facing the sun. Different implementations could be envisaged. A camera could be mounted on each cell for instance looking down a fiber or looking up. The camera may be designed to identify the sun spot position and guide the servomotors. The camera may be adapted to run a low-bandwidth vision detection algorithm or a trained machine learning algorithm for identifying the sun spot. Additional functionalities may be added for cloudy conditions or night time power down. Tiny cameras of millimeter size containing millions of pixels are commercially available. Alternatively, a photo resistor or a photodiode may be used. For instance, a photo resistor or a photodiode may be mounted on each cell and coupled to a processor. For example, a 4-Quadrant Silicon PIN Photodiode (K857PE from Vishay) could be used. The quad diode outputs 4 parallel power (current) readings from a sensor optimized for 850m. It can then be used to beam steer the panel in conjunction with a digital sensor controller. Different processors may be selected depending on the processing power required. In yet another example a photo transistor may be used. Figure 12 is a diagram of a steering structure for steering a lens. Another way of performing the sun tracking functionality is by changing the position of the lens based on the heat and / or the light flux received by the sun. In the structure 1200, the lens 1210 is held by a structure 1220 formed of legs 1221, 1222 and 1223. The structure 1220 is designed to be heat sensitive and / or photosensitive, such that when the structure changes its form based on an amount of heat or an amount of light received, or a combination of both. Different materials may be selected based for instance on their thermal expansion coefficients. Figure 13 is a diagram of a heating system. The heating system 1300 includes a collector such as the collector described above with reference to figures 1 to 12, coupled to a heater via the umbilical. The heater is implemented as an optical heating element. The heater is located in a tank for increasing the temperature of the fluid stored in it. For instance, the tank may be a water tank. When provided, the electrical wires can be used to implement a safety feature. For instance, a safety loop may be implemented. If the loop is broken (open circuit) the panel shuts off. This could happen for example if the umbilical is accidentally cut, disconnected from the panel, or unplugged from the heating element. An over temperature conductor may be used to deactivate the system when a threshold temperature is reached. For instance, the temperature conductor may break down when the threshold temperature is reached. Upon detection of an open loop circuit, a safety signal may be generated by the controller to disable the collector, for instance by covering the panel with a light-blind or by steering the collector away from the sun. The safety module of the controller may be configured to receive an electric signal traveling inside the umbilical. When the electric signal is not received, an open circuit is detected, and the safety module generates the safety signal. Figure 14 is a diagram showing the collector of figure 2A coupled to an optical heating element or optical heater. The optical heater includes a housing adapted to receive the umbilical cable. The optical heater may be provided with fastening means for attaching the optical heater to a chamber for receiving a liquid or substance to be heated. Figure 15 is a diagram of an optical heater provided with a transparent heating target. The optical heater 1500 includes an optical cable 1510. The optical cable 1510 may be an umbilical cable comprising a plurality of optical fibres. The umbilical cable 1510 is designed to receive light from an optical source, such as the sun light collector described above. The optional heating target 1520 is coupled to an end of the cable 1510. The housing 1530 encloses a portion of the cable and the heating target 1520. The housing 1530 has a cylindrical shape that extends between a first end and a second end. The housing 1530 is also tubular, hence forming a cavity for receiving the cable 1510, or the optical fibers 1512 within it. In this example the housing has a first portion 1531, a second portion 1532, also referred to as end cap, and a flange 1533 for securing the optical heater within an external chamber (not shown). The flange 1533 may be replaced by other fastening means. For instance, the external chamber (usually a cylinder or buffer tank, vat or still) may be provided with an opening designed to receive the optical heater. This opening is commonly formed by way of a tank connector and threaded differently depending on country, application and tank size and normally comes pre-installed with the chamber or tank. For example, for UK domestic heating 2.1 / 4 BSP is the standard tank connector. The flange 1533 may be designed to plug or screw into onto the opening so that the waterproof housing 1530 is kept within the chamber and securely attached to the chamber wall. This flange 1533 has several purposes. Firstly, it provides the means for a detachable yet waterproof seal between the optical cable and the liquid in the tank. It provides the possibility of an adapter between several thread types, thus allowing one model of optical element or tank to be sold to different markets and applications just by changing the flange. It provides a thermal insulator between the tank, element and outside world and can be further insulated with an insulating material coating surrounding. It could also act as a constituent of a safety mechanism whereby if the flange is not engaged within the chamber opening or / and housing within the flange, a safety circuit would be broken or incomplete or otherwise detect the lack of engagement, and this would prevent the optical source from producing light. A connector 1540, also referred to as cable gland, may be used to connect the cable 1510 to the housing 1530. The cable 1510 is preferably a continuous cable, as otherwise any joining of the cable would create optical losses, hence reducing efficiency. The cable gland 1540 has several functions. The umbilical cable 1510 may be provided with a protective sheath such as Kevlar or armored wire . In this case the umbilical cable 110 is wider than just the optical fibres within it. The cable gland 1540 marks the point at which this protective sheath stops. The cable gland 1540 may also be used to seal the optical fibers to the end of the protective sheath to prevent dislodgement. The content 1512 of the umbilical (that is the optical fibers and any electric wire that may also be providedjcontinues within the housing 1530 up to the region in which the heating target 1520 is provided. This reduces the overall diameter of the housing that would be required to reduce cost and reduces manufacturing cost. It also provides a detachable holder for attaching or removing the aligned umbilical into the housing whilst securing it, whilst not having to drain down or remove water from the tank (which may be under pressure) for servicing or maintenance. This detachable aspect of the optical heater provides several advantages. When the flange 1533 is screwed into the tank it can be done whilst allowing the cable to be inserted later without the rotational screwing motion breaking the fibres through twisting. The cable gland 1540 may also contain an upper additional threaded sealing nut (not shown) that secures into the housing flange 1533, for tightening down the umbilical post insertion. The sealing nut acts as a protecting seal against moisture and dust ingress that might otherwise fall into the housing cavity. It also acts as a light blocker and secondary thermal insulator, preventing light and heat loss towards the opening or umbilical or upwards into the umbilical itself. It also acts as a second aspect of a safety mechanism whereby should the gland 1540 not be properly or fully engaged within the housing, a safety circuit would be broken or incomplete or otherwise detected, and this would prevent the optical source from producing light. The gland 1540 (and sealing nut) may be pre-formed and shipped with the umbilical 1510 and target assembly so it best fits tightly around the individual multiple optical fibre strands. The gland 1540 may have a detachable locking and engagement mechanism to secure firmly to the housing 1530, with minimal twisting and stress, so called “zero insertion force” connection. The first end of the housing may be provided with external and internal threads for receiving the flange 1533, the cable gland 1540 and the sealing nut. In this example the heating target 1520 and the end cap 1532 are transparent. For instance, they may be made of glass or plastic . The heating target 120 is located at the end of the housing 1530 within the end cap 132, such that when engaged with the end cap 1532 the optical heater can be placed deeper within the tank to allow the heat to best permeate into the middle region of the volume of liquid. The transparent target 1520 then acts as a first dispersive lens, and the end cap 1532 a second, allowing the optical energy to project into the liquid rather than being absorbed by elements of the optical heater. This prevents excessive heat generation within the optical heater itself and instead disperses the energy more evenly into the liquid away from the heater housing 1530. The heating target 1520 also provides a solid and more robust end to the fibres 1512 of the umbilical cable 1510, that may have to be pushed through a building during the installation, potentially protected with a cover at installation time. The open end of the umbilical cable is directed toward the transparent target 1520 to allow the light emission, and thus the target 1520 acts as a lens to emanate the light into the liquid. Similarly, the end cap 1532 may also act or be designed as a lens. In order to have most effect and to minimize the chance of the cable not being completely inserted, the end of the umbilical and the heating target 1520 may be designed with a mating profile. Several mating profiles could be envisaged, including a wedge profile. The target 1520 and the end cap 1532 may be positioned with a pre-determined distance between each other. When 1520 and 1532 act as lenses, the pre-determined distance may be defined based on the focal lens of each lens so as to form a lens pair. The distance between the gland 1540 and target 1520 and internal distance with the element housing 1531 to the target internal face maybe fixed as the target and cap act as a pair of optical lenses designed with certain focal length and can be made to touch or offset depending on the design. The end of the fibres 1512 could be in contact with the target 1520, but it in some applications the fibers are only directionally aligned with and point towards the target 1520 and the end cap 1532. The transparent heating cap 1532 is in contact with the first portion 1531 of the housing. For instance, the end cap 1532 may be bounded to the first portion 1531 via a seal or with a layer of glue to make a water tight connection. The first portion 1531 of the waterproof housing may be made of a metal or a metal alloy material. For instance, brass may be used due to its workable yet corrosive resistant properties. The second portion 1532 may be made of a transparent material such as glass or plastic. This arrangement provides a detachable optical heater that can be connected to a liquid chamber for efficient optical to thermal energy conversion. As mentioned above the optical target is optional and the optical heater could be implemented without it. In this scenario light coming out of the optical fibres of the umbilical cable would be directly received by the end cap 1532. In an alternative implementation, an optical heater may be provided with a non-transparent heating target. In this case the housing may be formed in one part. A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the disclosure. Accordingly, the above description of the specific embodiments is made by way of example only and not for the purposes of limitation. It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.

Claims

1. A collector for collecting electromagnetic radiations from the sun, the collector comprising a plurality of cells , wherein each cell comprises an optical arrangement and an optical fibre, the optical arrangement being adapted to couple an incoming radiation into the optical fibre; and wherein the optical fibres are combined in a cable.

2. The collector as claimed in claim 1, comprising a connector formed of a plurality of optical fibre combiners.

3. The collector as claimed in claim 2, wherein each optical fibre combiner has an input for receiving a plurality of optical fibres from a single cell, and an output provided with a single output optical fibre; and wherein the output optical fibres of each optical fibre combiner are combined in the cable.

4. The collector as claimed in any of the preceding claims, wherein each cell is orientable, so that an outer surface of the cell projects along a desired direction.

5. The collector as claimed in any of the preceding claims, comprising a mechanical arrangement adapted to adjust an orientation of one or more cells.

6. The collector as claimed in any of the preceding claims, wherein one or more cells comprise an actuator configured to adjust a position of the optical fibre or a position of an optical steerer in the cell.

7. The collector as claimed in any claim 5 or 6, comprising a controllerconfigured to generate one or more control signals to control at least one of the mechanical arrangement and the actuator.

8. The collector as claimed in claim 7, comprising one or more sensorscoupled to the controller.

9. The collector as claimed in claim 8, wherein the controller is configured to receive sensor data from the sensor, and to generate the one or more control signals based on the sensor data.

10. The collector as claimed in any of the claims 7 to 9, wherein the controller comprises a safety module configured to generate a safety signal upon detection of a malfunction.

11. The collector as claimed in any of the preceding claims, wherein the optical arrangement is configured to focus the incoming radiation into the optical fibre.

12. The collector as claimed in any of the preceding claims, wherein the optical arrangement comprises one or more lenses.

13. The collector as claimed in claim 12, wherein the optical arrangement comprises an array of lenses or an array of microlenses.

14. The collector as claimed in any of the preceding claims, wherein each lens is coupled to the optical fibre via a coupling channel.

15. The collector as claimed in claim 14, wherein the coupling channel has a conical shape.

16. The collector as claimed in claim 12, wherein one or more cells comprise a set of secondary lenses, wherein a secondary lens is located at an input end of each optical fibre.

17. The collector as claimed in any of the preceding claims, wherein the cells comprise a frame having a first mount holding the optical arrangement and a second mound holding the optical fibres.

18. The collector as claimed in claim 17, wherein the second mount is movable along a translation axis with respect to the first mount.

19. The collector as claimed in claim 17, comprising a plurality of optical steerers provided between the optical arrangement and the optical fibres.

20. The collector as claimed in any of the preceding claims, wherein the cable comprises one or more electric wires.

21. A system comprising a collector as claimed in any of the preceding claims, coupled to an external element.

22. The system as claimed in claim 21, wherein the external element comprises an optical heater.

23. The system as claimed in claim 21, wherein the optical heater comprises a housing adapted to receive the cable; and a fastening means configured to attach the optical heater to a chamber for receiving a liquid or substance to be heated.

24. The system as claimed in claim 22 or 23 , comprising a chamber for receiving a liquid or substance to be heated, and wherein the24optical heater is located in the chamber to heat the liquid or substance.

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