Pyranometer

Abstract

A pyranometer comprises a thermoelectric sensor 504, perhaps a Peltier device, and an energy-reducing element to reduce solar energy reaching the sensor so as to lower power consumption requirements.

Description

FIELD OF THE INVENTION The present disclosure relates to a pyranometer or radiometer for measuring solar irradiance. BACKGROUND TO THE INVENTION The past few decades have seen prolific research and development in the realm of renewable energy. Solar energy-based solutions have become more and more prevalent, and the measurement of solar radiation energy requires precise measuring instruments. The use of these instruments is not limited to photovoltaic devices but is also required in different domains of atmospheric science. The solar spectrum contains radiation in the range of 0.15 pm to 4.0 pm. Above 96 % of the sun's energy lies in the spectrum range of 0.27 pm -2.6 pm. Radiation that lies in this range is known as short-wave radiation. Solar energy is beneficial for different applications, and hence its actual measurement is equally important. Measuring light intensity through a simple photodiode or photovoltaic cell is not a viable solution, because measuring the light intensity is not the only requirement to be met in the industry. The energy carried by solar radiation is also very important and this exacerbates the complexity of the problem, because this energy is difficult to measure accurately. The solar radiation from the sun does not come directly to the earth. Due to the impacts of clouds, particles in the atmosphere, dust, and other similar factors, the solar irradiance on all areas of the surface of the earth is not the same. Mainly, solar irradiance can be divided into direct and diffused components. Both components are energy carriers, and hence the measurement of both is equally important. Another factor that exacerbates the problem complexity is that the solar irradiance changes throughout the day, ranging from 0 kW / m2 at night to around 1 kW / m2 during the day. Hence time, weather conditions, and geological location are factors that can impact solar irradiance received on the surface of the earth. Even though solar-dependent devices have gone through rapid development in the past decades, a significant gap is still there that needs to be filled, especially when the known devices or systems’ cost, speed, and accuracy are factors that need optimisation at the same time. A pyranometer is a device that can measure direct and diffused solar irradiance. To date three main types of pyranometers have been proposed: thermoelectric-based pyranometers, photodiode-based pyranometers, and photovoltaic-based pyranometers. The operational principle and the spectral response of all types of pyranometers are different. Generally, pyranometers do not need any voltage source for their operation. But to increase the device accuracy and response-time, newer pyranometers require voltage sources. The photodiode and photovoltaic-based pyranometers have high response-time but they cover a small radiation spectral area. The thermoelectric-based pyranometers are more accurate and cover a large radiation spectral area, buttheir response time is low, and they require an external voltage source. A pyranometer device is disclosed in WO2009068710A1, which discloses of detection, control, a thermostat, and a transmission system. The device is low-cost and has a photodiode as a basic sensing unit. A Teflon diffuser was also introduced to protect the photodiode from UV radiation, rain, and weather conditions. A thermoelectric-based solution is disclosed in WO2017010022A1. The device is fast and more stable in extreme environmental conditions. The device mainly contains a silicon base thermopile sensor, a temperature compensation circuit, a diffusion member, and has a window material. The sensor is hermetically sealed in a CAN package and filled with gas. The temperature compensation circuit was used to correct the output signal of the thermal sensor. A double window pyranometer is disclosed in WO2016140565A1. The thermally conductive windows are selected to have relatively high transmission coefficients. An internal heating device is also disclosed in the housing to compensate for the effect of ice, dew, and moisture. The extension to the double window is disclosed in EP3265764A1. The heated air is blown in a space below the outer window by ventilator power to decrease the dew and extreme weather conditions that affect the pyranometer's normal working. A pyranometer with three thermal sensors is disclosed in US3876880A. The internal cooling system was introduced to compensate for the drift of filters. A system with the combination of pyrheliometer and pyranometers is disclosed in the US010598755B2. This system can measure direct normal irradiance, diffused horizontal irradiance, and global horizontal irradiance. A problem with known Peltier devices is their unstable response. After some time, the Peltier device tries to decrease a temperature difference required for its operation. In traditional pyranometers, an external heating device maintains the temperature difference, which also contributes to a disturbance in the natural or overall temperature inside the pyranometer. The devices described above are either designed to cover a small solar spectrum or require heating or similar temperature compensation mechanisms, which causes temperature offset issues to arise. The temperature compensation systems demand high power requirements as well. Another problem encountered in photovoltaic devices is that most photovoltaic materials have poor light coupling. The applicant considers there to be room for improvement. The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that the discussion is not an acknowledgment or admission that any of the material referred to was part of the common general knowledge in the art as at the priority date of the application. SUMMARY OF THE INVENTION In accordance with an aspect of the present disclosure there is provided a pyranometer comprising: a first thermoelectric sensor and a second thermoelectric sensor that are arranged for sensing solar radiation; and a temperature controlling device arranged to control an operating temperature of the first and second thermoelectric sensors in use. The first and second thermoelectric sensors may be Peltier devices. The first and second thermoelectric sensors may be stacked on top of one another. The temperature controlling device may be interposed between the thermoelectric sensors. The pyranometer may include an inverted dome having the first and second thermoelectric sensors installed thereto. The first and second thermoelectric sensors may be installed or supported by one or more supports to the inverted dome. The first and second thermoelectric sensors may be held inside a housing. The housing may have a reflective outer surface. The inverted dome may have a reflective inner surface. At least one of the first and second thermoelectric sensors may be arranged to measure direct solar irradiance. At least one of the first and second thermoelectric sensors may be arranged to measure diffused solar irradiance. The pyranometer may be arranged to distinguish between direct and diffused solar irradiance. The pyranometer may include a level monitoring device arranged to monitor a level of one or more components of the pyranometer in use. In accordance with another aspect of the present disclosure there is provided a pyranometer comprising at least one thermoelectric sensor arranged for sensing solar radiation and an energy reducing element arranged to reduce the solar energy that reaches the thermoelectric sensor so as to lower power consumption requirements of the pyranometer in use. The energy reducing element may be an optic configured to split an incident light beam into a plurality of beams having different energies. The optic may be positioned so that the split beams at least partially strike the thermoelectric sensor. The optic may be a prism. The optic may be arranged such that the split beams with different energies strike different areas of the thermoelectric sensor. The thermoelectric sensor may be a Peltier device. The energy reducing element may be a penetrable cover which is spaced apart from the thermoelectric sensor and which may be moveable relative to the thermoelectric sensor so as to selectively control the amount of radiation incident on the thermoelectric sensor. The penetrable cover may be moveable transversely relative to the thermoelectric sensor. The penetrable cover may be a filter arranged to selectively allow or inhibit light from passing therethrough. The penetrable cover may have a pattern thereon, the pattern including a plurality of transparent areas and a plurality of areas that inhibit transparency or that are less transparent. The penetrable cover may be a chess-pattern or chequered cover with lighter and darker squares thereon. The pyranometer may include a moving device arranged to move the thermoelectric sensor relative to the energy reducing element or vice versa. The moving device may be provided a moveable thermoelectric sensor assembly. A body of the sensor may be positioned on a pivot so as to be moveable. The sensor body may have a first end and a second end, the ends positioned at opposing sides of the pivot. At least one of the first and second ends may be operatively moveable about the pivot by way an electromagnetic actuator. The electromagnetic actuator may include an electromagnet which may be energized by a power source. At least one of the first and second ends of the sensor body may include magnetic material which is either repelled by or drawn towards the electromagnet to move the sensor body. The sensor body may be positioned on the pivot so that a first part of the body has a first weight and a second part of the body has a second weight which is greater than the first weight so that the second part is naturally pivoted lower than the first part under the influence of gravity. The electromagnetic actuator may be configured to move the sensor under the effects of applied electric power and gravity. The energy reducing element may be provided by an optical component such as a diffraction grating. The diffraction grating may have one or more slits that allow light to pass therethrough. The diffraction grating may be configured to manipulate incident light by way of beam steering. The pyranometer may be connected to one or more solar cells. One or more of the solar cells may be arranged to provide electric power for the beam steering of the diffraction grating. The pyranometer may include a thermal isolation layer of phase change material at an interior of the pyranometer. The pyranometer may include a desiccant to reduce or remove moisture inside the pyranometer. The pyranometer may be in data communication with a processing unit. The pyranometer may include an error signal generation component arranged to generate an error signal indicative of dust or fault in any of the components of the pyranometer. The pyranometer may have one or more transparent domes positioned above the sensor and energy reducing element. Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a three-dimensional view of an exemplary thermoelectric sensor such as a Peltier device placed above a heating device according to aspects of the present disclosure; Figure 2 is a three-dimensional view of an exemplary stack of two thermoelectric sensors according to aspects of the present disclosure; Figure 3 is a three-dimensional view of an example embodiment of two thermoelectric sensors and a layer of phase change material interposed between the two thermoelectric sensors; Figure 4 is a schematic diagram which illustrates an exemplary inverted dome pyranometer which may be arranged to measure and differentiate between direct and diffuse solar irradiance according to aspects of the present disclosure; Figure 5 is a schematic diagram of an exemplary arrangement of a cylindrical housing for thermoelectric sensors that may form part of the inverted dome pyranometer of Figure 4; Figure 6 is a plan view of the inverted dome pyranometer of Figure 4; Figure 7 is a three-dimensional view of an exemplary chess pattern or chequered cover that may be placed above a thermoelectric sensor according to aspects of the present disclosure; Figure 8 illustrates plan views of exemplary changes in an exposed area of the thermoelectric sensor with an exemplary movement of the chequered cover of Figure 7; Figure 9 is a schematic diagram of an exemplary prism-based pyranometer, illustrating a prism above a thermoelectric sensor according to aspects of the present disclosure; Figure 10 is a schematic diagram illustrating an exemplary working principle of the prismbased pyranometer of Figure 9; Figure 11 is a schematic diagram of an exemplary mechanical assembly that may be arranged to move a thermoelectric sensor or Peltier under the effect of gravity, according to aspects of the present disclosure; Figure 12 is a graph that illustrates normalized behaviour of a prism-based pyranometer and a traditional heating-based pyranometer; Figure 13 is a schematic diagram of an exemplary diffraction grating slotted structure which may allow complete solar spectrum to pass therethrough; Figure 14 is a schematic diagram of an exemplary thermoelectric-based pyranometer in which a diffraction grating is exploited to operate the thermoelectric sensor; and Figure 15 is a top view of an arrangement of exemplary solar cells associated with the pyranometer of Figure 14. DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS Embodiments of a pyranometer, also termed a radiometer or actinometer are disclosed. The present disclosure is related to solar irradiance measuring by pyranometer, which may have one or more thermoelectric sensors. Aspects of the present disclosure may implement thermoelectric sensors as a primary sensing device. In the various embodiments of the present disclosure, one or more thermoelectric sensors may be used, and one or more of these thermoelectric sensors may be a Peltier device. The different arrangements disclosed herein may increase the accuracy and sensitivity of the pyranometer device. The basic working principle of the majority of thermoelectric pyranometers is the same. One side of the thermoelectric sensor is kept black, preferably allowing maximum radiation absorption. The thermoelectric sensor usually requires an external potential for its operation, but embodiments are possible that do not require external potential. Other components of the pyranometer may include a heating device, a single or double dome which may be transparent, a desiccant, and a set of connectors. The pyranometer is a device that may be configured to measure both direct and diffused components of solar irradiance, which can give a fair estimation of the solar irradiance available at an instant of time. In embodiments of the present disclosure, the pyranometer may include an energy reducing element arranged to reduce the solar energy that reaches the thermoelectric sensor(s), so as to lower power consumption requirements of the pyranometer in use. The energy reducing element may be a penetrable cover, a diffraction grating, or an optic such as a prism. The energy reducing element may obviate the need for a heating device. Aspects of the present disclosure extends to a pyranometer having at least one or two thermoelectric sensors. The pyranometer may optionally have a heating device for controlling a temperature of the thermoelectric sensor(s). The pyranometer may include an inverted dome and an energy reducing element such as the penetrable cover, diffraction grating or optic may be spaced from the one or more sensors, so as to reduce an amount of radiation incident on the sensor(s). The pyranometer may include a moving device, such as an electromagnetic actuator, or other mechanical or electromechanical moving device for moving one or more components of the pyranometer. For example, the moving device may be arranged to move the one or more sensors relative to the energy reducing element, or the moving device may be arranged to move the energy reducing element relative to the sensor(s). The moving device may be arranged to increase or decrease the amount of energy received by the one or more sensors in use. As will be described in greater detail below, the pyranometer may include a processor and a memory component which may provide one or more of a controller, a data logger and an error signal generation component. The pyranometer may include one or more of a comparing component, dust detector, a fault detector, and a transmitter / receiver. The pyranometer may include a power source, which in some embodiments may be provided by one or more photovoltaic cells, or the like. An example embodiment (100) of a thermoelectric sensor (102) is shown in Figure 1. In this exemplary embodiment (100), the thermoelectric sensor (102) includes a Peltier device (104) which is placed on a temperature regulating or temperature controlling device, such as a heating device (106) (ora cooling device) which keeps the temperature of the sensor (102) in a suitable range. The heating or cooling device may be an electric heating or cooling device. The temperature controlling device (106) may be arranged to maintain the temperature of the sensor (102) in a selected operating range of the Peltier device (104). A top surface (109) of the thermoelectric sensor (102) is coated with a black coloured material which may help to absorb as much as possible, preferably maximum, radiation. It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. The embodiment (100) may be used as a Pyranometer. In Figure 2 another exemplary embodiment (200) of a thermoelectric sensor arrangement is shown. In the present embodiment (200), first and second Peltier devices (202, 204) are utilized as first and second thermoelectric sensors, and these may optionally also be used as temperature controlling device(s). The first and second thermoelectric sensors (202, 204) may be placed or stacked over, or on top of, each other. In the present embodiment, the first Peltier device (202) may be an upper thermoelectric sensor, while the second Peltier device (204) may function as a temperature controlling device. A top surface (209) of at least one of the thermoelectric sensors (202, 204) is coated with black coloured material, which may enhance or improve radiation absorption. The second Peltier device (204) may be a lower thermoelectric sensor, and it may be used as a temperature controlling device, ora heating device. In other words, the second Peltier device (204) may be used to maintain a temperature of a lower surface of the first Peltier device (209). The arrangement shown in Figure 2 may provide more flexibility of operation, especially in extreme weather conditions. It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. The embodiment (200) may be used as a Pyranometer. A processing unit (not shown) may be used to control the two thermoelectric sensors (202, 204) so as to control electrical potential of one of the sensors (used as a temperature controlling device) to regulate temperature, and to process a received signal from the other sensor which may sense solar radiation. The first Peltier device (202) may be used as a thermoelectric sensor, and it can be excited or energized by solar radiation so as to generate a voltage that can be measured by the controller or processing unit. The second Peltier device (204) may require continuous electrical power to provide heating or temperature control as described above. The second Peltier device (204) shown in Figure 2 may have relatively high power requirements. The first Peltier device (202) may generally have a hot and a cold surface. When energized by the solar radiation, the Peltier device may tend to transfer heat from the hot side to the cold side through conduction and / or convection. This may cause a temperature difference between the hot and cold sides to become less and less, which could lead to instability of the device in severe cases. These problems may be solved or alleviated by introducing a phase change material (207) between two thermoelectric sensors such as Peltier devices (203, 205), as shown in the exemplary embodiment (201) shown in Figure 3. The embodiment (201) may be used as a Pyranometer. The phase change material (207) may be capable of changing its phase according to the temperature. The process of phase changing may require some time and hence it may work against abrupt changes in temperature, so as to stabilise the device with its Peltier device(s) or sensor(s). In the present embodiment, the phase change material (207) may be interposed between the first and second thermoelectric sensors or Peltier devices. Embodiments of the present disclosure may provide more accurate measurements in extreme weather conditions. For example, one of the Peltier devices may be used in two modes, i.e. as a heating device or as a cooling device, by changing the polarity of the electrical potential applied thereon. Hence, the temperature of the pyranometer may be more accurately controlled, even if the prevailing weather conditions are very hot or very cold. In Figure 4 is shown a schematic representation of an exemplary embodiment (300) of an inverted dome pyranometer arrangement. The inverted dome pyranometer may be capable of measuring direct solar irradiance as well as diffused solar irradiance, and it may be arranged to differentiate between direct and diffused solar irradiance. The pyranometer (300) may include a controller (350) having a processor (352) and a memory (354). The controller (350) may further include a comparing component (356) which may be capable of differentiating between direct and diffused solar irradiance sensed by the pyranometer. A result of the comparison may be transmitted by a transmitting / receiving component (358) to another computing device, for example to an external datalogger for further processing. In the embodiment (300) of Figure 4, an inverted dome (306) has three levelling screws (312, 314, 316) which may help to adjust the pyranometer's level. It will be appreciated that other adjustable support devices may be used instead of levelling screws. One or more level gauges (308, 310) or level monitoring device(s) may be used to monitor the level of the pyranometer, or a level indication device may be provided. The level of the pyranometer may be adjusted automatically. In the exemplary embodiment, two level gauges (308, 310) may provide two-dimensional level adjustment and / or feedback and / or automatic adjustment or control. A first level gauge (308) may provide level information or feedback along a first axis, and a second level gauge (310) may provide level information or feedback along a second axis. The first and second axes may for example be orthogonal. In the present embodiment, the pyranometer arrangement may include a sensing unit (304). Optionally, the controller (350) may form part of the sensing unit (304). It will be appreciated that the present embodiment may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. An example embodiment of the sensing unit (304) is shown diagrammatically in Figure 5, and it may include a first and a second thermoelectric sensor (303, 307) with a temperature-regulating or heating device (305) preferably sandwiched or interposed between the thermoelectric sensors (303, 307). A single heating device may be used together with the two thermoelectric sensors. The heating or cooling device (305) may be arranged to regulate the temperature of the first and second thermoelectric sensors (303, 307) (e.g. so as to regulate their temperatures collectively). As before, the thermoelectric sensors may be Peltier devices. The sensing unit (304) may further include a housing (309) for the thermoelectric sensors (303, 307) as shown diagrammatically in Figure 5. Readings or measurements of the first and second thermoelectric sensors (303, 307) may be received by the controller (350). The second thermoelectric sensor (307) may be a lower thermoelectric sensor, and its reading may be indicative of diffused light beams. The first thermoelectric sensor (303) may be an upper thermoelectric sensor, and its reading may be indicative of direct and diffused light beams. The comparing component (356) of the controller (350) may be arranged to compare the received readings from the first and second thermoelectric sensors (e.g. by subtracting them from one another and obtaining a difference between them), so as to calculate the direct and diffused components of radiation sensed by the pyranometer (300). Figure 6 shows an exemplary top view of the inverted dome pyranometer arrangement (300), illustrating the inverted dome (306) by broken lines. The dome may have the first and second Peltier devices or thermoelectric sensors installed thereto, thereon, or therein. The housing (309) may be cylindrical, but other shapes may also be possible, such as spheres, oval shapes, rounded shapes, oblong shapes, tetrahedron shapes, polyhedral shapes etc. An outer surface of the housing (309) may be reflective, or at least partially reflective, which may help one or more beam(s) of light to focus on a lower one (307) of the Peltier devices. For example, a lateral circumferential surface of the housing (309) may be reflective, so as to cause more light beams to be reflected to an inner surface of the inverted dome (306). The inner surface of the inverted dome (306) may also be reflective, so as to focus light on the lower Peltier device (307). Hence, the reflective outer surface of the housing (309) may facilitate more light beams to be reflected onto the lower Peltier device or thermoelectric sensor. This may facilitate a more accurate calculation of direct and diffused solar irradiance by the controller (350). One or more supports (311, 313, 315, 317), may be attached to the housing (309), so as to position, fasten and / or hold the housing (304) inside or to the inverted dome (306). In the present embodiment, four supports (311, 313, 315, 317) are used, but it will be appreciated that other arrangements, or another number of support(s) are possible. It will further be appreciated that the embodiment of Figures 4 to 6 may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. In Figure 7 is shown an example embodiment (400) of a penetrable cover (402) which may be spaced from a thermoelectric sensor such as a Peltier device (404), preferably at a distance (406) therefrom. In embodiments of the present disclosure, the penetrable cover (402) may be positioned generally above the thermoelectric sensor (404), but any orientation may be possible. The present embodiment may provide a non-invasive apparatus or method whereby the thermoelectric sensor (404) may be enabled to provide similar or even better performance without requiring a heating device, as will be described in more detail below. The penetrable cover may have a pattern thereon, the pattern including a plurality of transparent areas (or translucent areas), and a plurality of areas that inhibit transparency or that are less transparent. The penetrable cover (402) may be a chequered cover, also termed a chess pattern cover. The penetrable cover may partially allow light to pass therethrough, and partially inhibit light from passing therethrough. In the exemplary embodiment, the penetrable cover includes lighter squares or areas (e.g. transparent or at least translucent) and darker squares or areas (e.g. opaque or not transparent or only translucent to a limited extent). However, other embodiments are possible and the lighter and darker areas can be shapes other than squares, e.g. hexagons, polygons, rounded shapes, rectangles, irregular shapes, etc. The penetrable cover may be capable of increasing the efficiency of the thermoelectric sensor or Peltier device, because each area (An to Ann, see Figure 8 discussion below) of the Peltier device (404) may be exposed to light for a short interval of time by moving the penetrable cover (402) or filter in relation to the thermoelectric sensor (404). Other uniformly distributed patterns may also be used. The cover (402) may enable the thermoelectric sensor or Peltier device (404) to function well without a heating device, because the cover (402) may be moved left and right (or it may be moved transversely relative to the thermoelectric sensor (404)), so that the dark and light squares change their position relative to the Peltier device, which may result in continuous temperature differences. This movement of the penetrable cover (402) is diagrammatically illustrated by directional arrows (407) in Figure 7. It will be appreciated that the penetrable cover (402) may have any number of lighter and darker areas thereon, and the chess patterns shown in Figures 7 and 8 are for exemplary purposes. The penetrable cover (402) may also be referred to as a light filtering device or filter. It will be appreciated that the embodiment of Figures 7 and 8 may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. Figure 8 shows exemplary shadow(s) that may be cast by the chess pattern cover (407) on a top surface (409) of the Peltier device (404) or sensor of Figure 7. It will be appreciated that a plurality of penetrable covers may also be used to cast the shadow(s). A first shadow (403) and a second shadow (405) are shown. The first and second shadows may also be shaped as chess patterns (if the penetrable cover is shaped as a chess pattern of course). In the exemplary embodiment, the chess pattern shadows (403, 405) are the complement of each other, or they are inverses of one another. In a first position of the chess pattern cover (402) the first shadow (403) is cast, causing half of the top (409) surface area of the thermoelectric sensor (404) to be exposed to light, and the other half remains in the dark, or has a shadow thereon. In a second position of the penetrable cover (402), the second shadow (405) is cast, causing an unexposed area to be exposed to light and the areas that had previously received light to be covered by shadow(s) of darker areas or squares of the cover (402). In the present embodiment, the energy reducing element may thus be provided by a penetrable cover which is spaced apart from the thermoelectric sensor and which is moveable relative to the thermoelectric sensor. This may enable selective control of the amount of radiation incident on the thermoelectric sensor. The energy reducing element may obviate the need for a heating device. The method and apparatus of the chess pattern cover may provide sensing without a heating device, since the temperature of the thermoelectric sensor may be regulated by movement of the cover or filter. As half of the top surface area of the thermoelectric sensor or Peltier gets exposed to solar radiation, the efficiency may reduce to half. This can be demonstrated by the following equations: AB = ZiLi + Ajt) i e Odd,j e Even Aw Sm=l Sn=l(^mn T ^(m+lXn+l)} Odd, Tn + 1 <N, n + 1 X N Ab = Aw = At / T. Where Ab is the total area of black or dark squares, Aw is the total area of white, lighter or transparent squares, and At is the total area of all squares. The penetrable cover (402) or filter may enable a temperature of the Peltier device (404) or sensor to be regulated. In other words, an exposed area of the top surface (409) may be controlled by moving the penetrable cover (402) or filter so as to change the amount of light that falls on the top surface (409) (i.e. also controlling the amount of radiation that is received by the top surface). In the exemplary embodiment, an equal number of lighter and darker squares are used (e.g. eight lighter squares and eight darker squares in Figure 8). However, other arrangements having a different number of lighter and darker areas are possible. The efficiency of the thermoelectric sensor or Peltier device can be improved or enhanced using a prism (502) or optic as is diagrammatically illustrated in the exemplary embodiment (500) shown in Figure 9. Alternatively, the prism may be used instead of the cover or filter of Figures 7 and 8. The prism (502) may be placed at a distance (506) from the Peltier device (504) or sensor. The prism (502) may split a beam (508) of light into a plurality of beams (510, 512, 514, 516, 518, 520) of different wavelengths at different angles. Each of the plurality of split beams may carry different energies (labelled Ei to En in Figure 10) or each beam may have a unique energy. It will be appreciated that the prism-based embodiment (500) may be used together with any of the embodiments of the present disclosure, or it may implement one or more features from the other embodiments. Figure 10 shows an exemplary schematic diagram (501) demonstrating an exemplary working phenomenon or working principle of the diffraction grating, lens or prism (502) of Figure 9. The top surface area of the thermoelectric sensor (504) may be divided into small areas An, A2i-Ann (e.g. similar to the areas of the squares depicted in Figure 8). Hence, the top surface may be divided into a plurality of rows and columns when viewed from the top. Each column may receive a particular energy ranging from Ei to En, as shown in the upper diagram of Figure 10. If the distance (506) of the Peltier device or sensor from the prism (502) is changed by a small amount (e.g. if the prism is moved, or if the Peltier device or sensor is moved), then the set of energies received by each square may also change as shown in the lower diagram of Figure 10 (e.g. from Ei - En to El1 - En'). It will be appreciated that the thermoelectric sensor (504) may be moved in various ways, relative to the prism (502), or the prism (502) may be moved in various ways relative to the thermoelectric sensor (504). An example embodiment of a moving device (600) or moving mechanism by which the Peltier device or sensor may be moved is shown in Figure 11. A similar moving device may be used to move the prism or optic. The moving device may also be referred to as a mechanical assembly or thermoelectric sensor assembly for moving the Peltier device or sensor. The Peltier device (602) or sensor may be provided on a pivot or balance wheel (606). The sensor may have its body positioned on the pivot, preferably with first and second ends (610, 616) of the sensor on opposing sides of the pivot (606). The balance wheel or pivot (606) may facilitate movement of the thermoelectric sensor by providing low or minimum friction. In the example embodiment, there may be a weight difference between the first end (610) and the second end (616) of the sensor body. The weight difference may be selected so as to tilt or pivot the thermoelectric sensor (602) to one side. For example, the weight (wi) of a first part of the thermoelectric sensor (602) may be less than the weight (W2) of a second part of the thermoelectric sensor (602). In the present embodiment, the Peltier device or sensor is tilted so that its second end (616) is lower than its first end (610) as shown in Figure 11, because of the greater weight (W2) of the second part relative to the first part’s weight (wi). An angle (608) may thus be formed between the thermoelectric sensor (602) and a base or ground level (604). In the embodiment of Figure 11, an electromagnet (612) may be provided, which may repel a permanent magnet (614), which may for example be attached to, or embedded in, the thermoelectric sensor (602). The Peltier device (602) or sensor may be moved away from, or towards the electromagnet (612) by controlling the electromagnet and the extent to which it retracts or repels the permanent magnet. A moving device may thus be provided to move the thermoelectric sensor, and an example of the moving device is the electromagnetic actuator. At least one of the first and second ends (610, 616) of the thermoelectric sensor may be moved by the electromagnetic actuator. In other words, a portion of the Peltier device (602) may be moved away from the prism (502), while another portion of the Peltier device (602) may be moved towards it, while the Peltier device (602) pivots about the balance wheel (606). Exemplary movement of the thermoelectric sensor (602) is depicted by directional arrows (617) in Figure 11. It will be appreciated that the moving device or moving mechanism of Figure 11 may be used with any of the other embodiments of the present disclosure, however, some of the embodiments may function without requiring the moving mechanism. It will further be appreciated that the present embodiment (600) may include one or more features of the other embodiments of the present disclosure. It will also be appreciated that other types of moving devices may be used to move the thermoelectric sensor, such as electric motors, gears, threaded moving devices, etc. The moving device may alternatively function by moving the sensor without requiring a pivot. For example, substantially planar movement of the sensor may be achieved by a threaded moving device to raise or lower the sensor (e.g. a screw or rack and pinion arrangement with electrical motor(s)). The moving device may be arranged to move the thermoelectric sensor relative to the energy reducing element such as the prism, the diffraction grating, or the penetrable cover. The moving device may additionally, or alternatively be arranged to move the energy reducing element relative to the sensor(s). As before, the energy reducing element may obviate the need for a heating device. Figure 12 shows a graph (700) of exemplary normalized behaviour of a Peltier device with a traditional heating source and with a prism or optic. The normalized irradiance (702) is taken along the x-axis and the normalized output voltage (704) is taken along the y-axis. The normalized response of the Peltier device with a standard heating device (706) and with the prism (708) or optic shows very similar behaviour. In some embodiments, an energy reducing element in the form of a diffraction grating may be provided. An example diffraction grating (802) is shown in Figure 13. In the present embodiment, the prism (502) may be replaced with the diffraction grating (802) as shown in the example embodiment (800) depicted. Beam steering is a well-known concept in optics, and with minimal potential (804, 806), an angle of incident light beams as they pass through the diffraction grating (802) can be controlled as is diagrammatically shown in Figure 13. The LIV and IR lights can be efficiently passed through slits (809) or slots in the diffraction grating (802), and the beam steering can change the incident energy per unit area. In use, diffracted wavelengths (807) of the solar spectrum may pass through the slits (809) of the diffraction grating (802). The beam steering may effectively reduce the power requirements of the pyranometer, and it may increase the radiation range capable of being measured, in other words increasing the operational spectrum. The diffraction grating may also enable a pyranometer having no moving parts, which may further reduce power requirements, and alleviate the need for accurate movement control or careful handling that may otherwise have been necessary. It will be appreciated that the present embodiment (800) may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. It will further be appreciated that a working principle of the diffraction grating (802) may correspond to the schematic diagrams shown in Figure 10. In other words, the diffraction grating may also diffract the solar radiation into corresponding wavelengths, and each wavelength may have a corresponding energy level. The diffraction grating may be an optical component which may provide an energy reducing element. In Figure 14 is sown an exemplary embodiment of a pyranometer (900) according to aspects of the present disclosure. The pyranometer (900) may implement features of the embodiment (800) of Figure 13. The pyranometer (900) may include double domes (902, 904). These domes may be made from a transparent or translucent material such as glass, polymers, etc. The domes may also be referred to as window domes. The domes (902, 904) may be arranged to cover a 180° field of view, and to provide thermal conductivity and high wavelength transmission. A corresponding refractive index may be selected such that the maximum solar spectrum passes through the domes (902, 904). A diffraction grating (906) having a number of slits, slots or apertures may be fitted underneath the domes (902, 904). As with the embodiment of Figure 13, the varying potentials across the diffraction grating (906) may be used to control an angle of the diffraction grating, or an angle by which light passes through the diffraction grating (906). One or more photovoltaic cells (908) may be connected (910) (e.g. by cable(s)) to the diffraction grating (906). The photovoltaic cells (908) may also be connected to a processing unit, component or processor (952) of an external datalogger (950) or other electronic device. The datalogger (950) may also include a memory (954). Embodiments are possible in which the datalogger forms part of the pyranometer (900), or in which the datalogger or processing component is separate or remotely provided. A desiccant (912) may also be provided, and it may decrease or remove moisture inside the pyranometer (900). In the present embodiment, a thermoelectric sensor or Peltier device (914) is provided underneath the diffraction grating (906), and the thermoelectric sensor (914) may be inside an interior (915) of the pyranometer (900). A phase change material layer (918) may, at least partially, enclose the interior (915). The interior (915) may also have the desiccant (912) therein. The phase change material layer (918) may provide thermal isolation from the environment. A plurality of level screws or adjustable supports (920, 922, 924) may be provided for balancing the pyranometer (900) and / or for adjusting a level of the pyranometer (900). A connector port (916) may be provided to connect the pyranometer (900) to the external data logger device (950) and processing unit. The pyranometer (900) of the present embodiment may function without requiring a heating device, because the diffraction grating (900) and / or beam steering may alleviate or eliminate the need for a dedicated heating device. This may provide a simpler and more cost effective pyranometer than currently known pyranometers, without sacrificing measurement accuracy. The energy reducing element, in this case the diffraction grating, may obviate the need for a heating device. In Figure 15 is shown an exemplary top view of the pyranometer (900) of Figure 14. In the present embodiment, multiple photovoltaic cells are placed such that at least one photovoltaic cell is in the sun's direction at one time during daylight hours. The photovoltaic cells (908) may provide the electric potential for beam steering as described above and / or for other circuitry or features of the pyranometer. A collective response of the photovoltaic cells (908) can be used to measure direct and diffuse solar irradiance. Moreover, they can be used for solar beam tracking as well. For example, an electrical potential generated by each of the photovoltaic cells (908) may be compared to one another by the processor (954), so as to track the solar position at that instant in time. This may add accuracy in the measurement of direct and diffuse solar irradiance. When the difference is significantly large, an error signal may be generated and transmitted to the external (or internal) datalogger (950). The error signal may be indicative of dust accommodation or a fault in any of the components of the pyranometer (900). The pyranometer (900) may include an error signal generation component (953) which may be arranged to generate the error signal and to transmit it to the datalogger or processing unit (950). The error signal generation component (953) may include a processor (970) and a memory (972). The error signal generation component may further include a dust detector (974) which may be arranged for detecting dust, for example on one of the domes, or on the diffraction grating, or on the solar panel(s), or on the thermoelectric sensor. The fault detector (976) may be arranged for detecting faults in any one or more of the components of the pyranometer. It will be appreciated that the present embodiment (900) may be used together with any of the other embodiments of the present disclosure, or it may implement one or more features of the other embodiments. The present disclosure extends to a pyranometer (200, 201, 300) that may include a first thermoelectric sensor (202, 203, 303) and a second thermoelectric sensor (204, 205, 307) that may be arranged for sensing solar radiation. A temperature controlling device (204, 205, 307) may be arranged to control an operating temperature of the first and second thermoelectric sensors (202, 203, 204, 205, 303, 307) in use. The present disclosure may further extend to a pyranometer (100, 200, 201, 300, 400, 500, 600, 800, 900) that may include at least one thermoelectric sensor (104, 202, 203, 303, 404, 504, 602, 914) arranged for sensing solar radiation. The pyranometer may include an energy reducing element (402, 502, 600, 800, 906) that may be arranged to reduce the solar energy that reaches the thermoelectric sensor so as to lower power consumption requirements of the pyranometer in use. The present disclosure may provide a new class of low cost, highly sensitive thermoelectric pyranometer based on, e.g., diffraction grating. Embodiments of the present disclosure may provide a variety of low-cost and highly accurate thermoelectric sensor-based pyranometer arrangements, for example implementing Peltier device(s). The thermoelectric sensor, diffraction grating slits and photovoltaic cells for beam steering may provide advantages over known technology. The Peltier-based sensor may be enabled to work without a heating device which reduces temperature offset issues and makes it suitable for extreme weather conditions. Aspects of the present disclosure may enable detection of dust and / or fault(s) in any of the components. Solar tracking may also be implemented. The aspects of the present disclosure may have applications including, but not limited to, climatology, photovoltaic technology, meteorology, and related fields. The pyranometer of the present disclosure may be arranged to work without any disturbance or offset in natural conditions. The embodiments of the present disclosure may be capable of covering a wide solar spectrum. At least some of the embodiments may not require a dedicated heating device or similar temperature compensation mechanism. For example, when using beam steering, the need for a temperature compensation mechanism may be inhibited. At least some of the embodiments of the present disclosure may inhibit or prevent temperature offset issues to arise. This may also alleviate or obviate the need for temperature compensation systems that demand high power requirements. Embodiments of the present disclosure may also alleviate problems encountered in known photovoltaic devices because the presently disclosed embodiments may have better light coupling than known devices. The foregoing description has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure. The language used in the specification has been principally selected for readability and instructional purposes, and it may not have been selected to delineate or circumscribe the inventive subject matter. It is therefore intended that the scope of the invention be limited not by this detailed description, but rather by any claims that issue on an application based hereon. Accordingly, the disclosure of the embodiments of the invention is intended to be illustrative, but not limiting, of the scope of the invention, which is set forth in the following claims. Finally, throughout the specification and accompanying claims, unless the context requires otherwise, the word ‘comprise’ or variations such as ‘comprises’ or ‘comprising’ will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A pyranometer comprising at least one Peltier device arranged for sensing solar radiation and a diffraction grating that can change the incident irradiance per unit area, wherein the 5 diffraction grating has one or more slits that allow light to pass therethrough, and wherein the diffraction grating is configured to manipulate incident light by way of beam steering and the diffraction grating acting as an energy reducing element that reduces the solar energy that reaches the at least one Peltier device, wherein the arrangement of the diffraction grating and Peltier device / s is configured so as to lower or obviate heating power consumption requirements 10 of the pyranometer in use.

2. The pyranometer as claimed in claim 1, wherein the pyranometer is connected to one or more solar cells, and wherein one or more of the solar cells are arranged to provide electric power for the beam steering of the diffraction grating.

153. The pyranometer as claimed in any one of the preceding claims, wherein the pyranometer includes a thermal isolation layer of phase change material at an interior of the pyranometer.> 4. The pyranometer as claimed in any one of the preceding claims, wherein the pyranometerzO includes a desiccant to reduce moisture inside the pyranometer.I 5. The pyranometer as claimed in any one of the preceding claims, wherein the pyranometeris in data communication with a processing unit, and wherein the pyranometer includes an error signal generation component arranged to generate an error signal indicative of dust or fault in any 25 of the components of the pyranometer.

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