Solar collector for a curing kiln

Abstract

There is provided a solar collector (2) for a curing kiln (1) comprising one or more translucent sections which are arranged to allow the passage of solar radiation therethrough; one or more solar radiation absorbing sections (8) for absorbing solar radiation which has passed through the one or more translucent sections; and one or more air channels (40) formed between the one or more translucent sections and the one or more solar radiation absorbing sections (8). In a mode of operation, process air is arranged to pass through the one or more air channels (40) in order to be warmed. The or each translucent section comprises a first translucent layer (3), a second translucent (4) layer and a thermal insulation layer provided between the first translucent layer (3) and the second translucent layer (4).

Description

[0001] SOLAR COLLECTOR FOR A CURING KILN

[0002] FIELD

[0003] The present disclosure relates to a solar collector for a curing kiln, a curing kiln and a method of curing.

[0004] BACKGROUND

[0005] Curing kilns for curing and drying tobacco leaves are known. The curing and drying of tobacco leaves is typically performed in a kiln wherein the temperature and humidity regime is varied during a curing cycle. A typical curing cycle may last approximately 144 hours.

[0006] The process of curing tobacco leaves typically involves a first step which involves curing and drying the tobacco leaves. The first step is typically initiated at ambient temperature and the temperature is then increased to 40 °C. This temperature is then maintained until the tobacco leaves acquire a yellowish color. This step is commonly referred to as a "yellowing” step.

[0007] A second subsequent step is then typically performed which involves further drying the leaves. This second step may be initiated at a temperature of 40 °C and the temperature may then be increased to 63 °C. This second step results in the dehydration of the leaves and the fixation of the orange-yellow color which was achieved in the first step.

[0008] The third and final step involves drying the stems and is typically performed at a temperature in the range 74-77 °C due to the greater difficulty in extracting the water from the stems (i.e. the main vein of the leaves).

[0009] The humidity of air which circulates within a kiln may be controlled during each of the steps.

[0010] One problem with known curing kilns is that they have a relatively low thermal efficiency. SUMMARY

[0011] According to an aspect there is provided a solar collector for a curing kiln comprising: one or more translucent sections which are arranged to allow the passage of solar radiation therethrough; one or more solar radiation absorbing sections for absorbing solar radiation which has passed through the one or more translucent sections; and one or more air channels formed between the one or more translucent sections and the one or more solar radiation absorbing sections, wherein in a mode of operation process air is arranged to pass through the one or more air channels in order to be warmed; wherein the or each translucent section comprises a first translucent layer, a second translucent layer and a thermal insulation layer provided between the first translucent layer and the second translucent layer.

[0012] The solar collector according to various embodiments has a higher thermal efficiency than a conventional arrangement and enables the fuel consumption of an associated curing kiln to be reduced. Accordingly, a solar collector according to various embodiments is environmentally friendly. The construction of the solar collector and the ability to use the roof of a curing kiln as a solar radiation absorbing section simplifies the design of an overall curing kiln system and hence reduces the manufacturing cost.

[0013] Optionally, the first translucent layer may comprise a glass layer, a glass sheet or a pane of glass.

[0014] Optionally, the second translucent layer may comprise a glass layer, glass sheet or pane of glass.

[0015] Optionally, the thermal insulation layer may comprise air, inert gas or a vacuum insulation layer.

[0016] Optionally, the one or more solar radiation absorbing sections may comprise one or more metals, polymeric substances, cement, concrete or wood. The one or more solar radiation absorbing sections may be coated with a dark or black coating on an upper surface which is arranged to receive solar radiation which has passed through the one or more translucent sections.

[0017] Optionally, at least some or all or the solar radiation absorbing sections may have a surface arranged to receive and absorb solar radiation which has passed through a translucent section, and wherein the surface is substantially dark, black or has a lightness U < 10 in the CIE L*a*b* colour scale.

[0018] Optionally, the solar collector may further comprise a frame wherein the frame may be used to suspend or secure the solar collector to walls or the ceiling of a curing kiln.

[0019] Optionally, the frame may comprise a plurality of supports which extend from the one or more solar radiation absorbing sections. The supports may be arranged to support the one or more first translucent layers and to support the one or more second translucent layers. The supports may be metallic and the plurality of supports may be arranged to maintain a separation of at least 4 cm, 5 cm or 6 cm between the rearmost surface of the first translucent layers and the upper surface of the second translucent layers.

[0020] Optionally, solar radiation is arranged to pass first through the first translucent layer before passing through the second translucent layer and the plurality of supports may be arranged to maintain a separation of at least 25 cm, 30 cm or 35 cm between the rearmost surface of the second translucent layer and an upper surface of the one or more solar radiation absorbing sections.

[0021] According to another aspect there is provided a curing kiln comprising a solar collector as described above and one or more meshes, grids or racks upon which organic matter may be placed in order to be air cured.

[0022] Optionally, the organic matter may comprise tobacco leaves. However, other embodiments are contemplated wherein the organic matter may comprise crops, organic material or vegetables.

[0023] Optionally, the curing kiln may comprise a plurality of walls. The solar collector may be arranged in one or more frames. The one or more frames may be suspended from or secured to the walls or ceiling of the curing kiln. In various embodiments the solar collector may be provided on the roof of the curing kiln and the roof of the curing kiln may form a solar radiation absorbing section.

[0024] Optionally, the curing kiln may further comprise one or more first air vents, one or more second air vents and a control system.

[0025] Optionally, The control system may be arranged to cause the first and second air vents to open in a first mode of operation in order to direct process air within the curing kiln through the one or more air channels in order for the process air to be warmed before the process air then passes back into the curing kiln.

[0026] Optionally, the control system may be further arranged to close a recirculation air vent within the curing kiln in the first mode of operation. This forces process air to pass through the solar collector.

[0027] Optionally, the control system may be arranged to operate in the first mode of operation upon determining that the temperature within the one or more air channels is greater than the temperature of process air within the curing kiln. This may occur, for example, during periods of high solar radiation.

[0028] Optionally, the control system may be arranged to cause the first and second air vents to close in a second mode of operation in order to prevent process air within the curing kiln from being directed into the one or more air channels of the solar collector.

[0029] Optionally, the control system may be further arranged to open a recirculation air vent within the curing kiln in the second mode of operation so that process air bypasses the solar collector.

[0030] Optionally, the control system may be arranged to operate in the second mode of operation upon determining that the temperature within the one or more air channels is lower than the temperature of process air within the curing kiln. This may occur, for example, during periods of low solar radiation when it is overcast or at nighttime.

[0031] According to another aspect there is provided a method of curing comprising: providing a solar collector as described above; and causing process air to pass through the one or more air channels in order to be warmed.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various embodiments will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0034] Fig. 1 shows a side view of a curing kiln equipped with a solar collector provided on the roof of the curing kiln; Fig. 2 shows a view of a curing kiln equipped with a solar collector provided on the roof of the curing kiln;

[0035] Fig. 3 shows a cross-sectional view of a solar collector according to an embodiment wherein the solar collector comprises an upper first translucent layer and a second lower translucent layer with an air gap therebetween and wherein the solar collector further comprises an air channel and a solar radiation absorbing layer;

[0036] Fig. 4 shows a cross-sectional view of a curing kiln and shows front and rear flaps which may be opened or closed to direct or prevent process air from flowing into and out from the solar collector and an air recirculation vent arranged between a first section and a second section of the curing kiln, wherein when the air recirculation vent is opened process air may be recirculated directly from the second section of the curing kiln to the first section of the curing kiln thereby bypassing the solar collector;

[0037] Fig. 5 illustrates an air path through the curing kiln in a mode of operation wherein both a rear flap and a front flap are opened in order to direct process air through the solar collector and wherein an air recirculation vent arranged between a first section of the curing kiln and a second section of the curing kiln is closed in order to prevent process air from bypassing the solar collector;

[0038] Fig. 6 illustrates the process of solar radiation being transmitted through an upper translucent layer and a lower translucent layer with an air gap therebetween whereupon the solar radiation is then absorbed by a solar radiation absorbing layer and wherein the solar radiation absorbing layer emits thermal (infra-red) radiation which is effectively trapped within the air channel of the solar collector due to the fact that the lower translucent layer is a poor transmitter of infra-red radiation; and

[0039] Fig. 7 shows in greater detail a cross sectional view of a portion of a solar collector according to various embodiments.

[0040] DETAILED DESCRIPTION

[0041] Various embodiments will now be described in more detail.

[0042] Fig. 1 shows a curing kiln 1 having a solar collector 2 arranged on a roof portion of the curing kiln 1 . The roof portion may be sloped and may have a lower end 100 and a higher end 101. A number of grids or racks (not shown) may be provided within the curing kiln 1 upon which organic matter may be lain in order to be air cured. According to various embodiments the organic matter may comprise tobacco leaves. However, other embodiments are contemplated wherein the organic matter may comprise vegetables or other organic matter or material.

[0043] The curing kiln 1 may comprise one or more air inlets which may allow air to flow from the outside environment into the curing kiln 1. The curing kiln 1 may also comprise one or more air outlets which may allow air to flow out from the curing kiln 1 to the outside environment. Air may be circulated within the curing kiln 1 as will be explained in more detail below by a recirculating fan. The curing kiln 1 may further comprise one or more inspection windows, a furnace or heating unit which may be operated when the solar collector is not in operation, one or more temperature sensors and one or more humidity sensors.

[0044] Within the curing kiln 1 process air may be circulated by a recirculation fan through a first section of the curing kiln 1 wherein the first section of the curing kiln 1 may further include a furnace or heating unit. The furnace or heating unit may be switched OFF during periods of high solar radiation (i.e. on sunny days) so that process air is effectively warmed or heated by the solar collector 2 which in turn is warmed or heated by solar radiation.

[0045] Process air within the curing kiln 1 may be arranged to pass from the first section of the curing kiln 1 into a second section of the curing kiln 1 which comprises a curing chamber in which the organic matter to be air cured is located or stored. The process air is directed to pass over the organic matter in order to cure the organic matter over an extended period of time. The process air, now cooled after having passed on heat to the organic matter, may then be arranged to pass into and through the solar collector 2 in order to be re-warmed or re-heated.

[0046] Process air, having been re-warmed or re-heated within the solar collector 2, may then be arranged to exit the solar collector 2 whereupon the process air is then recirculated by the recirculating fan which may be located in the first section of the curing kiln 1 . The process air is then passed back into the second section of the curing kiln 1 in order to continue the curing process of the organic matter located in the second section of the curing kiln 1 and the process is repeated.

[0047] It will be understood that process air is only directed through the solar collector 2 when the temperature within the solar collector 2 is greater than the temperature of the process air. If the temperature within the solar collector 2 is lower than the temperature of the process air within the curing kiln 1 (i.e. the weather is overcast or it is night time) then the process air may be directed so that it bypasses the solar collector 2. For example, when the temperature within the solar collector 2 is insufficient to warm the process air then process air within the curing kiln 1 may be diverted from the second section of the curing kiln 1 directly back into the first section of the curing kiln 1 without passing through the solar collector 2. In this mode of operation front and rear flaps which control the flow of process air into and out from the solar collector 2 may be closed and an air recirculation vent arranged between the first section and the second section of the curing kiln 1 may be opened so that process air passes directly from the second section back into the first section of the curing kiln 1 without passing through the solar collector 2. In this mode of operation the furnace or heating unit may now be switched ON in order to heat or warm the process air instead of using the solar collector 2 to heat or warm the process air.

[0048] The curing kiln 1 may have an external air inlet and a control system which may be arranged to control the humidity of the process air and to maintain the humidity of the process air at a desired level. The temperature of the process air at various sections throughout the curing kiln 1 and within the solar collector 2 may be monitored by the control system which may be arranged to monitor temperature sensors located at various positions within the curing kiln 1 and the solar collector 2.

[0049] Humidity control may be performed by opening and / or closing an external air inlet under the control of the control system.

[0050] Fig. 2 shows in more detail how the solar collector 2 may comprise a plurality of panels which may be located on the roof of the curing kiln 1 . The roof of the curing kiln 1 may be inclined so that the lowermost portion of the roof 100 is furthest away from the recirculating fan which is provided within the first section of the curing kiln 1 . Equally, the highest portion of the roof 101 may be located above the first section of the curing kiln 1 which includes the recirculating fan.

[0051] Fig. 3 shows in more detail a solar collector 2 according to various embodiments. The solar collector 2 comprises a plurality of upper sections. Each upper section comprises an upper translucent layer 3 and a lower translucent layer 4 with a gap 30 therebetween. The upper translucent layer 3 may comprise glass and the lower translucent layer 4 may also comprise glass. The upper translucent layer 3 and the lower translucent layer 4 are separated by a gap 30 which may comprise an air gap 30. However, other embodiments are contemplated wherein the gap 30 may comprise a vacuum or wherein an inert gas may be provided in the gap 30 between the upper translucent layer 3 and the lower translucent layer 4.

[0052] The upper translucent layer 3 and the lower translucent layer 4 may be supported by one or more support members 7. The support members 7 may be metallic. The one or more support members 7 may be arranged to maintain a spacing or separation between the upper translucent layer 3 and the lower translucent layer 4 of at least 5 cm. For example, the separation between a lower surface of the upper translucent layer 3 and an upper surface of the lower translucent layer 3 may be arranged to be at least 5 cm, 6 cm, 7 cm, 8 cm, 9 cm or 10 cm.

[0053] Solar energy is arranged to pass through the upper translucent layer 3, the gap 30 and the lower translucent layer 4 before impinging upon a solar radiation absorbing layer or surface 8. One or more air channels 40 are provided between the lower surface of the lower translucent layer 4 and the upper surface of the solar radiation absorbing layer or surface 8. The upper surface of the solar radiation absorbing layer or surface 8 is arranged or spaced at least 30 cm from the rearmost surface of the lower translucent layer 4. According to embodiments the upper surface of the solar radiation absorbing layer or surface 8 may be arranged or spaced at least 30 cm, 35 cm, 40 cm, 45 cm or 50 cm from the rearmost surface of the lower translucent layer 4.

[0054] The solar radiation absorbing layer or surface 8 may be coated with a dark or black coating in order to maximise the absorption of solar energy. For example, the solar radiation absorbing layer or surface 8 may be coated with a matte black coating. According to other embodiments the solar radiation absorbing layer or surface 8 may be coated with a photonic coating which is arranged to have a low reflectance of < 25%, < 20% or < 15% on average across the solar spectrum or across the visible spectrum (380-780 nm).

[0055] It will be understood that the solar radiation absorbing layer or surface 8 in addition to being an efficient absorber of solar radiation will also be a good emitter of thermal radiation. The solar radiation absorbing layer or surface 8 will absorb light in the visible wavelength (380-780 nm) but will emit radiation in the infra-red portion of the electromagnetic spectrum which has a longer wavelength than the visible spectrum. It will be understood that the lower translucent layer 4 is a poor transmitter of infra-red radiation and hence heat energy is essentially trapped within the body portion of the solar collector 2 with the result that process air passing through the one or more air channels 40 provided in the solar collector 2 between the lower surface of the lower translucent layer 4 and the solar radiation absorbing layer 8 will be warmed. It will be understood, therefore, that the effect of the lower translucent layer 4 in combination with the solar radiation absorbing layer 8 is that infrared radiation emitted from the solar radiation absorbing layer 8 are not substantially transmitted through the upper and lower translucent layers 3,4 and hence the infrared radiation is retained within the solar collector 2 and may be used to heat process air passing through the one or more air channels 40. In short, the upper and lower translucent layers 3,4 allow sunlight to pass into the solar collector 2 but the lower translucent layer 4 prevents heat radiated from the solar radiation absorbing layer 8 from escaping, i.e. the use of the upper and lower translucent layers 3,4 greatly reduces thermal loss from the solar collector by heat convection.

[0056] The upper translucent layer 3 also acts to keep a layer of air trapped between the upper translucent layer 3 and the lower translucent layer 4 thereby creating a thermal insulating effect which significantly reduces thermal loss due to heat conduction.

[0057] The upper translucent layer 3 is arranged several centimetres from the lower translucent layer 4 so that heat does not propagate easily by conduction or convection out of the system thereby greatly improving the thermal performance of the solar collector 2 compared with conventional arrangements. Indeed, field evaluations have demonstrated that a solar collector according to various embodiments having two layers of glass with an air gap therebetween has an approximately 39% improvement in the thermal yield. It will be understood that an improved thermal yield reduces the overall energy requirements of the system and may reduce the amount of time that the furnace or heating unit has to be used in order to warm the process air.

[0058] The double layered glass solar collector 2 according to various embodiments consists of a surface area for absorbing sunlight and may have lateral surfaces 5, front surfaces and rear surfaces arranged so that the upper and lower translucent layers 3,4 are maintained at least 5 cm apart each other. The upper and lower translucent layers are maintained at least 30 cm from the base of the solar radiation absorbing layer or surface 8.

[0059] According to various embodiments the side portions 5 and the base portion of the solar collector 2 are dark in color (e.g. black) and different types of material may be used for the construction of the lateral or side portions 5 and the base portion. For example, the lateral or side portions 5 and the base portion may be metallic, polymeric, cement or wood. According to various embodiments it is ensured that a solar radiation absorbing layer or surface 8 is provided which may be black and wherein the solar radiation absorbing layer or surface is located below a double translucent layer 3,4 which may comprise two layers of glass. As a result, the solar collector 2 utilises the greenhouse effect to trap heat energy within the solar collector 2 and the solar collector 2 also acts as an insulator to prevent heated retained within the solar collector 2 from being lost to the exterior or atmosphere.

[0060] In the particular embodiment shown in Fig. 3 the solar collector 2 is shown suspended from walls 6 of the curing kiln. Furthermore, the solar radiation absorbing layer 8 is shown a discrete layer which is separate from the roof of the curing kiln. However, other embodiments are contemplated wherein the solar collector 2 is not suspended from the walls of the curing kiln in the manner as shown in Fig. 3. Instead, according to other embodiments the solar collector 2 may be attached to the roof of the curing kiln and the roof of the curing kiln may form the solar radiation absorbing layer 8.

[0061] With reference to Fig. 4, the solar collector 2 may be connected to or provided on a roof of the curing kiln 1 . The interaction between the solar collector 2 and the curing kiln 1 takes place via two openings between a heating chamber of the solar collector 2 and the curing kiln 1 . In particular, a front flap 9 may be provided between a process air exit section of the solar collector 2 and the first section of the curing kiln 1 which may include a recirculation fan (not shown). A rear flap 10 may be provided between the second section of the curing kiln 1 and a process air entrance section of the solar collector 2. The rear flap 10 may be provided proximal to the lowermost portion 100 of the roof and the front flap 9 may be provided proximal to the highest portion 101 of the roof. As shown, one or more air channels 40 may be provided such that when the front flap 9 and rear flap 10 are opened then process air may flow through the one or more air channels 40 in a direction from the lowermost portion 100 of the roof towards the highest portion 101 of the roof.

[0062] With reference to Fig. 5, the front flap 9 and rear flap 10 may be controlled automatically by the control system. The control system may be arranged to monitor first temperature signals output from one or more temperature sensors 12 which may be located within the solar collector 2 and / or to monitor second temperature signals output from one or more temperature sensors 13 which may be located within the first section and / or second section of the curing kiln 1 . In the particular example shown in Fig. 5 a temperature sensor 13 is shown located within the second section of the curing kiln 1. However, one or more temperature sensors may be located within the first section of the curing kiln 1 which includes a recirculating fan 14. The recirculating fan 14 is shown located about a furnace or heating unit 50.

[0063] During times of high solar availability the front flap 9 and the rear flap 10 may both be opened. Similarly, during times of low solar availability the front flap 9 and the rear flap 10 may both be closed. Accordingly, the front flap 9 and the rear flap 10 may be opened or closed according to the thermal availability of the solar collector 2 and the thermal demand of the curing kiln 1.

[0064] An air recirculating vent 11 may be positioned between the first section and second section of the curing kiln 1 as shown in Fig. 5 in order to control the flow of process air through the curing kiln 1 . In particular, if it is desired to direct process air through the solar collector 2 then the air recirculating vent 11 may be closed. Similarly, if it is desired that process air should bypass the solar collector 2 then the air recirculating vent 11 may be opened.

[0065] In a mode of operation process air may be directed through the solar collector 2 and a thermal exchange may be performed by mixing the process air flow with air heated within the solar collector 2.

[0066] When the temperature of air within the solar collector 2 is higher than the process air, then the front flap 9 and rear flap 10 may be arranged to be opened and the recirculation air vent 11 between the first section and the second section of the curing kiln 1 may be closed. With this arrangement the air flow is forced to pass through the solar collector 2 whereupon the process air absorbs thermal energy by mixing with air which has been heated within the solar collector 2.

[0067] If the control system determines that heat available in the solar collector is inadequate to heat the process air to a desired temperature then the control system may arrange to close both the front flap 9 and rear flap 10 and to open the air recirculation vent 11 so that process air bypasses the solar collector 2. The process of bypassing the solar collector 2 may continue until it is determined that the solar collector 2 is of sufficient temperature to contribute again to heating the process air to a desired temperature.

[0068] Fig. 6 illustrates the process of trapping solar energy within the solar collector 2 according to various embodiments by permitting solar radiation to pass through the upper translucent layer 3, the air gap 30 and the lower translucent layer 4 whereupon the solar energy is then absorbed by the solar radiation absorbing layer 8. The solar radiation absorbing layer 8 then emits heat energy as infra-red radiation but the lower translucent layer 4 is an inefficient transmitter of infra-red radiation at the wavelength emitted by the solar radiation absorption layer 8. As a result, heat energy is effectively trapped within the solar collector 2 and may be used to warm process air which passes through one or more air channels 40 provided within the main body of the solar collector 2. The warmed process air may then be used to air cure organic matter which is located within the second section of the curing kiln 1. It will be understood that the solar collector 2 according to various embodiments comprises a double layer of glass 3,4 separated by an air gap 30. However, further embodiments are contemplated wherein three or more translucent layers may be provided with air gaps between. For example, according to an embodiment the solar collector 2 may comprise a first translucent layer, a first air gap, a second translucent layer, a second air gap and a third translucent layer. Either the first air gap and / or the second air gap may be replaced by a vacuum region or by an inert gas.

[0069] The double layered arrangement 3,4 according to various embodiments in combination with an air gap 30 increases the efficiency of the solar collector 2 since it prevents contact between warm process air within the solar collector 2 and environmental air external to the curing kiln 1 and the solar collector 2. As a result condensation is prevented and the temperature within the solar collector 2 may be maintained higher than conventional arrangements resulting in a more efficient solar collector 2 being provided. It will be understood that the air (or vacuum or inert gas) provided between the upper translucent layer 3 and the lower translucent layer 4 provides a relatively high level of insulation and that this insulation layer is not provided in known arrangements.

[0070] In contrast to known arrangements, the solar absorption layer 8 is provided at the bottom of the solar collector 2 which simplifies and improves the manufacturing process without affecting the operational efficiency. In contrast to a known arrangement wherein a solar absorption layer is suspended in a central region of the solar collector, according to various embodiments the solar radiation absorption surface 8 may comprise the ceiling of the curing kiln 1.

[0071] It will be appreciated, therefore, that the solar collector 2 and curing kiln 1 according to various embodiments is more energy efficient and simpler to manufacture than conventional arrangements.

[0072] According to various embodiments the solar collector 2 may be fully integrated into the curing kiln 1 and optionally the curing kiln 1 may be heated at times using wood fuel. It has been found that the solar collector 2 according to various embodiments decreases fuel consumption by approximately 20% compared with conventional arrangements.

[0073] Fig. 7 shows in greater detail a cross sectional view of a solar collector 2 according to various embodiments. The upper translucent layer has an upper surface 3a and a lower surface 3b. The lower translucent layer has an upper surface 4a and a lower surface 4b. The upper translucent layer and the lower translucent layer may be supported by one or more support members 7. The one or more support members 7 (which may be metallic) may be arranged to maintain a spacing or separation 15 between the lower surface 3b of the upper translucent layer and the upper surface 4a of the lower translucent layer of at least 5 cm. According to various embodiments, the plurality of supports 7 may be arranged to maintain a separation 15 of at least 4 cm, 5 cm or 6 cm between the rearmost surface of the first translucent layer 3b and the upper surface of the second translucent layer 4a.

[0074] Solar energy is arranged to pass through both the upper translucent layer, the air gap 30 and the lower translucent layer before impinging upon a solar radiation absorbing layer or surface 8. The upper surface of the solar radiation absorbing layer or surface 8 is arranged or spaced 5a at least 30 cm from the rearmost surface 4b of the lower translucent layer. The solar radiation absorbing layer or surface 8 may be coated with a dark or black coating in order to maximise the absorption of solar energy. For example, the solar radiation absorbing layer or surface 8 may be coated with a matte black coating. An insulation layer may be provided below the solar radiation absorbing layer or surface 8.

[0075] According to various embodiments solar radiation is arranged to pass first through the first translucent layer before passing through the second translucent layer and wherein the plurality of supports 7 are arranged to maintain a separation 5a of at least 25 cm, 30 cm or 35 cm between the rearmost surface of the second translucent layer 4b and an upper surface 8a of the one or more solar radiation absorbing sections 8.

[0076] The solar collector 2 according to various embodiments is particularly environmentally friendly as it reduces the fuel consumption of the curing kiln 1 thereby resulting in lower overall CO2emissions.

[0077] The various embodiments described herein are presented only to assist in understanding and teaching the claimed features. These embodiments are provided as a representative sample of embodiments only, and are not exhaustive and / or exclusive. It is to be understood that advantages, embodiments, examples, functions, features, structures, and / or other aspects described herein are not to be considered limitations on the scope of the invention as defined by the claims or limitations on equivalents to the claims, and that other embodiments may be utilised and modifications may be made without departing from the scope of the claimed invention. Various embodiments of the invention may suitably comprise, consist of, or consist essentially of, appropriate combinations of the disclosed elements, components, features, parts, steps, means, etc., other than those specifically described herein. In addition, this disclosure may include other inventions not presently claimed, but which may be claimed in future.

Claims

Claims1 . A solar collector for a curing kiln comprising: one or more translucent sections which are arranged to allow the passage of solar radiation therethrough; one or more solar radiation absorbing sections for absorbing solar radiation which has passed through the one or more translucent sections; and one or more air channels formed between the one or more translucent sections and the one or more solar radiation absorbing sections, wherein in a mode of operation process air is arranged to pass through the one or more air channels in order to be warmed; wherein the or each translucent section comprises a first translucent layer, a second translucent layer and a thermal insulation layer provided between the first translucent layer and the second translucent layer.

2. A solar collector as claimed in claim 1 , wherein the first translucent layer comprises a glass layer, a glass sheet or a pane of glass.

3. A solar collector as claimed in claim 1 or 2, wherein the second translucent layer comprises a glass layer, a glass sheet or a pane of glass.

4. A solar collector as claimed in any of claims 1 , 2 or 3, wherein the thermal insulation layer comprises air, inert gas or a vacuum insulation layer.

5. A solar collector as claimed in any preceding claim, wherein the one or more solar radiation absorbing sections comprise one or more metals, polymeric substances, cement, concrete or wood.

6. A solar collector as claimed in any preceding claim, wherein at least some or all or the solar radiation absorbing sections have a surface arranged to receive and absorb solar radiation which has passed through a translucent section, and wherein the surface is substantially dark, black or has a lightness L* < 10 in the CIE L*a*b* colour scale.

7. A solar collector as claimed in any preceding claim, further comprising a frame for suspending or securing the solar collector to walls or a ceiling of a curing kiln.

8. A solar collector as claimed in claim 7, wherein the frame further comprises a plurality of supports extending from the one or more solar radiation absorbing sections, wherein the supports are arranged to support the one or more first translucent layers and to support the one or more second translucent layers.

9. A solar collector as claimed in claim 8, wherein the plurality of supports are arranged to maintain a separation of at least 4 cm, 5 cm or 6 cm between the rearmost surface of the first translucent layers and the upper surface of the second translucent layers.

10. A solar collector as claimed in claim 8 or 9, wherein solar radiation is arranged to pass first through the first translucent layer before passing through the second translucent layer and wherein the plurality of supports are arranged to maintain a separation of at least 25 cm, 30 cm or 35 cm between the rearmost surface of the second translucent layers and an upper surface of the one or more solar radiation absorbing sections.

11. A curing kiln comprising: a solar collector as claimed in any preceding claim; and one or more meshes, grids or racks upon which organic matter may be placed in order to be air cured.

12. A curing kiln as claimed in claim 11 , wherein the organic matter comprises tobacco leaves.

13. A curing kiln as claimed in claim 11 or 12, wherein the curing kiln comprises a plurality of walls and wherein the solar collector is provided in a frame which is suspended from or secured to walls or a ceiling of the curing kiln.

14. A curing kiln as claimed in claim 11 , 12 or 13, further comprising one or more first air vents, one or more second air vents and a control system.

15. A curing kiln as claimed in claim 14, wherein the control system is arranged to cause the first and second air vents to open in a first mode of operation in order to direct process air within the curing kiln through the one or more air channels of the solar collector in order for the process air to be warmed before the process air passes back into the curing kiln.

16. A curing kiln as claimed in claim 15, wherein the control system is further arranged to close a recirculation air vent within the curing kiln in the first mode of operation.

17. A curing kiln as claimed in claim 15 or 16, wherein the control system is arranged to operate in the first mode of operation upon determining that the temperature within the one or more air channels is greater than the temperature of process air within the curing kiln.

18. A curing kiln as claimed in any of claims 14-17, wherein the control system is arranged to cause the first and second air vents to close in a second mode of operation in order to prevent process air within the curing kiln from being directed into the one or more air channels of the solar collector.

19. A curing kiln as claimed in claim 18, wherein the control system is further arranged to open a recirculation air vent within the curing kiln in the second mode of operation.

20. A curing kiln as claimed in claim 18 or 19, wherein the control system is arranged to operate in the second mode of operation upon determining that the temperature within the one or more air channels is lower than the temperature of process air within the curing kiln.21 . A method of curing comprising: providing a solar collector as claimed in any of claims 1-10; and causing process air to pass through the one or more air channels in order to be warmed.

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