WO2012032330A2

WO2012032330A2 - An energy collector device

Info

Publication number: WO2012032330A2
Application number: PCT/GB2011/051638
Authority: WO
Inventors: Kevin Wheatley
Original assignee: Solorno Limited
Priority date: 2010-09-06
Filing date: 2011-09-01
Publication date: 2012-03-15
Also published as: GB2482205B; GB2482205A; GB201014717D0; GB2484353A8; GB2484353B; GB201018939D0; WO2012032330A3; GB2484353A

Abstract

An energy collector device (1) comprises an enclosure (3) and tubing (7). The enclosure (3) incorporates a base (5) and cover (10), a thermal energy storage device(4)located between the cover (10) and the base (5), a circulatory fan(11) attached to the cover (10).The tubing (7) being at least partially located between the cover (10) and the energy storage device(4)for communicating a working fluid within the collector device (1), wherein the tubing (7) is configured into a layer, which in use, communicates the working fluid about an inner chamber of the device (1). The circulatory fan (11) circulates the air within the device (1) and facilitates the convection of thermal energy from the storage device (4) evenly across the layer of the tubing (7).

Description

AN ENERGY COLLECTOR DEVICE

Field of the Invention

The invention relates to an energy collector device, in particular to solar thermal collectors for heating water.

Background to the Invention

The closest art known to the Applicant are documents EP1947401 A1 (Solorno Systems S.L.) and FR2908870 A3 (Lyla Sari).

EP1947401 A1 is a previous application from the Applicant which is an invention for a flat plate collector that incorporates an energy storage means in the form of an energy storage layer. The absorbed thermal energy contained within the thermal energy storage means then dissipates the heat energy stored within the collector, whilst the available solar radiation diminishes, for example at sunset etc.

The invention of this prior art document has the following drawbacks:

• The energy storage layer is typically a heatsink incorporating a ceramic or mineral material. The ceramic and/or mineral material is preferably a granular stone material expelled from volcanoes, such as Picon. The ceramic and/or mineral material can store the thermal energy for relatively short period only. • A flat plate collector generally requires low flow rates in order to maximise the communication of the absorbed heat energy into the working fluid. The thermal layer dissipates the heat energy through conduction to the tubing directly and convectionally during periods when solar radiation diminishes.

Document FR2908870 A3 provides an alternative invention for a flat plate collector which incorporates a bundle of tubes for the circulation of a working fluid within a glass assembly. The tubes are connected directly to a hot water and cold water collecting assembly.

The disadvantage of this configuration is that it does not incorporate a thermal energy store which provides heat energy during a period where solar radiation has been diminished.

The present invention seeks to provide a remedy/solution to these problems by providing an improved energy collector, which transfers collected heat energy to a working fluid more uniformly over time.

Furthermore, the present invention seeks to provide a collector, which absorbs more heat energy per unit area than other conventional thermal collectors.

Furthermore, the present invention seeks to provide a water heating system, which minimises the loss of heat energy. The invention significantly lowers the cost of solar panels in that it is believed to be the cheapest and most efficient solar water heating system available for both swimming pools and domestic systems with rapid return on investment. Also, the device can be supplied to be fitted together by a non-skilled person to put it together, with some plumbing.

Summary of the Invention

In a first broad independent aspect, an energy collector device comprising an enclosure and tubing; said enclosure incorporates a base and cover; a thermal energy storage device located between said cover and said base; a circulatory fan attached to said cover: said tubing being at least partially located between said cover and said energy storage device for communicating a working fluid within said collector device; wherein said tubing is configured into a layer, which in use communicates said working fluid about an inner chamber of said device; said circulatory fan circulates the air within said device and facilitates the convection of thermal energy from said storage device evenly across said layer of said tubing.

This configuration provides an efficient means of maintaining the internal temperature of the collector at a constant temperature, which aids the convection of thermal energy across all the layers of tubing while preventing the thermal energy from collecting within the upper portion of the cover. Furthermore, this configuration provides a more consistent heating mechanism which is less susceptible to fluctuations in the available solar radiation, i.e. where large and dense clouds are present.

Another advantage of this configuration is that a thermal energy storage device formed from a preconfigured vessel filled with the heat absorbing fluid is cost effective and is easier to manufacture than other known energy storage devices, such as ceramic or mineral based storage devices which are expensive and require specialist manufacturing skills. Therefore a thermal energy storage device containing heat absorbing fluid can formed into complicated shapes and/or configurations which are not possible with ceramic or mineral, such as Picon.

Preferably, said thermal energy storage device further comprises a body portion which extends towards the inner surface of said cover, thereby extending said reservoir of heat absorbing fluid towards said inner surface of said cover. This provides a thermal energy storage device with an increased surface area for dissipating the stored thermal evenly about the tubing that communicated the heating fluid within the collector. Furthermore, the increased surface area enables the energy storage device to store thermal energy from the collected solar radiation more quickly and efficiently.

Preferably, said heat absorbing fluid is an ionic liquid or hydrocarbon liquid or mixtures thereof. This absorbs, retains and disperses thermal energy more effectively than ceramic or mineral material, such as Picon, therefore providing a more consistent heating mechanism which is less susceptible to fluctuations in the available solar radiation, i.e. where large and dense clouds are present.

Preferably, said tubing incorporates a corrugated surface. This provides the tubing which contains the working fluid with an increased surface area for collecting solar radiation.

Preferably, said tubing is configured into a plurality of coil configurations which are interconnected in a substantially helical configuration; whereby said working fluid is continuously communicated about and between each said coil configuration. This configuration initially circulates the colder working fluid within the bottom layer of the helical configuration. The working fluid is then subsequently heated as it is circulated within each of the ascending layers, which as advantageous due to the upper layer of the helical configuration being located within the upper portion of the collector that contains the majority of the contained thermal energy.

Preferably, an energy collector device further comprises a plurality of spacer members for separating and supporting adjacent tubing portions along both vertical and horizontal axes. This enables an area of free space to be formed, between each tubing layer and/or between each tubing portion, which transmits thermal energy to the working fluid within the tubing by conduction or convection.

Preferably, each said spacer member further comprises a corrugated surface. This provides the spacer with an increased surface area for collecting solar radiation.

Preferably, said tubing is configured into a grid configuration. This enables the tubing to be formed into a space efficient configuration for use in the inner chamber of small collecting device, where it is not possible to fit the tubing in interconnected coiled layers.

Preferably, said cover is configured into a predetermined shape incorporating a concave and / or convex portion formed from a substantially transparent material. This enables the collector to be of any shape, i.e. domed, hexagonal (honeycombed), rectangular, wavy, patterned, flat, oval, with different heights to fit different permutations, i.e. if space is limited where the device is fitted or to maximise the absorption or retention of the solar radiation. A mixture of concave and convex shapes has been found to offer maximum heat retention. The cover may itself be coated in a paint, spray or film which improves solar energy adsorption and/or with self cleaning properties such that it prevents panels in inaccessible areas from becoming dirty.

Such fixed shapes, such as, concave and convex portions would lend themselves to improving the efficiency of photovoltaic cells as well - they can offer improved efficiencies over flat surfaces.

Further more it enables the communication of solar radiation through the cover, onto the inner collecting surfaces of the device.

Preferably, an energy collector device further comprises a peripheral wall that incorporates a corrugated surface. This provides the peripheral wall with an increased surface for collecting solar radiation.

Preferably, said base further comprises an insulating layer that incorporates a corrugated surface. This provides the base with an increased surface for collecting solar radiation.

Preferably, said corrugated surfaces are formed from a substantially aluminium material coated in a black or reflective coating. This provides a corrugated surface which is resilient to high temperatures.

Preferably, an energy collector device further comprises a second heating source for communicating thermal energy to said working fluid within said tubing. This provides a means of heating the working fluid when solar radiation (sunlight) has been diminished for a prolonged period.

Preferably, said second heating source is an electrical heating source or gas heating source. This system could be used in conjunction with existing solar panels or pool heating systems, whether solar or not. This enables the working fluid to be heated via other typically available heating means available within an installation.

Preferably, an energy collector device further comprises a fan attached exterior of said cover for circulating the air within said device. This maintains the internal temperature of the collector at a constant temperature, which aids the convection of thermal energy evenly across all the tubing layers within the collector, by preventing it collecting within the upper portion of the cover. Therefore a multi-layer tubing system will work best with a circulatory fan, which homogenises the temperature inside the cover, i.e. lower most tubing gets identical heating to uppermost tubing.

Preferably, an energy collector device further comprises a tilting mechanism for tilting said device about an axis. This exposes as much of the collector's inner surface to direct sunlight, without the use of reflectors, to create heat within the collector. The unit itself could be angled or the dome could be angled/preferably shaped, or the tubing in relation to the dome could be angled for maximum performance. It is preferable that the tubing is in a horizontal position and the cover is shaped for maximum performance.

Preferably, an energy collector device further comprises a cooking means located between said cover and said base or said thermal energy storage; wherein said solar radiation produces thermal energy within said solar device which subsequently heats said cooking means that in use cooks or heats food.

Preferably, an energy collector device further comprises a reflective member located about a portion of the outer surface of said cover; whereby said reflective member incorporates a reflective surface that faces said cover and reflects solar radiation into said cover. This maximises the amount of sunlight hitting the cover, whilst the collectors are laid flat, to create additional heat within the collector.

In a second broad independent aspect, a method of heating a working fluid within a energy collecting device comprising the steps of ;

• Configuring a tubing into a layer which is at least partially located between a cover of said energy collecting device and a energy storage device incorporated within said energy collecting device;

• Communicating a working fluid incorporated within said tubing about an inner chamber of said energy collecting device; and • Circulating the air within said inner chamber of said energy collecting device with a circulatory fan, which facilitates the convection of thermal energy from said storage device evenly across said layer of tubing.

In a third broad independent aspect, a photovoltaic solar panel with a fixed dome structure comprising a concave portion and a convex portion.

In a fourth broad independent aspect, a solar oven comprising a cover and a base; a cooking means located between said cover and base; wherein solar radiation produces thermal energy within the said oven device which subsequently heats said cooking means that in use cooks or heats food.

In a fifth broad independent aspect, a sun oven for cooking purposes comprising oven body covered in reflective material, a cooking surface, a lid, a heat storage unit and a circulatory fan and wherein said lid is shaped with a mixture of concave and convex portions.

This configuration provides an improved efficiency in providing cooking temperatures, when compared with other known sun oven solutions, therefore enabling the oven to be used in climates previously thought to be too low to cook food by harnessing and utilising solar power.

Furthermore, this configuration does not get as hot as a conventional non-solar oven, and requires a longer period to cook the food. However, it enables the user to safely leave the food within the oven all day without the burning the food. The oven can also be used warm food and drinks and/or pasteurise water or milk. This enables the user save significant amounts of fuel, and its associated cost, when preheating water for cooking grain, soups or the like, to nearly boiling. Preferably, said heat storage unit comprises a chamber filled with an ionic liquid, a chamber filled with a hydrocarbon liquid or gas; or wherein the heat storage unit comprises a solid heat absorbent material. This enables the oven to be used when there are clouds present or for a period of time after dusk. This enables the heat storage unit to absorb, retain and disperse thermal energy more effectively than other ceramic or mineral material, such as Picon, therefore providing a more consistent heating mechanism which is less susceptible to fluctuations in the available solar radiation, i.e. where large and dense clouds are present.

Preferably, said heat storage unit forms the surface upon which cooking takes place. This configuration enables the heat storage unit to directly transfer its contained thermal energy, directly into the food in a simple and efficient manner.

Preferably, the temperature within said oven is homogenised by use of said circulatory fan. This configuration enables the oven the oven to evenly distribute thermal energy through out the oven and contribute to achieving consistent cooking performance form one part of the oven to another.

Preferably, said oven is tiltable upon its base to be positioned in optimum sunlight depending on the position of the sun and the terrain in which said oven is placed. This configuration enables the oven to expose as much of the inner surface of the oven to direct sunlight, without the use of reflectors, to create heat within the oven.

Preferably, said lid is tiltable upon said oven to be positioned in optimum sunlight depending the on the position of the sun and the terrain in which said oven is placed. This configuration provides a enables lid to expose as much of the inner surface of the to direct sunlight, without the use of reflectors, to create heat within the oven. Preferably, said cooking surface is either part of the reflective surface or is a raised grill above the base of said oven. This configuration provides a cooking surface, without using a dedicated cooking surface component, which simplifies the design and complexity of the oven structure.

Brief Description of the Figures

The following description is made by the way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a cross-sectional view of the energy collector device along a vertical plane of the preferred embodiment of the invention.

Figure 2A shows a plan view of the energy collector device according to preferred embodiment of the invention.

Figure 2B shows a cross-sectional view of the energy collector along axis A-A according to preferred embodiment of the invention.

Figure 3 shows a simplified view of the reflector panel situated on the north side of the collector.

Figure 4 shows a simplified view of six energy collectors connected in parallel configuration to supply heated water to a swimming pool.

Detailed Description of the Figures

Figure 1 shows an energy collector device generally indicated by 1 , incorporates an aluminium or plastic outer casing 3, which incorporates a base 5 and peripheral wall 2 lined with a polystyrene or other insulating layer 6 and is preferably ten to thirty millimetres thick. The inner surfaces of the insulating layer 6 are lined with a corrugated aluminium sheet 9, which have a black or reflective coating on their inner surfaces. Centrally located within the dome is a cylindrical thermal energy storage container 4 which contains a reservoir of heat absorbing liquid. The thermal energy storage container 4 extends substantially vertically, and also incorporates a lower body portion that extends radially outwards about the main body of the thermal energy storage container 4, towards the inner corrugated aluminium sheet 9. Upon the lower extending portion of the thermal energy storage device 4 is a plurality of spacer tubing 8 extending horizontally along multiple layers and are covered in either a reflective or black coating 8. The tubular spacing 8 may be either round or square in shape. Each layer of spacer tubing 8 supports and maintains the configuration of an array of tubing 7, which is placed in evenly spaced along a horizontal axis. Each layer of tubing 7 is also evenly spaced along a vertical axis. The tubing 7 communicates the working fluid about the inner chamber of the collector 1, to maximise the absorption of the thermal energy from the energy storage device 4, to the working fluid. The outer casing 3 incorporates a domed cover 10, which is lined with a solar radiation film and an air circulatory fan 1 1. The circulatory fan is mounted upon the domed exterior of the cover 10. The outer case 3 is mounted upon two base supports 13 formed from two lengths of tubing fixed to the underside of the base 5. The outer case 3 may be formed into a substantially circular shape, square shape, hexagonal or other predefined shape. Wherever desirable, e.g. for swimming pool applications, a flow rate of 20-50/ per minute can be achieved by using multiple collectors, whatever their size or m2, connected in parallel, dependant on the size of the pool and using a return flow manifold system.

Figure 2a shows an upper plan view of the energy collector device 1 , which was shown in Figure 1. The outer case 3 incorporates the substantially circular domed cover 10 and is typically formed from a plastic sheet, or moulded in a complete plastic casting. It may be of any solid material but preferably plastic or aluminium; it may be any shape (square, round, oval, etc. as desired) or any square meterage. The cover dome 10 is covers an area of one square metre. The sheet material used to form the base 5 and sides of the outer case 3 is between 2mm and 10mm in thickness, which is dependent upon the construction method used. The dome 10 further incorporates a substantially octagonal body portions which enclose the collector device. Centrally located within the collector device is the thermal energy storage container 4, along with the lower body portion which protrudes from the thermal storage device 4 in the form of an array of radially extending ribs that extend substantially towards the inner corrugated aluminium sheet 9. Figure 2b shows a cross sectional view along axis A-A in Figure 2a of the energy collector device 1. The peripheral wall 2 includes two holes 12 which are typically spaced 180° opposite each other to allow a tube access to the inner chamber of the collector 1. The base portion 5 of the collector may incorporate a lifting mechanism to allow the collector 1 to be tilted about an axis at an angle of typically 15-40°.

Figure 3a shows an energy collector device 1 as shown in Figures 1 and 2, which further incorporates a curved rectangular strip 14, which is fitted to the north side of the connector 1. The strip 14 incorporates a reflective surface constructed from one or more mirrors or other reflective material or the like. The amount of solar radiation hitting the dome surface is maximised when the energy collectors 1 are laid flat, therefore creating additional internal heat within the collector 1.

Figure 3b shows a cross sectional view of the energy collector device 1 , along vertical axis B-B in Figure 3a of the collector dome 10 and reflective strip 14.

In use, the energy collector can be used for both domestic use and swimming pool use. The only difference is in the amount of collectors required for the installation. For example, whether the energy collectors are connected in series or parallel which determines the flow rate of the working fluid (typically water) through the collectors. The tubing for the working fluid is constructed from a black exterior corrugated PVC with an approximate outside diameter of 18 to 22mm and an inside diameter of 14 to 18mm with a length of pipe to be dependent on how many layers and what diameter or m², which may be approximately one hundred and twenty metres. The tubing is secured through inlet and outlet holes within the peripheral wall of the outer case of the collector. Inlet and outlet holes may be located 180° opposite each other on the north and south faces of the peripheral wall, the inlet being at the lowest level and the outlet being at the highest level.

The tubing which contains the working fluid within the collector is coiled from outside inwardly to form a first layer of tubing. The then rises up and is coiled from the outside inwardly to form the second layer of tubing. The tubing then rises and is coiled from outside inwardly to form the third and fourth layers, and so on, dependent on the amount of layers, whereby the layers are linked together to form a substantially helical configuration.

The spacer tubing within the collector is made from a shaped plastic tube to enable the fluid tubing to be contained and prevent any lateral or horizontal movement. The spacer tubing is located at the plurality of distinctive positions between adjacent layers of the working fluid tubing, in the horizontal and vertical directions, to ensure a separation exists between them.

The thermal energy storage container is a sealed plastic container coated in a black material with a series of tubes attached to the outer surface extending radially outwards to the corrugated aluminium inner surface of the cover member and is partially filled with an oil can be free flowing solid, liquid or gaseous, or combinations thereof. Preferably liquid such as ionic liquid or hydrocarbon liquid or mixtures thereof, and more preferably one or more oils, this is typically a vegetable or mineral oil or antifreeze or any other heat absorbing material. The absorbed thermal energy is then dissipated within respective tubing layers and the open space which surrounds the tubing layers. The heat energy is then gradually transmitted by both conduction and convection to the working fluid contained within tubing. The heat convection is aided by an air circulation fan which helps to keep the internal temperature of the panel constant rather than the majority of hot air being at the top. The fan itself can be solar powered, wind powered or battery powered and works by homogenising the temperature inside the cover, i.e. lower most tubing gets identical heating to uppermost tubing.

The fluid is pumped either using a thermosyphon arrangement or external pump. The working fluid tubing is coiled such that the fluid enters the inlet and travels through the outermost portion of the bottom layer of the tubing towards the centre of the layer. On reaching the centre of the bottom layer the fluid travels upwards to the second layer and spirals inwardly and so on until the fluid reaches the outlet. This arrangement results in a colder working fluid being circulated within the bottom layer first, which is advantageous due to the upper portion of the connector maintaining the majority of the heat energy as mentioned previously. The sealed enclosure will gradually increase in temperature until it reaches thermal equilibrium through absorption and fan circulation, storage anticipation of the radiation energy in the storage container.

When the available solar radiation diminishes due to large clouds assembling in the atmosphere, the heat energy stored in the energy storage container dissipates through both conduction through the tubing directly and the convection to the relatively large air cavity surrounding the tubing by the fan assistance. This arrangement provides a more consistent heating mechanism which is less susceptible to fluctuations within the available solar radiation, which may be attributable to a number of large or dense cloud formations.

Figure 4 shows a simplified view of six energy collectors 1 , identical to the collector shown in Figures 1 to 3, are connected in parallel configuration in a heating system for heating water in a swimming pool 24. The collectors 1 are connected to two water supply circuits 20 and 21 which supply water in the direction indicated by arrows 22 and 23. The water is pumped from a swimming to the collectors 1 via a pump 25. The swimming pool 24 will be typically an in ground pool with a thirty thousand litre capacity.

In use, water is pumped from the swimming pool through each of the energy collectors and back to the swimming pool. Each energy collector is fed at an approximate four litres per minute flow rate giving a feed of approximately twenty four litres per minute back to the swimming pool. It is envisaged that one panel would be sufficient to heat five thousand litres of pool water to the required 28° Centigrade, which is the standard that most tour operators insist on when the air temperature averages around 20° Centigrade.

The water tubing allows the water to be pumped under low pressure through the coils at a rate of three to four litres per minute, for swimming pools, each panel connected in parallel using data from testing, each panel producing around 1 Kw of power. The spacing of the tubes both horizontally and vertically is extremely important to allow the fan assisted circulation air to work effectively. Pump generated heat would be zero as the existing pool pump would be used.

In the domestic system the water should be left in the tubes for 10-30 minutes to heat up before being pumped into the retention tank. (Instead of utilising an expensive insulated cylindrical metal tank, a well insulated plastic tank can be used with polystyrene balls on top of the water, this limits the overnight heat loss by a considerable amount). This heats the water to above double the ambient temperature outside the collector and reduces the pump generated heat and power to less than 3%. The Perspex dome works effectively in two ways: firstly, the sun always hits the dome at 90° as the sun rises and arcs rather than the rays bouncing off; this is whether the panel is laid flat or tilted slightly. In an aesthetic aspect, a panel which is tilted at an angle of 30 to 40° may become unsightly. When laid flat the airspace within the dome heats up extremely well. However other translucent materials such as flat glass or Perspex could also be used.

However, in an alternative embodiment of the invention, the cover can be of any shape, i.e. domed, rectangular, wavy, patterned, flat, oval, with different heights to fit different permutations, i.e. if space is limited where the device is fitted or to maximise the absorption or retention of the solar radiation. In experiments, a mixture of concave and convex shapes has been found to offer maximum heat retention.

In another alternative embodiment of the invention, the enclosure of the collector may be hermetically sealed; furthermore the enclosure may incorporate one or more holes, typically five millimetres in diameter incorporated within the base and/or peripheral wall, which prevents the condensation forming within the collector, therefore obviating the necessity of the domed cover from being double glazed. The one or more holes also contribute to the faster heating up of the collector.

In another alternative embodiment of the invention, the collector may further comprise an alternative heating source, which may be typically gas powered or an electrical heating source. For a domestic system an external booster pump can be used to facilitate power showers to multi-bathroom houses. The heating source may comprise a heater mat to accommodate colder winter climates, or may use a dump valve to empty the collector water tubes to expel water and stop them freezing.

In another alternative embodiment of the invention, the cover of the collector being shaped in the configuration of a dome made from translucent plastic or Perspex which incorporates a preformed pattern which may be typically a bulls eye or another design feature on the exterior of the cover. In another alternative embodiment of the invention, the thermal energy store device may be a simple oil container without any spokes or secondary reservoir means. The thermal energy store is located within the centre of the collector, because it is the hottest part of the collector and no tubes can be fitted there.

In another alternative embodiment of the invention, the thermal energy store device is detachable from the collector and is interchangeable with other energy store devices incorporating other various shapes and configurations, which may also contain a heat absorbing fluid of another type.

In another alternative embodiment of the invention, the collector can also be used as a heat exchange unit to cool an environment by removing heat. Here the shape of the cover, the type of heat storage material, and the material flowing through the tubing could all be changed to effect maximum heat removal.

In another alternative embodiment of the invention, the energy collector device further comprising a cooking means, such as a grill and/or hot plate, located between said cover and said base or said thermal energy storage; wherein said solar radiation produces thermal energy within said solar device which subsequently heats said cooking means that in use cooks or heats food.

In another alternative embodiment of the invention, the cover of the solar energy device maybe substantially domed in either a concave or convex shape.

Thermal energy is absorbed, stored and dissipated in a similar fashion to that which is described above in relation to the embodiment of Figures 1 to 4. The embodiments shown in Figures 1 to 4 are by way of example and should not be taken as the definitive solution to the problems.

The technical effect of the energy collector device is to provide an efficient means of maintaining the internal temperature of the collector at a constant temperature, which aids the convection of the thermal energy across all the layers of tubing while preventing the thermal energy from collecting within the upper portion of the cover. The objective technical problem of the energy collector device can therefore be defined as how to improve the efficiency of heating the fluid evenly across the tubing within the collector.

In an alternative embodiment of the invention the energy collector device is a solar oven or cooker. The solar oven / cooker is a device which uses sunlight as its energy source. Because they use no fuel and they cost nothing to run, they may be used worldwide since they reduce deforestation and desertification which is caused by burning wood during cooking.

It is usually necessary to use them only during daylight hours and in climates where there is sufficient solar energy to cook food.

There are a variety of types of solar cookers, their basic principles of all solar cookers are as follows:

• Concentrating sunlight: Some device, usually a mirror or some type of reflective metal, is used to concentrate light and heat from the sun into a small cooking area, making the energy more concentrated and therefore more potent.

• Converting light to heat: Any black on the inside of a solar cooker, as well as certain materials for pots, will improve the effectiveness of turning light into heat. A black pan will absorb almost all of the sun's light and turn it into heat, substantially improving the effectiveness of the cooker. Also, the better a pan conducts heat, the faster the oven will work.

• Trapping heat: Isolating the air inside the cooker from the air outside the cooker makes an important difference. Using a clear solid, like a plastic bag or a glass cover, will allow light to enter, but once the light is absorbed and converted to heat, a plastic bag or glass cover will trap the heat inside. This makes it possible to reach similar temperatures on cold and windy days as on hot days.

• Plastic Sheet: Uses plastic sheets to assure that liquids do not seep through into the oven. Also to prevent staining of the underlying sheet in the oven. Alone, each of these strategies for cooking something using solar energy is fairly ineffective, but most solar cookers use two or all three of these strategies in combination to get temperatures sufficient for cooking.

The top can usually be removed to allow dark pots containing food to be placed inside. One or more reflectors of shiny metal or foil-lined material may be positioned to bounce extra light into the interior of the oven chamber. Cooking containers and the inside bottom of the cooker should be dark coloured or black. Inside walls should be reflective to reduce heat loss via radiation and to bounce the light towards the pots and the dark bottom, which is in contact with the pots.

Until now, the use of optimally shaped hoods for the cooker and, optional heat collectors and circulatory fans have not been employed. However these further improve the efficiency of solar ovens such that cooking temperatures increase compared to products currently on the market or that the solar oven can be used in climates previously thought to be too low to cook food by harnessing solar power.

The solar box cooker typically reaches a temperature of 150 °C (300 °F). This is not as hot as a standard oven, but still hot enough to cook food over a somewhat longer period of time. Food containing a lot of moisture cannot get much hotter than 100 °C (212 °F) in any case, so it is not always necessary to cook at the high temperatures indicated in standard cookbooks. Because the food does not reach too high a temperature, it can be safely left in the cooker all day without burning. It is best to start cooking before noon, though. Depending on the latitude and weather, food can be cooked either early or later in the day. The cooker can be used to warm food and drinks and can also be used to pasteurise water or milk. If you use an indoor stove for your actual cooking, you can save significant fuel by using the solar cooker to preheat the water to be used for cooking grains, soups, etc., to nearly boiling.

There are several types of solar cookers:

1 ) Panel solar cookers are very inexpensive solar cookers that use shiny panels to direct sunlight to a cooking pot that is enclosed in a clear plastic bag. A common model is the CooKit. Developed in 1994 by Solar Cookers International, it is often produced locally by pasting a reflective material, such as aluminium foil, onto a cut and folded backing, usually cardboard corrugate. It is lightweight and folds for storage. When completely unfolded, it measures about three feet by four feet (1 m by 1.3 m).

The CooKit is considered a low-to-moderate temperature solar cooker, easily reaching temperatures high enough to pasteurize water or cook grains such as rice. On a sunny day, one CooKit can collect enough solar energy to cook rice, meat or vegetables.

The HotPot cooking vessel consists of a dark pot suspended inside a clear pot with a lid

To use a panel cooker, it is folded into a bowl shape. Food is placed in a dark coloured pot, covered with a tightly fitted lid. The pot is placed in a clear plastic bag and tied, clipped, or folded shut. The panel cooker is placed in direct sunlight until the food is cooked, which usually requires several hours for a full family-sized meal. For faster cooking, the pot can be raised on sticks or wires to allow the heated air to circulate underneath it.

High-temperature plastic bags (oven roasting bags) can be re-used for more than a month, but any plastic bag will work, if measures (such as sticks or wires) are taken to keep the bag from touching the hot cooking pot and melting to it. The purpose of the plastic bag is to trap heated air next to the pot; it may not be needed on very bright, windless days.

A recent development is the HotPot developed by US NGO Solar Household Energy Inc. The cooking vessel in this cooker is a large clear pot with a clear lid into which a dark pot is suspended. This design has the advantage of very even heating since the sun is able to shine onto the sides and the bottom of the pot during cooking. An added advantage is that the clear lid allows the food to be observed while it is cooking without removing the lid. The HotPot provides an alternative to using plastic bags in a panel cooker. Solar kettles are solar thermal devices that can heat water to boiling point through the reliance on solar energy alone. Some of them use evacuated solar glass tube technology to capture, accumulate and store solar energy needed to power the kettle. Besides heating liquids, since the stagnating temperature of solar vacuum glass tubes is a high 220 °C (425 °F), solar kettles can also deliver dry heat and function as ovens and autoclaves. Moreover, since solar vacuum glass tubes work on accumulated rather than concentrated solar thermal energy, solar kettles only need diffused sunlight to work and needs no sun tracking at all. If solar kettles use solar vacuum tubes technologies, the vacuum insulating properties will keep previously heated water hot throughout the night.

Scheffler cooker. The reflector has an area of 16 m², and produces 3 kW of heat.

Although these types of solar cookers can cook as well as a conventional oven, they are difficult to construct. Parabolic cookers reach high temperatures and cook quickly, but require frequent adjustment and supervision for safe operation. Several hundred thousand exist, mainly in China. They are especially useful for large-scale institutional cooking.

Parabolic reflectors that have their centres of mass coincident with their focal points are useful. They can be easily turned, to follow the sun's motions in the sky, rotating about an axis that passes through the focus. The cooking pot therefore stays stationary. If the paraboloid is axially symmetrical and is made of material of uniform thickness, this condition occurs if the depth of the paraboloid is 1.8478 times its focal length.

It is possible to use two parabolic troughs, curved in perpendicular directions, to bring sunlight to a point focus as does a paraboloidal reflector. The incoming light strikes one of the troughs, which sends it toward a line focus. The second trough intercepts the converging light and focuses it to a point. A Compared with a single paraboloid, using two partial troughs has important advantages. The troughs are "single curves", which can be made by bending a sheet of metal without any need for cutting, crumpling, or stretching. Also, the light that reaches the target - the cooking pot - is directed approximately downward, which reduces the danger of damage to the eyes of anyone nearby. On the other hand, there are disadvantages. More mirror material is needed, increasing the cost, and the light is reflected by two surfaces instead of one, which inevitably increases the amount that is lost.

Experimental arrangements of this kind have been made, and have worked well. The two troughs have been held in a fixed orientation relative to each other by being both fixed to a wooden frame. The whole assembly of frame and troughs has to be moved to track the sun as it moves in the sky. ) The Solar Bowl is a unique concentrating technology used by the Solar Kitchen in India. Unlike nearly all concentrating technologies that use tracking reflector systems, the solar bowl uses a stationary spherical reflector. This reflector focuses light along a line perpendicular to the sphere's surface and a computer control system moves the receiver to intersect this line. Steam is produced in the solar bowl's receiver at temperatures reaching 150 °C and then used for process heat in the kitchen where 2,000 meals are prepared daily. ) A hybrid solar oven is a solar box cooker equipped with a conventional electrical heating element for cloudy days or night time cooking. Hybrid solar ovens are therefore more independent. However, they lack the cost advantages of some other types of solar cookers, and so they have not caught on as much in third world countries where electricity or fuel sources simply do not exist. A hybrid solar grill consists of an adjustable parabolic reflector suspended in a tripod with a movable grill surface. These outperform solar box cookers in temperature range and cooking times. When solar energy is not available, the design uses any conventional fuel as a heat source, including gas, electricity, or wood.

A review of known prior art is as follows:

FR2787867 discloses the use of "a supple mirror made especially from a plastic with a reflective or metallised surface in the form of an umbrella with ribs that allow it to be deployed for use or folded for transport".

CN2366794Y discloses "a light condensing oven which can automatically track the sun. The utility model is composed of a bracket, a monitor, a main shaft, a water supply pipe, a gas outlet pipe, a light condensing cover, a self-ignition water tank, a valve, etc., wherein the monitor is arranged on the bracket and a power shaft of the monitor is connected with the main shaft. The power shaft of the monitor is connected with a spring of a clock, a gear wheel of the monitor is engaged with a gear wheel of a display and a dial plate of the clock is arranged on the display. While in use, as long as the light condensing oven is dialed every morning to face to the sun, the spring can be automatically and tightly wound and the light condensing oven can automatically track the sun after the spring is released. Therefore, water in the self-ignition water tank can be heated to produce water vapour which is used daily for cooking, showering, heating, etc"

CN 1200467 discloses a multi-purpose heat-storing solar furnace consists of two portions, the former is daylighting and light transmission means and the latter is the furnace equipment. It is characterized by that the sunlight focussed by collector lens is fed into optical cable through sunlight funnel, and the orientation of the sunlight is changed by optical cable, the output plug of terminal end of optical cable is inserted into the input socket of the furnace equipment so as to attain the goal of releasing heat or storing heat and storing energy. The output plug of terminal end of optical cable can be used as cutting and welding machine, and also can be matched with furnace equipment, for using as roasting plant, hot -water stove, steam oven or smelting furnace. When said invented product is used as steam boiler or smelting furnace having need of large power, several daylighting and light transmission devices can be used simultaneously to input high- density large-flux daylight beams into one furnace equipment.

None of these documents disclose the improvements in sun oven technology that we have found.

Whilst it is widely accepted that sun ovens should have reflective sheeting on its inner surface and have insulated walls and base, we have found that solar oven efficiency can be significantly improved by use of specific lid designs, by using heat storage chambers and by minimising heat loss through the place where most loss occurs - the lid. Furthermore, a circulatory fan helps to achieve consistent cooking performance. In order to address this, the present invention provides a sun oven in accordance with claim

Lids of known designs are either a flat cover (in line with the top of the walls of the oven) or at best a domed shape. However neither of these optimise the efficiency of the oven.

The lid preferably is configured into a predetermined shape incorporating a concave and convex portion or multiple concave and/or convex portions formed from a substantially transparent material. This enables the collector to be of any shape, i.e. domed, hexagonal (honeycombed), rectangular, "golf ball", parabolic, wavy, patterned, flat, oval, with different heights to fit different permutations, i.e. if space is limited where the device is fitted or to maximise the absorption or retention of the solar radiation. A mixture of concave and convex shapes has been found to offer maximum heat retention. The cover may itself be coated in a paint, spray or film which improves solar energy adsorption and/or helps prevent heat from radiating outwards and/or with self cleaning properties.

Minimising heat loss through the lid can be achieved in a number of ways. The material used, its thickness are the main routes, but applying reflective films or sprays can enhance heat retention within the oven or reduce loss by radiation from the oven. Furthermore, the lid can be double or treble walled or a cavity within the lid may be filled with an essentially transparent solid, liquid or may be a vacuum. All of these routes typically reduce loss of heat through the lid.

Preferably, the sun oven further comprising a tilting mechanism for tilting said device about an axis. This exposes as much of the ovens inner surface to direct sunlight, without the use of reflectors, to create heat within the oven. The unit itself could be angled or the lid could be angled/preferably shaped, or the tubing in relation to the dome could be angled for maximum performance.

No sun ovens presently use heat retention units to store heat. If there are clouds present, or if day is turning to dusk then traditional sun ovens will cool down or cease to be used. By employing a heat storage unit, the sun oven can be used despite passing clouds or for a period of time after dusk. The energy collector is preferably retained in close proximity to the cooking area. Its purpose is to heat up and store heat when exposed to thermal energy. In one embodiment, the energy collector may be the surface upon which cooking occurs. Alternatively, for optimal design within some sun ovens, there may be several discrete solar collectors within one oven which may either be connected or be separated from one another.

Energy collectors may also be chambers filled with gaseous material. Energy collectors may alternatively be solid materials which absorb and store heat. Such solid material may be metals, volcanic rocks, stone, ceramic or the like.

Optionally a fan is attached to the body of the sun oven. This may itself be powered by wind energy, solar PV energy, batteries, electrical mains or other means. Use of a fan will help to evenly distribute thermal energy throughout the oven and help achieved consistent cooking performance from one part of the oven to another.

Therefore, the technical effect of the solar oven/cooker is to provide an efficient means of maintaining the internal temperature of the solar oven/cooker at a constant temperature, when the solar energy levels are reduced due to cloud coverage and/or dusk, therefore preventing the solar oven/cooker from cooling down.

The objective technical problem of the solar oven/cooker can therefore be defined as how to improve the efficiency of maintaining the internal temperature within the solar oven/cooker.

Claims

1. An energy collector device comprising an enclosure and tubing; said enclosure incorporates a base and cover; a thermal energy storage device located between said cover and said base; a circulatory fan attached to said cover: said tubing being at least partially located between said cover and said energy storage device for communicating a working fluid within said collector device; wherein said tubing is configured into a layer, which in use communicates said working fluid about an inner chamber of said device; said circulatory fan circulates the air within said device and facilitates the convection of thermal energy from said storage device evenly across said layer of said tubing.

2. A device according to claim 1, wherein said tubing is configured into 3 or more layers.

3. A device according to claim 1 , wherein said thermal energy storage device

incorporates a reservoir of heat absorbing liquid; the absorbed thermal energy contained within said heat absorbing liquid is communicated from said thermal energy storage device to said working fluid within said tubing, when in use, the available solar radiation diminishes.

4. A device according to claim 1, wherein said thermal energy storage device further comprises a body portion which extends towards the inner surface of said cover, thereby extending said reservoir of heat absorbing fluid towards said inner surface of said cover.

5. A device according to any of the preceding claims, wherein said heat absorbing fluid is an ionic liquid or hydrocarbon liquid or mixtures thereof.

6. A device according to any of the preceding claims, wherein said tubing incorporates a corrugated surface.

7. A device according to any of the preceding claims, wherein said tubing is configured into a plurality of coil configurations which are interconnected in a substantially helical configuration; whereby said working fluid is continuously communicated about and between each said coil configuration.

8. A device according to claim 7; further comprising a plurality of spacer members for separating and supporting adjacent tubing portions along both vertical and horizontal axes.

9. A device according to claim 8; wherein each said spacer member further comprises a corrugated surface.

10. A device according to claims 1 to 6, wherein said tubing is configured into a grid configuration.

1 1. A device according to any of the preceding claims, wherein said cover is configured into a predetermined shape incorporating a concave and / or convex portion formed from a substantially transparent material.

12. A device according to any of the preceding claims; further comprising a peripheral wall that incorporates a corrugated surface.

13. A device according to any of the preceding claims; wherein said base further

comprises an insulating layer that incorporates a corrugated surface.

14. A device according to claims 9, 12 and 13, wherein said corrugated surfaces are formed from a substantially aluminium material coated in a black or reflective coating.

15. A device according to any of the preceding claims; further comprising a second heating source for communicating thermal energy to said working fluid within said tubing.

16. A device according to claim 15, wherein said second heating source is an electrical heating source or gas heating source.

17. A device according to any of the preceding claims; further comprising a tilting mechanism for tilting said device about an axis.

18. A device according to any of the preceding claims; further comprising a cooking means located between said cover and said base or said thermal energy storage; wherein said solar radiation produces thermal energy within said solar device which subsequently heats said cooking means that in use cooks or heats food.

19. A device according to any of the preceding claims; further comprising a reflective member located about a portion of the outer surface of said cover; whereby said reflective member incorporates a reflective surface that faces said cover and reflects solar radiation into said cover.

20. A method of heating a working fluid within a energy collecting device comprising the steps of ;

• Communicating a working fluid incorporated within said tubing about an inner chamber of said energy collecting device; and

• Circulating the air within said inner chamber of said energy collecting device with a circulatory fan, which facilitates the convection of thermal energy from said storage device evenly across said layer of tubing.

21. An energy collector device substantially as hereinbefore described and/or

illustrated in any of the accompanying text and Figures 1 to 4.

22. A method of heating a working fluid within an energy collecting device as

hereinbefore described and/or illustrated in any of the accompanying text and/or Figures 1 to 4.

23. A sun oven for cooking purposes comprising oven body covered in reflective material, a cooking surface, a lid, a heat storage unit and a circulatory fan and wherein said lid is shaped with a mixture of concave and convex portions.

24. An oven according to claim 23, wherein said heat storage unit comprises a

chamber filled with an ionic liquid, or a chamber filled with a hydrocarbon liquid or gas; or wherein the heat storage unit comprises a solid heat absorbent material.

An oven according to claim 23, wherein said heat storage unit forms the surface upon which cooking takes place.

26. An oven according to claim 23, wherein the temperature within said oven is

homogenised by use of said circulatory fan.

27. An oven according to claim 23, wherein said oven is tiltable upon its base to be positioned in optimum sunlight depending on the position of the sun and the terrain in which said oven is placed.

28. An oven according to claim 23, wherein said lid is tiltable upon said oven to be positioned in optimum sunlight depending the on the position of the sun and the terrain in which said oven is placed.

29. An oven according to claim 23, wherein said cooking surface is either part of the reflective surface or is a raised grill above the base of said oven.

30. A sun oven for cooking purposes substantially, as herein before described and/or illustrated in any of the accompanying text and/or Figures.