WO2010119071A2

WO2010119071A2 - Solar powered integrated collector and storage apparatus

Info

Publication number: WO2010119071A2
Application number: PCT/EP2010/054902
Authority: WO
Inventors: Edward Andrew Young
Original assignee: YRENEW SOLAR Ltd
Current assignee: YRENEW SOLAR Ltd
Priority date: 2009-04-15
Filing date: 2010-04-14
Publication date: 2010-10-21
Anticipated expiration: 2011-10-15
Also published as: EP2430371A2; WO2010119071A3; GB0906485D0

Abstract

System for providing solar heated hot water at an end user outlet, the system comprising a solar powered integrated collector and storage apparatus comprising a plurality of vacuum insulated collector tubes, each collector tube being arranged for the storage in the interior space thereof of a quantity of water heated at a temperature above a desired end user temperature; measurement means for measuring the temperature of the water stored inside the plurality of collector tubes or a variable representative for said temperature; mixing means between the solar powered integrated collector and storage apparatus and the end user outlet for mixing an amount of the stored water with a supply of cold water; control means adapted for controlling the mixing means.

Description

SOLAR POWERED INTEGRATED COLLECTOR AND STORAGE APPARATUS

The present invention relates to a solar powered integrated collector and storage apparatus for heating water, to a system for providing solar heated hot water and to a method of providing solar heated hot water to an end user.

The provision of domestic hot water is one of the highest energy costs in a typical home. Solar energy has been used for many years to heat domestic hot water and solar water heaters have increased in popularity in recent decades, particularly in hot, sunny climates. Solar water heaters can reduce the amount of gas and/or electricity needed to heat water, thereby saving on water heating costs. Furthermore, by using sunlight to heat water rather than using gas or electricity, fewer pollutants are released into the atmosphere.

A typical domestic solar powered hot water system is shown in Figure 1. The system

1 comprises a solar collector panel 10 and a boiler module 20. The solar collector 10 comprises a black metal absorber backing plate 15 with a glass cover, inside of which are one or more tubes containing a heat transfer fluid, typically a mixture of water and propylene glycol, that will not freeze. The solar collector is typically mounted on the roof of a building or the like. Light from the sun strikes the solar collector 10 and heats the black metal absorber 15. The heat is transferred to the heat transfer fluid that is pumped through the collector tubes by a pump 30. The pump returns the heated heat transfer fluid to a heat exchanger 25 in the boiler 20. The system further comprises a water storage tank 40 which is filled initially with cold water. The cold water is heated in the boiler 20 by heat from the heat transfer fluid in the heat exchanger 25. The solar heated water is then stored in the storage tank 40, where it naturally circulates to the top of the tank. An auxiliary electric or gas powered gas boiler 50 provides hot water to the domestic user. As the auxiliary tank 50 is depleted, it is replaced with solar heated water from the tank 40, thereby reducing the amount of energy required to increase the temperature of the solar heated water to the desired end user temperature. Whilst this system of pre -heating water using solar energy can reduce the fuel energy cost of providing hot water, it has several drawbacks. Firstly, the system uses a water storage tank to store the solar heated water. However, over fifty per cent of domestic boilers in UK homes are combi boilers that do not have a hot water tank. This system is therefore unsuitable for use with over fifty per cent of domestic boilers in UK homes. Furthermore, the system requires a pump to circulate the heat transfer fluid through the solar collector and the heat exchanger, which uses electrical energy. In sufficiently sunny climates, the electrical energy can be generated via a photo-voltaic cell 60 but in cooler climates this will not often provide sufficient energy to drive the pump. The system is also prone to heat losses such that the heat provided to the water in the heat exchanger 25 would be at a somewhat lower temperature than the heat that is reached in the heat transfer fluid in the collector 10. These collectors cannot operate in cooler seasons, climates or non-ideal mounting orientation, because the losses will become rapidly similar to the solar heat gain.

Combi boilers are compatible with integrated collector storage systems, known as ICS systems, in which the water is both heated and stored inside the collector. Known prior art ICS systems are suitable only for warm climates where there is no risk of the water freezing in the collector. The collector may consist of a flat copper plate, painted black to absorb solar radiation, and copper tubes containing water to be heated. The absorber and tubes are mounted in a transparent casing that is insulated to prevent heat loss. These ICS systems are not generally suitable for use in cooler climates such as the UK and northern continental Europe, because the water in the collector tubes is prone to freezing. Even in warmer climates, the system is prone to significant heat losses and therefore to inefficiency.

It is desirable to reduce to at least a certain extent one or more of the drawbacks of the prior art solar hot water systems.

According to an embodiment of the invention there is provided a system for providing solar heated hot water at an end user outlet, the system comprising: a solar powered integrated collector and storage apparatus; mixing means between the solar powered integrated collector and storage apparatus and the end user outlet for mixing an amount of the stored water with a supply of cold water; and control means adapted for controlling the mixing means. The collector and storage apparatus typically comprises a plurality of vacuum insulated collector tubes, and measurement means for measuring the temperature of the water stored inside the plurality of collector tubes or a variable representative for said temperature. Each collector tube is arranged for the storage in the interior space thereof of a quantity of water heated at a temperature above a desired end user temperature. In the event that the measured temperature is greater than a pre-determined temperature, the mixing means are controlled by the control means to mix an amount of the stored water with an amount of colder water.

By providing such a system heat is stored in a more efficient way. More in particular the storage volume needed for a certain amount of hot water is reduced compared to the systems of the prior art.

According to a preferred aspect the control means are adapted for controlling the mixing means such that the mixed water has a desired end user temperature. The desired end user temperature is typically lower or equal to the measured storage temperature.

According to another embodiment there is provided a solar powered integrated collector and storage apparatus comprising a plurality of vacuum insulated collector tubes, each collector tube having an inlet conduit and an outlet conduit and being otherwise substantially sealed from the ambient atmosphere. Preferably the inlet conduit is longer than the outlet conduit to minimize mixing and displacement of water inside the tube. Each collector tube is arranged for the storage in the interior space thereof of a quantity of water to be heated at a temperature above the temperature of the water needed by the end user. Each collector tube is a double walled, vacuum insulated glass tube having a closed end and an open end, and having an inner glass wall and an outer glass wall. The open end is sealed between on the one hand the inner wall, and on the other hand the inlet and outlet conduit, wherein insulation material is extending into said open end, surrounding said inlet and outlet conduit over a certain distance. In that way an improved insulation is provided compared to the systems of the prior art, leading to less heat losses.

The invention also relates to a vacuum insulated collector tube adapted for use in the above disclosed embodiment of the apparatus of the invention.

According to a preferred aspect of the vacuum insulated collector tube, the tube has a diameter which is smaller than 100 mm, preferably smaller than 80 mm, and most preferably smaller than 70 mm.

According to a preferred aspect of the vacuum insulated collector tube the insulation material extends over a distance of at least 10 mm, preferably at least 20 mm and most preferably at least 40 mm inside the collector tube.

According to a preferred aspect of the vacuum insulated collector tube the sealing between the inner wall of the tubes and the inlet/outlet conduits consists of a cylindrical flange part and an O ring between said cylindrical flange part and the inner wall. The inlet and outlet conduits extend through said cylindrical flange part. Preferably insulation material extends between said flange part and said open end. Preferably at least a part of said cylindrical flange part is made from a metal alloy having a low thermal conductivity.

According to a preferred aspect of the vacuum insulated collector tube the inlet and outlet conduit are manufactured from a metal with a high thermal conductivity, such as aluminium or copper.

According to a preferred aspect of the solar powered integrated collector and storage apparatus, it comprises a manifold, wherein the inlet conduit and the outlet conduit of each collector tube are arranged in fluid communication with the manifold. Typically the manifold has a manifold inlet pipe and a manifold outlet pipe. The plurality of collector tubes is arranged lengthwise adjacent one another, starting with a first collector tube and ending with a last collector tube. Connector pipes are provided between the outlet conduit and inlet conduit of adjacent collector tubes of said plurality of tubes. The manifold inlet pipe is connected to the inlet conduit of the first collector tube and the manifold outlet pipe is connected to the outlet conduit of the last collector tube. Preferably insulation material extends around the connector pipes and the manifold inlet and outlet pipes and all the way in the open ends of the tubes.

According to a preferred embodiment of the apparatus of the invention a bottom reflecting means, such a reflective outer coating or a bottom reflector, is arranged underneath each collector tube. In that way heat radiation leaving the tube at the underside thereof will be reflected back inside the tube. Also there may be provided at least one top reflector, said top reflector being moveable between a plurality of positions. Such a top reflector can e.g. be shaped in the form of a cylinder section fitting above the upper part of a tube. In this case each tube will typically be provided with a top reflector. Note that it is also possible to provide such a top reflector with a different shape such that it can extend over a number of tubes. Preferably, there is provided a controller for controlling the position of each top reflector in function of the temperature measured by the measurement means and/or in function of the outside temperature.

According to a further aspect the system of the invention further comprises a boiler or other system capable of providing hot water on demand connected in series with the mixing means; and a controller configured to control the boiler according to the temperature measured by the measurement means.

Finally the invention also relates to a solar powered integrated collector and storage apparatus for use in a system as described above, said apparatus having any one or more of the features described above; to a tube for use in a system as described above, said tube having any one or more of the features described above; and to a manifold for use in a system as described above, said manifold having any one or more of the features described above. According yet another aspect of the present invention, there is provided a solar powered integrated collector and storage apparatus for heating water, the apparatus comprising: at least one vacuum insulated collector tube having an inner wall and an outer wall enclosing an interior space, each collector tube including a high ultra violet absorption low infra red transmission coating disposed on an outer surface of the inner wall, each collector tube further comprising an inlet conduit and an outlet conduit and being otherwise substantially sealed from the ambient atmosphere, and in which each collector tube is arranged for the storage in the interior space thereof of a quantity of water to be heated.

An advantage of this apparatus is that the water can be heated to a very high temperature (in theory up to 300⁰C although legal requirements in some jurisdictions mean temperatures must be regulated to not climb above a certain level e.g. 100⁰C in UK), then stored in the collector tube without significantly losing heat. Due to the higher peak operating temperature, a sufficiently high domestic water temperature >60°C is maintained even at reduced thermal solar heat flux, such that in cooler seasons or non-ideal locations, the vacuum insulated collector tube insulates the water sufficiently well that the water is still adequately hot in the morning following an overnight period. Thus, the water cools down overnight by only a small amount and is still hot enough to be provided directly (i.e. without it requiring reheating) to the user in the morning. Furthermore, even if the ambient temperature plummets, the water retains sufficient heat that there is no risk of the water freezing in cooler climates such as the UK and northern continental Europe. Storing the water in the collector tubes also means that a separate storage tank and associated pipework and heat exchanger for heated water is not required. The system is less susceptible to thermal inefficiency as a result.

The collector tube may be manufactured from glass and may comprise a closed end and an open end at which the water can be fed into and out of the tube. The inlet conduit and outlet conduit may be housed in a seal in order to substantially seal the contents of the collector tube from the atmosphere and to minimise heat loss from the collector tube.

The apparatus may include a plurality of collector tubes, disposed adjacent to one another. The inlet and outlet conduit of each collector tube may be arranged in fluid communication with a collector tube manifold. The manifold may be arranged in fluid communication at an inlet end thereof with a water supply, and at an outlet end thereof with an auxiliary boiler. Preferably, the water supply is a mains water supply that provides water to the manifold at mains pressure (typically 2-3 bar in the UK). The auxiliary boiler may be a combi boiler, as no tank is required in which to store the heated water. The boiler may simply be used to provide top-up reheating of the solar heated water during colder months.

The apparatus may further comprise a sensor arranged for measuring a temperature of the water in one of the collector tubes or at the collector tube manifold. The measured temperature may provide an input to a controller. The controller may be configured to control the auxiliary boiler according to the measured temperature of the water in one or more of the collector tubes or at the collector tube manifold. The measured temperature may provide an input to a controller. The controller may be configured to control the auxiliary boiler according to the measured temperature of the water in the one or more of the collector tubes or at the collector tube manifold.

The apparatus may further comprise a solar concentrator having a reflective surface. Each collector tube may be disposed above the solar concentrator such that reflected rays from the sun are oriented towards the collector tubes.

According to a further aspect of the invention, there is provided a system for providing solar heated hot water to an end user, the system comprising a solar powered integrated collector and storage apparatus according to the first aspect of the invention, a mains water supply for supplying water to be heated to at least one collector tube of the apparatus, a boiler in fluid communication with at least one collector tube of the integrated collector and storage apparatus and an end user outlet. The end user outlet may comprise a faucet or it may comprise an electrical appliance such as a shower unit or washing machine.

According to a still further aspect of the invention, there is provided a method of providing hot water to an end user using a solar powered integrated collector and storage apparatus having at least one collector tube arranged in fluid communication with each of a cold water supply, a boiler and an end user outlet, the method comprising heating a quantity of water contained in the collector tube, storing the heat contained in the heated water inside the collector tube at a temperature above the temperature of the water required at the end user outlet, measuring the temperature of the heated water inside the collector tube, transporting the heated water into the boiler, controlling operation of the boiler according to the temperature measured and supplying the water from the boiler to the end user outlet.

The step of controlling operation of the boiler according to the temperature measured may comprise, in the event that the measured temperature in the collector tube is greater than a pre-determined temperature, and in the event that the boiler is switched on, switching the boiler off. Otherwise, the boiler is operated to re-heat the solar heated water until it is determined that the water has reached the pre-determined temperature.

The method may comprise the further step of, prior to supplying the water from the boiler to the end user, mixing the water supplied from the boiler with a supply of cold water. In this manner, the high temperature of the solar heated water may be brought down to a temperature more suitable for domestic use. For example, if the water in the collector tube is being stored at a temperature of 90⁰C, it may be mixed with a supply of cold water in order to bring its temperature down to 45°C. In this manner, the volume of the heated water is increased at the time it is required by the end user, rather than storing large volumes of water in a tank as in prior art systems. The step of mixing the heated water with a cold water supply may be undertaken in stages in an end user conduit that extends between the boiler and the end user outlet. For example, a first mixer valve could be provided in the conduit between the collector storage apparatus and the boiler in order to mix the solar heated water from 90⁰C down to a temperature of 70⁰C in a first stage. A second mixer valve may be provided in the end user conduit to mix the 70⁰C water down to a temperature of 45°C for actual domestic usage.

These and other aspects of the present invention will become apparent to the skilled person upon reading the following non-limiting description of preferred embodiments of the invention and with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a prior art solar heated hot water system;

Figure 2 is a schematic representation of an integrated collector and storage apparatus in accordance with the invention;

Figure 3 is a detailed schematic view of a section of the ICS apparatus of Figure 2;

Figure 4 is a detailed schematic representation of the collector tubes of Figures 2 and 3, positioned above solar concentrators;

Figure 5 is a schematic representation of an insulated vacuum collector and storage tube used in the invention;

Figure 6 is a schematic representation of a system for providing solar heated hot water, in accordance with the invention, shown installed in a house.

Figure 7 is a schematic diagram of a preferred embodiment of a system of the invention;

Figure 8 is a schematic diagram of a preferred embodiment of a collector and storage tube of the invention; Figure 9 illustrates schematically the use of bottom and top reflectors in an embodiment of the invention;

Figure 10 is a schematic diagram of a preferred embodiment of a collector and storage apparatus of the invention comprising a plurality of tubes as e.g. illustrated in figure

8.

Figure 2 shows an embodiment of an integrated collector and storage apparatus 100 in accordance with the invention. The apparatus 100 comprises a plurality of solar tubes 120 that are arranged adjacent one another in a row. In use of the apparatus, water is both heated and stored in the solar tubes such that no separate storage tank for the heated water is required. The solar tubes 120 each comprise a double walled, vacuum insulated elongate tube that is closed at a distal end 121 thereof. A proximal end 122 of each solar tube is open to admit a flow of water into and out of the tube. The embodiment of Figure 2 includes thirty solar tubes 120, each being attached at the proximal end 122 thereof to a manifold 130. The manifold 130 comprises an elongate housing having a water inlet end 131 and a water outlet end 132. The housing contains pipework for the transportation of water from the water inlet end 131, through each solar tube 120 and then out of the water outlet end 132. Figure 3 shows a detail view of a portion of the manifold 130 and its pipe connections with each of the solar tubes 120.

Associated with each solar tube 120 is at least one connector pipe 135. Each connector pipe 135 is generally U-shaped in the illustrated embodiment, although other appropriate shapes, such as a T-shape, are envisaged. Each connector pipe has an outlet end 136 that extends into the proximal end of and that is in fluid communication with a first solar tube 120a, and an inlet end 137 that extends into the proximal end of and is in fluid communication with a second solar tube 120b. The connector pipes 135 therefore connect adjacently positioned solar tubes 120 in series fluid communication. At the water inlet end 131 of the manifold, a manifold inlet pipe 138 is arranged at one end thereof for connection of the manifold 130 to a mains water supply (not shown). The manifold inlet pipe 138 extends at its other end into the first solar tube 120 to provide a flow of water through the tubes.

Figure 4 is a detailed schematic representation of a single solar tube 120. The solar tube 120 consists of a double walled vacuum insulated tube that is manufactured from glass. In an embodiment, the glass is borax glass. The outer surface of the inner wall of the double- walled tube 120 is coated with a high ultra violet (UV) radiation absorbing, low infra-red (IR) transmitting coating 125 such as CERMET (Ceramic

Metal composite), a known coating used in the art of vacuum insulated tubes. In an embodiment, the CERMET coating absorbs radiation in the visible and near- infrared spectra (300 to 3,000nm) and has a low emissivity in the thermal infrared spectrum

(4,500 to 45,000nm).

The solar tube 120 is substantially sealed at its proximal end 122 with a piston O-ring seal made from glass fibre or other low thermal conductivity sealing material. For example, iron-nickel has a similar thermal expansion to glass. Housed in the O-ring seal are the inlet end 137 of one of the connector pipes 135, and the outlet end 136 of an adjacent connector pipe 135. The connector pipes 135 are manufactured from a material having a low thermal conductivity such as stainless steel. Furthermore, the section of the connector pipe 135 that forms each of the inlet end 137 and the outlet end 136 is designed to be long enough to provide a sufficient temperature drop to minimise heat losses at the manifold surface. The manifold surface is therefore at a lower temperature than is the stored water. The connector pipes are held tightly in place in the O-ring seal 125 such that an interior space 128 of the solar tube is substantially sealed off from the ambient atmosphere. The manifold housing 130 and the connector pipes 135 are also well insulated using glass fibre or other suitable insulating material 139, as seen schematically in Figure 6.

In use of the apparatus, the solar tubes 120 are used to heat and then store a quantity of water. In the present embodiment, each solar tube has a capacity of approximately two litres. The coated tubes 120 absorb radiation from the sun. The coating 125 has an efficiency of approximately 90%, meaning that 90% of the radiation absorbed by the tubes is retained within the tube, and the outer wall can reach temperatures of up to 300⁰C. The glass material of the tube means that heat loss due to thermal conductivity at the tube inner wall is limited. The vacuum insulation of the tube eliminates convective heat losses from the solar tube. The combination of these factors provides a solar tube design that can heat a quantity of water inside the tube to a very high temperature. The heat in the water is retained to a very high level of efficiency due to the very low thermal losses from the solar tube 120. Hence, the heat in the water can be stored at a high temperature for a number of hours, without the temperature of the water dropping significantly. It is expected that during an overnight period of ten hours, the thermal efficiency of the tube is such that the water temperature will drop a certain amount but it will be adequately hot for direct use by an end user. This feature of the present invention is highly advantageous in cooler climates or low light conditions in which the temperature may drop significantly overnight, or in built-up or forested areas and also "out of season" in cooler months when ambient light conditions are low, or any combination thereof. In these conditions, it is expected that the temperature of the water inside the solar tubes may reach around 60⁰C and may drop to ~ 50⁰C.

The efficiency of the solar tubes 120 can be boosted by the addition of a solar concentrator 150 to the apparatus 100, as seen best in Figure 2 and Figure 5. The solar concentrator 150 consists of a series of parabolic sections that are covered in or have integrally formed thereon, a reflective surface, preferably a mirrored surface.

The solar concentrator 150 is placed beneath the solar tubes 120 such that each tube sits inside one of the parabolic sections. In this manner, the sun's rays bounce off the solar concentrator and are reflected towards the solar tubes 120, allowing the tubes to absorb an additional amount of solar radiation. The solar concentrator 150 may be omitted if the ICS unit is to be installed at a very sunny location.

Figure 6 shows a schematic representation of an integrated collector and storage apparatus according to the invention, as part of a solar water heating system in a house 200. The apparatus 100 is shown installed on the roof of the house at an orientation determined by the slope of the roof. However, it may be installed in any orientation from horizontal to vertical and all orientations in between these extremes. For the purpose of clarity, the water inlet to the apparatus is shown to be at the distal end 121 of the solar tube 120, although it will be appreciated that in the embodiment described above, the water inlet 131 is situated at the manifold 130. The water inlet 131 is attached to a water supply conduit 160 that draws water from the mains water supply 162 to the house. The mains water is pressurised above ambient pressure and so pumps itself towards the apparatus 100. The water from the mains supply flows into the manifold 130 and fills up the solar tubes 120 via the connector pipes 135. The temperature of the water contained within the solar tubes 120 then gradually increases as the solar tubes 120 absorb solar radiation. A temperature sensor 165 is located at one of the solar tubes 120 for measurement of the temperature of the water contained inside the tube. In another embodiment, the sensor may be located to measure the temperature of the water in the manifold 130.

The system further includes a combi boiler 170 or other "hot water on demand" system such as an electrical coil that is arranged in fluid communication via a conduit 172 with the manifold outlet end 132. The combi boiler can be operated to either reheat the solar heated water or it can be switched off if the water temperature is already sufficiently high. A controller 180 is arranged inside the house, in electronic communication with each of the temperature sensor 165 and the combi boiler 170. The controller 180 is configured to request the measured temperature of the water inside a solar tube 120 or at the manifold. If the temperature measured by the sensor 165 is > about 60⁰C, then the controller determines that the boiler 170 is not required to be switched on to re-heat the water and it either switches off the boiler or maintains it in an off condition if it is already off. However, if the temperature measured at the temperature sensor 165 is < 60⁰C, then the controller 180 determines that the boiler 170 should be operated to re-heat the water supplied from the apparatus 100. The controller 180 will either switch on the boiler 170 or, if it is already switched on, maintain it in an operating condition. As the water has already been heated inside the solar tubes 120 by solar energy, the gas energy required to re-heat the water in the boiler 170 is significantly less than heating via the boiler alone, providing a cost saving in both energy and financial terms. The boiler 170 thus supplies solar heated or solar and gas heated water to an end user conduit 190 that is in fluid communication with various end uses such as a faucet 300 or an electric shower 350. An ICS apparatus comprising thirty tubes at a capacity of 2 litres per tube is capable of providing 60 litres of heated water, which could be at a very high temperature, up to 100⁰C in the UK. Domestic hot water is generally provided at a temperature of between 45°C and 60⁰C depending on the appliance. For example, a mixer tap, in which a cold stream of water combines with a hot stream of water, is usually supplied with hot water at ~60°C. However, a shower requires no more than 45°C. Thus it is necessary to be able to cool down the heated water before it reaches the end user.

The system thus includes at least one mixer valve 195 disposed in the end user supply conduit 190 or in a mains supply conduit 200 that is in fluid communication with the end user supply conduit 190. A valve 195 can also be located in the conduit 172 between the ICS unit and the boiler 170. The mixer valve 195 consists in one embodiment of a bi-metallic switch that is configured to deform in response to heat at a certain pre-determined temperature. If the bi-metallic switch detects that the water temperatures in the end user supply conduit is above e.g. 70⁰C, it automatically deforms to open the mixer valve to allow a supply of mains cold water into the conduit 190.

A second mixer valve 195 can be provided further down the supply conduit 190, and is configured to open at a lower temperature of e.g. 60⁰C to bring the water temperature down to e.g. 45°C. It will be appreciated by the skilled person that other types of valve such as a ball valve could be used instead of a bi-metallic switch valve and that methods of operating and controlling such a valve are known in the art and will not be repeated here.

In reducing the temperature of the solar heated water with a supply of cold water, the quantity of water available to the end user increases significantly. An initial sixty litres of solar heated water can be increased to at least double the quantity through one or more stages of introducing a mixing supply of cold water into the end user supply conduit. As such, the system is capable of producing the hot water supply for a household for a day without requiring a storage tank at any point in the system or modules, saving valuable space and costs. In an embodiment, the ICS apparatus may be supplied in banks or modules of e.g. 8 tubes, thus the system capacity can be easily increased in multiples of 8 tubes to suit the requirements of the house or building or the like onto which it is to be installed.

A further advantage of the system is that in directly supplying mains water to the solar tubes and in using a gravity feed to the boiler, no pump is required to operate the apparatus or to run the system. The system is put into operation via an end user opening a faucet or switching on an electric shower and the system is switched off when the end user turns off the faucet or shower. The mains pressure and the low heat flux of the surface of the collector/storage tubes (< 0.2W/cm²) also ensures that even if the water inside the solar tubes reaches 100⁰C, it will not boil. The interior space 128 of the tubes will therefore not become sealed up in hard water areas, resulting in a longer life span for the tubes.

Embodiments of the apparatus also include a means of rejecting excess heat from the manifold if the temperature of the water reaches above 90⁰C. A heat exchanger may be utilised for this purpose. It is also desirable to provide a pressure relief valve at the manifold that is designed to operate if the measured water temperature exceeds 100⁰C.

It will be apparent to the skilled person that the apparatus, system and method of operation of the apparatus are capable of providing directly usable solar heated hot water to a domestic end user over a longer period of the year than is possible with prior art systems, due to the thermal efficiency of the apparatus and its capacity to store heat in the water at very high temperatures. It is expected that this apparatus can be used to supply directly usable hot water on demand to an end user from March to October in the UK, whereas the prior art systems of Figure 1 may provide the same between May and July and require both a tank and a pump in order to store the water and to transport it around the system. Furthermore, the energy saving advantage of a combi boiler, i.e. water is heated only as it is used, is maintained. The apparatus is also aesthetically pleasing, an important factor in saleability of the apparatus. Figure 7 illustrated schematically a second embodiment of a system of the invention. The illustrated embodiment comprises a solar powered integrated collector and storage apparatus 200 with ten vacuum insulated collector tubes 220. The collector tubes 220 are connected in series using a number of connector pipes 235. Cold water from the mains at a temperature TO enters the apparatus 200 through inlet 231. The collector tubes 220 are arranged for storing water heated at a temperature Tl above a desired end user temperature T3. E.g. for the UK, the water could be heated between 60 and 70 degrees Celsius in spring and up to 150 degrees in summer. Note however that for domestic usage this may be limited to 100 degrees by regulation. The apparatus 200 further comprises measurement means 265 for measuring the temperature Tl of the water stored inside the collector tubes 220. Note that this temperature could also be measured at the inlet 231 or at the outlet 232 or in the connector tubes 235. The heated water leaves through outlet 232 and is supplied to a mixer 295 for mixing an amount of the stored water at temperature Tl with a supply of cold water at temperature TO. A controller 294 controls the mixing means in the event that the measured temperature Tl is greater than a pre-determined temperature, e.g. the desired end user temperature which is typically the maximum temperature needed inside a household for domestic applications or the maximum temperature needed in a plant for industrial applications. The mixer may e.g. be an electronically controlled gate valve. Optionally the mixer 295 is connected in series with an auxiliary boiler 270 for further heating the water in the event that the temperature of the stored water Tl is below the desired end user temperature. This may e.g. be the case in winter. The auxiliary boiler 270 will typically be controlled by controller 294 configured to control the boiler 270 according to the temperature Tl measured by the measurement means 265.

By storing the water at a temperature Tl which is higher than the desired end user temperature a higher effective volume is obtained. In other words less water needs to be stored compared to conventional systems. Typically the tube diameter is chosen to be sufficiently small, such that there is a high ratio of collecting area to water volume. By having this high ratio, also in cooler seasons the water is heated to above the end user temperature, e.g. for an average day in March, Leeds UK, 72 degrees. The cost of having a larger collecting area is offset by the fact no tank with ancillary plumbing is required, and the subsequent lower installation cost. The higher water temperature is not only due to the larger collection area (e.g. approximately 25 percent more) but also to the fact that there is no need for a tank and the insulation can be made very good, see further.

Figure 8 illustrates a preferred embodiment of a collector tube 220 as used is a collector and storage apparatus of the invention, an embodiment of the complete apparatus being shown in figure 10. The collector tube 220 is a double walled, vacuum insulated glass tube having a closed end 221 and an open end 222. The double walled tubular container 220 has an inner glass wall 224 and an outer glass wall 225. The open end 222 is sealed between on the one hand the inner wall 225, and on the other hand the inlet conduit end 237 and outlet conduit end 236. Typically the inlet conduit will be longer than the outlet conduit to minimize mixing and displacement of water inside the tube. The sealing consists of a cylindrical flange part 240 and two O rings 241 between said cylindrical flange part 240 and the inner wall 225. The inlet and outlet conduits 237, 236 extend through the cylindrical flange part 240, and may for example be welded to the cylindrical flange part. The cylindrical flange part 240 is typically made from a material with a relatively low thermal conductivity such as an alloy, typically an aluminium alloy. The conduits 236, 237 are preferably made from a metal with a high thermal conductivity such as aluminium or copper. An insulation material 242 extends into the open end 222 of a tube up to the flange part 240, surrounding said inlet and outlet conduit 237, 236 over a certain distance. The insulation material 242 also surrounds the connector tubes 235 which are taken up in a manifold 230 with a manifold outlet 232 (see also figure 10). In that way the interior of the collector tubes together with the inlet/outlet/connector conduits 235-237 form a thermal entity at a temperature Tl which is well insulated from the outside. In that regard it is preferred that the length L over which the insulating material/flange extends in the collector tube is large enough for obtaining a good insulation and for preventing overheating of the closed end of the glass tube as this can lead to thermal stress and mechanical failure. According to a further aspect of the invention the tubes are mounted using brackets 260, 261, e.g. made of metal such as aluminium. The collector tube 220 typically has a diameter D which is smaller than 100 mm, preferably smaller than 80 mm, and most preferably smaller than 70 mm. The insulation material typically extends over a distance L of at least 10 mm, preferably at least 20 mm and most preferably at least 40 mm inside each collector tube.

Figure 9 illustrates an embodiment of a further developed storage and collector apparatus of the invention where a bottom reflector 370 is arranged underneath a collector tube 320 having an inlet conduit 336 and an outlet conduit 337. Preferably the bottom reflector has a cylindrically shaped wall which closely surrounds a tube 320. Further there may be provided a top reflector 371 moveable between an open position (figure 9B) and a closed position (figure 9A). Typically, there is provided a controller (not shown) for controlling the position of the top reflector 371 in function of the temperature inside the tube and/or in function of the outside temperature. The top reflector may e.g. be used to avoid overheating in the event that the temperature Tl of the water stored in the tubes exceeds a critical temperature, e.g. 100 degrees Celsius. Also the top reflector is useful to limit heat losses when there is no sun or when the outside temperature decreases below a critical value. There may be provided a top reflector for each tube of the storage and collector apparatus, but according to an alternative embodiment there may also be provided one single top reflector for the plurality of tubes of the apparatus.

The skilled person will appreciate that various modifications may be made to the above described apparatus system and method of operation without departing from the scope of the invention as defined in the appended claims.

Claims

1. A system for providing solar heated hot water at an end user outlet, the system comprising: a solar powered integrated collector and storage apparatus comprising a plurality of vacuum insulated collector tubes, each collector tube being arranged for the storage in the interior space thereof of a quantity of water heated at a temperature above a desired end user temperature; measurement means for measuring the temperature of the water stored inside the plurality of collector tubes or a variable representative for said temperature; mixing means between the solar powered integrated collector and storage apparatus and the end user outlet for mixing an amount of the stored water with a supply of cold water; control means adapted for controlling the mixing means in the event that the measured temperature is greater than a pre-determined temperature.

2. System of claim 1, characterized in that said control means are adapted for controlling the mixing means such that the mixed water has the desired end user temperature.

3. System of claim 1 or 2, each collector tube comprising an inlet conduit and an outlet conduit, characterized in that each collector tube is a double walled, vacuum insulated glass tube having a closed end and an open end, and having an inner glass wall and an outer glass wall; said open end being sealed between on the one hand the inner wall, and on the other hand the inlet and outlet conduit, wherein insulation material is extending into said open end, surrounding said inlet and outlet conduit over a certain distance.

4. System of claim 3, characterized in that each collector tube has a diameter which is smaller than 100 mm, preferably smaller than 80 mm, and most preferably smaller than 70 mm.

5. System of claim 4, characterized in that the insulation material extends over a distance of at least 10 mm, preferably at least 20 mm and most preferably at least 40 mm inside each collector tube.

6. System of any of the claims 3-5, characterized in that said sealing consists of a cylindrical flange part and an O ring between said cylindrical flange part and the inner wall, said inlet and outlet conduits extending through said cylindrical flange part, and said insulation material extending between said flange part and said open end.

7. System of any of the claims 3-6, characterized in that each inlet and outlet conduit is manufactured from a metal with a high thermal conductivity, such as aluminium or copper.

8. System of claim 7, characterized in that at least a part of said cylindrical flange part is made from a metal alloy having a low thermal conductivity.

9. System of any of the previous claims, characterized in that the solar powered integrated collector and storage apparatus comprises a manifold, wherein the inlet conduit and the outlet conduit of each collector tube are arranged in fluid communication with the manifold.

10. System of claim 9, characterized in that said manifold has a manifold inlet pipe and a manifold outlet pipe, said plurality of collector tubes being arranged lengthwise adjacent one another, starting with a first collector tube and ending with a last collector tube, wherein connector pipes are provided between the outlet conduit and inlet conduit of adjacent collector tubes of said plurality of tubes, said manifold inlet pipe being connected to the inlet conduit of the first collector tube and said manifold outlet pipe being connected to the outlet conduit of the last collector tube, wherein preferably the insulation material extending inside the open end of each tube also extends around the connector pipes and the manifold inlet and outlet pipes.

11. System of any of the previous claims, characterized in that a bottom reflecting means is arranged underneath each collector tube.

12. System of any of the previous claims, characterized in that there is provided at least one top reflector, said top reflector being moveable between a plurality of positions; wherein preferably there is provided a controller for controlling the position of each top reflector in function of the temperature measured by the measurement means and/or in function of the outside temperature.

13. System of any of the previous claims, characterized in that each collector tube includes a low infra red transmission coating disposed on an outer surface of the inner wall.

14. System of any of the previous claims, further comprising: a boiler or other system capable of providing hot water on demand connected in series with the mixing means; and a controller configured to control the boiler according to the temperature measured by the measurement means.

15. Vacuum insulated collector tube comprising an inlet conduit and an outlet conduit and being otherwise substantially sealed from the ambient atmosphere, said collector tube being arranged for the storage in the interior space thereof of a quantity of water to be heated, characterized in that the collector tube is a double walled, vacuum insulated glass tube having a closed end and an open end, and having an inner glass wall and an outer glass wall; said open end being sealed between on the one hand the inner wall, and on the other hand the inlet and outlet conduit, wherein insulation material is extending into said open end, surrounding said inlet and outlet conduit over a certain distance.