WO2016210339A1

WO2016210339A1 - Solar water heater element

Info

Publication number: WO2016210339A1
Application number: PCT/US2016/039381
Authority: WO
Inventors: Guang Pan; Kaoru Ueno
Original assignee: Nitto Denko Corporation
Priority date: 2015-06-25
Filing date: 2016-06-24
Publication date: 2016-12-29

Abstract

Wavelength converting elements are described herein that include a polymer and a 4, 7-benzotriazole chromophore. Solar water heaters are described herein that incorporate wavelength converting layers to improve their efficiency.

Description

SOLAR WATER HEATER ELEMENT

Inventors: Guang Pan and Kaoru Ueno

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application 62/184,767 filed June, 25, 2015, U.S. Provisional Application 62/271 ,501 filed December 28, 2015, and U.S. Provisional Application 62/298,881 filed February 23, 2016, the entire disclosures of which are incorporated by reference.

FIELD

[0002] This disclosure is directed to solar water heaters and wavelength converting films for use in solar water heaters.

BACKGROUND

[0003] Currently, solar water heaters are constrained by their capacity to absorb sunlight and convert that light energy into stored thermal energy in the water. Additionally, solar water heaters' efficiencies can be compromised as they become dusty or soiled due to weather. In addition, most solar heaters use glass collectors which are heavy and sometimes require structural modifications on residential or commercial buildings for installation. Although there are substitute materials with lightweight such as polycarbonates being used in solar heating devices, the problem is that unaltered polycarbonate absorbs UV radiation resulting in a total loss of energy absorbed into the heater and also the breakdown of the polycarbonate itself. Therefore, there is a need for a much improved water heater device that reduces the deficiency of current solar water heaters.

SUMMARY

[0004] The wavelength conversion element in some embodiments and their use in the associated solar water heaters disclosed herein can provide significant benefits to solar water heaters, such as increased efficiency. Furthermore, the solar water heaters in some embodiments are capable of utilizing ultraviolet (UV) radiation in conjunction with visible light to heat water using even ambient light and/or solar radiation. [0005] Some embodiments include a solar water heater, a wavelength converting element; a heat absorber layer that is in optical communication with the wavelength converting element; a fluid heating element that is in thermal contact with the heat absorber layer; and wherein the fluid heating element is configured to transfer heat to a fluid disposed within the fluid heating element; wherein the wavelength converting element comprises a transparent film comprising a polymer and a chromophore of Formula I:

Formula I wherein the chromophore absorbs ultraviolet radiation and emits visible light radiation; and wherein R¹ and R² are independently C_1-6 alkoxy, and R³ is a C_1-6 alkyl.

[0006] These and other embodiments are described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 depicts a top elevational view of an embodiment of a device described herein.

[0008] FIG. 2 depicts a cross-section view of a possible embodiment of a device described herein.

[0009] FIG.2A depicts a cross-section of an embodiment of a mini channel tube.

[0010] FIG. 3 depicts a cross-section view of an embodiment of a device described herein.

[0011] FIG. 4 depicts a cross-section view of an embodiment of a device described herein.

[0012] FIG. 5 depicts a cross-section view of an embodiment of a device described herein. [0013] FIG. 6 depicts a cross-section view of an embodiment of a device described herein.

[0014] FIG. 7 is a schematic depiction of a testing apparatus used in testing possible embodiments of devices described herein.

[0015] FIG. 8 is a graph depicting the efficiency change over the time in minutes of different solar water heater embodiments described herein.

[0016] FIG. 9 is a graph depicting the efficiency versus T_m (°C.m²/W) of different solar water heater embodiments described herein.

DETAILED DESCRIPTION

[0017] A solar energy collection apparatus, or a solar water heater, can include a wavelength converting element, a heat absorber layer, and a fluid heating element. Typically, light from a source such as the sun passes through the wavelength converting element to come into contact with the heat absorber layer. When the light passes through the wavelength converting element, at least some ultraviolet present in the incident light is absorbed by the wavelength converting element, which then emits visible light. The light passing through, or emitted from, the wavelength converting element is then absorbed by the heat absorber layer, which then transfers heat to a fluid through the fluid heating element.

[0018] A wavelength converting element is a structural feature, such as a layer or a film that is disposed between a light source (such as the sun) and a heat absorber layer. For example, a wavelength converting element may be a layer that overlays the heat absorber layer. In some embodiments, a wavelength converting element can comprise a transparent material, such as a transparent film. In some embodiments, the transparent film can comprise a polymer and a chromophore. For example, the chromophore may be dispersed within the polymer.

[0019] In some embodiments the polymer in the transparent film comprises a thermoplastic. In some embodiments, the polymer can comprise polyethylene terephthalate, polymethyl methacrylate, polyvinyl butyral, ethylene vinyl acetate, ethylene tetrafluoroethylene, polyimide, amorphous polycarbonate, polystyrene, siloxane sol-gel, polyurethane, polyacrylate and combinations thereof. In some embodiments the polymer comprises a fluoropolymer, such as polyvinylidene fluoride, or polyvinylidene difluoride (PVDF). [0020] In some embodiments, the chromophore absorbs UV radiation and emits visible light radiation, such as violet, blue, green, yellow, orange, or red light. In some embodiments the chromophore absorbs radiation less than about 400 nm, or about 320-400 nm. In some embodiments, the chromophore emits visible blue light, such as light having a wavelength of about 430-490 nm. In some embodiments, the chromophore can comprise a 4,7-diphenyl benzotriazole chromophore. In some embodiments, the 4,7-diphenyl benzotriazole chromophore can be a compound represented by formula 1 :

Formula I wherein R¹ and R² are independently C_r6 alkoxy and R³ is C_r6 alkyl.

[0021] In some embodiments, R is:

[0022] In some embodiments, R² is:

[0023] In some embodiments, R³ is:

[0024] Suitable compounds for use as a chromophore are described in US 2013/0074927 published March 28, 2013 and US 2013/626,679 filed September 25, 2012. In one embodiment, the 4,7-diphenyl benzotriazole chromophore is 2-isobutyl-4,7-bis(4- isopropoxyphenyl)-2/-/-benzo[c/][1 ,2,3]triazole (C-1) as shown below:

C-1

[0025] In some embodiments, the wavelength converting element can further comprise a transparent substrate which can be in optical communication with the transparent film, that can be disposed upon or in contact with the transparent substrate, wherein the optical communication refers to ultra violet and/or visible light radiation passing from or through the wavelength converting element and impinging upon or passing through the transparent substrate. In some embodiments, the transparent substrate can have a refractive index in a range of about 1.0-1.75, about 1.4-1.7, about 1.584-1.586 (e.g. polycarbonate), at least about 1.0, at least about 1.05, at least about 1.4, up to about 1.5, up to about 1.7, up to about 1.75, or any refraction index in a range bounded by any of these values.

[0026] In some embodiments, the transparent substrate can be a transparent polymer. In some embodiments, the transparent polymer can have a total through transmittance of at least about 50 Tt%, about 60 Tt%, about 70 Tt%, about 80 Tt%, about 85 Tt% and/or about 90 Tt%. Tt% refers to the percentage of radiation passing through the material as compared to the original amount of radiation striking the material.

[0027] In some embodiments, the transparent substrate can comprise glass. In some embodiments, the transparent substrate can comprise a polymer. In some embodiments, the transparent substrate can comprise a combination of glass and a polymer. In some embodiments, the polymer can comprise polyethylene terephthalate, polymethyl methacrylate (PMMA), polyvinyl butyral, polyethylene vinyl acetate, polyethylene tetrafluoroethylene, polyimide, amorphous polycarbonate, polystyrene, siloxane sol-gel, polyurethane, polyacrylate, or combinations thereof. In some embodiments, the polymer can comprise a thermoplastic. In other embodiments, the polymer can comprise a polycarbonate. While not to be bound by theory, it is generally believed that polymer substrates can comprise or consist of an ultraviolet radiation absorber. Using materials containing one or more ultraviolet radiation absorbers can inherently reduce the efficiency of a solar heater utilizing a polymer containing substrate as compared to using only a tempered glass substrate.

[0028] In some embodiments, the amount of radiation emitted by the wavelength conversion element can be greater than the amount of radiation passing through the transparent substrate alone. It is believed that a portion of the impinging radiation upon the wavelength conversion element is converted to useable visible light radiation, e.g. , radiation of about 320-400 nm. By increasing the amount of useable visible light radiation impinging upon the radiant energy absorber, it can increase the efficiency of the heater.

[0029] A wavelength conversion element can improve the efficiency of a solar water heater in converting electromagnetic light into thermal energy as compared to the same solar water heater without a wavelength conversion layer. For example, a solar water heater having a wavelength conversion element may have an increase in efficiency that is at least 0.01 , at least 0.05, or at least 0.1 when irradiated for 6 minutes by a new port, Oriel, Sol 3A solar simulator having a light intensity of 1000 W/m². In some embodiments, a solar water heater having a wavelength conversion layer may have an efficiency that is at least about 0.45, at least about 0.5, or at least about 0.55 when irradiated for 6 minutes by a new port, Oriel, Sol 3A solar simulator having a light intensity of 1000 W/m².

[0030] A solar water heater can comprise a heat absorber layer. A heat absorber layer is any suitable layer that can absorb electromagnetic radiation, such as visible light emitted by the wavelength conversion material, and convert the electromagnetic radiation to heat. A heat absorber layer can be composed of, or comprise, any suitable material, such as a material that can convert electromagnetic radiation to heat, e.g. by absorption of the electromagnetic radiation and conversion of the absorbed energy to heat. Typically, a heat absorber layer is positioned so that it can convert light that passes through, or is emitted by, the wavelength converting element, into heat. The heat absorber layer in turn transfers heat to the fluid heating element. A solar water heater typically comprises a material that can convert electromagnetic energy into heat such as dark or opaque materials, e.g. a graphite sheet, a composite of graphite foil and carbon fiber or graphite fiber; or a metal such as an aluminum sheet or a copper sheet.

[0031] In some embodiments, the heat absorber layer can comprise an infra-red absorbent material or a heat absorbent material. In some embodiments, the heat absorber layer can comprise a ceramic material, inorganic composite material and/or a metal. In some embodiments the metal can be aluminum. In some embodiments, metal can be coated or surfaced with a heat absorbing material. In some embodiments, the heat absorber material can be a dark material. In some embodiments, the heat absorber material can be a dark paint, e.g. black paint. In some embodiments, the heat absorbing material can be a blue absorbing film disposed upon an aluminum substrate, e.g. BJ Universal absorber.

[0032] In some embodiments, the heat absorber layer may have a transmittance of less than 10 Tt%, less than 5 Tt%, or less than 1 Tt%, for all light having a wavelength in the range of about 400-650 nm, about 400-450 nm, about 450-500 nm, about 500-550 nm, about 550-600 nm, about 600-700 nm, or about 700-1000 nm. In some embodiments, the heat absorbing layer can comprise a material having a high absorbance of solar irradiation of at least about 0.70, about 0.80, and/or about 0.90, for example 0.93. In some embodiments, the heat absorbing layer can comprise a material having a low emissivity of about 0.05 at 100° C. In some embodiments, the material can have an emittance in the wavelength range of radiation spectrum of less than about 0.05.

[0033] In some embodiments, the heat absorber layer can comprise a film that absorbs different spectral wavelengths, e.g. in the range of about 0.3-3.0 micrometer. In some embodiments, the heat absorber layer can also absorb blue light. In some embodiments, the heat absorber layer can be interposed between the radiation source and the fluid heating element. In some embodiments, the heat absorber layer can be disposed upon the fluid heating element. In some embodiments, the heat absorber layer absorbs radiation of about 470-570 nm. In some embodiments, the heat absorber layer absorbs radiation of about 430-500 nm. In some embodiments, the heat absorber layer can be a blue absorbing thin film (e.g. BJ Universal Absorber made by PIEP Solar Technologies Co, Ltd, Puyang, Dujiangyan, Sichuan, China) capable of absorbing blue light.

[0034] For some solar water heaters, the heat absorber layer is a graphite sheet. A graphite sheet may have a high absorption coefficient to solar radiation or visible radiation, and high thermal conductivity in an in-plane direction.

[0035] A fluid heating element is in thermal contact with the heat absorber layer and is in turn configured to transfer heat to a fluid (such as water, ethylene glycol, propylene glycol, glycerin, or a combination thereof) disposed within the fluid heating element. Some fluid heating elements comprises one or more channels configured to circulate a fluid within the heating element. In some embodiments, there may be multiple channels extending parallel within the length of a tube (see FIG. 2A). [0036] The channels may be relatively small to facilitate the transfer of heat to the fluid. For example, some channels may have a diameter that is less than 10 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, or less than 0.5 mm, 0.1 mm to 10 mm, or any diameter in a range bounded by any of these values. In some embodiments, the ratio of the length of the channel to the diameter of the channel may be at least about 10 (e.g. a 10 mm length and a 1 mm diameter), at least about 20, at least about 30, at least about 50, at least about 70, at least about 100, or at least about 200.

[0037] FIG. 1 represents an embodiment of a solar energy collection apparatus, also referred to below as solar water heater 10. The solar water heater 10, which may be described as a solar collector or thermal collector, can comprise a fluid heating element 11 . In some embodiments, the fluid heating element 11 can comprise multiple tubes 12 that fluidly connect a pair of manifolds 14 (14A and 14B), which can form a fluid circuit within framework 16. The framework 16 (as oriented in FIG. 1) can define a cavity 18 within which the tubes 12 can be disposed.

[0038] FIG. 2 represents a solar water heater 10 that may also include a heat absorber layer 20, a protective covering 24, a wavelength converting element 26, heat spreader layer 28, and/or insulation 30. In some embodiments, the layers/elements from proximal (on top and/or closest) to the radiation source to the most distal (at the bottom and or furthest) from the radiation source can be protective covering 24, wavelength converting element 26, a heat absorber layer 20, such as a blue absorbing film, fluid heating element 11 and insulation layer 30 such as an aerogel layer in various orders. In some embodiments, fluid heating element 11 can be disposed between heat absorber layer 20 and heat spreader layer 28.

[0039] Framework 16 can be made of various materials, including materials that have thermal insulating properties and/or reflective properties. For example, framework 16 may comprise aluminum. Framework 16 may comprise a bottom panel 36 and peripheral wall 38. In some embodiments, the framework 16 may have a reflective surface disposed on or over the interior surface 40. In some embodiments, the framework 16 can also include polymeric reinforcing materials, e.g. Nitto PE-7000AL and/or AS2000 polymeric laminating materials (Nitto, Osaka, Japan).

[0040] In some embodiments, a fluid heating element 11 can be configured to absorb heat from heat absorber layer 20. The fluid heating element 11 can comprise water or fluid conduits for transporting in and/or out heat absorbing fluid, e.g. water. In some embodiments, the fluid heating element 11 can comprise tubes 12 aligned with manifolds 14 (14A and 14B) to create a fluid circuit via the interior chambers 48 (FIG. 2A) within the manifolds 14 and channels 60 (FIG. 2A) within the tubes 12. Slots 52 (FIG . 2A) may be defined within the manifolds 14 for connecting tubes 12. The fluid heating element 11 can be in thermal contact with, disposed or positioned adjacent to and/or within the heat absorber layer 20, which comprises radiant energy absorbing material. In some embodiments, the water or fluid conduits for transporting in heat absorbing fluid can be or placed within a plurality of channels defined on the surface of the heat absorbing layer.

[0041] In some embodiments, a heat absorber layer 20 may be interposed between the solar irradiation source and the tube 12. In some embodiments, the tube 12 can be disposed in thermal or direct contact with the heat absorber layer 20. In some embodiments, the heat absorber layer 20 can comprise a material having high in-plane thermal conductivity.

[0042] As evident from FIG . 1 , the tubes 12 can be connected in fluidic parallel between the manifolds 14. As represented in FIGs. 1 , 2, and/or 2A the tubes 12 can be flat multiport extrusion tubes (MPE), also known as microchannel tubes or multichannel tubes commonly found in solar collectors. Each tube 12 can have a pair of oppositely-disposed flat surfaces 54a and 54b (of which the upper surfaces 54a are visible in FIG. 2A) between lateral edges 56 of the tube 12 and longitudinal ends 58 of the tube 12. As shown in FIGS. 1 and 2, each tube 12 can be made to have multiple channels 60 through which a fluid (such as water) flows for the purpose of receiving heat, and/or heating the fluid with absorbed solar radiation during the operation of the solar water heater 10. In FIG. 2. The adjacent channels 60 are separated by walls or webs 62 that interconnect the upper and lower flat surfaces 54a and 54b of the tubes 12. In some embodiments, the gap between the adjacent tubes 12 is in a range of about 2-10 mm, about less than 2 mm, about less than 1 .0 mm, about less than 0.5 mm, about less than 0.25 mm. In some embodiments, the tube 12 can be comprised of a plurality of parallel channels 60 defined therein. In some embodiments, the tube 12 can comprise at least one channel 60, two channels 60, three channels 60 defined therein. I n some embodiments, the single channel tubes 12 may have lateral or width dimension consideration related to providing sufficient resistance to compressive forces tending to squeeze opposite sides 54a and 54b inwards towards each other.

[0043] In some embodiments, the solar water heater (e.g. solar water heater 10) may further comprise a transparent protective layer, e.g. protective covering 24. In some embodiments, the transparent protection layer can comprise a thermoplastic polymer. In some embodiments, the thermoplastic polymer can comprise a thermoplastic fluoropolymer. In some embodiments, the thermoplastic fluoropolymer may comprise polyvinylidene fluoride (PVDF). In some embodiments, the transparent protection layer can comprise oriented polyethylene terephthalate (OPET), oriented polyamide (OPA) and/or oriented polyvinyl alcohol (OPVA). One suitable example can be view-barrier films (Mitsubishi Plastics, Tokyo, Japan). In some embodiments, the transparent protection layer may be disposed on top of the solar water heater element, in lieu of a glazing layer. In some embodiments, the transparent protection layer can be substantially impermeable to oxygen, minimizing or reducing the degradation of the chromophore contained within the wavelength converting layer. In some embodiments, the transparent protection layer can allow no more than 1 cc/m²/day of oxygen at room temperature and pressure to pass therethrough. In some embodiments, the transparent protection layer can allow less than 1 x10^"1 , 1 x10^"2, or 1 x10^"3 cc/m²/day of oxygen and/or water vapor (at 40° C and 90% humidity) to pass therethrough. Suitable methods to ascertain the amount of 0₂ passing therethrough are described in JIS K7126 and/or ASTM D3875-81 . In some embodiments, the transparent protection layer may be disposed between the solar radiation source and the wavelength conversion layer. In some embodiments, the transparent protection layer is disposed upon and/or in contact with the wavelength conversion layer. It is believed that direct layering or contacting the wavelength conversion layer can protect the chromophore from oxygen degradation.

[0044] In some embodiments, the solar water heater system may further comprise an insulation layer 30 which can reduce the amount of heat loss through the rear or bottom panel 36 and/or distally from the fluid heating element. In some embodiments, the insulation layer may comprise insulating material. In some embodiments, the insulation material can be polymer foam, polymer fiber felt, polyurathene foam, expanded polystyrene, melamine resin foam, polyester fiber fleece, inorganic mineral wools, aerogel, glass fiber felt, glass wool, glass fiber blanket. In some embodiments, the tube 12 may be disposed between the solar radiation source (arrows 8 in Figure 7) and/or the heat spreader 28 and the insulation layer 30. In some embodiments, the insulation material can be disposed on the tube side 54b opposite the solar irradiation source (arrows 8).

[0045] In some embodiments, where the insulation material is an aerogel, the aerogel can be disposed in the cavity defined below the fluid heating element. In some embodiments, the aerogel can be disposed in the cavity defined above the bottom of the frame. In some embodiments, the aerogel can be disposed on the distal side (more distant from the radiation source) of the fluid heating element. In some embodiments, spacers 66 can be disposed adjacent the aerogel layer so as to minimize compression of the aerogel layer by the weight of elements disposed thereupon. In some embodiments, the spacers can comprise polyurethane. In some embodiments, the aerogel is an open cell material, e.g., allows gas to enter and leave some or all of the individual cells. In some embodiments, the aerogel can have a low thermal conductivity. In some embodiments, the aerogel acts as an insulator to prevent heat loss from the radiant energy absorbent layer back out to the environment through the wavelength conversion element. In some embodiments, the aerogel can have a thermal conductivity of less than about 100 x 10^"3W/m K, less than about 50 x 10^"3 W/m K, or less than about 15 x 10^"3 W/m K at 25 °C. In some embodiments, the aerogel may have an apparent density within the range of about 20-200 kg/m³, where the density is not measured in a vacuum but at standard atmospheric conditions. In some embodiments, the aerogel may have an apparent density within the range of about 20-150 kg/m³, about 20-100 kg/m³, about 120-150 kg/m³. In some embodiments, the aerogel can be layered having an apparent density of about 65 kg/m³. In other embodiments, the aerogel can be layered with an apparent density of about 109 kg/m³. In some embodiments the heat transfer coefficient within aerogel filled space/the collector can be reduced by at least about 25%, about 35%, about 40% and/or about 50% with the insertion of aerogel between framework and the heating element. In some embodiments, the thermal resistance within the filled space can be increased by at least about 40%, about 50%, about 60%, about 70 %, about 75%, and/or about 80% with the insertion of aerogel between framework, e.g. bottom panel, and the fluid heating element.

[0046] In some embodiments, the aerogel can have a total transmittance of greater than about 50 Tt%, about 60 Tt%, about 70 Tt%, about 80 Tt%, and/or about 90 Tt%. In some embodiments, the aerogel can have a refraction index of about 1 .00-1 .1 . In some embodiments, the aerogel can have a refraction index of about 1 .05.

[0047] In some embodiments, the aerogel layer can be less than about 20 mm thick. In some embodiments, the aerogel layer can be less than about 7 mm thick. In some embodiments the aerogel can be granular. In some embodiments, the aerogel granules can be about 0.7-4.0 mm in average diameter. In some embodiments, the aerogel can be a silica aerogel, e.g. Si0₂ aerogel.

[0048] In some embodiments, the tube 12 can be disposed in thermal contact with a heat spreader layer 28. It is believed that the heat spreader layer distributes thermal energy from the heat absorber layer and/or conveys the thermal energy to the back side (distal from the solar radiation source) of the tubes 12. In some embodiments, the tube 12 can be in direct contact with the heat spreader layer. In some embodiments, the heat spreader layer can be disposed distal to the tube 12. In some embodiments, the heat spreader layer can be disposed in between adjacent tubes 12. In some embodiments, the tube 12 can be interposed between the heat spreader element 28 and the radiation source, indicated by arrows 8 (FIG. 7). In some embodiments, the heat spreader layer can be interposed between the multichannel element and the radiation source. In some embodiments, the heat spreader layer can comprise a material having high in thermal conductivity. In some embodiments, the heat spreader layer can comprise graphite. In some embodiments, the graphite may have a thermal conductivity in a range from about 25 W/m K, about 50 W/m K, about 100 W/m K to about 200 W/m K, about 300 W/m K, about 470 W/m K, and/or any thermal conductivity in a range bounded by any combination of these values.

[0049] In some embodiments, as shown in FIG. 1 , a solar water heater 10 comprising a frame 16 and a cavity 18 within the frame is for interacting with solar radiation 90 (FIG. 7) indicated by arrows 8 (FIG. 7). In some embodiments, insulation 30 can be disposed on the bottom of the frame to prevent heat loss through the back of the device. In some embodiments, as shown in FIG. 1 and FIG. 2, the solar water heater 10 can also comprise a heat absorber layer 20, to absorb radiant energy impinging thereupon, disposed upon the insulation. In some embodiments, the solar water heater can also comprise a heat absorber layer 20 to absorb radiant energy impinging thereupon, disposed upon or in contact with the fluid absorbing layer. In some embodiments, the solar water heater 10 can comprise a fluid heating element 22 in thermal contact with the heat absorber layer 20. The solar water heater can also comprise a wavelength converting element 26 which is placed across the frame's aperture 16 and/or within defined cavity 18. In some embodiments, the wavelength converting element 26 is in optical communication with the radiant heat absorbent layer 20 and /or fluid heating element 11 . In some embodiments, the heat absorber layer 20 can be interposed between the fluid heating element 22 and wavelength converting element 26. In some embodiment, the heat absorber layer 20 and/or wavelength converting element 26 can be interposed between the multiport extrusion (MPE) tubes and the protection covering 24. In some embodiments, the wavelength converting element 26 or protective covering 24 can be geometrically modified so as to focus the radiation on the absorbent layer to prevent back scatter of transmitted radiation back into atmosphere.

[0050] In some embodiments, the heat absorber element 20 (as shown in FIGs. 3 and 4) can be interposed between the fluid heating element 11 and the radiation source 90 indicated by arrows 8 (FIG 7). In one embodiment, the heat spreading element 28 can be disposed between the gaps defined between the adjacent tubes 12 (FIG.3).

[0051] It is believed that when heat spreader layer 28 is a graphite sheet placed beneath the tube 12 and in physical contact with the tube 12, it can absorb additional solar or thermal irradiation that passes through the gap between the tubes 12 and provide heat by spreading the absorbed heat to the bottom side of the tube 12 which may not receive the solar irradiation. Meanwhile, heat loss by the emission from graphite sheet can be minimized by the coverage of tubes 12 on the graphite sheet.

[0052] In some embodiments, as shown in FIGs. 4, 5 and 6, a heat absorber 20 (FIG 4) or no additional heat absorber20 (FIGs. 5 and 6) may be utilized within the solar water heater 10. In the case where no additional heat absorber element 20 is used, the outer surface of the fluid heating element doubles as a heat absorbing layer. In addition, the heat spreader 28 may be disposed between the fluid heating element and the insulation/base panel instead of the fluid transferring element (proximal the radiant energy source) as described above. In these embodiments, the wavelength converting element 26 and/or the heat absorber layer 20 can be in direct contact, interposed between the radiation source and the fluid heating element.

[0053] In some embodiments, a system for solar heating of water is described. In some embodiments, a system for solar heating of water is depicted in FIG. 7. For determining solar water heater efficiency, an irradiated closed loop system as described in FIG. 7 can be constructed. A reservoir 70 retains a heat absorbing fluid, e.g. water, for insertion into the solar water heater 10. The first thermo-couple 72 can be disposed at the reservoir and in fluid communication with the water therein to provide water temperature information at this location. Water may be delivered from the reservoir by a pump 74 through fluid lines 76 to the input manifold of the solar water heater 10. Gear pump 74 (Model WU-7521 1 -15, Cole-Parmer, Vernon Hills, IL, 20-200 ml/min) can be used to provide a flow rate of about 260 ml/minute to the solar water heater 10. A digital flow sensor 78 can be placed in-line to provide digital data regarding the flow rate of water in the system. In one embodiment, the digital flow sensor used to monitor the in-line water flow rate can be an Omega Engineering digital flow rate sensor (FLR1008ST, 20-200 ml/min). A valve 81 and analogue flow sensor 80 can be placed in-line to provide the ability to adjust the flow rate within the system. In one embodiment, the flow rate through the fluid conduits was monitored by an analogue flow meter (Brooks Instrument H₂0, 2.77 - 216 CCM/min). The water passes into the solar water heater 10 through the solar heater collector inlet. A second thermocouple 82 can be disposed at the collector inlet to provide water temperature information at this location. A solar radiance simulator, e.g. a 500 watt halogen lamp (Phillips, Halonite QVF 133) can be utilized in conjunction with a solar simulation (New Port, Oriel, Sol 3A) to impinge radiation upon the solar water heater 10. A third thermocouple 84 can be positioned to measure the water temperature of the heated water as it passes out from the water heater 10 outlet. Water passes out from the water heater 10 through a return line to the reservoir, for example a 4 liter Dewar flask. A data logger 86 can be connected to the thermocouples and the digital flow rate sensor to record the various system parameters, e.g. temperature at the various thermocouple positions and the fluid flow rate at the digital sensor. Computer 88 or other data storage unit can be connected to the data logger 86 to process the data generated.

EXAMPLES

[0054] The embodiments of the solar water heater described herein have improved effectiveness as compared to using only polycarbonate alone which allows for the use of polycarbonates in solar heating applications. These benefits are further shown by the following examples, which are intended to be illustrative of the embodiments of the disclosure, but are not intended to limit the scope or underlying principles in any way.

Example 1 : Preparation of the Wavelength Converting Element

[0055] The 4,7-diphenyl benzotriazole chromophore C-1 , was made as described in US 2013/074927, published March 28, 2013 and US 2013/626,679 filed September 25, 2012.

[0056] A wavelength conversion composition testing sample was prepared similar to that described in co-pending PCT/US2016/12503 filed January 7, 2016, which is incorporated by reference in its entirety. The components of the composition were shown in Table 1 wherein EVA is ethylene vinyl alcohol; chromophore 1 is 2-isobutyl-4,7-bis(4- isopropoxyphenyl)-2/-/-benzo[c/][1 ,2,3]triazole; KBM-503 is a silane coupling agent: 3- methacryloxypropyltrimethoxysilane; Tinuvin 144 is bis(1 ,2,2,6,6-pentamethylpiperidin-4-yl) 2-butyl-2-[(3,5-di-fe/f-butyl-4-hydroxyphenyl)methyl]propanedioate; TMPTMA is a crosslinker: trimethylolpropane trimethacrylate; and Perbutyl E is an organic peroxide: t- butylperoxy-2-ethylhexylmonocarbonate.

[0057] Table 1

[0058] To prepare the composition, a wavelength conversion layer comprising the components listed above was fabricated into a film structure following the wet processing procedure. The wavelength conversion layer was fabricated by following the following steps (i) preparing a polymer solution by dissolving the EVA powder or pellets in a solvent such as toluene at a predetermined ratio; (ii) preparing a chromophore solution by dissolving chromophore 1 in the same solvent as that used in the polymer solution at the predetermined concentration; (iii) preparing a stabilizer solution by dissolving a stabilizer (which one? KBM-503?) in the same solvent as that used in the polymer solution at the predetermined concentration; (iv) preparing a wavelength conversion (WLC) solution by mixing the polymer solution with the chromophore solution and the stabilizer solution, and then adding the adhesion promoter (Tinuvin 144) , the crosslinking agent (TMPTMA), and the peroxide (Perbutyl E), independently and at the predetermined weight ratio; and (v) preparing the wavelength conversion layer by first directly casting the wavelength conversion solution onto a non-stick PTFE dish , then drying the WLC solution at room temperature for at least 24 hours followed by further drying the resulting mixture under vacuum at 50-60 °C for 4-5 hours, and finally completely removing the remaining solvent by vacuum hot pressing at 100 °C for 5 min to a thickness of 200 μηι. The wavelength conversion film was then laminated between two pieces of clear low-iron glass that were 2 mm thick and approximately 5 cm x 5 cm in dimension. Following lamination, the testing device was then cured to induce crosslinking. The curing temperature for the Example 1 testing device was 160 °C with a curing time of 15 minutes.

Example 2: Fabrication of Solar Heater (Ex-2) :

[0059] A solar water heater frame similar to that described above and illustrated in FIG 1 was constructed. A frame made of a composite of glass fiber fabric and epoxy resin (NitoHard AS-2000) having a length of 12 inches, a width of 12 inches, and a height of 1 .5 inches was used, forming an aperture across the top of the frame and an aluminum bottom. An 8 mm thick layer of glass fiber blanket with embedded Si0₂ aerogel (Thermal Wrap TW800 low dust aerogel blanket, Cabot Inc. , Alpharetta, GA, USA) was disposed in the cavity, resting upon the back panel of the framework. Polyurethane spacers were disposed around the periphery of the aerogel to minimize compression of the aerogel. Aluminum Multiport Extrusion (MPE) tubes of 2 cm in width with 6 holes of 2 mm by 2 mm were used to construct the flowing channels. Nine pieces of MPE tubes were connected to aluminum header/manifold of 12.5 mm in diameter and 1 mm thick wall through apertures/slots defined in the manifold. The gap between adjacent MPE tubes was 1 cm. The MPE tube protruded into the header manifold about 1 mm. The fluid heating element described above was disposed on the aerogel layer, supported in part by spacer elements at the periphery of the aerogel. Commercial heat absorber film with selective spectral coating (BJ Universal absorber, PIEP Solar Technologies Co. Ltd.) was used to form the collector. A WLC sheet (RAYCREA, Nitto Denko) with UV down-conversion chromophore dispersed in ethyl vinyl acetate (EVA) was thermally laminated onto the selective spectrum absorber plate. A barrier film (Mitsubishi Plastic Co. Ltd, Tokyo, Japan) was applied on the top of WLC sheet during lamination for protecting the chromophore from degradation. An absorber plate integrated with WLC sheet above was connected to MPE tubes on the side without WLC sheet by thermally conductive epoxy (CC3-450, Cast-Coat Inc.) cured at room temperature overnight to form the collector. A heat spreader made of flexible graphite foil of 0.5 mm (Grade GS- GSFT, Ceramsource Inc., East Brunswick, NJ, USA) was placed under the collector in contact with MPE tubes.

[0060] A solar water heater was formed by stacking the collector with a insulation layer comprising a 8 mm thick blanket composite of Si0₂ aerogel with glass fiber felt (Thermal Wrap™, Cabot) and bottom sheet made of composite of glass fiber fabric and epoxy resin (NITTOHARD AS-2000, Osaka, Japan) in the sequence from the top to the bottom, as protection barrier film/WLC/absorber plate/MPE tubes/heat spreader/Aerogel insulation.

Example 2A: Fabrication of Comparative Example of Solar Heater (CE-1):

[0061] Comparative Example of a solar water heater (CE-1) was made in a similar manner to that of Example 2, except that a glazed glass sheet was used instead of the transparent protective film and no wavelength conversion layer was used.

Example 2B: Fabrication of Solar Heater (Ex-2A):

[0062] Another solar water heater (Ex-2A) was made in a similar manner to that of Example 2, except that no wavelength conversion layer was used.

Example 3: Solar Water Heater Efficiency Measurements:

[0063] For determining solar water heater efficiency, an irradiated closed loop system as described in FIG. 7 was constructed. A solar water heater element made as described above, was attached to the system described in FIG. 7 and the efficiency was determined as previously described (Anderson, K. R., et al, Int. J. of Energy Engineering (IJEE) 4(1):31 -37 (2014); Struckmann, Fabio, Project Report 2008 MVK 160 Heat & Mass Transport, 08 May, 2008, Lund Sweden). Circulating water of about four liters was heated up through solar water heater by irradiation from a solar simulator (new port, Oriel, Sol 3A) at an intensity of about 1000 W/m². The solar simulator described in EXAMPLE 2 (Ex-2) was placed horizontally with respect to solar collector. Water flow rate was kept at 163 ml/min by monitoring with a digital flow sensor (Omega Engineering, FLA-1000st). Water temperature at inlet, outlet of solar water heater and Dewar flask was recorded by thermal couples and data logger (Omega Engineering) during 4 hour irradiation from solar simulator. The efficiency of Ex-2, Ex-2A and CE-1 was determined. The results are shown in FIG. 8 and FIG. 9. In FIG 9, T_m = ΔΤ/GT = (T_av -T_a)/Gr wherein T_av is the arithmetic average temperature of the inlet and outlet fluid, T_a is the ambient temperature in °C and GT is the intensity of incident solar radiation in W/m², and T_m has an unit of °C.m²/W. Comparing with solar water heaters of CE-1 and Ex-2A where no wavelength conversion layer was used, the efficiency of solar water heater of Ex-2 with wavelength conversion layer increased significantly, by about 0.20 (from about 0.36 to about 0.56) in the beginning. Although the amount of efficiency increase was decreased over the time, it was still noticeable after 2 hours. Furthermore, the amount of efficiency increase by using Ex-2 comparing with Ex-2A was still noticeable and beneficial even after 4 hours.

[0064] The following embodiments are contemplated:

Embodiment 1. A solar water heater comprising:

a wavelength converting element; an optional heat absorber layer that is in optical communication with the wavelength converting element; a fluid heating element that is in thermal contact with the heat absorber layer, or if the heat absorber layer is not present, is in optical communication with the wavelength converting element; and wherein the fluid heating element is configured to transfer heat to a fluid disposed within the fluid heating element; wherein the wavelength converting element comprises a transparent film comprising a polymer and a chromophore of Formula I:

Formula I wherein the chromophore absorbs ultraviolet radiation and emits visible light radiation; and wherein R¹ and R² are independently C_1-6 alkoxy, and R³ is a C_1-6 alkyl. Embodiment 2. The solar water heater of embodiment 1 , wherein R¹ is:

Embodiment 3. The solar water heater of embodiment 1 or 2, wherein R is:

Embodiment 4. The solar water heater of embodiment 1 , 2, or 3, wherein R is:

Embodiment s. The solar water heater of embodiment 1 , 2, 3, or 4, wherein the chromophore is:

Embodiment 6. The solar water heater of embodiment 1 , 2, 3, 4, or 5, further comprising a heat spreader layer.

Embodiment 7. The solar water heater of embodiment 1 , 2, 3, 4, 5, or 6, wherein the fluid heating element comprises a channel configured to circulate a fluid within the fluid heating element.

Embodiment 8. The solar water heater of embodiment 7, wherein the fluid heating element comprises a tube having multiple channels extending parallel within the length of the tube.

Embodiment 9. The solar water heater of embodiment 1 , 2, 3, 4, 5, 6, 7, or 8, further comprising an insulation layer.

Embodiment 10. The solar water heater of embodiment 9, wherein the insulation layer comprises an aerogel.

Embodiment 11. The solar water heater of embodiment 10, wherein the aerogel having a low thermal conductivity is disposed distal to the fluid heating element.

Embodiment 12. The solar water heater of embodiment 10 or 1 1 , wherein the aerogel is silica aerogel.

Embodiment 13. The solar water heater of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , or 12, having an efficiency in converting electromagnetic light into thermal energy that is greater than the same solar water heater without a wavelength conversion layer.

Embodiment 14. The solar water heater of embodiment 13 having an increase in efficiency that is at least 0.05 when irradiated for 6 minutes by a new port, Oriel, Sol 3A solar simulator having a light intensity of 1000 W/m². Embodiment 15. The solar water heater of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, or 14, having an efficiency that is at least 0.5 when irradiated for 6 minutes by a new port, Oriel, Sol 3A solar simulator having a light intensity of 1000 W/m².

Embodiment 16. The solar water heater of embodiment 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, or 15, wherein the chromophore emits blue light.

[0065] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0066] The terms "a," "an," "the" and similar referents used in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. , "such as") provided herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of any claim. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0067] Groupings of alternative elements or embodiments disclosed herein are not to be construed as limitations. Each group member may be referred to and claimed individually or in any combination with other members of the group or other elements found herein. It is anticipated that one or more members of a group may be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

[0068] Certain embodiments are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, the claims include all modifications and equivalents of the subject matter recited in the claims as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is contemplated unless otherwise indicated herein or otherwise clearly contradicted by context.'

[0069] In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the claims. Other modifications that may be employed are within the scope of the claims. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the claims are not limited to embodiments precisely as shown and described.

Claims

WHAT IS CLAIMED IS:

1. A solar water heater comprising:

a wavelength converting element; a heat absorber layer that is in optical communication with the wavelength converting element; a fluid heating element that is in thermal contact with the heat absorber layer; and wherein the fluid heating element is configured to transfer heat to a fluid disposed within the fluid heating element; wherein the wavelength converting element comprises a transparent film comprising a polymer and a chromophore of Formula I:

Formula I wherein the chromophore absorbs ultraviolet radiation and emits visible light radiation; and

wherein R¹ and R² are independently C_1-6 alkoxy, and R³ is a C_1-6 alkyl. 2. The solar water heater of claim 1 , wherein R¹ is:

3. The solar water heater of claim 1 or 2, wherein R² is:

4. The solar water heater of claim 1 , 2, or 3, wherein R³ is:

The solar water heater of claim 1 , wherein the chromoph

C-1

6. The solar water heater of claim 1 , 2, 3, 4, or 5, further comprising a heat spreader layer.

7. The solar water heater of claim 1 , 2, 3, 4, 5, or 6, wherein the fluid heating element comprises a channel configured to circulate a fluid within the fluid heating element.

8. The solar water heater of claim 7, wherein the fluid heating element comprises a tube having multiple channels extending parallel within the length of the tube.

9. The solar water heater of claim 1 , 2, 3, 4, 5, 6, 7, or 8, further comprising an insulation layer.

10. The solar water heater of claim 9, wherein the insulation layer comprises an aerogel.

1 1 . The solar water heater of claim 10, wherein the aerogel having a low thermal conductivity is disposed distal to the fluid heating element.

12. The solar water heater of claim 10 or 1 1 , wherein the aerogel is a silica aerogel.

13. The solar water heater of claim 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , or 12, having an efficiency in converting electromagnetic light into thermal energy that is greater than the same solar water heater without a wavelength conversion layer.

14. The solar water heater of claim 13 having an increase in efficiency that is at least 0.05 when irradiated for 6 minutes by a new port, Oriel, Sol 3A solar simulator having a light intensity of 1000 W/m².

15. The solar water heater of claim 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, or 14, having an efficiency that is at least 0.5 when irradiated for 6 minutes by a_new port, Oriel, Sol 3A solar simulator having a light intensity of 1000 W/m².

16. The solar water heater of claim 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, or 15, wherein the chromophore emits blue light.