Patent Application
20050011513
This invention is in the field of solar energy systems and in particular in the field of solar energy collectors which use lenses to concentrate solar radiation for use in heat exchange applications.
The use of lenses to concentrate solar radiation on an absorbing device is known in the art. Solar concentrators utilizing Fresnel lenses have also been disclosed in the prior art. U.S. Pat. No. 5,915,376 to McLean discloses a solar heat collecting apparatus comprised of glass domes consisting of Fresnel lenses. Solar radiation entering the solar heat collecting apparatus is absorbed by an absorber plate, and transferred to a remote storage system by conventional heat transfer means.
U.S. Pat. No. 6,384,320 to Chen discloses a compound parabolic concentrator (CPC) which is mounted under a Fresnel lens that concentrates the intensity of solar radiation to five to ten times above normal level. The focused solar radiation is further concentrated twenty to fifty times by the CPC collector. The intensified solar radiation is focused onto the top of a stainless steel heat pipe or heat exchanger.
The use of Fresnel lenses for concentrating solar energy is disclosed in U.S. Pat. No. 6,399,874 to Olah, U.S. Pat. No. 6,299,317 to Gorthala, and U.S. Pat. Nos. 5,959,787 and 6,091,020 to Fairbanks. The devices disclosed in these patents provide for concentrating solar energy for photovoltaic cells.
It is an object of the present invention to provide a simplified, economical and efficient solar collector for heat transfer applications.
It is a further object of the present invention to provide a solar collector using a pipe for an energy absorber.
It is a further object of the present invention to provide a solar collector that is flexible as to the intensity, distribution and geometry of concentration of solar radiation on an energy absorber.
It is a further object of the present invention to provide a solar collector that incorporates an energy absorber with enhanced energy absorption efficiency.
It is a further object of the present invention to provide a solar collector that uses a pipe with an energy retaining capsule encapsulating the absorption zone as an energy absorber.
It is a further object of the present invention to provide a solar collector with a simple and economical solar tracking drive.
It is a further object of the present invention to provide a solar collector that is readily incorporated into a solar collector installation that is flexible as to size and geometry.
It is a further object of the present invention to provide a simple, economical and efficient solar collector installation.
It is a further object of the present invention to provide a solar collector installation that is simple and economical to operate and maintain.
It is a further object of the present invention to provide a solar collector installation that utilizes pipes as energy absorbers.
It is a further object of the present invention that provides a solar collector and energy extraction installation that is simple and economical to construct, operate and maintain.
The solar energy collector of the present invention uses one or more Fresnel lenses. Typically the Fresnel lens used for the present invention is a extruded or molded from a thin, lightweight plastic sheet with concentric grooves formed in one side of the lens. The grooves act as individual refracting surfaces, like small prisms when viewed in cross section, bending parallel rays in a very close approximation to a common focal length. Because the lens is thin, very little energy is lost by absorption.
For a preferred embodiment, the Fresnel lenses are mounted on a support frame above an absorption conduit which is typically a metal pipe. If the Fresnel lenses are designed for a point focus or a distributed focus on an absorption zone, the absorption conduit may have an energy absorber mounted on the conduit in the absorption zone which is enclosed in an energy retaining capsule with a high solar radiation transmission rate and a low thermal conductivity rate, thereby providing for transmission of the focused incident solar radiation to the absorption zone of the energy absorber while minimizing the loss of energy from the energy absorber to the surrounding air. An in-line or attached spherical energy absorber with a spherical energy retaining capsule or a hemispherical energy absorber with a hemispherical energy retaining capsule may be used. Alternatively, a spherical or hemispherical energy retaining capsule can simply be used to encapsulate an absorption zone on the absorption conduit. For a linear absorption zone, a cylindrical capsule is preferred on the absorption conduit. The absorbed energy is transferred to an absorption liquid flowing through the absorption conduit.
An absorption fin can also be incorporated inside the energy absorber which extends into the absorption duct and is in contact with the absorption zone, thereby assisting in the transfer of energy to the absorption liquid which flows through the energy absorber. The absorption fin would normally be made of high thermal conductivity material thereby rapidly transferring the energy of the incident solar radiation from the absorption zone to the absorption liquid. A preferred material for the absorption zone and absorption fins is tungsten due to its high thermal conductivity rate, its high melting point and its glass to metal sealing capabilities.
Each Fresnel lenses is mounted on a support frame which is attached to a solar tracking drive. The solar tracking drive continually aligns each Fresnel lenses with the sun, during a desired period of operation, thereby providing for continual point focus or distributed focus of the incident solar radiation on an absorption zone of the energy absorber. The absorption conduit, or other energy absorber, can be positioned so that the Fresnel lens top surface is separated from the absorption conduit top surface by a distance which is equal to the focal length of the lens, thereby providing for the incident solar radiation to be focused at a single point in the absorption zone of the energy absorber or can be positioned such that incident solar radiation is distributed on a larger area of the absorption zone. If the incident solar radiation is focused on a single point in the absorption zone of the energy absorber, substantially higher temperatures will be experienced at the focal point. Having the focal point coincident with the center of the energy absorber, rather than a point on the surface of the energy absorber, results in distribution of the energy and therefore substantially reduced temperatures. The focus of the incident solar radiation can be varied between the center of the absorption conduit and a point on the surface of the absorption conduit thereby varying the distribution of the focused solar radiation and thereby the maximum temperature experienced in the absorption zone.
Rather than a circular pattern of grooves, the Fresnel lenses may have longitudinal grooves which result in the incident solar radiation having a line focus rather than a single focal point. This offers an advantage of distributing the focused incident solar radiation over a larger area, thereby reducing the temperature of the absorption zone. The expanded absorption zone for embodiments utilizing a Fresnel lens with longitudinal grooves can be encapsulated in an energy retaining capsule with a high solar radiation transmission rate and low thermal conductivity rate such as glass. Other portions of the absorption conduit which do not receive focused incident solar radiation can be insulated or merely be covered with the energy retaining capsule material to reduce energy loss to the surrounding air. Similarly, Fresnel lenses with oval grooves may be used to provide for distribution of energy on the absorption zone as the lens will distribute the concentrated radiation on an expanded area rather than a single focus point. Further distribution of the energy can be accomplished, regardless of the pattern of grooving on the Fresnel lens, by positioning the Fresnel lenses so that the energy absorbers have absorption surfaces which are displaced radially from the focal point or focal line of the respective lenses. The extent of the distribution can be selected based upon the desired range of surface temperatures for the absorption zone.
The Fresnel lens itself is preferably constructed of an optically clear material. These materials include but are not limited to acrylic, glass, rigid vinyl, polycarbonate, polyethylene, polyester blends including PET and PETG respectively, poly IR, polystyrene, polyurethane, polypropylene, polyacrylonitrile, Kevlar, Nomex, rubber, germanium, silicon, zinc sulfide, quartz and other such materials. The inventor's preferred materials are polyester (PET or PETG) or a blend thereof.
A Fresnel lens can be formed or manufactured in a number of ways from the substrate materials identified above. This includes but is not limited to press thermalforming, roll thermalforming, casting, emboss extruding, injection molding, milling, lathing, or UV curing. Emboss extrusion is the preferred method of creating Fresnel lenses. Extruding allows for the creation of an inexpensive, thin, flat plastic sheet with an embossed Fresnel image imprinted on one side of the lens. The preferred materials, namely polyester (PET or PETG) can be utilized with or without protective additives. Protective additives may include ultraviolet light and antioxidant additives, both of which reduce yellowing and clouding of the Fresnel lens. These additives can be introduced into the resin prior to the extrusion process or during the extrusion process in a step referred to a co-extruding. A protective co-extruded cap layer is preferred, promoting longevity of the Fresnel lens.
Each Fresnel lens is secured in a focal position for focusing solar radiation passing the Fresnel lens on the absorption zone on the energy absorber by a support frame. A preferred embodiment consists of a lens retainer to which the perimeter of the lens is attached and secured on its perimeter and a pair of pivot brackets. A preferred embodiment of the solar tracking drive is comprised of a base frame, a base drive, a pivot rail, pivot bar, a pivot drive, a pivot drive plate, anchor pedestals and base bearings. Each of the support frames is pivotally attached to the base frame by base pivot bearings which pivotally attach the bottom of the pivot bracket, thereby providing for longitudinal pivoting of the support frames respectively. The longitudinal pivoting of the support frames is controlled by the pivot drive which varies the position of the pivot bar, which is pivotally attached to the pivot rail by a pivot bar bearing. The pivot rail is pivotally attached to the top of one of side of each of the solar collector support structures by top bearings.
Lateral pivoting of the solar collector support structures is accomplished by lateral rotation of the base frame which is controlled by the base drive and facilitated by base bearings. The number of anchor pedestals and base bearings can be varied as needed to provide for adequate support and reliability. By controlling the lateral pivoting and the longitudinal pivoting of the support frames the axis of each of the Fresnel lenses can be maintained in alignment with the sun during a desired period of operation thereby maintaining the focus of the incident solar radiation on the desired absorption zones of each of the energy absorbers. The base drive and the pivot drive can each be controlled by a sensor which continually adjusts the alignment of the axis of the Fresnel lenses to match the position of the sun in the sky during a desired period of operation. This allows the Fresnel lenses to be aligned with the incident solar radiation for the time of day and season of the year.
Depending upon the material used for the Fresnel lens and the thickness of the lens, the lens may be rigid or somewhat flexible. Because the solar collector will generally be used in an exterior, unprotected environment, the support frame and the solar tracking drive must be able to withstand wind loading, moisture and temperature variations. Further, because of the wind and other environmental conditions to which the lens will be subjected, it must be securely attached to the lens retainer. This can be accomplished by many attachment means known in the art including.
The Fresnel lens support frame as well as the solar tracking drive components, can be constructed from a variety of materials including, but not limited to, steel, aluminum or plastic. A preferred material for the support frames and the solar tracking drive is steel. A non-corrosive coating such as galvanizing, paint or powder coating, would be needed.
The base drive and the pivot drive, which comprise the drive means of preferred embodiments of the solar tracking drive, can be comprised of any of common drive mechanisms known in the art. These drive means will generally be composed of a combination of electric motors and gears. Chains and belts may also be used. The solar tracking can be accomplished through simple programming to a vary the longitudinal angle and the lateral angle based on the orientation of the solar collector, the longitude and latitude of the installation, the time of day, and the day of the year. Alternatively, a sensor can be used to continually align the axis of the Fresnel lenses with the incident solar radiation during a desired period or operation.
Many variations of geometry and grooving of the Fresnel lens may be used. As discussed above, longitudinal grooving will provide for distributed focus of the incident solar radiation on a absorption conduit. If a spot focus is desired, then the grooving will be circular. A rectangular or square lens is more practical and economical to manufacture and utilize and is more efficient for a normal application, since the grooving provides for the concentration of solar radiation incident to the corners of the lens on the absorption zone as well. One of the main advantages of the present invention is economy. One preferred embodiment utilizing rectangular lenses with longitudinal grooving, providing for a distributed focus on an absorption conduit, and a solar tracking drive which is actuated by a sensor can be very economical and very effective compared to other solar energy collection systems known in the art. Preferably, the longitudinal axis of the solar collector installation will be aligned in an east/west direction and the lateral axis will be aligned in a north/south direction.
One or more absorption liquid pumps typically circulate the absorption liquid through absorption liquid lines to the absorption conduit and back to an energy transfer device which can be one or more of a number of energy exchange devices which are known in the art. A variety of absorption liquids may be used for circulating through the absorption conduits, which include but are not limited to water, oil or salt. Absorption liquids preferred by the present inventor are heat transfer oil for lower temperatures and molten salt for higher temperature absorption liquid applications. Salt materials which work well for high temperature applications include sodium nitrate, sodium nitrite or potassium nitrate. Heat transfer oil can be synthetic, organic or a combination of synthetic and organic oil.
A preferred embodiment of an energy transfer system comprises the energy transfer device, transfer liquid circulation lines and transfer liquid pumps. Transfer liquid is circulated through the transfer liquid circulation lines by the transfer liquid pumps to the energy transfer device and back to an energy extraction device such as a steam turbine engine. Again, any number of liquids may be used for the transfer liquid but to eliminate the necessity of another heat exchange process at the energy extraction device, water is preferred. The steam turbine engine illustrated in
Referring first to
Each groove 38 of the Fresnel lens is a small piece of an aspherical surface 39. The tilt 41 of each surface is varied with distance 42 from the center 43 of the lens to provide for focus of the incident solar radiation at the focal point of the lens. The cross section shown in
The Fresnel lens of
A cement coating can be placed on the absorption zone to increase the absorption rate of the focused incident solar radiation. Alternatively, an energy assimilator of high thermal conductivity material can be placed on the absorption conduit or other energy absorber. Further the energy assimilator can be thermally connected to an absorption fin extending into the absorption duct, thereby increasing the energy transfer rate to the absorption liquid.
Material selection for the absorption zone of the energy absorber or energy assimilator placed on the energy absorber in the absorption zone will be selected based upon anticipated maximum temperatures and desired absorption and thermal conductivity rates. Materials that can be used include stainless steel, carbon steel, tungsten, titanium, molybdenum, rhenium, niobium, platinum, copper and other metals and non-metallic materials. A preferred material for the absorption zone and absorption fins is tungsten due to its high thermal conductivity rate, its high melting point and its glass to metal sealing capabilities.
The energy retaining capsule 35, whether it is spherically shaped as indicated on
It is preferred for the retaining capsule material to be bonded or hermetically sealed to the absorption zone or to the absorption conduit. This generally increases energy retention by the absorption conduit or other form of energy absorber. Alternatively a space may be provided between the energy absorber and the energy retaining capsule, whether the energy retaining capsule is spherically shaped, hemispherically shaped or cylindrically shaped, which may be air evacuated, thereby providing a vacuum space separating the energy retaining capsule from the energy absorber, thereby further enhancing the energy retention of the energy retaining capsule.
The Fresnel lens itself is preferably constructed of an optically clear material. These materials include but are not limited to acrylic, glass, rigid vinyl, polycarbonate, polyethylene, polyester blends including PET and PETG respectively, poly IR, polystyrene, polyurethane, polypropylene, polyacrylonitrile, Kevlar, Nomex, rubber, germanium, silicon, zinc sulfide, quartz and other such materials. The inventor's preferred materials are polyester (PET or PETG) or a blend thereof.
A Fresnel lens can be formed or manufactured in a number of ways from the substrate materials identified above. This includes but is not limited to press thermalforming, roll thermalforming, casting, emboss extruding, injection molding, milling, lathing, or UV curing. Emboss extrusion is the preferred method of creating Fresnel lenses. Extruding allows for the creation of an inexpensive, thin, flat plastic sheet with an embossed Fresnel image imprinted on one side of the lens. The preferred materials, namely polyester (PET or PETG) can be utilized with or without protective additives. Protective additives may include ultraviolet light and antioxidant additives, both of which reduce yellowing and clouding of the Fresnel lens. These additives can be introduced into the resin prior to the extrusion process or during the extrusion process in a step referred to a co-extruding. A protective co-extruded cap layer is preferred, promoting longevity of the Fresnel lens.
Referring now to
Referring to
A preferred embodiment of the longitudinal pivot means comprises a pivot rail 59, pivot bar 61, a pivot drive 63, a pivot drive plate 65, base pivot bearings 71, pivot bar bearing 77, and top bearings 81. Each of the support frames is pivotally attached to the base frame by the base pivot bearings 71 which pivotally attach the bottom 73 of the pivot bracket, thereby providing for longitudinal pivoting 75 of the support frames respectively through a longitudinal angle. The longitudinal pivoting of the support frames is controlled by the pivot drive 63 which varies the position of the pivot bar 61, which is pivotally attached to the pivot rail by a pivot bar bearing 77. The pivot rail is pivotally attached to the top of one of side 79 of each of the solar collector support structures by top bearings 81.
A tracking control means controls the lateral pivoting 83 and the longitudinal pivoting 75 of the support frames so that the axis 11 of each of the Fresnel lenses is maintained in alignment with the sun during a desired period of operation thereby maintaining the focus of the incident solar radiation on the desired absorption zones of each of the energy absorbers. For a preferred embodiment, the tracking control means consists of a sensor which controls the base drive and the pivot drive, thereby continually adjusting the alignment of the axis of the Fresnel lenses to match the position of the sun in the sky during a desired period of operation. An alternative embodiment of the tracking control means is a simple computer which controls the base drive and the pivot drive and continually positions the support frames, during a desired period of operation, based upon the physical orientation of the solar collector installation, the date, the time of day, and the longitude and latitude of the installation. This allows the Fresnel lenses to be continually aligned with the incident solar radiation.
Referring to
Referring now to
Referring now to
Depending upon the material used for the Fresnel lens and the thickness of the lens, the lens may be rigid or somewhat flexible. Because the solar collector will generally be used in an exterior, unprotected environment, the support frame 47 and the solar tracking drive must be able to withstand wind loading, moisture and temperature variations. Further, because of the wind and other environmental conditions to which the lens will be subjected, it must be securely attached to the lens retainer 49. This can be accomplished by many attachment means known in the art including, but not limited to, springs, wire, bungee cords, plastic strips or ties, glue, screws, clamps or slidable inserts. A preferred attachment means is springs. Springs allow for thermal expansion, wind loads, hail stones or any other type of contraction or expansion that the Fresnel lens may encounter. Referring to
Referring to
The Fresnel lens support frame 47 as well as the solar tracking drive components, can be constructed from a variety of materials including, but not limited to, steel, aluminum or plastic. A preferred material for the support frames and the solar tracking drive is steel. A non-corrosive coating such as galvanizing, paint or powder coating, would be needed.
Referring to
The solar tracking can be accomplished through simple programming to a varied longitudinal angle 75 and the lateral angle 83 based on the longitude and latitude of the installation, the time of day, and the day of the year. Alternatively, the sensor can be used to continually align the axis of the Fresnel lenses with the incident solar radiation during a desired period or operation.
Many variations of geometry and grooving of the Fresnel lens may be used. As discussed above, longitudinal grooving as shown in
One of the main advantages of the present invention is economy. One preferred embodiment utilizing rectangular lenses with longitudinal grooving, providing for a distributed focus on an absorption conduit, and a solar tracking drive which is actuated by a sensor can be very economical and very effective compared to other solar energy collection systems known in the art.
Referring now to
A variety of absorption liquids may be used for circulating through the absorption conduits, which include but are not limited to water, oil or salt. Absorption liquids preferred by the present inventor are heat transfer oil for lower temperatures and molten salt for higher temperature absorption liquid applications. Salt materials which work well for high temperature applications include sodium nitrate, sodium nitrite or potassium nitrate. Heat transfer oil can be synthetic, organic or a combination of synthetic and organic oil.
Transfer liquid 121 is circulated through transfer liquid circulation lines 123 by transfer liquid pumps 125 through the energy transfer device 119 and back to an energy extraction device 127 such as the steam turbine engine 129 illustrated in
Other objects, features and advantages of the present invention will become apparent from the preceding detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. Therefore, the foregoing is intended to be merely illustrative of the invention and the invention is limited only by the following claims.
