Collecting solar radiation using fresnel shifting
Solar energy is concentrated on a target by at least one group of Fresnel light-shifting devices.
Using solar radiation as an efficient energy resource for photovoltaics, heating, lighting applications and the like often requires using the solar radiation in concentrated form. The present state-of-the-art is to concentrate solar radiation mainly by using focusing technology to concentrate the solar radiation prior to use. Focusing is typically accomplished using light transmission lenses including convex lenses and Fresnel lenses, by reflective lenses such as various reflective parabolic structures, or by reflecting solar radiation onto the target using banks of small mirrors. The mirror-based technologies are difficult to manufacture and maintain, while the focusing technologies are limited mainly by constraints of focal lengths.
SUMMARY OF THE INVENTIONAn object of this invention is to enable inexpensive manufacture of devices to effectively concentrate solar radiation.
Another object is to provide devices that are also more flexible in application than focusing devices.
These and other objects are realized using the present invention, which is based upon using groups of Fresnel grooves designed to shift solar radiation collected from large areas onto the much smaller solar radiation receptors used to convert the solar radiation into more useful forms such as electricity, heat, and more concentrated light for illumination. By using shifting, most of the limitations of lenses and focusing can be overcome.
This invention uses a family of Fresnel light shifting constructs based upon groups of Fresnel grooves to shift solar radiation onto solar energy receptors or devices. Using groups of shifting grooves enables solar radiation impacting large areas to be shifted onto the small areas of solar energy devices, effectively collecting or concentrating the solar radiation at the targeted site.
This shifting method effectively concentrates solar radiation without the stringent limitations imposed by the various focusing methods used as the current convention of the art.
Freeing the design and applications of Fresnel technology from the constraints imposed by focusing, i.e. freedom from the theoretical and practical limits of traditional lenses, the effective concentration of solar radiation can be greatly facilitated in a cost effective manner. Using the designed Fresnel shifting groups described below enables projecting shifted solar radiation to a common area. Indeed, for some arrangements, the positioning of the solar radiation shifting grooves is effectively independent of the distance between the solar radiation shifting grooves and the targeted solar energy device. The principles of Fresnel shifting as described herein enable collecting solar radiation efficiently and in amounts related to the need. The solar radiation collected by shifting can be directed onto any type of solar energy receptor including non-limiting examples such as photovoltaics, heat collectors including fluid filled pipes, cooking containers, or light tubes or fiber optic cables for transferring light into a structure.
The manufacture of the shifting devices is also relatively simple in comparison to most types of lenses and other devices used to concentrate solar radiation. Because of the flexibility and simplified design, along with lighter weight, esthetics, varied geometrical options and diversity in locations, shifting applications are more cost effective and relevant to many applications, and often useful even where focusing technologies would be problematic or impossible.
Because the science of these shifting constructs or devices is based principally upon the historical teachings attributed to Fresnel, as part of the background to understanding this invention some salient features of Fresnel lenses are shown in
Lenses, including reflective lenses such as parabolas, transparent convex lenses, and flat Fresnel lenses are commonly used to concentrate or focus light for applications to solar energy, as well as to focus light for use magnification, and other forms of imaging. Lens focusing properties, based upon the contour of the refracting surface of a convex lens, have been known for centuries. According to the principles of the curved lens surface, the curve is relatively flat at the center of the lens surface, gradually increasing in bending of the curved surface until near the edges of the lens circumference, the curve of the lens becomes quite steep, as diagramed in
Fresnel lenses in varying formats are used in a variety of ways, especially for magnification, in addition to numerous applications to focus light as a mechanism to concentrate solar radiation. Because of lens physics and practical limits of the refractive index of useful substrates etched with the Fresnel grooves to construct Fresnel lens, useful sizes of Fresnel lenses seem typically limited to approximately 12 to 14 inches in diameter. Fresnel lenses are also known to be very effective at focusing, forming precise focal points or lines of highly concentrated solar radiation. This is true because each arrangement or line of Fresnel grooves is designed to mimic a specific part of the curve on a convex lens, effectively focusing the light as would that part of the curve on the lens, (See
The principle of this invention is to forego the lens concept and instead to use Fresnel grooves in sets or groups to essentially shift solar radiation onto solar energy targets such as photovoltaic or heat, or other receptors. Because groups of functionally similar or identical Fresnel grooves cannot, by definition, mimic the curve of a lens, such groups can not form such extreme hot spots and can be designed so that the energy distribution across the surface of a solar radiation receptor is uniform in intensity. Depending upon the need, this can be accomplished without focusing as is more preferred, or if desired with various degrees of focusing as preferred for some applications where very dense collections of solar radiation are required as concentrated such as to form a focal line, depending upon the broad embodiment of this invention.
Through variations of Fresnel shifting, solar radiation can be collected and delivered to a solar radiation target or receptor either evenly across the target in modest amounts or evenly in intense amounts, or as very high intensity hot spots or intense areas linear in character such as a near focal point or line. Because a lens is not used, the size restriction attributed to Fresnel lenses no longer applies, greatly increasing the area and therefore the amount of solar radiation that can collected. This concept also allow different groups or areas of the Fresnel shifting device to be located along the same plane, as is the character of the Fresnel lens, or at different planes enabling additional options for how solar radiation can be collected. Furthermore, and of particular importance, the parallel shift design enables the shifted solar radiation to travel in concert relatively long distances prior to interacting with the solar energy target.
With this invention, linear devices can be very long (as can be Fresnel lenses) but via this invention can also be very wide, and groups of shifting grooves can be treated independently such that shifting groups can be at different levels if needed, or widely separated yet still transfer solar radiation to the same target. Such is possible by working with groups of Fresnel groves with the same or related solar radiation shifting characteristics within each group rather than with a Fresnel lens or section of a Fresnel lens.
Although sharp focal areas are possible, they are generally less preferred for home use because they can constitute a fire hazard if improperly used. The flexibility of the Fresnel shifting motif allows incredible variability in design of solar radiation devices to collect solar radiation by shifting the direction of solar radiation wave travel. For example, wherein the shifted waves of solar radiation remain parallel long distances are possible between the location of solar radiation collecting devices and the solar radiation targets, therefore high placement of the Fresnel shifting grooves is feasible. Examples of placement could include off the edges of builds or on other available structures such as supports for wind turbines where the necessary electric grid is in place. Cogeneration of electricity via solar and wind using established fields of wind generators is cost effective because some of the structural support needed for solar radiation collection, and access to an electric grid to transport the generated electricity are already in place. High placement of separate groups of shifting grooves would likely limit the collector geometry to rectangles, the orientation east-to-west, and the solar radiation target to be long such as a heat pipe to account for a moving area of solar radiation concentration. Other arrangements, including circular or even branching such as peddles of a daisy are possible and can result in concentration of large amounts of solar radiation within a small area. This freedom of design is very important to promote applications both for improving energy efficiencies in “developed” countries as well as in “developing” countries where even small improvements such as replacing much of the wood used as fuel to providing safe drinking water, to even inexpensive ways to generate at least modest amounts of electricity can have a great impact in the quality of life for many people.
By using groups of functionally related Fresnel groves, the limits imposed by the lens equations, and structural limits in lens design are no longer valid, liberating the applications of Fresnel to solar radiation, based principally upon solar radiation shifting groups of Fresnel grooves rather than the traditional lens approach. For most, but not all, applications, the solar radiation shifting grooves are arranged in groups such that the diameter and length of each Fresnel-based shifting group, are approximately the same as the solar energy target. Where the direction of light propagation is extensively altered, where the angle of shifts are very sharp, the diameter of the shifting groups can be larger than the diameter of the target yet all the shifted waves can still contact the target. Fortunately, Fresnel groves, especially in linear arrays are relatively easy to produce in sheets of various types of glazing by common methods including but not limited to etching, extrusion, molding, and imprinting. Such materials are also acceptably attractive, relatively easy to clean, and cost effective in comparison to the major competing technologies such as reflective parabolic troughs or banks of mirrors. The Fresnel shifting devices can of course be tilted to remain more perpendicular to the daily path of the sun, or by accepting some reduction in efficiency orientated more east-to-west along the long axis, perhaps changing angle of position to be more perpendicular to the general path as the seasons change, depending upon the latitude. It should be noted that the transparent Fresnel light shifting devices can be made much lighter in weight than many of the other technologies used to collect and concentrate solar radiation. They are less expensive and easier to maintain under most circumstances than other technologies such as reflective parabolas, or banks of mirrors designed to reflect solar radiation onto a target.
DEFINITIONSTargeted solar energy receptor or device includes but is not limited to photovoltaic devices such as to generate electricity directly from solar radiation; heat collecting devices such as pipes or tubes containing liquid or gas fluids, heating solid surfaces such as for cooking, cooking pans and pots and the like; light collecting devices such as to transport light into a building via tubes channels or fiber optics.
Transparent substrate refers to any glazing or other material enabling visible and or UV and or infrared light to pass through.
Group of Fresnel grooves means three or more grooves of sufficiently similar character with respect to changing the direction of light waves to enable the solar radiation shift of claim one.
Domain of the solar radiation shifting device or group refers to the area directly below the group or device, in reference to the direction of incoming rays of solar radiation striking perpendicular to said group or device.
Solar Energy and Solar Radiation for purposes of this invention mean the broad spectrum of solar radiation including UV, visible and infrared radiation.
Fresnel shifting means changing the direction of radiation as a consequence of passing through glazing containing Fresnel grooves. For this invention the radiation refers to solar radiation and is not intended to refer to light such as coming from a light bulb.
Fresnel groove and Fresnel facet are interchangeable terms used to describe the alteration in plane of substrate used to change the direction of solar radiation travel.
A single solar radiation shifting device comprises one or more groups of Fresnel grooves such that the shifted light reaches the common target of the device. Different groups involved in the concentration of light at a common target though perhaps separate and in different locations are functionally and therefore considered part of the same single solar radiation shifting device.
In the accompanying drawings,
In
Claims
1-3. (canceled)
4. A method for shifting solar radiation onto a solar energy receptor using a transparent substrate having Fresnel grooves selected from the category consisting of:
- at least one group of Fresnel grooves sufficiently identical within the group such that parallel waves of solar radiation are altered in direction of travel to the same extent, as a consequence of passing through that group,
- at least one group of Fresnel grooves sufficiently similar within that group such that parallel waves of solar radiation passing through said group remain sufficiently parallel to each other from said group, such that the majority of the solar radiation waves interact with the solar energy receptor,
- at least one group of Fresnel grooves each group focusing parallel rays of solar radiation passing through that group to form a focal area outside the domain of the solar radiation shifting group, and
- Fresnel grooves focusing parallel rays of solar radiation passing through the grooves such that a focal line is formed line outside the domain of the solar radiation focusing grooves.
5. The method of claim 4 wherein solar radiation passing through the Fresnel substrate is reflected back through the substrate prior to interacting with the solar energy device.
6. A solar energy concentrating apparatus comprising at least one group of Fresnel light-shifting devices.
Type: Application
Filed: Oct 13, 2009
Publication Date: Apr 14, 2011
Inventor: William James Todd (Baton Rouge, LA)
Application Number: 12/587,719
International Classification: F24J 2/08 (20060101); F24J 2/00 (20060101);