Harvesting, transmission, spectral modification and delivery of sunlight to shaded areas of plants

Abstract

A light harvester or collector collects solar radiation from an unshaded location adjacent a growing plant. The light harvester can be either imaging (e.g., parabolic reflectors) or non-imaging (e.g., compound parabolic concentrator). The concentrated solar radiation is projected into a light transmitter that conducts the light through the plant's outer canopy and into the inner canopy to a diffuser which disperses and reradiates the light into the inner canopy. The diffused light transforms a non-productive, potentially leafless zone of the plant into a productive zone so that more fruit can be produced per volume of land surface. The system can prevent transmission of infrared into the inner canopy so that the inner canopy zone is not heated and the amount of water lost to transpiration is reduced. The system can also modify other spectral components to affect plant development and to control pests and diseases.

Claims

1. A system for delivering diffused light to an inner canopy of a plant and thereby modifying growth and development of the plant, the system comprising: a light reflector for collecting and concentrating solar light source energy from a solar light source above and outside of an inner canopy of the plant; a light transmitter comprising an internally reflective light pipe in optical communication with the light reflector for conducting the concentrated solar light source energy from the light reflector to the inner canopy of the plant; and a light diffuser in optical communication with the light transmitter placed within the plant's inner canopy for receiving the concentrated solar light source energy from the light transmitter, diffusing and re-radiating the solar light source energy so as to illuminate a portion of the inner canopy of the plant, thereby modifying the growth and development of the plant.

2. The system of claim 1, wherein the light transmitter is formed of plastic, aluminized cardboard, or glass.

3. The system of claim 1, further comprising a filter in at least one of the light reflector, the light transmitter, or the light diffuser, wherein the filter modifies the spectral quality of the collected and concentrated light source energy.

4. The system of claim 1, wherein the diffuser comprises a diffusively reflecting surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

(2) The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which:

(3) FIG. 1 shows a diagrammatic overview of one embodiment of the invention;

(4) FIG. 2 shows a diagrammatic representation of a simple design that is a predecessor to the current CPC design;

(5) FIG. 3 shows the coordinate system used in equations describing CPC design;

(6) FIG. 4 shows the angle used in parametric equations describing the CPC;

(7) FIG. 5 shows the common descriptive terms used for the parabolic CPC;

(8) FIG. 6 shows several CPC designs with varying angles of collection;

(9) FIG. 7 is a diagram of the CPC showing heat rejection

(10) FIG. 8 shows an alternate rectangular embodiment of non-imaging light collectors;

(11) FIG. 9 shows a diagram of an imaging light harvester based on parabolic mirrors;

(12) FIG. 10 shows a transmitter/conveyer;

(13) FIG. 11a is convex-concave mirror combination used as a diffuser for citrus and similar tree applications;

(14) FIG. 11b shows a ray diagram of the device of FIG. 10a;

(15) FIG. 12 shows a hammock linear diffuser made from flexible reflective material;

(16) FIG. 13 shows a trough diffuser constructed from rigid reflective materials;

(17) The foregoing and other features of the present disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

(18) The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the general principles of the present invention have been defined herein specifically to provide a system to collect solar energy and deliver it to strategic locations within the canopy of a growing plant.

(19) FIG. 1 shows a general overview of the components used in one embodiment of the present invention. The diagrammatic arrow 50 represents the daily movement of the sun 50 relative to the harvester/collector component, a compound parabolic concentrator (CPC) reflective element 56. The lines 54 represent the acceptance limits of the CPC, and these limits define the acceptance angle 52. The CPC 56 transmits light through a light pipe 58 which penetrates the canopy 60 and projects the light onto a disperser 64 which radiates the dispersed light 62 into the inner part of the canopy. A supplemental light source 97 (e.g.: LED) is also illustrated. These components will now be described in more detail.

(20) The system harvests the natural sunlight from above/beside the plant/tree/vine/bush, and transmits it through the outer, productive canopy of plant/tree, thereby delivering and scattering it throughout the inner/lower, most shaded, non-productive portions of the foliage. A direct, reflective design for this is preferred (e.g., light beams directed by mirrors, prisms, etc.). The device is composed of three principal parts. The first component is a light harvester/collector/concentrator (generally a wide angle/compound parabolic collector, with or without a condenser system) and designed to be disposed above, or adjacent to the plants/trees.

(21) The light harvester can comprise a number of forms, each of which could be applicable depending upon the end users agriculture needs and general environment. A preferred embodiment of the harvester design employs a reflective element known as a CPC (compound parabolic concentrator). This design has many advantages including reducing manufacturing cost, minimizing heat buildup within the system and easing installation due to its tolerance for misalignment with the sun.

(22) The light collection and dispersal systems described herein are all based on the principle of non-imaging optics. The CPC design is an evolution of a primitive form of non-imaging concentrator, the light cone or cone concentrator, has been used for many years (see, e.g., Holter et al., 21; Senthilkumar and Yasodha, 36). FIG. 2 shows the principle. If the cone has semi-angle and if i is the extreme input angle, then the ray indicated will just pass after one reflection if 2=(/2)i. It is easy to arrive at an expression for the length of the cone for a given entry aperture diameter. Also, it is easy to see that some other rays incident at angle i such as the one indicated by the double arrow, will be turned back by the cone. If we use a longer cone with a larger number of reflections, we still find some rays at angle i being turned back. Clearly, the cone is far from being an ideal concentrator. Williamson (42) and Witte (49) attempted some analysis of the cone concentrator but both restricted this treatment to meridian rays.

(23) Descriptions of this type of optical device appeared in the literature in the mid-1960s in widely different contexts. Baranov and Melnikov (6) described the same principle in three-dimensional geometry, and Baranov (4) suggested three dimensional CPCs for solar energy collection. Baranov (3; 5) obtained Soviet patents on several CPC configurations. Axially symmetric CPCs were described by Ploke (30), with generalizations to designs incorporating refracting elements in addition to the light-guiding reflecting wall. Ploke (31) obtained a German patent for various photometric applications. The CPC structure was described as a collector for light from Cerenkov counters by Hinterberger and Winston (19, 20).

(24) In other applications to light collection for applications in high-energy physics, Hinterberger and Winston (19, 20) noted the limitation to 1/sin 2 of the attainable concentration, but it was not until sometime later that the theory was given explicitly (Winston, 43). In the latter publication the author derived the generalized tendue and showed how the CPC approaches closely to the theoretical maximum concentration.

(25) The CPC in two-dimensional geometry was described by Winston (44). Further elaborations may be found in Winston and Hinterberger (48) and Rabl and Winston (32). Applications of the CPC in 3D form to infrared collection (Harper et al., 16) and to retinal structure (Baylor and Fettiplace, 8) have also been described. The general principles of CPC design in 2D geometry are given in a number of U.S. patents (Winston, 45, 46, 47).

(26) FIG. 3 illustrates the r-z coordinate system used in mathematical description of the CPC. Whereas FIG. 4 shows the definition of angle used in CPC parametric equations, and FIG. 5 illustrates the descriptive terms used with the parabolic CPC to relate the various angles to the focal point of the parabola. FIG. 6 shows diagrams of four different CPC devices with angles of acceptance ranging from 10 degrees to 25 degrees (top to bottom). The diagrams are all to the same scale and all have the same size exit apertures and illustrate how the dimension change according to angle of acceptance.

(27) The CPC light collecting design is a highly efficient way of collecting light and is utilized in nature in many optical systems including the cones of the human retina. Utilizing a CPC for the collection of sunlight delivers a number of advantages to the system.

(28) The first advantage of the CPC collector geometry is that it possesses a large acceptance angle or numerical aperture meaning that a fixed unit can effectively collect sunlight over a wide range of angles of incidence as the sun processes overhead during the course of the day. A typical CPC with a 45 degree acceptance angle will be able to effectively collect sunlight for 6-8 hours; hence an active tracking subsystem is not required, reducing system complexity and cost. It is also possible to use two or more CPC units with different orientations to further extend the period of maximum light collection. The straightforward design and ability to use low cost materials allow for easy industrial mass production meaning that the system could be used at the density of at least one unit per tree. The large acceptance angle also allows device setup and use by non-experts, as alignment with the sun is not critical, and means once installed the collection efficiency is not sensitive to the change in position of the sun as the seasons change.

(29) The second advantage is that the CPC design has over an imaging optical system that must track the sun to collect sufficient light is that there is much less heat generated within the device. Imaging system designs generally require fiber optics to allow for the movement of the tracking head unit. For fiber optics to efficiently transmit the light, the collected light must be concentrated into a very small area thereby causing immense heat stress on device component parts. Such systems generally require high-cost exotic materials to prevent equipment failure.

(30) The third advantage is the ability to vastly reduce the amount of heat entering the system and thus reduce heat stress on plants and, as a consequence, reduce plant water consumption. To enable the delivery of cool light to the inner canopy the system will employ filters, such as those used in energy efficient low-E glass, at the entrance aperture of the collector as shown FIG. 7 where incoming sunlight 70 strikes a filter (dichroic) 74 covering the entry to the CPC 78. The infrared radiation 72 is rejected whereas the PAR 76 is transmitted into the CPC 78. A bonus of the overall modularity of the system is that these filters can be designed to be easily detachable. Hence, at temperate latitudes these filters could be removed in the early growing season when overall temperatures are low and the additional warmth from the collected light would be a benefit to the plants and replaced in the summer months to reduce heat stress. The fourth advantage is that imaging systems work only for clear, unobstructed sunlight, in contrast, the CPC design collects diffuse light as well as direct sunlight so that even on cloudy days extra light will be transferred to the inner canopy.

(31) It will be appreciated that the light harvester should be located so as not to significantly shade the outer parts of the plant. Depending on the spacing of the plants, the light harvester can be placed between the rows or between the individual plants (e.g., trees) in the row, and, via the shape of the diffuser element, able to deliver light to multiple (e.g. four) trees simultaneously. To avoid shading the outer parts of the plant, the light harvester can be placed either lower than the canopy or significantly above it. If the harvester is placed significantly above the canopy, light diffraction and seasonal-diurnal movement of the harvester's shadow will avoid any significant shading of the plants. If the light harvester is placed in a low position, it will be unable to significantly shade the plants; however, the plants may significantly shade the harvester unless they are widely spaced. This militates in favor of a high location for the harvester. Because of the diffraction-movement effect mentioned above, the harvester can also be located at a distance more or less directly above the plant. The harvester will utilize the light transfer pipe as a base structural element to hold it in position. This support can be integrated with the plant itself or already existing supports (e.g., grape vine trellises).

(32) Other embodiments of a non-imaging light harvester include geometries such as the rectangular version of FIG. 8. Harvesters with such four-fold symmetry and flat reflective surfaces offer less optical efficiency than the round CPC design. However potential advantages in modularity and the ability to flat pack (i.e., collapsibility) for transportation allow for reduced production costs. Other implementations of flat-plane designs will be obvious to those skilled in the art.

(33) The non-imaging inventive devices described above are generally passive and operate without an additional energy source. It will be appreciated that with the exception of equatorial regions, the position of the sun in the sky changes seasonally. Therefore, for maximum efficiency solar collectors must be constantly adjusted to track the sun's position. Tracking the sun on a diurnal/continuous basis is complex and expensive due to the high cost of the technology needed. However, the seasonal changes in solar position are relatively slow; therefore, adjustment on a weekly/monthly basis by changing the collector's angle in a small number of fixed increments yields most of the advantages of daily tracking at a very low cost. A simple manual adjustment interface is provided to keep the collectors aimed in spite of seasonal change in solar position.

(34) FIG. 9 shows an alternate embodiment on the light harvester system is based around an imaging optical system consisting of a pair of a wide angle/parabolic mirrors arranged to condense collected light into a narrow bodies transfer device such as a bundle of fibers. In this embodiment the larger diameter lower parabola 100 collects light rays 96 and reflects it onto a smaller diameter secondary parabola 102 which creates a collimated beam. This beam is directed through an aperture 104 located at the center of the larger parabola into the transfer tube (not shown). The dual parabola harvester design has optimal collection while aligned directly with the sun and efficiency falls sharply as the sun progresses across the sky throughout the day. Therefore such a system will need a mechanism to automatically move the dish to track the sun. Solar tracking technology is very mature and control mechanisms to enable its use are readily available. The additional complexity and cost of these elements can be mitigated by delivering light to a given threshold number of trees per base station. The smaller mirror 102 can advantageously by a cold mirror which has filter capabilities. As shown in the diagram some light (near infrared) passes through the mirror 102 and so is not concentrated and transmitted into the canopy.

(35) In addition to providing additional light for photosynthesis, the invention also allows ready adjustment of light quality. Light collected and transmitted to the lower/inner part of a plant can be modified before delivery to within/underneath to the canopy, by altering its wavelength (using optical filtration), diffusivity (by appropriately chosen diffusers), intensity (by partial obturation, if and when appropriate) all of which have been found to positively modify crop yield or quality. Adjustment of the light quality can be achieved with filters (both band-pass and dichroic) and by adding light from a supplemental source such as LEDs 97, as shown in FIGS. 1 and 11a.

(36) Spectral optimization of light before re-delivery provides a number of advantages. Solar radiation provides heat energy as well as photosynthetic energy so that boosting the total solar irradiance to enhance photosynthesis can also result in thermal damage. It is possible to remove selected thermal components (NIR and IR) of the solar spectrum, thus avoiding over-heating the illuminated area beyond the naturally occurring microclimate. In addition, the delivered light can be wavelength-filtered to match the best known spectral signatures for productivity (Raj apakse and Shahak, 35; Shahak et al., 38, 39; Shahak, 37; Longstaff, 26), pest and disease regulation (Karpinski et al., 22; Ben-Yakir et al., 9; Antignus, 2), etc.

(37) The second component of the invention is a transmitter/conveyer that attaches to the light harvester so as to convey or transmit the concentrated solar radiation. Although the drawings generally show a single light harvester per transmitter, there is no reason that a plurality of light harvesters cannot be operatively coupled to a single transmitter. Such a transmitter can be a purely reflective system constituting as an inverse periscope constructed from mirrors and/or prisms. Typically the transmitter is a rigid pipe with a reflective inner surface able to penetrate through the outer plant canopy or the cover of a glass or plastic greenhouse or net-house. FIG. 10 shows such device 98. The pipe is designed such that multiple sections 99 can easily be slotted together to customize the length depending on the application scenario. The transmitter will act as the support and main anchoring point for the system as a whole, attaching either to the plant directly or to infrastructure already present such as trellis systems. This component will have cross sectional symmetry to match that of the harvester unit to allow for most efficient light transfer.

(38) For transmission purposes an open, internally reflective pipe is generally preferable. These can be made from plastics or aluminized cardboards that are readily recyclable and can even be selected to be biodegradable. The presently preferred plastic construction of the whole device will be entirely from UL 746C (fl) certified plastics able to withstand prolonged exposure to UV, water and high temperatures. One of the beneficial features of the present invention is that by stimulating photosynthesis, the invention actually reduces atmospheric greenhouse gases (carbon dioxide). Using recyclable materials can lead to an even smaller carbon footprint for the entire system.

(39) Another embodiment of the transmitter subsystem is a dense bundle of flexible optical fibers in a flexible protective sheath that can be threaded through the outer plant canopy or the cover of a glass or plastic greenhouse or net-house. Optical fibers have previously been used to monitor penetration of light through plant canopy layers (Bauerle and Bowden, 7) but not to actively deliver light into plant canopies. For communication (i.e., data transmission) purposes optical fibers are generally formed from high purity glass so that signals can be transmitted for great distances without significant attenuation. For the present invention it is often more economical and ecological to use optical fibers made of plastic. Although plastic optical fibers (POF) show greater attenuation than glass fibers, plastic is readily recyclable and can even be selected to be biodegradable. The presently preferred plastic fibers are made from polyperfluorobutenylvinyl ether; these fibers have larger diameters than glass ones, high numerical apertures, and good properties such as high mechanical flexibility, low cost, low weight, etc. Importantly, progress has been made on the attenuation, which now can be easily brought down to less than 1 dB/meter which represents an insignificant loss considering that the fibers in the present invention will be typically no more than a couple of meters in length. One of the beneficial features of the present invention is that by stimulating photosynthesis, the invention actually reduces atmospheric greenhouse gases (carbon dioxide). Using recyclable plastic materials can lead to an even smaller carbon footprint for the system.

(40) The third component of the system is a diffuser that is attached to the end of or positioned slightly below transmitter/conveyor opposite the light harvester. The job of the diffuser is essentially the reverse of the light harvester. Whereas the light harvester collects solar radiation from a relatively large area (the surface area of the harvester) and concentrates it into the smaller area of the transmitter (e.g., the hollow tube or fiber-optic bundle), the diffuser reverses this process and scatters the light around the inner canopy of the plant. The horticultural advantages of diffused light are well known (Sinclair et al. 40; Hemming et al., 18; Nissim-Levi et al., 28; Hemming, 17; Dueck et al., 13).

(41) There are a number of designs for the diffuser to allow for customization of the system to various agricultural applications and plant geometries. For non-imaging systems the diffuser can consist of a combination of shaped diffusively reflecting surfaces. As shown in FIGS. 11a and 11b a combination of a large concave mirror 90 and a smaller convex mirror 92 can spread the light rays 96 exiting the aperture 94 of a transfer tube 98. This spread beam is ideal for use in a tree inner canopy such as with a citrus tree. For plants in rows such as grape vines these surfaces can include shapes such as elongated hammock style reflectors of flexible reflective material such as aluminized Mylar are shown in FIG. 12. The flexible reflective Mylar (or similar material) 106 is supported by a wire frame 108. Straps (not shown) can be attached to the peripheral parts 110 of the wire frame to suspend the reflector/diffuser. Linear troughs made of rigid reflective materials as shown in FIG. 13. The trough has reflective surfacesinner or outer depending on the mounting configuration. The unit can be suspended by wires to hang beneath plants or simply rested on the ground. Many other possible geometries will be apparent to those skilled in the art.

(42) For imaging systems where light transfer is via a fiber optic system terminating the transmitter within a diffusing sphere such as an internally coated Mylar balloon or a translucent ball provides an effective diffuser. Depending on the shape of the plant the diffuser can be designed to diffuse light into a number of different three dimensional shapes. For example a conventional citrus tree having a rounded canopy would use a diffuser that projects a sphere or partial sphere of light. A single optical fiber transmitter can terminate in several diffusers arranged within the plant for the best coverage.

(43) There are a number of additions or modifications to the three basic components. As already mentioned the light harvester can be equipped with various mechanical interfaces to allow it to be adjusted to follow the seasonal and/or diurnal changes in solar position. Modification of the spectrum of the transmitted light has also been mentioned above. For this purpose filter materials (either absorptive or interference/reflective) can be applied to the light harvester and/or diffuser. It is also possible to add filtering substances to the optical fibers themselves. For wavelengths (e.g., infrared) that are generally rejected, an optical device such as a prism, dichroic or grating can be used to reject these wavelengths so as not to heat any of the components. In some cases it could be beneficial to add supplementary light sources 97 (e.g. LEDs) to the system to supply light in excess of that available from the sun and/or to augment certain wavelengths of light. This would be used where the economic benefits of the added light outweigh the energy costs. The additional light sources can be aimed into the Light Harvester, directly coupled to the Transmitter or disposed within the Diffuser.

(44) The benefits for the users include increased plant productivity and fruit yield resulting from enhanced photosynthesis, and/or enhanced photo-morphogenetic activities such as flowering induction and bud initiation in the otherwise shaded, inactive parts of the canopy. Also, the supplementary irradiation provided by the invention can result in improved fruit quality: size, color, postharvest quality/storability/shelf life/nutritional value. Because the system makes the plant healthier, one sees improved pest and disease controlpossibly achieved through spectral manipulation deterring pests and diseases, and/or enhancing plant resistance to biotic stresses (Karpinski et al., 22; Ben-Yakir et al., 10, 2014; Kong et al., 24). This results in reduced need for applications of agrochemicals such as pesticides, fungicides and plant growth regulators. Because the system is capable of providing PAR without thermal (near infrared (NIR) and infrared) radiation, there is less heating of the plant tissue resulting in a reduction of water use (improved water-use-efficiency). There can also be saving occasioned by lowered use of such traditional practices as pruning, training and use of light-scattering materials. The problem of determining optimum plant spacing is also reduced because the inventive system can be moved and rearranged to accommodate changes caused by plant growth. Finally, the amount and direction of a plant's growth can be controlled by the additional light supplied, and its spectrum, e.g. by reducing tree height for easier harvesting (without sacrificing per tree yield), or by achieving a certain shapee.g., for decorative purposes (Warrington and Mitchell, 41; Mortensen and Moe, 27; Rajapakse et al., 34; Oren-Shamir et al., 29; Raj apakse and Shahak, 35; Aiga et al., 1).

(45) The system is ideal for perennial crops although it can be used with almost any plant. It can advantageously be applied on individual trees in orchards. It can be used in small fruit vineyards (table grapes, wine grapes, kiwi fruit and berries) where horizontal light dispersion can be particularly valuable. It is also useful for protected cultivation of vegetables, ornamental crops, berries (blueberries, raspberries, blackberries, strawberries) and nurseries in greenhouses, net-houses, screen houses, plastic tunnels (hoop greenhouses), and plant factories (Kozai, 25). In these cases the invented devices will cross the construction roof. The number of units per house area can be readily adjusted according to the cultivated crop.

(46) Use of prototype units provides some idea of how much light the system can readily harvest and deliver to a given location on the plant. PAR reading (mol photons/m.sup.2/s) were made at mid-day in a citrus grove using a PAR meter (Apogee Instruments, Logan, Utah) with the sensor face held sun-oriented (i.e., perpendicular to the sun's rays). Peak readings in a region without citrus trees were 2040-2060; peak readings between the rows of trees were 1920-1945; while peak readings within the inner canopy of the trees were only 8-15. The experimental light harvester was located at the outer canopy layer so it was partly shaded by adjacent trees. Nevertheless, the peak readings at the exit of the harvester were 1800-2500. Measurements within the canopy at a distance of approximately 150 cm from the exit of the light transmitter were 800-1000. (When the light harvester was placed in full, unobstructed sun light it delivered 8500-9500 photons/m.sup.2/s; the upper reading of the meter is 3000 so these figures were obtained by using a neutral density filter on the meter.)

(47) Similarly, in a pistachio orchard, the reading between the rows was 1800-1900, while the reading underneath the trees ranged from 40-350. This is because the canopy of a pistachio tree is less dense than that of a citrus tree. The shade regions receiving the output of the light harvester gave a reading of 2000-3000 as measured on the ground. In a table-grape vineyard the reading away from the vines was about 2000, while the reading beneath the trellis-grown vines was only 13-25. The exit from the light collector/transmitter gave a reading in excess of 3000. Using Mylar diffusers similar to those of FIG. 12 with the meter sensor located adjacent to the illuminated fruit clusters (with the sensor plane making an approximately 45 degree angle with the ground plane) gave a reading of 800-1045, which should be sufficient to significantly affect fruit maturation.

(48) Of course, the devices can also be used in other forms for husbandry where light can have a beneficial effect even though photosynthesis may not be involved. Animal husbandry, particularly poultry cultivation, can be benefited by increased light. Aquiculture is also a natural use for the inventive devices.

(49) While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

REFERENCES

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