1. Technical Field of the Invention
The present invention relates to an economical sunlight concentration apparatus for gathering sunlight and concentrating it to shine on a plurality of narrow strips of photovoltaic material.
2. Related Art
In recent years, various types of sunlight collection apparatuses for gathering sunlight, i.e. natural light, and guiding the light to shine on photovoltaic material have been proposed. Some involve fiber optics, electro-optic lens, or large motion bases. For any of such systems to be commercially viable, they must maximize the usage of available space and minimize the cost of generated electricity by substituting economical apparatus for expensive apparatus and by maximizing the usage of available space. In most cases, photovoltaic material is the most expensive component of solar electric energy systems so its usage must be minimized. Also expensive tracking systems are not viable, and glass, or sophisticated highly polished plastic lenses and mirrors are too expensive, heavy, or both. Also the solar systems, when installed on buildings, must be installable on roofs without requiring expensive modifications to the property. Generally this means minimal building intrusion and minimal roof reinforcement. Preferably, a solar system installed on a roof should be light enough that no building reinforcement is required and the only intrusion is for an electrical cable.
The present invention includes solar panels, each having an array of linear plastic lens fixed in an East-West orientation, parallel to the horizon and facing the sun. Generally, the lens are positioned so they are perpendicular to the sun's rays at mid-morning and mid-afternoon on the first day of spring, or at its position for maximum daily received sun power. The latitude angle may be manually adjustable for large commercial systems when such is economic by having manually movable fixed positions which are adjusted for the summer and winter seasons. An East-West tracker for the panels may be employed for increased received solar radiance for tracker systems that have economical benefit. Since the motion of the sun is predictable, such motion may be controlled by a computer with a clock.
The lens array is aligned perpendicular to the horizon, such results in a larger acceptance angle requirement so usually, the lens are aligned parallel to the horizon to collect sunlight over a wide arc of solar movement and to concentrate the collected light onto relatively expensive narrow strips of photovoltaic material positioned beneath and parallel thereto. A concentration ratio of 20 to 1 for sunlight onto the photovoltaic strips is typical, the ratio required being a function of photovoltaic material cost to lens cost with the high ratios being limited by the heat buildup in the photovoltaic material, aberrations at extreme off axis collection, mechanical alignment tolerance costs, and panel profile height limitations of weight, cost and wind resistance. Generally 5 to 1 concentration is the minimal concentration ratio for the present economical system invention.
The plurality of photovoltaic strips are fixed to a heat conductive panel which is moved in an atculate path and maintained parallel to the lenses so that the lines of light concentrated by the lenses remain on the photovoltaic strips to produce electricity over a large portion of the sun's path across the sky, 60° or more. The area of the photovoltaic strips is minimized for economy. Usually the sun's energy is diminished by the atmosphere and angle when positioned beyond 60° from high noon and becomes uneconomic to collect.
The back side of the heat conductive panel is a convection radiator of solar energy accumulated as thermal energy in the panel and may be is finned to reject heat so that the temperature of the photovoltaic strips does not rise to an extent that the efficiency of the photovoltaic is significantly reduced. Although not as heat conductive as copper, the silicon of the photovoltaic material is effective in spreading the heat. Therefore, the line of light can be allowed to focus relatively sharply on the photovoltaic strip without damage thereto, or loss of system photovoltaic conversion efficiency. Normally the heat concentration from a sharp focus is not a problem because the economic lenses used do not have to have the optical quality required to produce a sharp focus.
Since the sun moves across the sky relatively slowly each day, the controller to move the heat conductive panel may be small, light weight, inexpensive and reliable. Typically, a small dither built into the controller and a monitor of electrical output, or a computer with a clock can be used to keep the heat conductive panel in the proper position throughout the day. Being small and driving a light weight panel, the controller can be solar powered from a small fixed solar cell on the solar panel, sized to produce enough electrical power to operate the controller when the sun is beyond the 30° from mid-afternoon, or a rechargeable battery charged during the preceding day. Since the morning “start” and afternoon “stop” positions of the heat conductive panel are the same, the controller is required to move the heat conductive panel only when sufficient solar should exist. By mounting the heat conductive panel by at least three pins in at least three mated arculate grooves, the heat conductive panel can be maintained parallel to the lens and in proper position so that the plurality of lines of solar energy produced by the lenses remain on the plurality of photovoltaic strips. The controller may be a single chip computer with a look up table memory or an equation of the sun's movement for the installation position for time and position synchronism.
The lenses are made from acrylic plastic that is extruded, or extruded with calendar rolls, embossing drums or other shape controlling processes and then cut to the proper length. Optically, the lenses in the lens array meet the system optical tolerance requirements, such as focal length and pitch at an economic system cost. Other lens array fabrication methods such as casting, injection molding, and polishing are generally too expensive for consideration. The arculate path of the heat conductive base allows some compromise in line width about the theoretical focus depth so that solar energy is collected most economically. The heat conductive panel is environmentally sealed within the case of the solar panel by a flexible bladder to prevent contamination by insects, dust, or moisture in the volume between the array of lenses and the heat conductive base. The flexible bladder may be molded with accordion folds to reduce the stresses therein and provide a reasonable lifetime even though the bladder may be subject to damage due to temperature and wind thrown debris. Therefore, removable mounting for the bladder is preferred so it can easily be replaced.
It is therefore a principle object of the present invention to provide efficient stationary solar panels at an economic cost.
Another object is to concentrate solar energy to minimize the amount of photovoltaic material required to convert the solar energy falling on a given area into electricity.
Another object is to minimize the space required, especially for solar module depth profile, and weight for a solar array.
Another object is to provide solar panels that maximize the use of available roof space for the production of electricity while minimizing the need to modify the roof of a commercial building for “after market” installation.
Another object is to provide solar generated electricity in areas of direct sunlight.
These and other objects and advantages of the present invention will become apparent to those skilled in the art after considering the following detailed specification along with the accompanying drawings wherein:
Referring to the drawings more particularly by reference numbers, number 20 in
The assembly 82 is an extrusion of five cylindrical linear lens, 86, 88, 90, 92, and 94. The lens 86, 88, 90, 92, and 94 being extruded and of extrudible plastic, are of sufficient optical transmission quality, but must be very economical to manufacture. Higher quality lens arrays may be produced by injection molding, casting, or machining and optical polishing, but their cost, at the present, is high and their usage increases the cost of the panel 20 to a level where little if any money is saved by the present invention in converting solar energy to electricity. As will be explained, the panel 20 is very tolerant of optical aberrations and is a light concentrating system, not an imaging system.
The plastic lenses need be fabricated in high optical clarity material that is resistant to optical and mechanical degradation from environmental exposure of solar radiation, moisture, and weather. A common lens material used is acrylic resin or poly methyl methacrylate (PMMA).
As aforesaid, the panel 20 is oriented with the lens 86, 88, 90, 92, and 94 extending from side 56 to side 58 on the panel 20. The effect of the movement of the sun 24 is shown in
The effective theoretical concentration zone is as illustrated. In these minimized cost solutions optical aberrations are introduced which result in a widening of the concentration zone shown in
In a typical lowest cost solar concentrator configuration of this invention has an optical concentration ratio of at least 20 to 1, with lens aperture of 20 mm, a spherical lens array with 22mm radius-of-curvature made by extrusion and embossing roll processing in PMMA plastic, and the photovoltaic cell strip width of 1 mm, and concentrator module depth profile of 5 cm, has the arculate path focal depth alignment tolerances shown in
Heat spreader and electrical bus bar elements 122, 130, 132, 146 and 148 are physically bonded to heat sink 80 by electrically insulating adhesive to provide a direct thermal conduction path to cool the photovoltaic cell strips and to provide a flat mechanical support panel to panel arculate path motion in aligning the plurality of photovoltaic cell strips with the plurality of light concentration lines at all sun positions throughout the day.
Therefore there has been shown and described novel solar panels and arrays thereof which fulfill all the objects and advantages sought therefore. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings. All such changes, modifications, alterations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention which is limited only by the claims which follow: