Field of the Invention
The present invention relates to the area of solar energy, and more particularly to a design and fabrication of a high efficiency, low cost, local concentrator type solar photovoltaic (PV) panel and a local concentrator panel.
Description of Related Art
It is well known that for PV technology to be viable for wide-spread adoption, there are two primary requirements: cell efficiency of at least 20% and the total system cost enabling a pay-back time of a few months to a couple of years. Unfortunately, most PV technology has problems with either one or both of these requirements.
One object of the invention is to enable the fabrication of high efficiency solar photovoltaic systems that are cost effective for wide-spread house-hold and industrial applications.
One way to reduce the cost of a PV system is to reduce the total area of semiconductor devices (PV cells). This is possible by using optical concentrators such as parabolic mirrors or lenses to focus the sunlight onto a smaller area (focal point) where the PV cell is placed. Concentration ratios as high as 1000 times (1000 Suns) have been achieved. The usage of concentration also helps in boosting the spectral power density. However there are a few problems that need to be addressed for concentrator technology: (a) active cell cooling becomes absolutely necessary due to higher temperatures by power concentration and (b) the entire concentrator module needs to be continuously rotated during the day to track and face the sun as it traverses the sky during the day. If the concentrator is not rotated, there is a spike in the power around noon and the power generated before noon and afternoon are significantly less than the non-concentrator based systems.
This latter problem is a significant one, since solar concentrators are required to track the movement of the sun, this decreases the efficiency of the system since it can only collect light from a particular angle at any one time. Furthermore the requirement of tracking the sun increases the costs of manufacture significantly.
The usage of a local light concentrator helps to reduce PV cell area which leads to significant reduction in systems cost. Unlike traditional concentrator type PV systems, the proposed system need not be continuously rotated to face the sun during the day, and thus tracking is not necessary. The employment of light concentrator in form of spherical lenses, hemispherical lenses, conical reflectors, or parabolic reflectors, for example, in conjunction with a linear array of PV cells placed such that the focal point of the light concentrator moves along the linear array eliminates the need for moving the solar power panel to face (track) the sun. Furthermore, by employing double sided and edge exposed PV cell configurations, illumination from top, bottom as well as the edge of the cell enables a better light capturing process enhancing the overall power conversion efficiency of the system as compared to an existing non-concentrator type flat solar panel. By optimizing the concentration ratios depending on geographical location of the solar panel, one can eliminate the need for active cooling of the PV devices during operation.
According to one embodiment of the invention, there is provided an apparatus. The apparatus comprises: an array of photovoltaic cells arranged along an elongated strip; and one or more optical elements arranged to direct and optically concentrate sunlight onto the photovoltaic cells such that position that the directed sunlight impinges onto the strip follows a path moving along the strip without the optical elements tracking the sun as the sun traverses the sky during the day.
According to one embodiment of the invention, there is provided an apparatus. The apparatus comprises: an array of photovoltaic cells arranged along an elongated strip; and one or more spherical lens arranged to direct and optically concentrate sunlight onto the photovoltaic cells such that position that the directed sunlight impinges onto the strip follows a path moving along the strip as the sun traverses the sky during the day
According to another embodiment of the invention, there is provided an apparatus for collecting solar energy. The apparatus comprises an array of spherical concentrators held by a grid mesh and positioned above an array of photovoltaic cells and heat sinks. The spherical concentrators allow light to be concentrated independent of the angle from which it enters, thus making tracking of the sun unnecessary. Furthermore, the array of spherical concentrators can be arranged above any desired arrangement or design of PV cells, thus making the resulting apparatus modular in design. The spherical concentrators can also be composed of a variety of transparent materials including glass and plastic. The size of the spherical concentrators will only be limited by the amount of heat dissipation needed in the specific application.
In the following detailed description of various embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that compositional, structural, and logical substitutions and changes may be made without departing from the scope of this disclosure. Examples and embodiments merely typify possible variations. Individual components and functions are optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others. The following description is, therefore, not to be taken in a limiting sense.
The array of optical elements 20 may be arranged to direct and optically concentrate sunlight from the sun 30 onto the PV cells 14 such that the position that the directed sunlight impinges onto the cells 14 on the strip 16 follows a path moving along the strip without the optical elements 20 tracking the sun 30 as the sun traverses the sky during the day, for only a portion of the daylight hours, or during the entire daylight hours. The array of optical elements 20 may be arranged to direct and optically concentrate either direct and/or indirect sunlight from the sun 30 onto the PV cells 14. For example, indirect sunlight that is scattered by the sky or reflected off a building may be directed and optically concentrated.
In the case the optical elements 20 are concentrating lenses, such as spherical lenses or hemi-spherical lenses, the concentrating lenses should be made of an appropriate material. The concentrating lenses may be made of a high index of refraction material, for example, where a high index of refraction is an index of refraction greater than about one. The concentrating lenses may be made of glass or plastic, for example. In the case that the concentrating lenses are spherical, the lenses may be glass marbles, for example. The concentrating lenses may comprise hollow spheres of an optically transparent solid filled with a high refractive index liquid. The high refractive index liquid may comprise a material comprising at least one of water, oil, glycerol, acetone, methanol, or another liquid, for example. The optically transparent solid may be glass or plastic, for example.
The concentrating lenses may comprise an optically clear composite solid. The concentrating lenses may comprise a core-shell structure with different refractive indices for the core and shell. The concentrating lenses comprise at least one of a mixture of glass and plastic, high refractive index solid dispersed in liquid, or glass embedded with air bubbles. The concentrating lenses may comprise an anti-reflection coating on the lens surface to reduce sunlight reflection. The concentrating lenses may comprise a structure with multiple layers, each layer having a different refractive index, or a structure having concentric hollow layers filled with liquids having different indices of refraction. The concentrating lenses may comprise a solid transparent high refractive index cylindrical rod, or a hollow cylindrical solid tube filled with liquid.
The PV cells 14 may comprise a single bandgap material such as silicon, germanium, compound semiconductors, such as Cu(In,Ga)Se2, for example, or organic semiconductors, for example. The PV cells 14 may comprise gratzel cells, for example. The PV cells 14 may comprise a multiple bandgap materials.
The elongated strip may have a width and length, as appropriate, and may have a width between about 1 to 5 mm and a length between about 0.5 to 5 cm, for example.
The apparatus 10 is arranged such that the optical elements 20 need not track the sun as the sun traverses the sky. Thus, the orientation of the optical elements, as well as the orientation of the array relative to the sun need not change as the sun traverses the sky. The apparatus of claim 10, while not requiring tracking, still allows that the midday spike in power generation is prevented by providing that the focus point of the sunlight onto the array 12 follows a path along the orientation of the array 12.
For proof of concept experiments, a concentration ratio of 80 was used with a single PV cell. In the case of a single PV cell with maximum power generation at noon, the amount of PV cell material is reduced by 80 times. On the other hand for a strip with an array of cells mounted thereon, where the concentrated light follows along the strip as the sun traverses the sky, the reduction in PV material usage is approximately 10 times. The spherical lenses 40 were glass lenses and are significantly less expensive than PV cell materials.
Another important point is that the system need not be rotated to track the sun unlike existing concentrator type systems. Foregoing tracking saves a significant amount of PV power and system cost involved with motors and mechanical frames used for tracking. Another advantage of the use of an array of optical elements, such as spherical shaped elements, is that the system is modular in design and can be simply adapted to use with various PV cells, or any other use that requires passive concentration of light without the need for tracking of the sun.
The apparatus comprises a heat sink or sinks 50 onto which individual cells 14 are mounted. The apparatus includes a grid mesh 52 which functions to support the spherical lenses 40. Spacers 54 are arranged to separate the grid mesh 52 from the underlying strip 16 with cells 14. The grid mesh may be attached to the spacers 54 with nuts and bolts 56. The top surface of the heat sink 50 where the PV cells 14 are mounted could be textured mirrors to reflect any stray radiation onto the edge of the PV cells that are exposed. This allows for the generation of additional power.
For the
The local concentrator apparatus design enables the manufacturing of very high efficiency systems. Stacked PV cells with semiconductor materials having different bandgaps can be used instead of the single bandgap cells. The stacked PV cells will further boost the efficiencies of the system. Since the individual cells may have a small areas (0.1-1 mm2), it is possible to provide metal contacts on the p-type and n-type sides using ring configuration as shown in
While the discussion has described the present invention in the context of solar light concentration and power production, many other applications can be envisioned. Additionally, the use of translucent spherical balls to locally concentrate light allows the light to enter the sphere from many different angles and therefore different sources simultaneously. For example the source could be direct light from the sun as well as diffused light reflected off surfaces such as nearby buildings. Furthermore the source of light concentrated could be from outside the visible spectrum of the electro-magnetic radiation spectrum (such as infrared and ultraviolet radiation).
While the above embodiments describe an apparatus without the optical elements tracking the sun as the sun traverses the sky during the day, in a less preferred embodiment, the optical elements may be driven to track the sun. The optical elements in this case may be spherical lenses, for example. The low cost and readily available spherical lenses provide that the system is low cost.
This application is a National Stage application of PCT/US2008/008246, filed Jul. 3, 2008, which claims priority to U.S. Provisional Application 60/948,260 filed on Jul. 6, 2007, which are incorporated by reference in their entirety.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2008/008246 | 7/3/2008 | WO | 00 | 1/5/2010 |
Publishing Document | Publishing Date | Country | Kind |
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WO2009/008996 | 1/15/2009 | WO | A |
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International Search Report and Written Opinion dated Jan. 28, 2009, in PCCT/US2008/008246), 12 pages. |
Number | Date | Country | |
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20100132763 A1 | Jun 2010 | US |
Number | Date | Country | |
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60948260 | Jul 2007 | US |