Patent Abstract:
A concentrated photovoltaic device that is capable of generating thermal and electrical energy from solar radiation using a three-dimensional solar cell design structure with no need for a sun-tracking system is provided. The three-dimensional solar cell structure uses liquid cooling to provide maximum energy utilization from both stored thermal and electrical solar energy.

Full Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to the photovoltaic field and, more particularly, to a three-dimensional (3-D) solar cell for a concentrated photovoltaic system. 
         [0003]    2. Description of the Related Art 
         [0004]    The use of silicon material in the design of concentrated photovoltaic (CPV) solar cell brings about the advantages of overall cost reduction and power conversion efficiency. Many CPV solar cell systems use highly efficient monocrystalline or polycrystalline silicon solar cells with a light collecting lens such as Fresnel lens, a plastic convex lens, or a lens duct. These lenses focus solar radiation into the solar cell to generate electricity. The current problem with CPV solar designs, however, is that the solar cell has to face the solar rays directly to generate adequate amounts of electricity. As a result, many current designs have incorporated a tracking system which follows the Sun to maximize the conversion efficiency. Typically, the tracking system is a relatively expensive component. Furthermore, its mechanical nature makes it an implicitly unreliable component over many years of continuous operation. A novel 3-D solar cell structure removes the need for a tracking system and allows for the collection of all solar rays without the need to track the movement of the Sun. This design will improve long term reliability and reduce the total system cost. 
         [0005]    In the case of CPV design, the solar cell has to maintain a certain temperature range to maintain the optimum electrical conversion efficiency. The cooling of the CPV design is another important factor in achieving long term reliability of the solar cell and maximum energy efficiency. Currently, many designs have been developed with a heat-fin or other structure mounted to the solar cell frame to cool the solar cell to a certain temperature; without such structures, the solar cell performance would be degraded when the solar cell exceeds a certain temperature threshold. In this invention, we have designed a liquid cooling scheme for the 3-D solar cell to maintain an optimal operating temperature for the CPV solar cell. In addition, the thermal solar energy coming from the liquid cooling is recycled to heat a hot-water tank. 
         [0006]    The captured solar energy can be converted into both electricity and thermal energy. The shorter wavelengths of the solar spectrum (e.g. ultra-violet) can be converted into electricity while the longer wavelengths (e.g., infrared) can be converted into thermal energy. Because the thermal energy is also absorbed into the solar cell, a large heat sink is often used to cool off the solar cell in CPV designs and the solar cell loses its efficiency as the temperature rises beyond a certain threshold. This invention will utilize not only the shorter wavelength to generate electricity but also extract and store the thermal energy generated by the longer wavelengths into a hot-water reservoir. This scheme will improve the solar energy conversion efficiency of the CPV solar cell design to the highest conversion efficiency by utilizing both electrical and thermal energy derived from the incident solar energy. 
       SUMMARY 
       [0007]    The concentrated photovoltaic solar cell device has a focusing lens element that focuses all solar energy into a 3-D solar cell structure with a liquid cooling feature on the backside. The 3-D construction of the solar cell eliminates the needs of mounting a tracking system since the 3-D solar cell structure captures all sunlight throughout the day. 
         [0008]    In this invention, 3-D solar cells are designed with liquid channels made from Silicon MEMS etching or an RIE process. Most of the solar cells are made from silicon or III-V semiconductor material and these bulk materials can be chemically or plasma etched to form a micro- or macro-liquid channel that can be used for cooling very hot surfaces. The surfaces of all 3-D solar cells are cooled by liquid transported through the channels. 
         [0009]    The most unique feature of the 3-D solar cell device is that it captures all sunlight from any latitudinal or longitudinal change in solar position without moving the 3-D solar cell device. Most current CPV solar cell systems move their focusing lens to face directly to sunlight so the solar focus can be projected onto a solar cell. The new 3-D solar cell device solves the tracking problem of solar movement by building a special 3-D solar cell structure. A 2-D solar cell structure has a solar cell laid on a flat surface and a tracking system moves the solar cell normal to the incident sunlight; however, the 3-D solar cell structure adds to the 2-D solar cell structure in the out-of-the-plane direction to capture all sunlight that is not normal to the solar cell structure. The 3-D solar cell structure eliminates the needs of solar tracking system to improve reliability and lower production cost. 
         [0010]    Another feature of the 3-D solar cell structure is that it can be designed with a corner-cube configuration to compensate for all latitudinal and longitudinal changes due to seasonal and daily solar movements. The corner-cube configuration has the advantage of collecting sunlight from impinging on any angle and the out-of-the plane solar cell is highly effective at collecting sunlight during the sunrise and sunset periods. All 3-D solar cell devices are incorporated with a liquid cooling channel at the back of the solar cells so maximum solar intensity can be used for generating solar electricity. 
         [0011]    The new CPV solar cell system combining the special 3-D solar cell structure and liquid cooling can achieve high solar energy efficiency and lower manufacturing costs. The CPV solar cell system is designed to deliver a lower cost system with maximum solar energy conversion efficiency since the liquid cooling keeps the operating temperature of the solar cell at reasonable levels. The cooling liquid of the 3-D solar cell device can be recycled to warm up a hot-water tank in a household. Once the liquid warms from the active 3-D solar cell device, the liquid is circulated to a heat-exchanger for cooling down by cold water. The cold water heats up and the water temperature in the hot-water tank rises as it accumulate the converted solar thermal energy. The hot water in the tank can be used for a variety of household uses, including heating and washing. 
         [0012]    This summary is provided to introduce concepts relating to a thermal energy storage apparatus that absorbs thermal energy from a compact heat-generating device. Some embodiments of the thermal energy storage apparatus are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of the present disclosure. The drawings illustrate embodiments of the disclosure and, together with the description, serve to explain the principles of the disclosure. It is appreciable that the drawings are not necessarily in scale as some components may be shown to be out of proportion than the size in actual implementation in order to clearly illustrate the concept of the present disclosure. 
           [0014]      FIG. 1  shows an assembly view of a 3-D solar cell device with a metal-fin heat sink. 
           [0015]      FIG. 2  shows an assembly view of a 3-D solar cell device with liquid cooling channel attached on the back of the solar cell. 
           [0016]      FIG. 3  shows an assembly view of a 3-D solar cell device with two corner-cube configuration mounted on a metal-fin heat sink. 
           [0017]      FIG. 4  shows an assembly view of a 3-D solar cell device with two corner-cube configuration mounted on liquid cooling block. 
           [0018]      FIG. 5  shows an assembly view of a 3-D solar cell device with four corner-cube configuration mounted on a metal-fin heat sink. 
           [0019]      FIG. 6  shows an assembly view of a 3-D solar cell device with four corner-cube configuration mounted on a liquid cooling block. 
           [0020]      FIG. 7  shows an illustration view of the 3-D solar cell device working in various positions of daily solar movement. 
           [0021]      FIG. 8  shows an illustration view of the 3-D solar cell device working in various positions of seasonal solar movement. 
           [0022]      FIG. 9  shows a conceptual design of a CPV solar cell system using a 3-D solar cell device. 
           [0023]      FIG. 10  shows an illustration view of a CPV solar cell system in seasonal solar tracking. 
           [0024]      FIG. 11  shows an illustration view of a CPV solar cell system in daily solar tracking. 
           [0025]      FIG. 12  shows a block diagram of a CPV solar cell system. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    In the following subsections, we provide details on the elements involved in the construction of the 3-D solar structure for a CPV solar device. Detailed assembly views are included in this section to assist in the understanding of the structural design and functionality of the 3-D solar cell and CPV solar device. 
         [0027]      FIG. 1  shows an assembly view of a 3-D solar cell device. The 3-D solar cell structure comprises a base solar cell chip  1 , a vertical solar cell chip  2  and a mounting block  3 . The base solar cell chip  1  comprises a face of an n-type solar cell  1 A and  1 B, and a groove  1 C. The vertical solar cell chip  2  comprises a face of n-type solar cell  2 A and a face of an n-type solar cell  2 B. The vertical solar cell chip  2  can be formed by bonding two pieces of a solar cell back-to-back so that the n-type face of the vertical solar cell  2  shows on the n-type face of  2 A and  2 B. Then, the vertical solar cell chip  2  is interconnected to the groove  1 C to form a perpendicular vertical wall shown in  FIG. 1 . The n-type faces  1 A,  1 B,  2 A and  2 B are connected by conducting wires  22  for an electrical connection on all n-type surfaces. Sunlight is focused by a lens element such as a convex or Fresnel lens to the faces of  1 A,  1 B,  2 A and  2 B as the sun travels from east to west. The n-type face  2 A and  2 B of the vertical solar cell chip  2  is a critical element for collecting all sunlight during the sunrise and sunset periods. The combined solar cell structure consisting of the base solar cell chip  1  and the vertical solar cell chip  2  is then mounted to the mounting block  3  for structural strength and heat sinking of the 3-D solar cell structure. The faces  1 A,  1 B,  2 A and  2 B of the solar cell chip  1  and  2  are electrically connected to collect all electricity that is generated by the focused sunlight impinging on its surfaces. All n-type surfaces of the solar cell are connected to a conductor  23  and all p-type surfaces of the solar cell are connected to a conductor  24 . 
         [0028]      FIG. 2  shows an assembly view of a 3-D solar cell device with liquid cooling channels attached on the backside of all solar cell surfaces. The 3-D solar cell structure comprises a base solar cell chip  1 , a vertical solar cell chip  2 , a mounting block  4 , and an input and output port  5  and  6 . All components in  FIG. 2  are the same as those described in  FIG. 1  of Section 6.1; however, the base solar cell chip  1  is designed with a liquid cooling channel that is etched on the backside of the base solar cell chips  1 , or a separate liquid cooling channel is bonded to the backside of the solar cell chips  1 . The vertical solar cell chip  2  is also formed by bonding a silicon chip with liquid cooling channels, or two pieces of the solar cell are bonded together on the p-type side where the solar chip is etched to form liquid cooling channels. Bonding of a liquid cooling channel on the solar cell chips  1  and  2  maintains the solar cell efficiency as increasing solar power density impinges on these surfaces. Depending on the cooling capacity of the liquid cooling channel, the solar cell can generate significant amount of electricity without any thermal breakdown or reduction in solar cell efficiency. 
         [0029]      FIG. 3  shows an assembly view of a 3-D solar cell device with two corner-cube configurations. The basic construction of the 3-D solar cell is the same as described in section 6.1; however, a back solar cell chip  7  is added to the solar cell chips  1  and  2  forming a perpendicular plane to these solar chips. The vertical solar cell chip  2  is added to collect all sunlight throughout daytime operations which eliminates the need of a sunlight tracking system. The detailed functionality of the vertical solar cell chip  2  will be described in a later section. In addition to the changing sun position during daily operations, the altitude of the sun position is also changed by seasonal changes and the solar cell has to track the sun position for maximum generation of solar electricity. To compensate for the seasonal position change, the back solar cell chip  7  is added to accommodate for the seasonal adjustment. Adding the vertical solar cell chip  2  and the back solar cell chip  7  allows all sunlight to be collected without moving the 3-D solar cell device. The 3-D solar cell device provides maximum solar cell efficiency without tracking the sun&#39;s position throughout the year. 
         [0030]      FIG. 4  shows an assembly view of a 3-D solar cell device with two corner-cube configuration attached to a liquid cooling channel. All base components are same as described in section 6.3; however, all n-type surfaces,  1 A,  1 B,  2 A,  2 B,  7 A and  7 B, are cooled by liquid cooling channels that are bonded onto the backside of these surfaces, or the liquid cooling channels are etched on the backside of the solar cell chips  1 ,  2  and  7  forming a liquid cooling channel. The mounting block  4 A provide a structural holding fixture for the solar cell chips  1  and  7  and it has an input port  5  and output port  6 . All n-type surfaces,  1 A,  1 B,  2 A,  2 B,  7 A and  7 B, are connected by conducting wires  22  and all n-type surfaces are connected to a conductor  23 . All p-type surfaces are also soldered together for electrical continuity and all p-type surfaces are connected to conductor  24 . 
         [0031]      FIG. 5  shows an assembly view of a 3-D solar cell device with four corner-cube configurations mounted on a heat sink. The 3-D solar cell structure comprises two base solar cell chips  1 , two vertical solar cell chips  2 , a back solar cell chip  7 , and a mounting block  8 . The solar chips  1 ,  2  and  7  are orthogonal to one another, forming a four corner-cube configuration as shown in  FIG. 5 . This configuration is needed to capture all sunlight from any latitude and longitude where the sun location changes dramatically during the day and during the year. This solar cell configuration captures all available sunlight without using a solar position tracking system. All n-type surfaces are connected by conducting wire  22  and all n-type surfaces are connected to a conductor  23 . All p-type surfaces are also soldered together for electrical continuity and all p-type surfaces are connected to a conductor  24 . 
         [0032]      FIG. 6  shows an assembly view of a 3-D solar cell device with a four corner-cube configuration attached to a liquid cooling channel. All base components are the same as those described in section 6.5; however, all n-type surfaces exposed to sunlight  1 A,  1 B,  2 A,  2 B,  7 A,  7 B,  7 C and  7 D are cooled by a liquid cooling channel that is either bonded or etched onto the backside of these surfaces. A mounting block  4 B provides a structural holding fixture for the solar cell chips  1 ,  2  and  7 , and it has an input port  5  and output port  6 . 
         [0033]      FIG. 7  shows an illustrated view of how the 3-D solar cell device is working in various positions of the sun. The focusing lens  8 A is placed in an early morning position and the focus spot of the sunlight  25  is projected onto the surface  2 A of the vertical solar cell chip  2 . The focusing lens  8 B is placed in mid-morning position and the focus spot of the sunlight  25  is projected onto a part of the surface  1 A and  2 A of the solar cell chip  1  and  2 . The focusing lens  8 C is placed in an afternoon position and the focus spot of the sunlight  25  is projected onto the surface  1 A and  1 B of the base solar cell chip  1 . The focusing lens  8 D is placed in a mid-afternoon position and the focus spot of the sunlight  25  is projected onto a part of the surface  1 B and  2 B of the solar cell chip  1  and  2 . The focusing lens  8 E is in placed in a late afternoon position and the focus spot of the sunlight  25  is projected onto the surface  2 B of the vertical solar cell chip  2 . The  FIG. 7  demonstrates a concept of the 3-D solar cell device that can effectively collect all sunlight  25  throughout the day without tracking the sun position. 
         [0034]      FIG. 8  is another illustration of the 3-D solar cell device with two corner-cube configuration. As the Sun changes its altitude depending on each season, a solar cell has to move the position of the focusing spot normal to the Sun. The focusing lens  8 F is in the position of the winter season for northern hemisphere and the focus spot of the sunlight  25  is projected mostly on the back solar cell chip  7 . The focusing lens  8 G is in the position of the spring and autumn seasons for the northern hemisphere and the focus spot of the sunlight  25  is projected onto a part of the base solar cell chip  1  and the back solar cell chip  7 . The focusing lens  8 H is in the position of the summer season for the northern hemisphere and the focus spot of the sunlight  25  is projected mostly on the base solar cell chip  1 . This  FIG. 8  shows the 3-D solar cell device can capture all sunlight from any solar position. 
         [0035]      FIG. 9  is a conceptual design of a concentrated photovoltaic (CPV) solar cell system using a 3-D solar cell device. The advantage of the 3-D solar cell device is capturing all sunlight from any position of the Sun without tracking the Sun&#39;s movement. A dome  11  is constructed to hold focusing lenses  11 A and  11 B projecting a focus spot onto the 3-D solar cell device. The focusing lens  11 A is designed to be a hexagonal shape and the focusing lens  11 B is shaped like an octagon due to the geometric construction of the dome shape. The dome  11  can be constructed with glass or optical plastic and the focusing lenses  11 A and  11 B can be built with a convex or Fresnel lens. The 3-D solar cell device is placed at the center of the dome  11  where the focus spot is projected. 
         [0036]      FIG. 10  shows an illustrated view of a concentrated photovoltaic (CPV) solar cell system performing seasonal solar tracking. The 3-D solar cell device with the four corner-cube configuration is placed at the center of the dome  11  and the angles of the dome  11  show various solar positions in different seasons. For instance, the Sun is at a 90° position during the summer season at the Equator and the sunlight  25  is projected onto the base solar cell chip  1 ; however, the solar altitude of North Pole is about 16° during the summer season and the sunlight  25  is mostly projected on the back solar cell chip  7 . This figure demonstrates a visual projection of sunlight in various solar altitude positions onto the 3-D solar cell device. The 3-D solar cell device captures all sunlight efficiently without tracking the sun&#39;s movement during the season. 
         [0037]      FIG. 11  shows an illustrated view of a concentrated photovoltaic (CPV) solar cell system performing daily solar tracking. The 3-D solar cell device with a four corner-cube configuration is placed at the center of the dome  11  and the angles of the dome  11  show various solar positions from sunrise to sunset. The sunrise position is set at 0° in the east position and the sunset position is set at 180° in the west position. The Sun is moving from east to west as the focused spot is also projected from the vertical solar cell chip  2  to the base solar cell chip  1  and back to the base solar cell chip  2  at sunset. This figure demonstrates a visual projection of sunlight captured by the 3-D solar cell device throughout the day and demonstrates its ability to capture all incident sunlight without using a solar tracking system. 
         [0038]      FIG. 12  shows a block diagram of a concentrated photovoltaic (CPV) solar cell system. The CPV solar cell system consists of a dome  11 , a 3-D solar cell device  12 , a liquid pump  14 , a heat-exchanger  18 , a water tank  17 , and a solar power inverter  13 . The cold liquid is pumped into an input liquid port  5  and the liquid temperature rises as it cools down the 3-D solar cell device  12 , which is exposed to a high solar power density. The hot liquid is pumped out from the output port  6  after cooling down the 3-D solar cell device  12  and circulates to a heat-exchanger  18 . The hot liquid is cooled down by the heat-exchanger  18  by releasing the energy into cold water that is stored in the water tank  17 . The water tank  17  accumulates solar thermal energy from the hot liquid until it reaches a certain temperature, after which the water tank  17  circulates the warm water from the water tank  17  to a water output port  15  injecting cold water from a water input port  16 . The warm water from the water output port  15  can be used for any hot-water application in household, or to heat up a room during cold weather. 
         [0039]    The solar electricity generated by the 3-D solar cell device  12  can be connected to a power inverter  13  by connecting to a positive terminal port  19  and negative terminal port  20 . The power inverter  13  converts a direct current (DC) from the 3-D solar cell device  12  into an alternating current (AC), and the AC is transported out to an AC terminal port  21 . The AC is directly used in the household for any electrical application. The CPV solar cell system with the 3-D solar cell device utilizes both solar electricity and solar thermal energy and has significant advantage of lowering the cost of a CPV solar cell system. 
         [0040]    The above-described techniques pertain to thermal energy storage with a phase-change material contained in a non-metal-based container. Although the techniques have been described in language specific to certain applications, it is to be understood that the appended claims are not necessarily limited to the specific features or applications described herein. Rather, the specific features and applications are disclosed as exemplary forms of implementing such techniques.

Technology Classification (CPC): 7