Double-layer photovoltaic installation structure

Abstract

A two-layer photovoltaic mounting structure comprising a top layer and a bottom layer wherein: the top layer of the mounting structure consists of a plurality of two-sided photovoltaic strings (A) arranged parallel to one another, each photovoltaic string having a top surface (Fs) and a bottom surface (Fi), both surfaces being capable of generating electrical energy from the sun; the single-axis solar tracking system is connected to the photovoltaic string (A), the former being adapted to rotate the latter about its axis of rotation (5) by an angle (alpha); the solar tracking system positions the photovoltaic strings (A) such that the top surface (Fs) and the bottom surface (Fi) of each photovoltaic string (A) are located parallel to the incident light beam, thereby projecting a minimum shadow on the bottom layer of the mounting structure; the bottom layer of the mounting structure consists of additional photovoltaic strings or reflective surfaces.

Description

Cross-reference to related applications

[0001] This patent application claims priority to Italian Patent Application No. 102023000011895, filed on June 9, 2023, the full disclosure of which is incorporated herein by reference. Technical Field

[0002] This invention relates to a photovoltaic installation structure that generates electricity by converting sunlight. To optimize the overall utilization of sunlight incident on the installation structure, a double-layer photovoltaic string system is proposed, consisting of a top-layer photovoltaic string and a bottom-layer photovoltaic string. Furthermore, compared to existing technologies, a single-axis tracking system that tracks the sun's position controls the top-layer photovoltaic string according to entirely new logic. Therefore, this invention falls within the category of so-called photovoltaic generators equipped with a single-axis solar tracker. Background Technology

[0003] As is well known, photovoltaic cells (special foils made of semiconductor materials, most commonly silicon) can convert sunlight into direct current (DC) electricity when exposed to sunlight. The conversion efficiency of a photovoltaic cell is typically determined by evaluating the ratio of the electrical energy produced by the cell to the light energy captured by the cell, using the entire surface area of ​​the cell exposed to sunlight in the calculation. To date, the conversion efficiency of photovoltaic cells remains low due to various factors. The latest generation of commercially available photovoltaic cells has a maximum efficiency slightly above 20%, while those showing a maximum efficiency of around 30% are still under research. To break through these values ​​and reach the recent record of approximately 46%, it is necessary to employ special "multi-junction" photovoltaic cells, coupled with equally special (large and expensive) solar optical concentrators.

[0004] It is also known that the conversion efficiency of photovoltaic cells is highly sensitive to the angle of incidence of light onto their sun-exposed surfaces. Maximum efficiency is achieved when the beam of light strikes the surface perpendicularly. Therefore, systems specifically designed and manufactured called "solar trackers" are used to detect and track the sun's position in real time, continuously adjusting the photovoltaic cells to their maximum power generation efficiency. The most advanced trackers are those equipped with two degrees of freedom (simultaneously controlling azimuth and tilt angles). Due to their use, photovoltaic installations can generate up to 40% more electricity annually than "fixed" photovoltaic installations, given the same light and environmental conditions. However, these complex systems are costly to manufacture and operate, and have a high rate of unavailability. Therefore, less complex tracking systems with only a single degree of freedom, known as single-axis solar trackers, can be considered. Their lower complexity significantly reduces manufacturing and operating costs and makes them more reliable. Under the same light and environmental conditions, photovoltaic cells exposed to the same light and environmental conditions can generate up to 30% more electricity annually using a polar-axis single-axis solar tracking system (with the axis of rotation parallel to the Earth's north-south direction) than a fixed installation. However, if the axis of rotation is not aligned north-south, the percentage increase in annual power generation will inevitably decrease. Regardless, even with single-axis solar trackers, various issues remain related to manufacturing costs and downtime associated with subsequent photovoltaic installations based on the system. Among the most critical issues are: (i) the cost of additional components for the rotational support of the photovoltaic modules and components specifically for their command and control; (ii) the energy consumption of the solar tracking drive servo mechanism (up to 5% of power generation); and (iii) the decreased reliability and availability of the photovoltaic generator due to the increased complexity of the installation structure and its direct exposure (including the solar tracking system components) to a corrosive atmospheric environment (primarily wind and corrosive conditions).

[0005] Furthermore, photovoltaic (PV) installations employing solar tracking systems, including those using only single-axis solar tracking, face an additional and significant challenge: a large footprint. In fact, to maximize the power generation efficiency of a solar tracking system, the PV strings mounted on specially designed trackers must be arranged in parallel rows, ensuring that they do not obstruct each other throughout the day and during tracking rotation—not even partially. When the installation consists of a large number of PV strings, this necessitates their arrangement in parallel rows with significant spacing between them. Therefore, given the same usable and effectively sun-exposed ground area, the PV capacity per unit area of ​​a PV installation using a single-axis solar tracking system (i.e., "vertical" tracking) manufactured with current technology is significantly lower than that of a fixed PV installation. This is because in a fixed installation, there is no mutual shading between the PV strings, allowing them to be arranged closely together. The result is that although photovoltaic installations using single-axis solar tracking systems increase power generation, this gain is often insufficient to offset the losses caused by the reduction in photovoltaic capacity per unit area. In other words, for the same land area, the power generation of a photovoltaic installation equipped with a single-axis tracker is roughly equivalent to that of a fixed installation (containing more photovoltaic modules).

[0006] All of the above is largely due to the fact that, to date, traditional solar tracking systems (including single-axis solar tracking systems) have been conceived with dedicated "additional" movable support systems on which to mount entirely conventional photovoltaic modules, typically also used in fixed installations. Furthermore, traditional solar tracking systems are still designed and built for ground-mounted or flat-roof installations, thus following the logic of complete exposure to the landscape, especially unfavorable atmospheric conditions. Finally (but this is not unimportant), all solar trackers (and single-axis trackers) are conceived based on the fundamental idea that the primary purpose of solar tracking is to ensure that the surface of the photovoltaic string exposed to sunlight is always perpendicular to the incident beam, thereby maximizing the direct generation of electricity.

[0007] In summary, based on existing technologies, the resulting photovoltaic installation structures are large in size, expensive, and have poor reliability, and have a significant impact on the environment, especially in terms of occupying a large amount of land, resulting in a low photovoltaic installed capacity per unit area.

[0008] Therefore, it is believed that a photovoltaic installation structure with technical features that can overcome the above-mentioned shortcomings of the existing technology is needed. Summary of the Invention

[0009] The purpose of this invention is to provide a double-layer photovoltaic installation structure, the basic technical features of which are described in independent claim 1, and the additional or auxiliary technical features are described in claims 2 to 7.

[0010] Another object of the present invention is to provide a method for generating electrical energy using a photovoltaic installation structure, the basic technical features of which are described in independent claim 8, and the additional or auxiliary technical features are described in claim 9.

[0011] Unlike existing single-axis solar tracking photovoltaic installation structures, the photovoltaic installation structure of this invention aims to significantly improve the utilization rate of incident sunlight on a fixed ground surface, which is mainly achieved through the following two new approaches.

[0012] The first approach is to create a photovoltaic installation structure by setting up two layers of stacked photovoltaic strings on available ground (in fact, the first layer of photovoltaic strings is located on top of the second layer of photovoltaic strings).

[0013] The second approach is to equip the upper (top) photovoltaic string with a single-axis solar tracking system, which is structurally very similar to existing systems, but based on a completely new control logic, namely a new orientation method for the photovoltaic string relative to the incident sunlight.

[0014] As will be explained in more detail later, the single-axis solar tracking system configured on the top photovoltaic strings ensures that these photovoltaic strings are always parallel to the incident light beam, rather than perpendicular to the beam as in existing technologies.

[0015] Based on the above principle, sunlight incident on the top photovoltaic string, after "passing" across its surface, can almost entirely pass through, thus allowing it to continue illuminating the surface of the lower (or bottom) photovoltaic strings. The lower photovoltaic strings are designed to capture sunlight projected from the top photovoltaic strings using existing technologies. That is, their design and construction methods can vary, but all can utilize existing known and used technologies and processes. For example, the lower photovoltaic strings can use bifacial modules and be equipped with a single-axis solar tracking system (distinct and independent of the single-axis solar tracking system of the top photovoltaic strings); they can also be singlefacial, fixed, and completely opaque or semi-opaque.

[0016] To control the cost of the installation structure while still aiming to increase the amount of electricity generated per unit area, the underlying photovoltaic strings can also be replaced by simple reflective surfaces.

[0017] In general, the photovoltaic installation structure according to the present invention aims to convert incident sunlight into electrical energy using two stacked photovoltaic strings. The first photovoltaic string is only passed through by sunlight (i.e., transmitted through), and only the scattered and reflected light components are converted into electrical energy. The second photovoltaic string, according to existing technology, converts sunlight from the top layer into electrical energy while reflecting the light back to the upper photovoltaic string.

[0018] Experiments have shown that, compared with existing technologies, this invention can significantly increase photovoltaic installed capacity and power generation within a fixed footprint.

[0019] Furthermore, even if the lower photovoltaic strings of the installation structure are equipped with a single-axis solar tracking system that is distinct from and independent of the upper layers, the transmittance of the entire installation structure to the incident light beam can still be controlled, provided it is considered economically viable. In this way, the installation structure effectively possesses a dual function: simultaneously and optimally regulating both power generation and the amount of natural light used to illuminate the environment below. Attached Figure Description

[0020] Some embodiments are described below in a non-limiting manner with reference to the accompanying drawings, wherein: Figure 1 The structure of each bifacial photovoltaic string (A) that makes up the top layer of the installation structure is shown; Figure 2 The top layer shows multiple bifacial photovoltaic strings installed in a side-by-side parallel manner (A); Figure 3 An installation structure is shown, wherein the bifacial photovoltaic string (B) forming the lower layer of the installation structure has the same construction characteristics as the top photovoltaic string (A), but its number can be different, it can be installed in different directions, and it can rotate independently under the control of its own single-axis solar tracking system. At the same time, its orientation logic to the sun can also be different. Figure 4 An installation structure is shown, wherein the lower layer of the installation structure consists of a single bifacial semi-transparent photovoltaic string (C), without a solar tracking system, and is equipped with a flat surface whose area is equal to the total planar area covered by all the photovoltaic strings (A) on the top layer; Figure 5 An installation structure is shown, wherein the bottom layer of the installation structure consists of a single single-sided opaque photovoltaic string (D), without a solar tracking system, and is equipped with a flat surface whose area is equal to the total plane area covered by all the photovoltaic strings (A) on the top layer; Figure 6 An installation structure is shown, wherein the bottom layer of the installation structure consists of a reflective surface (E), which is fixed and non-flat, but its ground projection area is equal to the total planar area covered by all the photovoltaic strings (A) on the top layer; Figure 7A first application example (photovoltaic agricultural greenhouse) is shown, in which the photovoltaic installation structure is installed inside a light-transmitting shell to protect it from adverse atmospheric factors; Figure 8 A second application example (double-layer photovoltaic module) is shown, in which the light-transmitting protective shell of the photovoltaic string is specially designed for further integration into general buildings or industrial products.

[0021] Basic components of the mounting structure of this invention The purpose of this invention is to construct a double-layer photovoltaic installation structure consisting of two layers of photovoltaic strings (including a top-layer photovoltaic string and a bottom-layer photovoltaic string). The top-layer photovoltaic string is equipped with a single-axis solar tracking system. Its structure is very similar to the prior art, but unlike the prior art, its control method follows a completely new solar tracking logic.

[0022] The main components of the photovoltaic installation structure according to the present invention include: - Top-level photovoltaic strings: adopt a "bifacial" type and must be equipped with a single-axis solar tracking system; - The bottom layer of photovoltaic strings can be bifacial or monofacial, equipped with a single-axis solar tracking system that is distinct from and independent of the tracking system of the top layer of photovoltaic strings, or it can be fixed (i.e., without a solar tracking system). - Optional reflective surface: If present, it replaces the underlying photovoltaic string and can have a non-flat surface; - Optional housing: Equipped with a light-transmitting cover, in certain cases, the entire photovoltaic installation structure according to the invention can be manufactured within this housing.

[0023] The structural characteristics and special features of the aforementioned basic components, as well as other possible auxiliary components, will be further explained in the following detailed description of the present invention. Prior to this, a brief introduction and description of the accompanying drawings and illustrations will be provided to aid in a clear understanding of the construction and working principle of the photovoltaic installation structure of the present invention. Detailed Implementation

[0024] The construction and operational characteristics of the photovoltaic installation structure of this invention are also illustrated by the accompanying drawings, which are listed in this section as several figures and are only briefly described. These drawings will be described in more detail in the following paragraphs.

[0025] Similar to existing photovoltaic installation structures, the basic element of the installation structure of this invention remains photovoltaic cells, as briefly described in the introduction. First, a suitable number of photovoltaic cells are used to form a so-called photovoltaic module, which is formed by physically and electrically connecting the aforementioned photovoltaic cells in a certain number of series. Then, a suitable number of photovoltaic modules are assembled and connected together to form a so-called photovoltaic string; finally, a suitable number of photovoltaic strings are placed side-by-side to constitute a so-called overall photovoltaic field (or generator).

[0026] Similar to practices in certain areas of the prior art, particularly in photovoltaic installation structures using solar trackers or modular and transparent / semi-transparent photovoltaic strings, the modules (and the photovoltaic strings formed therefrom) used to construct the photovoltaic generator of this invention can be wholly or partially bifacial. It is understood that "bifacial" refers to a module (and photovoltaic string) equipped with two sides (a top surface and a bottom surface), both capable of converting sunlight incident upon them into electrical energy. Such bifacial modules can be manufactured using different processes and technologies: they can be manufactured using individual bifacial cells (commercially available), each cell having two sides (a top surface and a bottom surface), typically with different capabilities in converting sunlight into electrical energy on the top and bottom surfaces. However, they can also be manufactured using the same conventional single-sided cells, which are installed on both sides (top and bottom) of the module, to ensure, for example, that both sides have the same (but independent) capability in converting sunlight into electrical energy.

[0027] Still referring to photovoltaic modules, these modules are assembled together to form photovoltaic strings of the photovoltaic mounting structure of the present invention. They can be commercial modules (i.e., completely conventional), but in some cases, they can also be custom-designed and manufactured on demand, as will be illustrated in the following detailed description of several application examples.

[0028] As the invention title suggests, the photovoltaic installation structure of the present invention consists of two distinct and independent layers of photovoltaic strings: an upper top layer and a lower bottom layer.

[0029] The top-level photovoltaic (PV) string must be equipped with a single-axis solar tracking system. Structurally, this system is completely similar to existing single-axis trackers. Specifically, one or more motors and a specially designed drive system are connected to the rotating shaft of the top-level PV string, and a specially designed electronically controlled driver applies axial rotation to the motors to make the PV string operate according to a predetermined solar tracking logic.

[0030] Therefore, the primary innovation and characteristic of the photovoltaic installation structure according to the present invention lies in the special control logic employed in the orientation of the top photovoltaic string relative to the incident solar beam. In effect, this solar tracking system requires, in a completely new way, that the top photovoltaic string be oriented parallel to the beam incident upon it.

[0031] Even though this tracking logic, which is called "parallel tracking" for convenience, seems counterproductive in terms of efficiency in converting sunlight into electricity, we believe that if it is associated with the second layer of the photovoltaic string, it can actually exhibit new and very useful properties, such that it can make fuller use of sunlight incident on a fixed footprint than any other solution in the prior art.

[0032] As is well known, the efficiency of a photovoltaic cell in converting incident sunlight into electrical energy largely depends on the angle at which the light beam strikes the cell surface: the conversion efficiency is highest when the beam strikes the surface perpendicularly, and almost zero when the beam strikes the surface parallel to it. In other words, it is clear that the aforementioned "parallel tracking" principle does not guarantee any "direct" electrical energy conversion from incident sunlight by the photovoltaic mounting structure of this invention. However, it is also true (and well known) that photovoltaic cells convert sunlight into electrical energy not only by intercepting beams of light directly incident upon them, but also by intercepting sunlight that exists in the environment surrounding the photovoltaic cell installation and indirectly illuminates its surface due to known scattering and / or reflection phenomena. This "indirect" sunlight depends largely on the physical characteristics of the environment surrounding the photovoltaic cell installation; this phenomenon can also be attributed to the well-known "albedo" of a particular physical environment.

[0033] Thanks to the above phenomena, it can be clearly understood that although the top photovoltaic string of the photovoltaic mounting structure according to the present invention is oriented parallel to the light beam incident on it, it is still able to generate a certain amount of electrical energy through the conversion of scattered and reflected light captured by its two sides (top and bottom), and the amount of electrical energy depends significantly on the albedo value of the installation environment around the photovoltaic string.

[0034] First, it's important to emphasize that the amount of "indirect" electricity generated by aligning the top photovoltaic (PV) string parallel to the incident light beam largely depends on the amount of incident light that passes through the PV string and into the environment below, which is then reflected back to the top string. The stronger the light beam that passes through the top PV string, the more light is reflected back, allowing it to re-enter the top PV string and indirectly increasing the electrical energy generated by the upper PV string.

[0035] It is clear from this that, in stark contrast to the solutions in the prior art (“vertical” tracking), the purpose of the parallel tracking described in this invention is, at the primary level, to simultaneously maximize the transmittance of the top photovoltaic string to the incident light beam, and to achieve the “indirect” power generation by maximizing the scattered and reflected light from the lower layers.

[0036] It is important to emphasize that, conversely, the purpose of vertical tracking in existing technologies is solely to maximize the electrical energy directly generated by the photovoltaic string, while the indirectly generated electrical energy is inevitably significantly reduced. To understand this, simply consider that a photovoltaic string arranged perpendicular to the beam will strongly shade (block light) the physical environment below it, thereby reducing the component of reflected light.

[0037] According to existing installation structures, the significant reduction in lighting in the physical environment beneath the photovoltaic strings can lead to negative environmental impacts; for example, in agriculture, the land beneath such installation structures may be difficult to cultivate effectively. Conversely, the installation structure according to the present invention can bring positive environmental benefits by maximizing the illumination of the environment below, in terms of more efficient and economical land use; these benefits largely depend on the structural and functional characteristics of the underlying structure.

[0038] To ensure that the expected energy performance of the photovoltaic installation structure according to the invention meets both user expectations and, more importantly, their economic affordability, the underlying photovoltaic strings can be of different types and can be designed and constructed with reference to various existing technologies and processes. For example, by designing and constructing the underlying photovoltaic strings as the same type as the top photovoltaic strings, even in a completely distinct and independent manner, the energy performance of the photovoltaic installation structure according to the invention can be maximized. However, in this case, achieving maximum energy output will correspond to the highest manufacturing cost and greatest complexity of the installation structure. By designing and constructing the underlying photovoltaic strings differently from the top photovoltaic strings, a solution with lower performance but also lower cost and complexity can be achieved. For example, by using "fixed" (without solar trackers) single-sided photovoltaic strings as the underlying layer, or even by using a simple reflective surface instead of additional photovoltaic strings to manufacture the underlying layer, a photovoltaic installation structure with lower cost, simpler structure, but relatively lower performance can be achieved.

[0039] Before delving into the structural details of the proposed photovoltaic installation structure, it is essential to emphasize a further aspect of the photovoltaic installation structure according to the present invention, particularly the solar tracking system that must be equipped with the top-level photovoltaic string. In existing photovoltaic installation structures, to perfectly achieve the "vertical" solar tracking logic, a dual-axis tracking system is strictly required (thus resulting in high cost, structural complexity, and low reliability). If a single-axis tracking system is used to reduce the cost and complexity of the tracking system and improve its reliability, the "vertical" tracking will inevitably be imperfect, leading to a decrease in the efficiency of sunlight conversion into electrical energy. Furthermore, the light energy conversion efficiency depends not only significantly on the tilt angle (fixed) of the photovoltaic string installation but also on the direction of its rotation axis (also fixed), with the direction of maximum efficiency being the polar axis direction, i.e., the same direction as the Earth's rotation axis. Unlike the above, to achieve the proposed "perfect" parallel solar tracking, only a simple single-axis solar tracker is needed. Moreover, this tracking can be (perfectly) achieved regardless of the orientation of the photovoltaic string's rotation axis or the installation tilt angle. In fact, experiments can easily verify that for a photovoltaic string equipped with a single-axis rotation system, regardless of the direction and tilt angle of the rotation axis, there can always be a rotation angle around the relative axis that makes the photovoltaic string appear parallel to the incident beam, thus producing only a very small shadow projection on the environment below.

[0040] Another related effect of parallel single-axis solar tracking is that photovoltaic strings can be arranged in parallel rows and columns, performing the aforementioned solar tracking daily without shading each other, even when installed very close together. In this case, the spacing can be optimized to always avoid mutual shading between photovoltaic strings, and the solution depends on the installation direction of the rotation axis of the parallel photovoltaic strings. Specifically, when the rotation axis coincides with the east-west geographical direction, the minimum spacing for unshading between photovoltaic strings is guaranteed; while when the rotation axis is aligned with the north-south geographical direction, the spacing is at its maximum, but still very small, only equal to the width of a single photovoltaic string. This means that, given the same floor space, parallel solar tracking (always) allows for the installation of a potentially larger number of parallel photovoltaic strings compared to existing vertical solar tracking technologies, thus reasonably achieving the goal of generating more electricity per unit floor space.

[0041] After describing the basic principles of the double-layer photovoltaic installation structure, its construction and manufacturing process will be explained in detail below.

[0042] Clearly, the most fundamental importance lies in the main photovoltaic strings that make up the top layer, the so-called "bifacial photovoltaic strings (A)".

[0043] These photovoltaic strings are typically rectangular or square; they have transverse sides (1) and longitudinal sides (2), defining a flat surface (S). AThe surface has a width (a) and a length (b), and its upper and lower surfaces—the top surface (F) S ) and bottom surface (F I — It can also be manufactured using different technologies and materials.

[0044] The photovoltaic string (A) is also equipped with end members (3) mounted on its lateral side (1), each end member (3) having a dedicated longitudinal pin (4). The aforementioned longitudinal pin (4) can be set at any position on the end member (3), but for each photovoltaic string (A), these longitudinal pins must be aligned with each other in the longitudinal direction, thus actually forming a longitudinal rotation axis (5).

[0045] With the help of the end component (3) and the corresponding longitudinal pin (4) equipped with the photovoltaic string (A), the solar tracking system can be mechanically connected to it, enabling the photovoltaic string to perform single-axis rotation with a rotation angle of up to 180°.

[0046] The rotation axis (5) of the photovoltaic string (A) can be arranged in any direction.

[0047] The photovoltaic strings (A) are arranged in parallel rows and columns, and the spacing (d) between each rotating shaft (5) is selected according to the installation direction of the shaft (5). Its maximum value (when the shaft is installed in the north-south direction) will not be significantly greater than the width (a) of a single photovoltaic string (A) so as to achieve a maximum rotation of 180° when necessary.

[0048] In order to maximize the use of sunlight incident on the photovoltaic string (A)—light that passes through the photovoltaic strings due to its parallel tracking characteristics—the photovoltaic installation structure according to the invention requires the addition of a second layer below the top layer to improve the system.

[0049] The lower layer (or bottom layer) can be constructed by setting additional photovoltaic strings, which can be the same as photovoltaic string (A) and have the same size, structure, and orientation characteristics. However, the additional photovoltaic strings of the bottom layer can also be different from photovoltaic string (A); for example, they may not be equipped with a solar tracking system and may have a double-sided but semi-transparent structure, or a single-sided structure that is completely opaque to incident light.

[0050] In this way, by combining the top photovoltaic string (A) with other additional photovoltaic strings placed below it, the entire (double-layer) photovoltaic installation structure can present different configurations and achieve differentiated synergistic effects of power generation and natural lighting under the entire installation structure on a fixed and fully exposed surface area.

[0051] To control the manufacturing cost of photovoltaic installation structures while ensuring their significant power generation capacity, in addition to manufacturing additional photovoltaic strings, the underlying layer can be manufactured as a simple reflective surface (E). This reflective surface can also be non-flat, but it can be fixed and equipped with a single-axis solar tracking system independent of the photovoltaic strings (A).

[0052] However, if the incident sunlight itself has important added value (for example, when the photovoltaic installation structure is installed on agricultural land), the double-layer installation structure can be constructed in terms of structure and function to enable a certain amount (controllable) of natural light to shine through the installation structure to the ground below while achieving full power generation.

[0053] In certain specific cases of significant practical importance, the photovoltaic mounting structure according to the invention can also be conveniently housed within a specially configured protective enclosure (G). In this case, the enclosure (G) firstly has a light-transmitting cover (H) that allows light beams to penetrate to the top photovoltaic string (A). Furthermore, the enclosure must have sufficient dimensional characteristics to accommodate both the double-layer mounting structure and all components of a single-axis solar tracking system.

[0054] The photovoltaic installation structure conceived according to the detailed description in this specification has the main (but not only) advantage that its entire manufacturing process is completely protected from adverse or disruptive atmospheric factors such as wind, rain, hail, and ultraviolet radiation. This is undoubtedly more reliable and safer than similar installation structures built in an "open-air environment."

[0055] By giving the housing (G) specific structural and dimensional characteristics, the photovoltaic mounting structure according to the present invention can also gain further advantages, namely, it can be (partially or entirely) integrated into any building product (e.g., buildings, agricultural greenhouses, sheds or canopy roofs, etc.), and even integrated into any vehicle used for transporting people and / or goods (e.g., motorhomes or ships, etc.).

[0056] Furthermore, photovoltaic installation structures manufactured in the manner described above can also be manufactured as a whole by assembling multiple housings (G) together, thereby achieving the size and structural characteristics required for a specific application.

[0057] As is evident from the foregoing, the photovoltaic installation structure according to the present invention aims to maximize the effective utilization of incident sunlight on a fixed-occupancy surface by employing two stacked, independent, and separate layer structures. The top layer consists of bifacial photovoltaic strings equipped with a single-axis solar tracking system with "parallel" control, converting only scattered and reflected light into electrical energy and allowing unabsorbed sunlight to pass through to the bottom layer. If the bottom layer is composed of photovoltaic strings, sunlight from the top layer is further converted into electrical energy, while the unabsorbed portion is reflected back to the top layer. Depending on the structure and functional characteristics of the bottom layer photovoltaic strings, when needed, some sunlight from the top layer can also pass through the lower layer and controllably illuminate the ground below the device. If the bottom layer is equipped with a simple reflective (non-flat) surface instead of additional photovoltaic strings, all sunlight from the top layer is reflected back to the top layer, thereby increasing the ability to convert into electrical energy. If the bottom layer is also equipped with a single-axis solar tracking system, then a portion (controllable) of natural light incident on the photovoltaic installation structure can also pass through the bottom layer and into the environment below.

[0058] The beneficial effects of the photovoltaic installation structure according to the present invention can be further illustrated through several specific application examples.

[0059] If an agricultural plot of land is fully exposed to sunlight, the photovoltaic installation structure according to the present invention can convert only a portion of the sunlight incident upon it into electrical energy, while allowing another portion of the sunlight to be transmitted to the cultivated ground. The proportion of transmitted light can be controlled according to the needs of crop growth. Specifically, the top layer (composed of bifacial photovoltaic strings equipped with a "parallel" single-axis solar tracking system) can convert only scattered and reflected light into electrical energy, while allowing almost all direct sunlight to be transmitted to the bottom layer. The bottom layer (composed of additional bifacial photovoltaic strings equipped with a single-axis solar tracking system, and independently separate from the top layer's photovoltaic strings) can intercept the sunlight transmitted from the upper layer, converting only a portion (controllably) into additional electrical energy, while voluntarily allowing the remaining portion to be transmitted to the ground below. The proportion can be adjusted according to the natural light requirements of the cultivated crops. In this way, not only can the electrical energy output of the double-layer photovoltaic installation structure be realized, but also optimal control of the natural light required by the crops can be achieved. On the other hand, if the sole aim is to maximize the conversion of incident sunlight into electrical energy on a given surface, the double-layer photovoltaic installation structure according to the invention can be used to achieve multiple conversions of sunlight into electrical energy without allowing any incident light to penetrate below it. In this case, the incident sunlight first passes through the upper photovoltaic strings, and through the implementation of "parallel" solar tracking, only scattered and reflected light is converted into electrical energy, allowing the incident sunlight to be almost completely transmitted to the lower layer. The additional photovoltaic strings in the lower layer then intercept the incident sunlight according to existing techniques (e.g., in an almost vertical manner) and optimally convert it into additional electrical energy. Furthermore, the portion of sunlight that hits the bottom photovoltaic strings but is neither absorbed nor converted into electrical energy is still reflected back to the upper photovoltaic strings, thereby further increasing the overall power output generated by the double-layer installation structure. Based on this principle, the explicit objective of the photovoltaic installation structure of the present invention is to achieve a power output far exceeding that of existing photovoltaic installation structures under the same surface conditions of occupation and exposure to sunlight. If, after determining the available ground area for photovoltaic installation structure construction, it is compared with the expected daily power generation of a conventional photovoltaic installation structure equipped with a single-axis solar tracker, single-layer, vertical tracking, then the expected daily power generation of the optimized double-layer photovoltaic installation structure can be increased by about 60% to 80%.

[0060] To better understand the construction details and working principle of the double-layer photovoltaic installation structure of the present invention, several drawings and some photorealistic schematic diagrams are provided, which are shown in the dedicated drawings and will be described and discussed below.

[0061] Figure 1The figure illustrates the structural features of a single general-purpose bifacial photovoltaic string (A), which is the foundation and an indispensable element of the upper layer of the photovoltaic mounting structure according to the present invention. Its lateral side (1), with a width of (a), and its longitudinal side (2), with a width of (b), are highlighted in the figure. The figure also shows so-called “end members” (3) mounted on its two lateral sides (1). Corresponding longitudinal pins (4) are also shown on the end members (3). When the end members are mounted on the lateral sides of the string (A), the longitudinal pins align with each other, thereby effectively forming the longitudinal axis of rotation (5) of the string (A). The figure clearly shows how the string (A) is oriented under the action of a single-axis solar tracking system so that the incident beam is aligned with its top surface (F). S ) and bottom surface (F I ) remain parallel.

[0062] Figure 2 The diagram illustrates the top-level configuration of the photovoltaic installation structure according to the invention, where strings (A) are installed in parallel rows. Specifically, the diagram shows that in this case, the rotation axes (5) of the strings (A) are installed at a certain spacing d. This spacing d can be optimized according to the installation direction of the rotation axes (5), and it should be considered that, theoretically, its value can vary from zero (when the rotation axes are installed in the east-west direction) to the maximum value equal to the width (a) of a single string (A) (when the rotation axes are installed in the north-south direction). Obviously, once the installation direction of the rotation axes (5) of the strings (A) is determined, the maximum number of strings (A) that can be installed side by side per unit area is fixed, provided that they do not obstruct each other and do not cast shadows on each other during their daily rotation.

[0063] Figure 3This diagram illustrates a double-layered installation structure in which, to increase power generation while maintaining a certain degree of light transmittance to incident sunlight, an additional photovoltaic string (B) is installed below the top string (A). This additional photovoltaic string (B) is also bifacial and equipped with a single-axis solar tracking system. The diagram shows that string (B) and string (A) are distinct and independent of each other, each including its own solar tracking system. The diagram also shows that the number of strings (B) can differ from the number of strings (A). Although not shown in the diagram, it should be noted that string (B) can be installed with its corresponding rotation axis facing a different direction than that of string (A). Furthermore, string (B) can also be oriented according to a different control logic than string (A) via its solar tracking system; for example, according to existing technology, it can be perpendicular to the incident light beam. To ensure complete independence between the various solar tracking systems, as mentioned above, the diagram also indicates that string (B) must be installed below string (A), and a distance (h) must be maintained between the planes containing the rotation axes of strings (B) and (A). This distance must be large enough to ensure that strings (A) and (B) can rotate freely, and their rotation angle can reach 180° when needed.

[0064] Figure 4 This diagram illustrates a double-layer installation structure where, to increase power generation while maintaining a certain degree of light transmittance to incident sunlight, an additional photovoltaic string (C) is installed below the top string (A). This additional photovoltaic string (C) is also bifacial but semi-transparent to sunlight and is not equipped with a single-axis solar tracking system (therefore, it is fixed). The photovoltaic cells constituting the string (C) are spaced apart by a certain quantity (□) to ensure that the string (C) has a certain degree of light transmittance, which can be optimized during the design phase according to specific circumstances. The diagram shows a single string (C), but its footprint surface on the ground is the same as the maximum footprint surface of the entire top layer composed of (n) strings (A). Finally, to ensure the full functionality and independence of the single-axis solar tracking system equipped with string (A), it is also noted in the figure that string (C) must be installed below string (A) and maintain a sufficiently large distance (h) between it and the plane containing the axis of rotation of string (A) so as not to hinder the required rotational movement of string (A).

[0065] Figure 5This diagram illustrates a double-layer installation structure in which, to further increase power generation while sacrificing the overall structure's transparency to incident sunlight, an additional photovoltaic string (D) is installed below the top string (A). This additional photovoltaic string (D) is single-sided (opaque) and does not have a single-axis solar tracking system (therefore, it is fixed). The diagram shows string (D) as a single line, but its projected area on the ground is the same as the maximum projected area of ​​the entire top layer composed of (n) strings (A). Finally, to ensure the complete functionality and independence of the single-axis solar tracking system equipped on string (A), the diagram also indicates that string (D) must be installed below string (A) and maintain a sufficiently large distance (h) between it and the plane containing the axis of rotation of string (A) to avoid hindering the required rotational movement of string (A).

[0066] Figure 6 This diagram illustrates a two-layer installation structure where, to reduce installation costs and complexity while maintaining the goal of increasing power generation per unit area of ​​utilized space, the overall installation structure's transparency to incident sunlight is sacrificed. An additional reflective surface (E) with a non-uniform geometry is installed below the top string (A). The diagram shows the reflective surface (E) as a single unit, but regardless of its geometry (which may be non-uniform), its projected area on the ground is the same as the maximum projection of the entire top layer composed of (n) strings (A). Finally, to ensure the complete functionality and independence of the single-axis solar tracking system equipped on the strings (A), the diagram also indicates that the reflective surface (E) must be installed below the strings (A) and maintained at a sufficiently large distance (h) from the plane containing the axis of rotation of the strings (A) to avoid hindering the required rotational movement of the strings (A). The geometry of the reflective surface (E) and the choice of its constituent materials actually constitute the bottom layer of the installation structure and can significantly affect the power generation of the top bifacial string (A); therefore, these aspects can be the subject of research and experimentation to determine the most cost-effective solution.

[0067] Figure 7 A first application example is shown, and specifically relates to a typical agricultural greenhouse equipped with a photovoltaic generator. Unlike prior art, this photovoltaic generator is manufactured according to the present invention.

[0068] In practice, the photovoltaic installation structure is first and foremost installed as a whole inside the light-transmitting outer shell (G)—essentially the same agricultural greenhouse—to protect it from adverse atmospheric conditions. Secondly, the installation structure clearly shows two layers of photovoltaic strings. The top layer consists of bifacial photovoltaic strings (A) equipped with a single-axis solar tracking system. These strings (A) are manufactured based on "special" (custom-made) bifacial photovoltaic modules, which are narrow and elongated, with their corresponding photovoltaic cells encapsulated between two layers of specially designed high-transmittance plastic material (instead of glass), without any metal frames for fixing or reinforcement. In this way, the modules and the resulting photovoltaic strings (A) are both lightweight and low-cost. The strings (A) are installed in parallel rows, their arrangement conforming to the geometry of the greenhouse's light-transmitting cover structure, and maintaining a certain spacing (d) between them so that the greenhouse's light-transmitting cover can be completely "opaque" if necessary. The bottom layer of the installation structure consists of bifacial photovoltaic strings (B), which are also equipped with a single-axis solar tracking system. String (B) and string (A) are distinct and independent of each other, and their corresponding single-axis solar tracking systems are also independent. Furthermore, the number of strings (B) is less than the number of strings (A). The function of string (B) is to intercept sunlight passing through the upper strings (A) and, based on the energy and natural light requirements of the greenhouse and crops, convert all or part of the sunlight into additional electrical energy in a controlled manner. In this way, the natural light requirements of specific crops can be incorporated into the overall design of the photovoltaic installation structure, thereby optimizing the overall power generation of the photovoltaic installation structure.

[0069] Figure 8A second application example is shown, explicitly involving a scenario where a double-layer photovoltaic mounting structure is housed within a light-transmitting and protective enclosure (G), which can also be integrated into building / industrial structures. The design goal of this mounting structure is to maximize the electrical energy generated on the surface area actually exposed to light and available for installation. In this case, the double-layer photovoltaic mounting structure is essentially a double-layer photovoltaic module. It has the shape of a conventional photovoltaic module, but is noticeably thicker. It is equipped with a specially designed light-transmitting cover (H), which can be made of various materials, including glass, polycarbonate, or others. Similarly, the top photovoltaic string (A) is bifacial and equipped with a single-axis solar tracking system with parallel tracking. Similar to the previous embodiment, it is made of bifacial photovoltaic modules (custom-made), which are elongated strips and narrower than those in the previous embodiment. Again, the cells in the bifacial module are encapsulated between two layers of highly transparent, lightweight plastic material (rather than glass), and there is no metal frame for fixing and reinforcement. Furthermore, the strings (A) are installed in parallel rows, and their number can be maximized according to the installation direction of the corresponding rotation axis (which is determined by the solar exposure characteristics of the available light-receiving surface) to maximize the interception of scattered sunlight and reflected light from the bottom layer, thereby maximizing the generated electrical energy. The bottom layer of this installation structure consists of a single opaque single-sided photovoltaic string, which completely occupies the area below the top string (A). In this way, the overall power generation of the photovoltaic installation structure can be maximized by maximizing the use of sunlight transmitted through the top layer, and some experimental results have shown that its power generation is expected to be increased by about 60% to 80% compared with conventional fixed single-layer single-sided modules of the same footprint.

[0070] In summary, based on the above, it is clear that this invention proposes a method for manufacturing a double-layer photovoltaic installation. This installation structure is equipped with at least one single-axis solar tracking system and controlled according to a novel "parallel tracking" logic. Compared with existing photovoltaic installation structures, this invention is expected to significantly improve the energy conversion efficiency of incident sunlight over a predetermined footprint. If deemed suitable and convenient, the double-layer photovoltaic installation structure of this invention can also be used to achieve two different objectives: maximizing the generated electrical energy and directly and controllably (and thus economically) utilizing sunlight.

Claims

1. A double-layer photovoltaic installation structure comprising a top layer and a bottom layer, wherein: - said top layer of said installation structure is composed of a plurality of bifacial photovoltaic strings (A) arranged parallel to each other, each of said photovoltaic strings having a top surface (Fs) and a bottom surface (Fi), both of which are capable of generating electrical energy from the sun; - a single-axis solar tracking system is associated with said photovoltaic strings (A), the former being adapted to rotate the latter around its rotation axis (5) through an angle (a); - said solar tracking system positions said photovoltaic strings (A) so that said top surface (Fs) and said bottom surface (Fi) of each of said photovoltaic strings (A) are located in a position parallel to the incident light beam, thereby casting the least shadow on said bottom layer of said installation structure; - said bottom layer of said installation structure is composed of additional photovoltaic strings or reflective surfaces.

2. The photovoltaic mounting structure of claim 1, wherein, - said bottom layer of said installation structure is composed of photovoltaic strings (B) which: - have the same structural characteristics as said strings (A) of claim 1, but can differ in number; - are equipped with single-axis solar tracking systems which are distinguished from and independent of the single-axis solar tracking systems of said strings (A), so that said strings (B) perform an axial rotation around the respective rotation axis (5) through an angle (β); - are installed below said strings (A) in such a way as not to hinder the independent rotation of said strings (A) of claim 1.

3. The photovoltaic mounting structure of claim 1, wherein, - said bottom layer of said installation structure is composed of bifacial semi-transparent photovoltaic strings (C) without a solar tracking system, said strings (C) being installed below said strings (A) in such a way as not to hinder the independent rotation of said strings (A) of claim 1.

4. The photovoltaic mounting structure of claim 1, wherein, - said bottom layer of said installation structure is composed of monofacial opaque photovoltaic strings (D) without a solar tracking system, said monofacial photovoltaic strings (D) being installed below said strings (A) in such a way as not to hinder the independent rotation of said strings (A) of claim 1.

5. The photovoltaic mounting structure of claim 1, wherein, - said bottom layer of said installation structure is composed of reflective surfaces (E) which: - can be fixed or equipped with single-axis solar tracking systems which are distinguished from and independent of the solar tracking systems of said strings (A), so that said reflective surfaces (E) perform an axial rotation around the respective rotation axis through an angle (β); - are installed below said strings (A) in such a way as not to hinder the independent rotation of said strings (A) of claim 1.

6. A photovoltaic mounting structure according to any preceding claim, wherein, - said photovoltaic installation structure comprises an outer shell (G) for housing both said top layer and said bottom layer of said photovoltaic installation structure; said outer shell G comprises a light-transmitting cover (H) which is resistant to atmospheric agents and has structural characteristics which enable it to be partially or completely integrated in any architectural product and / or means of transport.

7. A photovoltaic mounting structure according to any preceding claim, wherein, - said rotation axes (5) of said photovoltaic strings (A) of said top layer are coplanar with each other.

8. A method for generating electrical energy using a double-layer photovoltaic installation structure comprising a top layer and a bottom layer, wherein: Said top layer of the installation structure is composed of a plurality of bifacial photovoltaic strings (A) arranged parallel to each other, each of said photovoltaic strings having a top surface (Fs) and a bottom surface (Fi), both capable of generating electrical energy from the sun; A single-axis solar tracking system is connected to said photovoltaic strings (A), the former being adapted to rotate the latter around the respective rotation axis (5) through an angle (a); Said bottom layer of the installation structure is composed of additional photovoltaic strings or reflective surfaces; Said method is characterized by comprising a solar tracking operation adapted to position said photovoltaic strings (A) so that the respective top surface (Fs) and bottom surface (Fi) are located in a position parallel to the incident light beam.

9. The method of claim 8, wherein, An operation of filtering the variable sunlight is included, in which said additional photovoltaic strings or said reflective surfaces are rotated independently of said photovoltaic strings (A) of the top layer, thus controlling the total amount of sunlight intercepted and filtered, as well as the total amount of sunlight transmitted through the entire photovoltaic installation structure.

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