SELF CLEANING SUPPORTING STRUCTURE FOR BIFACIAL PHOTOVOLTAIC

MODULES EAST-WEST ARRANGEMENT

TECHNICAL FIELD OF THE INVENTION

The useful model refers to a self cleaning supporting structure for bifacial photovoltaic modules east-west arrangement and is from the field of energy and green energy in particular. The invention is from the field of renewable energy, based on the free source of solar energy using the photovoltaic effect. In particular, the useful model is in the field of structural construction solar parks of all types and sizes, aiming maximum generating density per unit of used area, where the efficient arrangement of single-sided photovoltaic panels is ensured and especially focused on the maximum optimization of bifacial modules, without shading from their supporting structure.

BACKGROUND OF THE INVENTION

Standard two-slat construction are known, composed of two independent pergolas, not connected to each other, but touching with their high ends and forming a ridge, in the form of a roof, located opposite each other. Assembled side by side with their high parts, they form a ridge with two slats, which represents the first degree of inclination of the supporting structure for photovoltaic modules. Each of them is mounted to itself and is strengthened by multiple supports, in order to be resistant to hurricane winds and storms.

A disadvantage of this type of two-slat supporting structures is the presence of many structural elements, parts of the structure, which in using bifacial modules will lead to shadows under the panel, worsening the effect of operation, and thus maximum electrical power generation values cannot be reached. These structures are intended for photovoltaic modules - single-faced, portrait-oriented, which are the cheapest and widely distributed, but in two-sided modules of a new generation it causes the rear active part of the module to be shaded, and therefore, loss of generating power. The use of single pergolas assembled in a two-slat structure in this way of mounting the photovoltaic modules do not have sufficient stability in case of hurricane winds, snow load and other weather phenomena. It also lacks a sufficiently good self-cleaning effect due to the lack of inclination of the horizontal module frame. For example, in case of snow, part of it falls from the working part of the photovoltaic panel, but some of it is retained by the edge of the horizontal module frame and shadows the working surface, so the efficiency ratio of the energy generated by the corresponding photovoltaic module deteriorates, and in case of using a two-sided module covered with snow on these structures, due to its own rear shading caused by the structure, the module does not operate at maximum power and therefore does not it heats up enough to melt the remaining snow in a short time.

It is known a two-slat construction (pergola) for arranging photovoltaic modules, which is composed of two-slat ribs equipped with three support legs each, ending with seating shoes. One central leg located below the top of the meeting point of both arms of the slat and two shorter legs of equal length located opposite at the end of the low parts of the arms forming the slat. The difference in the lengths of the short supporting legs and the long supporting leg forms the magnitude of the slope of the slat, which slope in turn, the photovoltaic modules themselves receive, located subsequently on the whole structure. The useful model claims an opening angle between the two arms of the slat from 140° to 170°. The whole structure of the pergola for installation of photovoltaic modules is made up of at least three such ribs, stuck in a common structure, through longitudinal elements, arranged parallel to each other at certain distances along the slats, similarly and on the principle of under-tiled slats on the roofs of buildings.

The structure formed in this manner, is reinforced with diagonal connectors of the same material from which the ribs and legs are made, each diagonal connector being installed between the central leg and the left and right slopes of each rib, as well as one diagonal connector of the same leg to the ridge of the supporting structure - to the left and right of the corresponding leg. Thus a cross relationship is formed. The angle between both arms of the slat is between 140° and 170°. The solar modules are placed next to each other, with a certain distance between them, on the structural grid obtained. At the top, on the ridge of the two-slat supporting structure , the solar modules are assembled side by side, with no gap between the modules on both slats, and along the ridge. Chinese Useful Model - CN 13072514U;

A disadvantage of the known useful model is that it is intended only for single-sided modules, with one working, generating surface. If bifacial modules are installed, the structure, subject to this useful model, does not provide sufficient light to the lower working surface of photovoltaic elements located on this structure. Also, the supporting structure is designed for many rows of modules on each single slat, and in the summer months the modules are not cooled efficiently, as the low-lying ones unnecessarily heat up the adjacent higher ones, reducing their conversion efficiency (due to the photovoltaic effect of silicon which, irradiated with light, heats up and reduces the efficiency of converting light into electrical energy). The construction made in this manner does not provide optimal use of two-sided modules, and in particular the second (bottom) side, because the complicated and heavy, multi-element construction shadows the generating surface closely (makes a dense shadow) and does not provide sufficiently equal in intensity light reflected from the earth's surface to the lower working surface of the bifacial modules, located on this structure. Another disadvantage of the known construction is that the pergola constructed in this manner does not allow the modules to self-clean from dust and I or other dirt, which in contact with the humidity of the air sticks to the generating surface of the photovoltaic modules, and eventually turns into mud, which dries and forms an opaque dense film. Pollution is caused by particles carried by dry air, polluted rain, snow, winds, which, as a result of atmospheric changes and influences, additionally contaminate the working surfaces. Accumulated dirt in contact with moisture dries quickly on the warm generating surface and forms a dense shading film in relatively short periods of operation - within only hours, days, weeks or a month (a month, two in clean and remote areas). Such pollution reduces by 10 to 33% the efficiency of operation of each single module, and from there, of the entire energy generated by the photovoltaic installation.

Thus constructed, the pergola in the highest part of the two-slat supporting structure does not allow movement of a cleaning wheeled lightweight robot, due to the lack of distance between the slats of the ridge, and the wheels of the robots have to move only on the high and low parallel own frames of the modules, using them like rails. These are the only devices approved for this purpose. Module manufacturers prohibit movement of wheeled and rubber- tracked cleaning robots directly on the active part of the module glass, due to vibrating and heavy loads at one point bending the glass, resulting in micro-cracks invisible to the human eye in the silicon cells and voiding the panel's manufacturing warranty, deteriorating the quality of work and compromising the photovoltaic park.

The task of the useful model is to create a self cleaning supporting structure for bifacial photovoltaic modules east-west arrangement, which in arranging the photovoltaic modules, provides sufficient working light on the second (lower) energy-generating side, for each module; to have the ability to self-clean gravitationally from atmospherically generated pollution, due to its double slope, south-west and south-east, and if cleaning is still required, to enable existing cleaning wheeled light robots to perform this action without imposing undesired loading pressure at a single point on the working areas of the solar glass(es), protecting the active silicon cells.

SUMMARY OF THE INVENTION

The task of the useful model is solved by a self cleaning supporting structure for bifacial photovoltaic modules east-west arrangement, which is built with a double slope: once on two opposite to each other slats, forming an obtuse angle between themselves, located in the east-west direction, and at the same time, together and in the same direction, along their axis, are being inclined downwards in north-south direction, as the slats are built of at least two 2-slat ribs with supports, equipped with reinforcing supports, where a support leg is installed, as between both two-slat ribs with supports, one two-slat rib is located, without supports and without supporting legs, all connected to each other through a longitudinal relationship, located on both sides - left and right, of the structure, as the two-slat ribs located one after the other, with distance between them, according to the width of a photovoltaic module, as the two-slat construction obtained along its length - at the ridge, is blocked by a connecting link. At both lower ends of each two-slat rib with supports, a pair of supporting legs is mounted. The difference in heights between the first two supporting legs of the structure, (mounted at the left and right ends of the first rib), and the last two legs of the structure, provide total inclination of the structure from 1.5° to 2° relative to the horizon along the north-south axis. Also, the distance “h” between the installation height (the ground) and the lowest edge of the lowest southern module to the ground is “h” - 1 m, and the distance from the ground to the lowest edge of the highest bifacial photovoltaic module located on the structure - the northern and last one in the row along the slat, is hl, whose maximum value is 1.9 m. In order to ensure these parameters, namely the slope of the self-cleaning structure along its length, from 1.5° to 2° and at the same time the lowest distance of the photovoltaic modules to the ground at the beginning of the structure - I m and the distance to the ground of the last photovoltaic modules on the structure 1.9 m, each subsequent pair of legs increases ascending in height relative to the previous pair.

The specific dimensions in these leg ranges are determined for each construction, according to the relief of the terrain, where the self-cleaning supporting structure is installed. Apart from that, each two-slat rib with supports is composed of two vertical parts at both ends, connected by two inclined arms - left and right, linked to each other by a straight part A, in order to form a whole element - rib. Reinforcing supports are mounted between the vertical and inclined parts of the rib with supports. Ribs without supports have the same construction and dimensions as the rib with supports, but without reinforcing supports mounted and without support legs installed at both ends. The ribs without supports in the structure are mounted on the longitudinal connecting link. The inclination of both opposite slats formed by the successive arrangement of the ribs is from 5° to 15° relative to the horizon. The inclined parts of the ribs are connected at the top by a straight part. The length of the connecting straight part is equal to Δ.

A of each rib - the straight part located between both slats, is determined by the sum of the lengths: twice the length marked as A1, which represents the projection on the horizon, at the distance from the last mounting hole of the bifacial photovoltaic module, to its end, reduced by 50mm, plus a length ranging from 100mm to 800mm marked Δ2.

In this way, on the ridge, between the ends of the photovoltaic modules, a clearance is provided with a width equal to the width of Δ2, and a clearance strip μ is formed along the length of the pergola. Unilaterally, at the end of projection Al, from the left or right of the ribs, a supporting structure along the entire ridge is blocked by the connecting link. Also, along the entire horizontal surface of the ribs, including on the connecting straight part, are perforated holes, with diameter of Ø 10 mm to Ø 30 mm or holes with shape of ellipses, squares or other geometric figures, spaced from each other along the entire circumference of each arm, at a center distance of 40 mm to 60mm between perforations.

The advantage of the self-cleaning construction for bifacial modules - an east-west arrangement system, is the opportunity, due to the provided slope of 1 .5° to 2°, relative to the horizon, along the length (north-south axis) of the self-cleaning structure and the two- slat arrangement of the photovoltaic modules, that the system cleans itself by gravity, from the pollution - product of atmospheric processes. Another advantage is penetrating the maximum possible light from all sides under the structure and providing enough light reflected from the ground back up for efficient operation of the bifacial modules and in particular on the downward directing face, its generating bottom area, located below the slat, by the strip Jl formed on the ridge aØd by the perforations of the ribs and by the distance between two adjacent self-cleaning supporting structures.

As the sun moves, this strip provides enough reflected light on the lower generating areas, subject of one of the main advantages of the useful model. The inclination of 1.5° to 2°, relative to the horizon along the length of the self-cleaning structure provided by supporting legs provides another advantage - as the sun moves on its daily trajectory, several side-by- side pergolas with photovoltaic elements in the same plane on each slat are not overshadowed. Supporting structures arranged and aligned in the same lines (north-south, east-west) parallel to each other forming a solar park, do not overshadow each other or each one itself. The inclination from 1 .5° to 2°, relative to the horizon, provides both slats not only with autonomous cleaning, but also with the maximum degree of operation of the photovoltaic modules.

EXPLANATION OF THE FIGURES ATTACHED

Fig. 1 shows a self-cleaning supporting structure in axonometry;

Fig. 2 shows a self-cleaning structure in a side view;

Fig. 3 shows a two-slat rib with supporting legs;

Fig. 4 shows a detail of the ridge;

Fig. 5 shows a detail of the self-cleaning structure supporting photovoltaic modules;

Fig. 6 shows the supporting self-cleaning structure with solar cells located on it;

EXAMPLES OF EMBODIMENT OF THE INVENTION

A specific exemplary implementation is shown in figures from 1 to 6. A self cleaning supporting structure for bifacial photovoltaic modules east-west arrangement is made, as the photovoltaic modules have dimensions of 2384 mm x 1303 mm, and the structure consists of six two-slat ribs with supports 1, provided with reinforcing supports 8, as a pair of supporting legs is mounted to them - on the left and right, respectively 7.1, 7.2, 7.3, 7.4, 7.5, 7.6; Between the six two-slat ribs with supports 1 , five two-slat ribs without supports 2 are located, which are without supporting legs 7. _1+n

Fig. 1 All six two-slat ribs with supports 1 and five two-slat ribs without supports 2 are linked to each other through a longitudinal connection 6, located on both sides - left and right of the structure, with the two-slat ribs located one after the other, at the distance of 1303 mm between them, according to the width of the photovoltaic module, and the two-slat supporting structure thus obtained reaches 13.5 m in length. At the ridge, the structure is suspended by a connecting relationship 5.

The height difference between the first two legs of the pergola - 7.1, mounted at the left and right ends of the first rib, and the last two legs of the pergola - 7.6, ensures, through the successively located two-slat ribs with different leg heights, a total slope of the supporting structure from 1.7°, relative to the horizon. Here, the distance “h” between the mounting height (the ground) and the lowest edge of the lowest southern module, to the ground is “h” = 1 m, and the distance from the ground to the lowest edge of the northern last module is hl = 1.35 m at the indicated inclination of 1.7°. In order to ensure these parameters, of the self-cleaning supporting structure along its length, each subsequent pair of legs between 7.1 and 7.6, namely - 7.2, 7.3, 7.4, 7.5, increases its height compared to the previous pair, according to the relief of the terrain where the selfcleaning supporting structure is mounted.

Fig. 2 Apart from that, each two-slat rib with supports 1 is composed of two vertical parts at both ends, connected by two inclined arms 10 - left and right, linked to each other by a straight part A, in order to form a whole element - rib.

Fig. 3 Reinforcing supports 8 are mounted between the vertical and inclined parts of the rib with supports 1. The ribs without supports 2 have the same supporting structure and dimensions as the rib with supports 1, but without reinforced supports 8 installed and without supporting legs 7 mounted at both ends. The ribs without supports 2 are mounted on a longitudinal connecting relationship 6. The inclination of the two opposite sides of the ribs 1 and 2 is 8°, relative to the horizon. The inclined parts of the ribs are connected at the top by a straight part 3. The length of the connecting straight part 3 is equal to A. A of ribs 1 and 2, located between both slats, is determined by the sum of the length - denoted as Al, which represents the projection on the horizon, at the distance from the last mounting hole of the photovoltaic module 9, to its end, reduced by 50mm, taken twice, for the left and right part of the rib, which totally amounts to 100 mm (for twice Al). In the exemplary implementation, the length of Δ2 is 110 mm.

Fig. 4 Thus, on the ridge, between the ends of the photovoltaic modules, a clearance is provided with a width equal to the width of Δ2, and a clearance strip p is formed along the length of the pergola. Unilaterally, at the end of Al projection, from the left, a supporting structure, along the entire ridge on the inclined arms 10, the connecting relationship 5 is installed, at the distance Al from the beginning of the straight part 3. The connecting relationship 5 is mounted just below the end of the photovoltaic module vertically, under its own metal module frame, without shading its active surface. Also, light-transmitting holes 4, with diameter of 0 30, are perforated on the entire horizontal surface of ribs 1 and 2, including the connecting straight part 3. Essentially, these holes can be not only round, but also elliptical, square or other geometric figures, spaced from each other along the entire circumference of each shoulder. The inter-center distance of the holes is 50 mm. The operation of a such built supporting structure leads to a two-slat arrangement of photovoltaic modules mounted on it, portrait oriented at a slope and in the east-west direction, on a fixed supporting metal supporting structure oriented along its length from north to south with decreasing height, without moving components. The orientation of the entire metal supporting structure does not necessarily have to be located strictly following the axis of the north-south line. The low inclination of the modules and the perforation of the structural elements, and especially the ribs, as well as the absence of multiple supporting connections close to the generating rear active surface, inside supporting structure, guarantee zero self-shading losses.

The supporting structure allows and facilitates the project developers to rotate it from the pure south to the southeast or southwest direction, without loss from shading by its neighboring identical supporting structures, in the process of the maximum possible generation of electrical energy, without loss, according to the available area.

The invented supporting supporting structure is universal and complies with the factory warranty requirements for maximum load by snow, wind and earthquakes for the different geographical latitudes of the photovoltaic module manufacturers, providing tranquility and security for investors, financial and insurance institutions.

The invented fixed metal supporting structure is aligned with the leading internal electrical design of the new generation of photovoltaic single-sided and two-sided modules of all sizes, optimizing the early-morning at sunrise and late-evening at sunset shading that automatically turns off the whole, half or one-third module, according to the design (including module models with whole, half or one-third cells) through the built-in bypass diodes and / or the line-by-line switching off the internal cell strings (sequentially connected cells in groups, strings) for modules with the so-called tile cell arrangement (shingled technology type), including two-sided shingled.

The technologies and design of the internal module strings oblige project developers for their correct spatial orientation according to the respective used photovoltaic module, optimizing its maximum potential for light conversion and, accordingly, maximum generation of electrical energy without loss. Modules in the east-west orientation must be electrically connected to identically oriented modules on both, the same and adjacent supporting structures in east-to-east and west-to-west strings.

Groups of module strings with different orientations are compulsory connected to the inverter at different points for tracking their maximum power or so-called MPP trackers. The invented supporting metal supporting structure totally eliminates the shading of the bifacial modules, or more specifically is focused on the downward facing side of the module to the reflective surface. Unlike similar unified supporting structures, the new and technical design completely eliminates the load-bearing shading profiles mounted near the active photovoltaic cells, negatively affecting the maximum light conversion potential and, accordingly, the maximum generation of electrical energy without loss.

The construction thus presented is 100% universal, including for installation of single-sided photovoltaic modules with a back opaque film and of two-sided modules with a back transparent film available on the market today.

The invented supporting metal structure for fixed ground installation, including horizontal roofs and or limited horizontal or semi-horizontal spaces, has low height of the photovoltaic modules, which height rises from the south of the low side, to the north of its high side, respectively up to 1600 mm for the support of the highest northern module. The raising efficiency is up to 1900 mm or up to 2° inclination. Photovoltaic modules installed in this way allow and facilitate 100% physical access to each of them from both sides, without redundant aids, such as ladders and platforms for visual inspection, technical inspection, control and replacement if necessary.

The invented supporting metal structure for the bifacial modules is the ideal self-cleaning model for areas with snowfall. Due to the fact that the face of the photovoltaic cells from below is active during the light part of the day, generating electrical energy, the cells emit heat helping to quickly melt the snow accumulated on the module, and as a result the entire photovoltaic system reaches maximum efficiency and reduced loss for the minimum time. Thus they differ from the conventional single-faced modules, which after snowfall need at least few days to completely self-clean of the snow cover, even if the ambient temperature rises above zero. If the ambient temperature remains below zero, this period increases in time.

Thus presented self-cleaning supporting structure for the bifacial modules is a cost-saving self-cleaning system, because the self-cleaning is done by gravity, in rain or snowfall, because the whole structure is inclined from north to south, and the modules on it are also inclined to the east and west, leading away from the module the accumulated dust in the direction of the lowest corner. This method of spatial arrangement, subject to the design patent, minimizes the risk and losses during activation, failure and the risk of overheating of the bypass diodes which self-disconnect the internal module strings of the serially connected cells caused by the dense shadow of the dust dried on the glass. In the worst case scenario - without any cleaning and maintenance, the double slope system guarantees losses of only 1/6 maximum with 6 string modules and/or (1/9 maximum with 9 string modules 2022 by "REC Solar"), because manufacturers of new generation and large-gauge modules seek to reduce their size and cost by bringing the active cells almost to the shading metal supporting frame with the risk of shading and generating a hot spot and the respective losses. These modules have 6 internal strings connected to 3 bypass diodes, of which only one of the two diode strings would self-disconnect 1/6, with a large amount of dried concentrated dust forming a pocket of solid shadow at its lowest drain angle.

USE OF THE INVENTION

The useful model self-cleaning supporting structure for bifacial modules - east-west system, especially the supporting structure, is mainly used for two-sided and/or single-sided frameless modules. The system of arranging the modules on the supporting structure is eastwest of the generating areas, which ensures efficient operation of the solar park, built with such structures. There are established conditions for effective self-cooling without transferring heat to an adjacent higher module, maximum penetration of light between and below them, self-cleaning using gravity during rain, fast and efficient snow removal by melting due to an active bottom face of the module, generating heat and cleaning the modules in the park, if necessary, by robotic lightweight systems on wheels, using the own module frame as a guiding rail.

Conventional photovoltaic systems of a new generation with tilted modules, facing the clear south begin low power generation at first light in the sky, wait hours for direct sunlight to hit the cells, and slowly increase their efficiency, peaking at midday. In contrast, east-west systems start generating at first light in the sky and after only a few minutes reach almost 50% peak once the sun rises 10 degrees above the horizon, because 50% of the modules face east, and remain stable at maximum, through the whole daylight time, without unnecessary peaks at midday, when energy consumption drops, until in the late afternoon they reach generation drop of up to 50% and gradual termination under 10 degrees of sun inclination, before it hides behind the horizon at sunset. This optimization of maximum generating of clean energy coincides with the morning peak of consumption by households on weekdays, before their occupants leave.

The optimized distance at the highest point between the modules (support) has several advantages that facilitate the utilization in case of a lightweight robotic cleaning system that operates safely with batteries (up to 12 kg total weight, 2 x ~ 6 kg per metal module frame) and the robot, mandatory moves only on the metal frame of the module, according to the warranty conditions of the manufacturers, which state: absolute prohibition of moving heavy objects directly on the glass, concentrating weight in one point, which causes micro invisible cracks in the active silicon cells. The other long-term advantage is that the distance at the highest point between the modules is mandatory for the penetration of reflected sunlight under the supporting structure for optimization and further stimulation of the energy generation potential of the back side of the bifacial moduless. The distance at the highest point between the modules also optimizes to the maximum the cooling of the modules in windless summer months at maximum ambient temperatures, in general each one cools itself, and does not raise unnecessarily the temperature of the neighboring higher module.

Literature:

1. Chinese useful model - CN 13072514U;

2. Publications in Internet;