EP4630241A1

EP4630241A1 - Groundcover for enhancement of albedo effect

Info

Publication number: EP4630241A1
Application number: EP23824976.7A
Authority: EP
Inventors: Kyriakos Mystikos; Alexandros DROUDAKIS; Georgios TZINOGLOU
Original assignee: Thrace Nonwovens & Geosynthetics SA
Current assignee: Thrace Nonwovens & Geosynthetics SA
Priority date: 2022-12-06
Filing date: 2023-12-01
Publication date: 2025-10-15
Also published as: WO2024121695A1

Abstract

A groundcover with two layers, disposed one on the top of the other, with one layer, i.e. the top layer, being a white fabric or a white film configured to reflect light with a wavelength in the range of 400 to 1100 nm and the other layer, i.e. the bottom layer, being a dark color fabric or a dark color film that hinders the transmission of visible light with wavelength at least within the range of 400 to 500 nm or/and 600 nm to 700 nm therethrough. The top layer and the bottom layers are joined together in individual points or along lines or over areas, so that they are areas of loose contact of the layers, where the top layer and the bottom layer are not connected, so as to facilitate separation.

Description

GROUNDCOVER FOR ENHANCEMENT OF ALBEDO EFFECT The present invention relates to Albedo Enhancement Materials (abbreviation: AEMs) and ground cover fabrics. Albedo Enhancement Materials are placed beneath arrays of photovoltaic modules in photovoltaic parks to increase energy productivity by means of their high solar reflectance (compared to the natural ground) that enhances ground albedo. Examples of Albedo Enhancement Materials are concrete slabs-on-ground painted white, geomembranes, single layers of white fabrics, pebbles & chippings, gravel etc. Known Albedo Enhancement Materials present engineering and environmental deficiencies/disadvantages, such as: • Known fabrics that increase ground albedo deteriorate fast and lose their effectiveness. • Concrete and geomembranes currently used are impermeable and require the construction of extended drainage networks to facilitate water management, which is neither economical nor ecological. Moreover, given the large surfaces required to be covered for the needs of a solar park, such solutions may alter substantially the hydrology of the location where installation takes place. • Pebbles, gravel or other types of aggregate, which are used as Albedo Enhancement Materials, are natural resources and their extraction, transportation, installation are rather costly and non-ecological procedures. Their use may provide in some cases desirable values of water permeability, but, at the same time, has negative environmental and ecological footprint and contradicts sustainability principles. • Solid technical solutions, such as the use of concrete, present limited possibilities regarding promoting reusability/recyclability. Whilst photovoltaic parks have a finite lifespan of 20 to 30 years, such solutions most probably stand as permanent solutions in terms of land covering and raise concerns regarding their fate at the end of their service life. Overall, such solutions apart from being costly, permanently affect the biodiversity and the ecology of the location the installation takes place and do contradict to sustainable land restoration. The object of the invention is a groundcover that is appropriate for albedo enhancement that overcomes the problems of materials currently used. A further object of the invention is a groundcover that has sufficient level of water permeability. A further object of the invention is a method to lay such groundcover materials. A further object of the invention is a groundcover and a method to lay a groundcover which is effective for a relatively long period. The invention is defined in the independent claims. Dependent claims define further features that offer further advantages to the invention. The following terms are used in the present application: A “filament” is a single continuous thread, or a thin flexible threadlike object limited in length only by its spool and a “fiber” is a single continuous thread with limited length. The term “filament” is used in relation with woven fabrics and the term “fiber” is used in relation with non-woven fabrics. “Yarn” is a continuous often plied strand composed of either natural or man-made fibers or filaments and used in weaving and knitting to form a fabric. “Tape yarn” is a two-dimensional yarn. The terms "reflectivity/transmissivity" refer to the property of the material or a single layer itself, while the terms "reflectance/transmittance" pertain to the property of the groundcover. The invention is defined in the independent claims. A groundcover of the invention has two layers disposed one on the top of the other. When in use underneath a photovoltaic array, one layer is below the other. The layer on the top that faces the photovoltaic array is the “top layer” and the layer that is below the top layer on the ground is the “bottom layer”. A groundcover of the invention has two layers, disposed one on the top of the other. One layer i.e., the top layer, is a white fabric or a white film configured to reflect light in the visible range or light within a wavelength in the range of 400 to 1100 nm. The other layer i.e., the bottom layer, is a dark color fabric or a dark color film that hinders the transmission of visible light. Each layer is either a fabric or a film. The fabric may be woven, non-woven or knitted. Non-woven fabrics may be made of directionally or randomly orientated fibres, filaments or other elements, mechanically and/or thermally and/or chemically bonded. Knitted fabrics are produced by inter-looping one or more yarns, filaments or other elements. Woven fabrics are produced by interlacing, usually at right angles, two or more sets of yarns, filaments, tape yarns or other elements. The invention suggests a groundcover with two layers, disposed one on the top of the other, with each layer being made of tape yarns comprising polyolefins. The one of the two layers is made of yarns that includes carbon black pigment so as to enhance performance against UV radiation and to hinder sunlight permeation through its yarns and the other is made of yarns including TiO2 pigment, so as to increase reflectivity. The present invention relates to a groundcover of two enhanced fabrics, which when properly placed together they function as a system to serve for weed suppression and surface soil erosion protection along with ground albedo enhancement. The system is intended to be used mainly in existing and/or new solar parks that involve bifacial photovoltaic modules so that solar parks’ operation is optimized in terms of energy generation and frequency of maintenance both in an economic and sustainable manner. The system may also be applied in existing and/or new solar parks that involve mono- facial modules so that solar parks’ operation is optimized in terms of energy generation and frequency of maintenance both in an economic and sustainable manner, although the expected optimization level in such cases is of a lower degree. Being aligned with the sustainability principles both layers, either fabrics or films, are recyclable and may contain recycled content promoting a circular economy approach through the use and/or reuse of materials with a low environmental and ecological footprint. The applicant noted that the combined use of the two layers as a system adds value to one another’s performance: the use of a single white layer may increase the productivity of the solar panels, but only temporarily, since a single white layer is not capable of inhibiting weed development. The growth of weeds negatively affects the productivity of the solar panels since they tend to penetrate, destroy or uplift the white layer, which lays on the ground. In the latter case, the clearance i.e., the vertical distance from the ground up to the lower side of the panel, becomes shorter than designed and, therefore, the productivity decreases dramatically. Placing the black layer beneath the white layer allows for the white layer to perform its role as an Albedo Enhancement Material for a significantly increased period of time. Further, placing only a black layer beneath a bifacial module for weed suppression that would negatively affect the electricity production because the albedo of the black fabric is lower than the albedo of the natural surface (earth, grass etc.) and it would increase the temperature beneath the modules that is observed to reduce modules' productivity. Additionally, the use solely of a black layer suffers from the direct exposure to the solar radiation, which would accelerate the degradation rate and would decrease its performance as a weed suppression material. The use of the white layer on top of the black layer prevents the direct exposure of the latter to solar radiation and contributes to prolong its service life. The bottom layer may be black, green, grey, beige or any other dark color to prevent transmittance of sun rays through its structure. It hinders photosynthesis and has a Weed Suppression Function that prevents weed development. Dark color layers, either fabric or film, absorb the wavelengths λ that are responsible for photosynthesis. The applicant has further observed that a layer being colored with a pigment that can absorb either the 400 nm – 500 nm i.e., violet-blue light or 600 nm – 700 nm i.e., red light, would also be effective. Such a layer is effective when it provides a transmissivity of light less than 15% and in some examples less than 10%. Figure 1 presents the impact of the wavelength on the rate of photosynthesis. Black groundcover fabrics are used in agriculture. They are used as single layers for ground covering to protect plants from unwanted weeds and to maintain the moisture retention in the soil and to protect the soil from solar radiation. Within a system according to the invention, the bottom layer serves the function of weed suppression which aims at eliminating weeds growth and/or at keeping the height of weeds as low as possible so that the clearance i.e., the vertical distance from the ground up to the lower side of the panel of the PV modules, is kept as built and therefore the energy generation remains unaffected in the long-term with minimum to zero maintenance. For maximum effectiveness for the weed suppression function, this fabric is black for permitting zero or almost zero sunlight permeation through its yarns. With a suitable weaving pattern a woven fabric with tape yarns provides total coverage/blinding for protecting soil from solar radiation without inhibiting water infiltration that comes from rainfall/snowfall. Dark color is achieved by appropriate pigments. In some examples all types of carbon black pigments, preferably P and RCF pigments, are suitable for coloring fibers filaments or yarns and present relatively higher resistance to UV radiation rendering the layers more effective for longer periods in preventing photosynthesis. Dark color may be provided carbon black that absorbs all wavelengths that are present in visible light, approximately 380 to 800nm, and is appropriate for preventing photosynthesis mobilization. The top layer is to provide an appropriate albedo in the ground beneath PV modules to increase the energy production by PV modules. Albedo is the amount of solar radiation, sunlight, reflected by the layer and is usually expressed as a percentage or a decimal value, with 1 (=100%) being a perfect reflector and 0 (0%) absorbing all incoming light. Top layer should present high reflection ability, which is defined as the ratio of the reflected radiant flux of the layer to the incident radiant flux on its surface. This is the result of the combined effect of reflectivity, transmissivity of the material and thickness of the white top layer. Reflection is effected via two mechanisms: a) specular reflection i.e., reflection off of smooth surfaces such as mirrors or a calm body of water, and b) diffuse reflection i.e., reflection off of rough surfaces such as textiles, asphalt roadway. The roughness of the fabric allows for the development of both reflection mechanisms. The top layer may include pigment, preferably TiO₂ pigment, so as to increase reflectivity. The TiO₂ pigment renders a white color to the top layer. When the top layer is a non- woven needle punch the fibers are transparent and when bonded the fabric has a white color. In this case the pigment is only used to enhance the reflectivity, as the white color attributes reflectivity to the fabric. The top layer has a reflectance that is at least 60%, for example within the range of 60% to 85% for incident radiation with a wavelength within a range of 400 nm to 1100 nm. The system of layers that forms the groundcover may be produced as a composite groundcover by attaching the one layer to the other. In some examples of the invention, the layers are bonded together using one of the following methods: thermally bonded, chemically bonded, for example gluing, mechanically bonded, for example needling, seaming, sewing. Particular advantages are offered when the bonding of the two layers is effected in individual points, along lines or confined areas, so as there are surfaces of the two layers next to each other that remain free i.e., not connected. Even more advantageous is a solely mechanical bonding of the two layers is effected in individual points, along lines or confined areas, so as there are surfaces of the two layers next to each other that remain free and the layers may be disconnected i.e., they are not permanently connected. The top layer and the bottom layers may be joined together in individual points or along lines or over areas, so that they are areas of loose contact of the layers, where the top layer and the bottom layer are not connected, so as to facilitate separation. Simultaneously, the loose contact between the layers facilitates the creation of liquid paths from the free surface of the top layer to the free surface of the bottom layer, and from the free surface of the bottom layer to the ground covered. The paths extend normally or almost normally to the plane of the groundcover. Mechanical bonding may be also achieved, in a simple and efficient manner by rolling both layers together on a single roll, providing an easy and accelerated installation process. A stronger connection between the two layers is not necessary, as they are securely anchored to the ground and concurrently joined together in-situ with fasteners, for example staples, pins etc. By keeping both layers loosely connected, with optionally only seam lines along the width of the rolls, it becomes convenient to replace the top layer at the end of its service life. Thus, both the detachment of the top layer and subsequently the reusability of the bottom layer and the recycling of the top layer are facilitated. With mechanical bonding there is no need to use lamination, such as hot melt or gluing. The connection of the seam line along the width of the roll facilitates unrolling and deployment of the groundcover. The width is the direction normal to the rolling direction of the groundcover. In some examples of the invention, the bottom layer includes a dark color pigment with dark color particles, which have an average size within the range of 10 nm to 30 nm, preferably between 15 nm and 25 nm. The applicant noted that the effectiveness of the pigment depends on the pigment particle size and pigment’s tinting strength. It has been found that smaller size pigments absorb relative more light per gram of pigment. This effect may be, because light is absorbed by the molecules and molecules in the core of a big particle do not have the ability to absorb light because the light was already absorbed by the molecules that exist on the surface of the particle. Average size may be defined by standard tests for determining the morphological characterization of carbon black, such as ASTM D3849. The pigment’s tinting strength represents the performance of a carbon black pigment in absorbing both UV and visible light wavelengths and its ability to provide a polymer with black color. Preferably, the tinting strength of Industry Reference Black No.3 of a carbon black pigment should be higher than 100%. Tinting strength is influenced by the surface area and the structure of the carbon black pigment. The Iodine Adsorption Number, for example according to ASTM D1510-21, is used to characterize carbon blacks in terms of the surface area and preferably should have a value higher than 110 mg/gr. The DBP Method (DBP: DiButyl Phthalate according to ASTM D2414-22) is used to characterize the structure of carbon black pigment i.e., the length among the chains of agglomerates. Higher structure i.e., higher DBP Absorption value, correlates to better dispersibility. Although the use of a pigment with small particles that have increased surface area would reduce dispersibility, a DBP level of at least 90 ml / 100 gr according to ASTM D2414-22 is preferred. The groundcovers could be pervious. Such groundcovers exhibit high-permeability characteristics. The quantification of the permeability characteristics of the said material may be tested applying national or international standards. As an example, the measurement of the coefficient of permeability may be done according to EN ISO 11058. In some examples groundcovers of the invention have a coefficient of permeability that is equal or greater of 10^-4 m/sec. Such performance is comparable to the coefficient of permeability of permeable to very permeable soils - with range from poorly graded sands at 10^-4 m/sec to uniform gravels at 1m/sec - that may also be used for the same reflective function in PV installations. However, the performance of permeable soils typically degrades over time in PV installations due to contamination from fines in the subsoil or from nearby sources. After becoming contaminated, their performance can drop dramatically, by approximately 100 times or even more. European Commission’s Soil Strategy for 2030 highlights the need to reduce “Soil Sealing” which is defined as the loss of soil resources due to the covering of land by using impervious and impenetrable artificial materials for housing, roads or other construction work. In this context, many countries in Europe have adopted best practices for mitigating “Soil Sealing” including restrictions on the use of impervious artificial materials in PV installations. In addition to soil protection legislation, the use of impervious artificial materials in PV installations can lead to the formation of water puddles on the surface of the top layer, reducing reflectivity and effectiveness of the layer while also causing accumulation of dirt that hinders recyclability and/or reuse of the fabric. The coefficient of permeability of groundcovers with a reflective woven top layer and a woven bottom layer is at least 1000 times higher i.e., 1000 times more permeable), than soils with low to very low permeability, such as organic silts (10^-7m/sec) and clays (<10^-8 m/sec). The bottom layer may have a laminated surface i.e., lamination using hot melted PP and/or PE7 or any other polymer to laminate on one or both sides of the fabric, in order to create a surface that is more resistant to weeds development. The optional feature may be added to any fabric i.e., nonwoven, woven, knitted. If the surface is laminated, permeability may be achieved via openings in the lamination. In some examples weed killer substances could be incorporated to the elements, for example tapes, fibers, filaments, yarns of the bottom layer. The fabrics and films may consist of PP, PE (any type), PET, PVA, AR, PA, PVC or any other polymer or any combination of the aforementioned. Optionally the fabrics may contain recyclable materials and may be recyclable or biodegradable. In some examples both layers of the groundcovers are at least partially manufactured from recycled materials. In some examples of the invention the top layer or/and the bottom layer may be reinforced with welded straps to increase its tensile strength, in particular when these layers are made of nonwoven fabrics. In some examples the top layer or the bottom layer or both are woven fabrics. Groundcovers with the top layer and the bottom layer being woven fabrics enhance the advantages of the invention: • Woven layers do not absorb moisture, reducing the risk of dirt accumulation. This, in turn, preserves reflectance and recyclability. Figure 2 shows an example of a groundcover according to the invention after one year of operation and Figure 3 shows a groundcover with accumulated dirt after one year of operation. • Woven layers have bi-dimensional openings that facilitate water flow and do not trap weeds or soil, making them less conducive to weed growth on top of the groundcover. Thus, the opening of holes, such as perforations to enhance water permeability from any woven layer, either top or bottom, is not necessary. • Woven layers consist of nearly opaque tapes that have a denser structure compared to porous nonwoven layers that consist of nearly translucent fibres. This structure reduces light transmissivity, enhancing the reflectance of the groundcover. The use of such tapes do not require any glossy substance either to the fabric or the tapes to enhance reflectivity. • The relative dense structure for the same mass per unit area of woven layers, provides better protection to the underlying layer against solar irradiation. • Achieving the low sunlight transmissivity of a woven layer, with a non-woven layer requires a higher mass per unit area compared to a woven layer. This results in increased demands for UV stabilizers and TiO2, adding to the economic burden of the end product. • To achieve the transmissivity of woven layers, with non-woven layers necessitates a higher mass per unit area, increasing the weight of the roll and the effort required during installation. Figure 4 and Figure 5 highlight the solar irradiation transmissivity through the body of a woven layer of 100 gr/sqm and a nonwoven layer of 270 gr/sqm, respectively. While the shadow of the rope 31 is not visible in the case of the woven layer, it is easily visible in the case of the nonwoven layer despite it is 2.7 times heavier. • Woven layers at the same mass per unit area exhibit relative superior mechanical properties, including higher tensile strength and stiffness compared to nonwoven layers. This makes them more resistant to installation damage and wind loads. The bottom layer may be a woven fabric made of yarns comprising polymers and including a black pigment, such as a carbon black pigment, and the top layer may be a woven fabric made of yarns comprising polymers and optionally a white pigment. The yarns of the top layer and/or the bottom layer may be tape yarns. In some examples the top layer has elements, filaments, yarns or tape-yarns with a weight content of TiO₂ pigment at least 10000 parts per million (abbreviation ppm) and less than 70000 parts per million. In some examples the weight content of TiO₂ pigment is 21000 parts per million or about 21000 parts per million. Fabrics that are woven with tape yarns may be characterized by high values of cover factors. A cover factor (CV) can be determined in both machine direction (MD) and cross direction (CD) and are defined as: CV_MD=(weft tape width (mm)×weft tapes per meter)/(1000 mm)×100% CV_CD=(warp tape width (mm)×warp tapes per meter)/(1000 mm)×100% Either top layer or bottom layer or both may have a cover factor higher than 100%. That may be achieved by tape yarn warpage during weaving - U-shaped tape yarns. This yarn warpage leads to the formation of a light 3D fabric surface. In some examples both layers are non-woven and in others one of the two layers is non- woven. In some examples the bottom layer is a woven fabric and the top layer is a non-woven fabric. The top layer may a non-woven needle-punched fabric. The mass of a non-woven top fabric may be within the range of 200 to 800 gr/sqm, optionally 300 to 500 gr/sqm. Light color of top non-woven fabric may be provided or enhanced by TiO₂ pigment. The bottom layer may be woven made of tape yarns and/or monofilaments, which in some examples include black pigment, such as carbon black pigment. In some examples the top layer is a woven fabric and the bottom layer is a non-woven fabric. The bottom may be a non-woven needle-punched fabric. The mass of a non-woven bottom layer may be greater or equal to 200 gr/sqm Light color of top woven fabric may be provided or enhanced by TiO₂. The top layer may be woven made of tape yarns or monofilaments, which in some examples include TiO₂ pigment. A groundcover may include a mid-layer between the top layer and the bottom layer. The mid-layer may include any of the following materials or any combination therefrom: sand, gravel or any aggregate, a permeable granulated active clay, such as Attapulgite, a permeable active natural material such as zeolite, apatite, cement powder. In some examples the mid-layer is a three-dimensional geonet, geomat or geospacer layer. A further advantage of groundcovers according to the invention is that it enhances flame retardance: typically, solar parks are installed in environments that are distant from forestry areas or areas that are prone to fire events. However, fire may start in the case of PV modules that present electric defects which would put the whole PV installation at risk. Given the fact that such fires can spread over large areas via the rapid combustion of weeds, the function of weed suppression brings further value. Moreover, the latest advances show the trend of installing such solar parks close to industrial facilities, therefore, a fire event constitutes danger to personnel and can be destructive to an industrial building and to its contents with major financial losses. Apart from the weed suppression, the groundcover further contributes against fire events by halting or delaying fire spreading over a larger area by means of its slow-burning performance and its ability to produce no flame, which provides additional time for fire-fighting interventions. Both layers of the groundcover according to the invention adhere to the same production principles and present identical performance in terms of fire retardancy. One or both layers of the groundcover may include HALS - Hindered Amine Light Stabilizers - or/and NOR-HALS additives that provide flame retardant properties to the fabrics. Thus, such a groundcover achieves improved safety when placed in external conditions as it presents both Fire Retardacy (abbreviation: FR) and Ultra Violet (abbreviation: UV) resistance properties and may remain in place intact and efficient for longer time periods. The groundcover may not include flame retardant additives, which are used in known polyolefin oriented film and tape yarns, such as halogen-based flame retardant substances or sulphur or phosphorus containing flame retardants additives, and which hinder the commonly UV inhibitors such as HALS that are used in polyolefin film production. Thus, the groundcover may be broadly used in external conditions for flame retardant purposes as they may resist sunlight radiation and the enhancement of the flame-retardant properties is not realized at the expense of the UV stability. The service life of groundcovers according to the invention is also relatively increased: typical groundcovers, being exposed in the solar radiation, contain suitable pigments and additives for being UV resistant. Being the top layer of the system, the white fabric is the one that is being exposed to solar radiation the most. Typically, when exposed to solar radiation in Mediterranean environments, regular white groundcovers present a service life that does not exceed 2 years. Since most solar parks are designed for service lives up to 20-30 years, the increase of the service life of the top white fabric is vital. Examples of the invention include white fabrics with a minimum service life of 2 years and optionally with a service life of 5 years in southern Europe. The service life of the fabrics including in the invention may be evaluated on the basis of EN12224 Standard: a fabric is subject to cyclic testing for certain hours under UVA lamp irradiation with wavelength 340 nm, irradiance intensity 0.83 W/m² comprising of the following stages: exposure for 5 hours at a black standard temperature of 50 °C ± 3 °C (°C: grad Celsius) and 1h spray at 25 °C. A certain duration of a service life implies that at the end of the cyclic testing the fabric retains at least 50% of its initial tensile strength and does not show significant signs of wear. Different approaches may be adopted for establishing the service life of such a fabric following the principles of EN12224 by considering the exact location and the specific requirements imposed by each installation. Temperature, solar radiation, relative humidity and/or moisture conditions are defined depending on the location of the park, for example in southern Europe. A method to cover ground below a photovoltaic array includes covering the ground with a groundcover including two layers of fabric disposed one on the top of the other, with one layer. i.e., the top layer, being a white fabric or a white film configured to reflect light with a wavelength in the range of 400 to 1100 nm and the other layer i.e., the bottom layer, being a dark color fabric or a dark color film that hinders the transmission of visible light with wavelength at least within the range of 400 to 500 nm or/and 600 nm to 700 nm therethrough. The invention suggests a method to cover ground below a photovoltaic array, with at least two layers, whereby one of the two layers is made of dark color fabric or film that enhances performance against UV radiation and hinders sunlight permeation through its yarns and the other is made of white fabric or film that increases reflectivity. Hindering sunlight permeation may be achieved by incorporation of carbon black pigment to the layer and increasing reflectivity by incorporation of TiO₂ (titanium dioxide) pigment. The photovoltaic array has arrays of photovoltaic modules, which may be mounted on poles/piles that are driven in the ground. The photovoltaic array has arrays of photovoltaic modules, which photovoltaic modules may be bifacial or monofacial. The use of the top white layer aims at enhancing ground reflectance in a way that the solar light impacting the backside of the photovoltaic (abbreviation: PV) modules is increased through both specular and diffuse reflection mechanisms. Enhancing ground albedo leads to the increase of the electricity generation by the PV modules, particularly when using bifacial modules. Examples of the invention are described below with reference to Figures 1 to 13 Figure 1 presents the relation of the wavelength of light on the rate of photosynthesis Figure 2 shows an example of a groundcover according to the invention after one year of operation Figure 3 shows a groundcover with accumulated dirt after one year of operation Figure 4 shows the transmissivity of a black woven fabric of 100 gr/sqm Figure 5 shows the transmissivity of a black non-woven fabric of 100 gr/sqm Figure 6 shows the transmissivity a white non-woven fabric of 270 gr/sqm Figure 7 shows a groundcover with two layers beneath a photovoltaic array and Figure 8 shows a groundcover with three layers beneath a photovoltaic array. Figure 9 shows a woven fabric with slit film tapes Figure 10 shows a woven fabric with typical plain weaving pattern Figure 11 shows the reflectance of a groundcover with two woven fabrics Figure 12 shows a non-woven groundcover of 270 gr/sqm with and to its front a groundcover of 230 gr/sqm with two woven layers after two months of operation Figure 13 shows schematically the plan of a needle-punch non-woven white fabric Figure 14 shows schematically the cross-section of a needle-punch white non-woven white fabric Figure 7 shows a two-layer groundcover that is placed on top and in contact with the soil, right below the photovoltaic modules 1 to serve both weed suppression and ground albedo enhancement functions. Figure 8 shows a three-layer groundcover below the photovoltaic modules 1. In the examples that are described below, the system consists of two layers: a white top layer 6 and a black bottom layer 8. The top layer is a fabric that serves for the function of albedo enhancement and it aims at enhancing ground reflectance in a way that the solar light impacting the backside of the photovoltaic (abbreviation: PV) modules. The bottom layer is a black or dark color layer that hinders weed development. Groundcover with two woven layers The black or dark color and white color is provided by the carbon black pigment and TiO₂ pigment respectively. The white top layer contains white TiO₂ pigment. In one example the weight or mass content of TiO₂ pigment is 21000 parts per million or about 21000 parts per million. Other examples have a weight content of more than 7000 ppm, preferably equal or less than 21000 ppm. TiO₂ may be added through the incorporation of masterbatch, whose content i.e., the content of masterbatch, in TiO₂ may vary. Woven fabrics may be of any type, for example tape woven fabric, multifilament woven fabric, monofilament woven fabric. It is observed that woven monofilament fabrics present higher permeability in any saturation state, either saturated or non-saturated, than tape woven fabrics and relatively lower risk of creating paddles on top of the top layer. Permeability is required by law in many states for ecological reasons. Further, water paddles on the surface of the top layer reduce reflectivity and effectiveness of the layer and cause accumulation of dirt that hinder recyclability and/or reuse of the fabric. In some examples the groundcover fabrics are made of PP tape yarns with NOR-HALS and/or HALS additives and they are formed into continuous woven products by weaving, with improved flame retardancy. The system maintains the permeability of the woven structure through the paths that are formed between the compressed yarns. Details on production procedures relating to the characteristics of the fabrics made of tape yarn including flame retardancy, solar reflectance and service life are reported in documents EP3578036, GR20180100240 that describe a flame retardant groundcover fabric for greenhouses. The content of documents EP3578036 and GR20180100240 are incorporated by reference to the present application. The two layers of examples of the invention are fabrics with cover factors that are higher than 100% due to the form of tape yarn warpage upon weaving, for example U-shaped form. This yarn warpage leads to the formation of a light 3D fabric surface. The yarn warpage and the formation of U-shaped tape yarns in the fabric offers two major benefits: a) adequate water and air permeability properties of the fabric due to the efficient water and air transfer through the fabric and in the soil. b) relatively high values of cover factor (CV) which, in turn, leads to constriction of the sunlight rays path and weed protrusion, through the groundcover fabric c) relative light structure, as the two fabrics are woven fabrics on one hand and low light transmittance on the other d) the groundcover is thin, around 1mm, without compromising structural strength. Thus, with a cover factor in one of both directions equal or higher 100%, it is possible to achieve water permeability and an effective barrier for weed on one hand and light on the other. The coverage factor of 100% or higher in combination with water permeability is achieved during weaving process, as the yarns are compressed and water paths are formed therebetween. Permeability is required by law in many states for ecological reasons. Further, water paddles on the surface of the top layer reduce reflectivity and effectiveness of the layer and cause accumulation of dirt that hinder recyclability and/or reuse of the fabric. In some examples either the top layer or the bottom layer is a fabric made of tape yarns and either the bottom layer or the top layer is a monofilament woven fabric respectively. Figure 10 shows a plain-weave woven fabric. Other weaving patterns are also possible. Figure 11 shows the reflectance of a woven fabric with a woven top layer and a woven bottom layer. Figure 12 shows a non-woven groundcover of 270 gr/sqm with two non- woven fabrics and next to it a groundcover of 230 gr/sqm with two woven layers after two months of operation. It can be seen that the ground cover with two non-woven fabric has failed. Groundcover with a reflective non-woven top layer and a woven bottom layer Any non-woven fabric may be incorporated into the system as a top layer, for example spunbond, meltblown, needle punched (NonWoven-NeedlePunched) or any other known non-woven fabric. Figure 13 shows a needle-punched non-woven white fabric and Figure 14 shows schematically the cross-section of the same fabric. NW-NP fabrics present white surface although they are made of transparent or translucent fibers. By using pigments for giving them white color, their performance as albedo enhancement fabrics is expected to be further improved. As a result of their 3D structure, the NW-NP layer may achieve better diffusion of the solar irradiation that is reflected from their surface and increases reflectance, thus promoting albedo enhancement function. The increase in mass and thickness of a NW-NP fabric would also increase its reflectance ability. The white non-woven presents a relative high mass i.e., the mass may be within the range of 300 - 500 gr/sqm and needs a thin/light black layer as a backing to serve for weed suppression. NW-NP fabrics have higher thickness and better protect the bottom layer from abrasion and mechanical damage. The UV resistance of the top layer may be enhanced if the fibres are made of PET. It was observed that when they are saturated, NW-NP fabrics maintain their reflective properties. Permeability is required by law in many states for ecological reasons. Further, water paddles on the surface of the top layer reduce reflectivity and effectiveness of the layer and cause accumulation of dirt that hinder recyclability and/or reuse of the fabric. The use of a woven bottom layer offers further advantages to the invention: • Woven layers do not absorb moisture, reducing the risk of dirt accumulation. This, in turn, preserves reflectance and recyclability. • Achieving the low sunlight transmissivity of a woven layer, with a non-woven layer requires a higher mass per unit area compared to a woven layer (see photos below). This results in increased demands for UV stabilizers and TiO₂, adding to the economic burden of the end product. • To achieve the transmissivity of woven layers, with non-woven layers necessitates a higher mass per unit area, increasing the weight of the roll and the effort required during installation. • Woven layers at the same mass per unit area exhibit relative superior mechanical properties, including higher tensile strength and stiffness compared to nonwoven layers. This makes them more resistant to installation damage and wind loads. Groundcover with a reflective woven top layer and a non-woven bottom layer The particular configuration takes advantage of the advantages of non-woven fabrics when used as bottom layers: they present relatively higher water permeability of non- woven fabrics over tape woven fabrics of the same mass per unit area when saturated. Any non-woven fabric may be incorporated to the system as a bottom layer, for example spunbond, meltblown, needle punched (Non-Woven Needle-Punched) or any other known non-woven fabric. NW-NP fabrics have higher thickness and therefore they better protect the top layer from being damaged when in contact with the ground. Both fabrics/layers 6, 8 of all examples described above may be mounted directly on the ground 3 with the use of suitable recyclable and/or recycled metallic or plastic pins of suitable length that optionally is not less than 200 mm. An approximate example installation frequency of pins would be 1 pin per 2 sqm of fabric and in such manner that pins create a square or any other form of grid that allows a distance among pins being not longer than 1.50 m. Any other schemes of installation may be applicable provided the local conditions are suitable for such adjustments. The white and the dark layers of the multi-layer groundcover are placed one on top of the other either as separate layers or as a composite. When they are connected to make a composite, the layers may be thermally, chemically or mechanically bonded together. Mechanical bonding offers excellent properties since it provides a strong connection between the layers through stiches or seam lines while keeping permeability as high as possible on one hand and easy disconnection and separation of the layers on the other. The separation of the layers is not anticipated when the layers are bonded over their contact surfaces. Separation of the layers offers further advantages, such as replacement of the one layer, for example in case of damage, reuse or recycle of the any of the layer, unobstructed flow of water between the layers etc. Further, with such a connection of fabrics, there is no need to open holes or perforations to enhance water tpermeability. The multi-layer groundcover is placed on top and in contact with the soil, right below the photovoltaic modules 1, in order both weed suppression and ground albedo enhancement functions to be properly served. The multi-layer groundcover offers the following advantages. • it serves for combining the functions of weed suppression and surface soil erosion protection along with ground albedo enhancement • the coupled arrangement of the fabrics serves for the function of surface soil erosion protection • the fabrics comprising the system are flame retardant and present a service life of minimum 2 years against UV exposure on the basis of EN12224 • it is aligned with the sustainability principles both fabrics are recyclable and may contain recycled content • it aligned with circular economy principles and allows for the complete land restoration in the end of solar parks’ service life. In some examples a mid-layer 7 is inserted between the top layer 6 and the bottom layer 8. The mid-layer hinders the accumulation of water within or on the top and bottom active layers, for example as a water collector or water drainage element. The mid-layer may consist of sand, gravel or any aggregate, a permeable granulated active clay, such as Attapulgite, a permeable active natural material such as zeolite, apatite, cement powder. The optional mid layer may be a drainage geosynthetic element such as geonet, geomat, geospacer, in particular when the bottom layer is water impermeable, for example if it includes a geomembrane, a PE film, tarpaulin, dimple/egg-shaped sheet. In case of a drainage geosynthetic element the mid layer may comprise PP, PE (any type), PET, PVA, AR, PA, PVC or any other polymer. A geonet has a three dimensional structure made of struts and a geomat is a drainage and erosion geosynthetic element. The arrangement described above i.e., the use of two fabrics with the one placed on top of the other, aims at fulfilling an additional function by the system, which relates to the surface soil erosion protection. The arrays of the photovoltaic modules are typically mounted on poles/piles that are driven in the ground. The length of the mounting system that is anchored in the ground is selected to meet both the stability requirements and the safety principles of a solar park overall. Runoff and wind may develop erosive actions that during flood events may be powerful enough to significantly erode surface soil which in turn brings risk to the operation of a solar park by reducing the anchoring length of the mounting system. The groundcover with a system of two layers is efficient in keeping the ground resistant to erosive forces caused by rain drop and surficial runoff, since it acts as a shielding membrane that absorbs the energy developing from the impact of the droplets on the ground during rainfall events. At the same time the system also acts as a water flow rate controller i.e., a dual water flow controlling system, which decelerates the runoff motion and diminishes the erosion action. Groundcovers according to the invention are particularly effective when used in combination with bifacial photovoltaic module. Monofacial photovoltaic modules also benefit from their properties and the reflected light.

Claims

CLAIMS 1. Groundcover with two layers, disposed one on the top of the other, with one layer, i.e. the top layer, being a white fabric or a white film configured to reflect light with a wavelength in the range of 400 to 1100 nm and the other layer, i.e. the bottom layer, being a dark color fabric or a dark color film that hinders the transmission of visible light with wavelength at least within the range of 400 to 500 nm or/and 600 nm to 700 nm therethrough, whereby the top layer and the bottom layer are joined together in individual points or along lines or over areas, so that they are areas of loose contact of the top layer and the bottom layer where the top layer and the bottom layer are not joined, so as to facilitate separation.

2. Groundcover according to claim 1, with water paths through the groundcover, from a free surface of the top layer to a free surface of the bottom layer, arranged normally or almost normally to the groundcover.

3. Groundcover according to claim 1 or claim 2, whereby the top layer and the bottom layer are joined mechanically, preferably by needling along lines.

4. Groundcover according to any one of claims 1 to 3, whereby the bottom layer is a woven fabric made of yarns comprising polymers and including a black pigment, such as a carbon black pigment, and the top layer is a woven fabric made of yarns comprising polymers and a white pigment.

5. Groundcover according to claim 4, whereby the yarns of the bottom layer are tape yarns and/or the yarns of the top layer are tape yarns.

6. Groundcover according to any one of claim 4 or claim 5, whereby the top layer includes a TiO2 pigment and the weight content of TiO2 pigment in top layer is at least 10000 parts per million and preferably less than 70000 parts per million.

7. Groundcover according to any one of claims 3 to 6, with at least one of the woven fabric of the top layer and the woven fabric of the bottom layer has a cover factor in machine direction of at least 100%.

8. Groundcover according to any one of claims 3 to 7, with at least one of the woven fabric of the top layer and the woven fabric of the bottom layer has a cover factor in cross-machine direction of at least 100%.

9. Groundcover according to any one of claims 1 to 3, whereby the bottom layer is a woven fabric and the top layer is a non-woven fabric.

10. Groundcover according to claim 9, whereby the top layer is a non-woven needle- punched fabric.

11. Groundcover according to claim 9 or claim 10, whereby the top layer has a mass within the range of 200 to 800 gr/sqm, optionally 300 to 500 gr/sqm.

12. Groundcover according to any one of claims 9 to 11, whereby the top layer comprises TiO₂ pigment.

13. Groundcover according to any one of claims 9 to 12, whereby the bottom layer is a woven fabric made of tape yarns or a monofilament woven fabric.

14. Groundcover according to claim 13, whereby the bottom layer the tape yarns or filaments including black pigment, such as carbon black pigment.

15. Groundcover according to any one of claims 1 to 3, whereby the top layer is a woven fabric and the bottom layer is a non-woven fabric.

16. Groundcover according to claim 15, whereby the bottom layer is a non-woven needle-punched fabric.

17. Groundcover according to claim 15 or claim 16, whereby the bottom layer has a mass greater or equally to 200 gr/sqm.

18. Groundcover according to any one of claims 15 to 17, whereby the bottom layer is made of fibers including a black pigment, such as a carbon black pigment.

19. Groundcover according to any one of claims 15 to 18, whereby the top layer is a woven fabric made of tape yarns or a monofilament woven fabric, comprising TiO₂ pigment.

20. Groundcover according to any one of claims 1 to 19, with a mid-layer between the top layer and the bottom layer.

21. Groundcover according to claim 20, whereby the mid-layer includes any of the following materials or any combination therefrom: sand, gravel or any aggregate, a permeable granulated active clay, such as Attapulgite, a permeable active natural material such as zeolite, apatite, cement powder 20. Groundcover according to claim 20 or claim 21, whereby the mid-layer is a three- dimensional geonet, geomat or geospacer layer.

22. Groundcover according to any one of claims 1 to 21, whereby the groundcover does not include halogenated flame-retardant additives, which hinder UV inhibitors such as HALS.

23. Groundcover according to any one of claims 1 to 22, whereby the groundcover does not include substances including halogen, sulphur or phosphorus.

24. Groundcover according to any one of claims 1 to 23, with a service life of at least 2 years, preferably 5 years, evaluated on the basis of EN12224.

25. Method to cover ground below a photovoltaic array, with a groundcover including two layers of fabric disposed one on the top of the other, with one layer. i.e. the top layer, being a white fabric or a white film configured to reflect light with a wavelength in the range of 400 to 1100 nm and the other layer, i.e. the bottom layer, being a dark color fabric or a dark color film that hinders the transmission of visible light with wavelength at least within the range of 400 to 500 nm or/and 600 nm to 700 nm therethrough, whereby the top layer and the bottom layer are joined together mechanically in individual points or along lines or over areas, so that they are areas of loose contact of the top layer and the bottom layer where the top layer and the bottom layer are not joined, so as to facilitate separation.

26. Method according to claim 25, whereby the photovoltaic array has arrays of photovoltaic modules, which arrays of photovoltaic modules are mounted on poles/piles that are driven in the ground.

27. Method according to claim 25 or claim 26, whereby the photovoltaic array has arrays of photovoltaic modules, which photovoltaic modules are either bifacial or monofacial.

28. Method to cover ground below a photovoltaic array with a groundcover according to any one of claims 1 to 27.