A hypothesis on sustainable transformations of solar panels in the environment of modern city

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A hypothesis on sustainable transformations of solar panels in the environment of modern city

Murugesh Munaswamy,

G. L Samuel

ГИПОТЕЗА ОБ УСТОЙЧИВОЙ ТРАНСФОРМАЦИИ СОЛНЕЧНЫХ ПАНЕЛЕЙ В УСЛОВИЯХ СОВРЕМЕННОГО ГОРОДА

Муругеш Мунасвами,

Дж. Л. Самуэль

Абстракт

Современная городская среда требует эффективного использования ресурсов. Среди них использование электроэнергии является одним из самых важных ресурсов, на которые следует обратить внимание. В последние годы многие современные городские проекты/сооружения начали включать в себя систему солнечного энергоснабжения с самого начала. В этой статье рассматривается структурирование солнечных панелей для повышения выходной мощности солнечных элементов. Структурирование панелей направлено на увеличение светоулавливающей способности солнечных элементов. Недавно разработанная передовая технология импульсного лазера оказалась эффективной в достижении быстрого метода текстурирования поверхности большой площади. В этой статье обсуждается влияние основных параметров лизинга, необходимых для получения различных типов поверхностных структур. Представленные результаты получены при лазерном облучении титанового сплава марки 5 (Ti6Al4V). Технический подход, использованный в данной статье, может быть применен к другим материалам, включая солнечные элементы/панели. Гальвосканер в сочетании с ультракороткой импульсной лазерной микрообработкой позволил добиться гибкого высокоскоростного текстурирования. Микромасштабные поверхностные структуры наблюдались в диапазоне 5-15 мкм, а наномасштабные структуры в диапазоне длины волны падающего лазерного излучения, т. е. от 500 до 1030 нм. Геометрические вариации в текстурировании могут быть включены вместе с лазерно-индуцированными поверхностными структурами.

Ключевые слова: текстурирование поверхности, солнечные панели, модифицированные поверхности, импульсные лазеры.

Abstract

Modern city environment demands the effective utilization of resources. Among these, electricity utilization is one of the foremost resources to be considered. In recent years, many of the modern city designs/constructions started to include the solar power supply system from the initial designs. In this article, structuring of solar panels are discussed to enhance the output power of solar cells from the panels. The structuring of panels aims to increase the light trapping capacity of the solar cells. Recently developed advanced pulsed laser technology found to be effective in achieving fastest large area surface texturing method. In this article, the influence of major leasing parameters required to get various types of surface structures are discussed. The reported results are from laser irradiation on Titanium grade 5 alloy (Ti6Al4V). The technical approach used in this article can be applied to other materials including solar cells/panels. The galvo scanner coupled with ultra-short pulsed laser micromachining resulted in achieving flexible high-speed texturing. The microscale surface structures observed to be in 5-15 qm and the nanoscale structures in the range of incident laser wavelength i. e., 500 to 1030 nm. Geometrical variations in the texturing can be included together with the laser induced surface structures.

Keywords: Surface Texturing, Solar panels, modified surfaces, Pulsed Lasers.

Introduction

Sustainable urban design is one of the thrust areas in the recent years. Power supply in the modern cities is one of the primary needs. Many of daily activities in this modern era is directly or indirectly relying on electricity. Inclusion of sustainable power supply unit is equally important in this modern city environment. There is significant research is available on photovoltaics and solar cells development and utilization. Yet, the increase in demand raises the quest towards increasing output power. The latest commercially available short and ultrashort pulsed lasers given a way to achieve improved output power by precise surface texturing on solar panels. Besides the advanced laser technology, high-speed motion controls lead to have large scale texturing and surface modifications. The major challenge in the solar cells is to improve the output power, that can be done by achieving improved absorption and light trapping capacity.

Hypothesis and Methodology

The current hypothesis is based on surface processing methods and results investigated on Ti6Al4V alloy. The hypothesis covers the scope of research towards improved output power from solar cells by adopting the techniques discussed. The reported results can be considered as benchmark studies towards texturing solar panels. Geometrical texturing is essential, but laser induced hierarchical surface structures are more challenging. The article discusses the various lasing parameters that influence the hierarchical surface structures induced by laser irradiation.

Laser Micromachining - State of Art

Prior to the availability of short and ultrashort pulsed lasers, micro-, nano-, and picosecond pulsed lasers were employed to produce micro features and were proven to be faster and better than the conventional (turning, milling, drilling etc.,) machining techniques. The long-pulsed laser processing has a difficulty in achieving precise microscale features because of the thermal shock that could result in the formation of recast layer on the target surface. The development of pulsed laser technology gives a way to achieve precise control over feature size [1].Technological advancements of laser pulse control have given the way to regulate the damage/removal onto the target workpiece, specifically the recently developed short and ultrashort laser pulse processing systems [2]. Machining with femtosecond pulsed laser processing is an advanced tool for precision material processing, such as drilling, cutting texturing, and grooving into the metal [3], because of high peak power and intensities.

Surface texture plays a vital role in many industrial applications, including biomedical, tribological, photovoltaics, and electronics [4]. The application areas of these micro/nano periodic surface features include tribology [5], wettability studies [6], biomedical implants and tissue culture [7] and solar cells for improving absorption or lighttrapping capacity [8]. Investigations from surface texturing patterns such as LIPSS will also help micro polishing applications achieve desired roughness. The femtosecond laser ablation makes it possible to get such varieties of engineered surface structures from the cutting-edge research of bio mimicking. Considering these features are machined with fs without thermal damage can lead to unique advantages. Laser mater interaction can be observed in (Figure 1). The figure gives the understanding about the surface damage on the target. Ultrashort pulse laser machining/ablation of semiconductor shows some characteristics of metals and less sensitive to the pulse duration. Ultrashort pulse laser ablation of dielectrics proven to be attributed to Coulomb explosion from a multiphoton surface ionization process. Also, mentioned that for metals and semiconductors, the Coulomb Explosion is not a dominant mechanism, due to the screening effect triggered by the free electrons and their high density.

Figure 1. Laser matter interaction: a - classical laser beam (shortpulse) - material interaction; b - ultrafast laser beam - material interaction [9]

For semiconductors, the mechanism shows some of the characteristics like that of metals and is sensitive to laser pulse width. For ultrashort pulse laser ablation of metals, the energy transfer is accepted as a photon to electrons before lattices [10]. However, the metal ability of electron - lattice energy exchange, temperature attributes can differ because of the difference in fluence and laser pulse width. Several ablation mechanisms are proposed to have a significant influence while laser ablation happens at a low fluence regime: phase explosion from homogeneous nucleation of gas bubbles [11], photomechanical spallation in solids [12], vaporization [13], and fragmentation [9]. As thermal and nonthermal both effects can contribute to ultrashort pulse laser ablation [14], typically two ablation mechanisms in low fluence laser ablation are provided thereafter: spallation mechanism and melting mechanism. Spallation in solid was found to occur in the range around the threshold fluence.

It is reported that this spallation phenomenon is closely related to ps and fs pulsed ablation processes [15]. The overall melting mechanism by laser ablation in metals can be well explained by considering both heterogeneous and homogenous melting phenomena. The relative contributions of both homogenous and heterogeneous melting mechanisms result in the melting of metal films that can be defined by laser pulse width, fluence, and electron phonon coupling [16]. Phase explosion term is used to explain the process that happens while a liquid approaches the thermodynamic critical point temperature and massive homogeneous nucleation takes place [17]. This concept comes into picture when the laser fluence is further increased than low fluences resulting in a complex ablation process. As the fluence and pulse duration change, the ablation mechanisms will become more complicated, and the pressure rise will also be observed. The heating rate is extraordinary in ultrashort pulse laser processing of metals.

Laser Induced Multiscale Hierarchical Surface Structures - State of Art

Femtosecond laser pulses have been instrumental in achieving highly reproducible micro/nanostructures. This method is straightforward and cost-effective to achieve the required multi-scale surface features. Depending on the involved physical mechanisms, the LIPSS formation process can be driven by feedback loops leading to selforganization processes [18]. A similar phenomenon has been used for periodic structure generation at the surfaces of various materials such as metals [19], semiconductors [20], dielectrics [21], ceramics [22], and polymers [23]. Periodic microdot structures produced on titanium target in the range of fluence 0.25 - 1.5 J/cm2 for 10 to 110 pulses. The repeated cone-like protrusions sizes in the range of 5 - 10 pm were produced at a fluence of 0.75 J/cm2 on Titanium surface [4], the structures kept increasing by bridging with neighboring microdots/cone-like structures. A pulse width of 60 fs was applied on the titanium surface at a high intensity of 1015 W/cm2 and at reduced intensity of 1013 W/cm2. At high intensity, the craters appeared at 5 pulses itself and at reduced intensity shallow craters were observed after 10 pulses and deep craters were observed after 50 and 100 pulses with periodic structures on their periphery [24]. Accurate sized micro dimple arrays have been achieved by adjusting pulse energy and the number of pulses, In addition, the dimple array is covered with ripples having a period of about 1100 nm when the fluence and scanning speed is 0.107 J/cm2 - 0.218 J/cm2 and 30 - 50 mm/s respectively [25].

Multiscale Hierarchical Structure - Processing Methods

The conventional definition of texturing is by programming required texture by adopting corresponding geometries (circle, square, and triangle) with required spacing. In recent years generation of laser-induced surface structures by altering input lasing parameters gained wide attention across the scientific community. In this research, two major methods are implemented, which are represented in (.Рідиге 2).

Figure 2. Methods of controlling pulses per spot and hatching. a - dot hatching - direct control through burst time b - line hatching - indirect control using scanning speed

The number of pulses per spot is controlled along with pulse energy, PRR, and scanning speed to get various surface structures. The following methods also can be adopted for large area polishing, such as solar panels. The increasing trend in demand for surface textures resulted in a thrust for new methods of fabrication. Emerging technologies, by default having the expectations of short time and enhanced throughput. Pulse laser processing is one of the key methods used in the recent decade, known for its quick processing time and controllable thermal damage to the surface. Technological advancements of laser pulse control have given the way to regulate the damage onto the workpiece, especially recently developed short and ultrashort laser pulse processing systems [2]. Machining with femtosecond pulsed laser processing is an advanced tool for precision material processing, such as drilling, cutting texturing, and grooving into the metal [1]. Irradiation on any material surface with short/ultrashort pulses with required energy per material properties results in the instantaneous surface patterns called Laser- induced periodic surface structures (LIPSS).

Experimental observations relevant to the hypothesis

The major influencing lasing parameters considered in the article are pulse ener- gy/fluence, number of pulses and pulse to pulse overlap. ablated surface with LIPSS can be seen in Figure 3 for the pitch of 10 to 50 pm (dot hatch) at two levels of pulse energy 16 pJ and 40 pJ. At both levels of pulse energy, the microdots/ripples/pillars have different sizes and geometry. At 40 pJ, the multiscale surface structures are prevalent and at 16 pJ microdots/pillars size is reduced with an increase in pitch.

Hot spots or holes were observed on Titanium surface structures in (Figure 3) (H - J). The hot spots in the results could be because of the uneven/incomplete energy absorption. From the results and discussion, this article proposes the method of geometrical texturing together with Laser induced hierarchical structures can enhance the solar cells output power. The testing and validation on solar cells maybe the future scope of results in this article.

Conclusions

The modifications of solar cells or solar panels surfaces can be one of the ways to have improved light trapping and absorption capacity there by increasing solar cells output power. Hybridizing the surface texture with geometrical texturing designs can be considered for possible improvements in the solar cell's efficiency. Nanostructures over microstructures coupled with geometrical texturing can lead to achieve various combinations of texturing on desired solar panels.

Figure 3. Influence of increase in pitch (dot hatching) on surface induced periodic structures while keeping other lasing parameters to be constant (250 Pulses)

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