1. What is Thin-film Solar Panels?
Unlike the first-generation solar cells being made of single- or multi-crystalline silicon, thin-film solar panels are manufactured using a single or multiple layers of PV elements over a surface comprised of a variety of glass, plastic, or metal to convert sunlight into electricity. And the most commonly used ones for thin-film solar technology are cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon (a-Si), and gallium arsenide (GaAs).
2. The Structure of Thin-film Solar Panels
Thin-film Solar Panels consist of a large number of thin-film solar cells and use light energy (photons) from the Sun to generate electricity through the photovoltaic effect. It also includes layers,backsheet and junction box, all of them work together to ensure the normal operation of the solar panels.
What is Thin-film solar cells?
Thin-film solar cells are electronic devices that convert sunlight into electrical energy by the photovoltaic effect.Thin-film cells trend to use much less material -the cell's active area is usually only 1 to 10 micrometers thick. Also, thin-film cells can usually be manufactured in a large-area process, which can be an automated, continuous production process.
What’s more, thin-film solar panels uses a thin layer of a transparent conducting oxide, such as tin oxide to work. While thin-film cells are made of many tiny crystalline grains of semiconductor materials to better create the electric field with an interface, called a heterojunction. Generalloy this kind of thin-film devices can be made as a single unit - that is, monolithically -with layer upon layer being deposited sequentially on some substrate, including deposition of an antireflection coating and transparent conducting oxide.
What is layers?
Usually thin-film solar panel has a very thin (less than 0.1 micron) layer on top called the "window" layer to absorb light energy from only the high-energy end of the spectrum. It must be thin enough and have a wide enough bandgap (2.8 eV or more) to let all available light through the interface (heterojunction) to the absorbing layer. The absorbing layer under the window, usually doped p-type, equipped with a high absorptivity (ability to absorb photons) for high current and a suitable band gap to provide a good voltage.
What is backsheet?
As a polymer or a combination of polymers with various additives, backsheet is designed to provide a barrier between the solar cells and the outside environment. From which we can see the backsheet is a critical component in the durability, efficiency, and longevity of a solar panel.
What is junction box?
As an electrical enclosure used to house and protect electrical connections, junction box is specially designed to provide a safe and secure environment for electrical connections so as to prevent accidental contact with live wires and to simplify future maintenance or repairs. Usually a PV junction box is attached to the back of the solar panel and functions as its output interface. External connections for most photovoltaic modules use MC4 connectors to facilitate easy weatherproof connections to the rest of the system. A USB power interface can also be used.
3. The Development History of Thin-film Solar Panels
The history of thin-film solar panels dates back to 1970s, when researchers began their fist exploration on the use of thin film (a-Si) of semiconductors to harness solar energy, at that time the interest in thin-film technology for commercial use and aerospace applications promote development of amorphous silicon thin-film solar devices.
In 1980s, advancements in technology facilitated the expansion of existing thin-film materials into new ones, such as cadmium telluride (CdTe) and copper indium gallium selenide (CIGS), which has higher conversion efficiencies and lower production costs.
1990s and 2000s was a time of significant advances in the exploration of new third-generation solar materials–materials with the potential to overcome theoretical efficiency limits for traditional solid-state materials. Mang new products such as dye-sensitized solar cells,quantum dot solar cells were developd.
In the 2010s and early 2020s, innovation in thin-film solar technology has included efforts to expand third-generation solar technology to new applications and to decrease production costs. In 2004, the National Renewable Energy Laboratory (NREL) achieved a world-record efficiency of 19.9% for a CIGS thin-film module.In 2022, flexible organic thin-film solar cells were integrated into fabric.
Nowadays, flexible organic thin-film solar cells integrated into fabrications make them a better choice than traditional silicon panels.And thin-film technology captured approximately 19% of the total U.S. market share in the same year, including 30% of utility-scale production.
4.The Types of Solar Panels
There are several types of materials used to manufacture thin-film solar cells, based on their raw materials, they can be divided into four kinds.
l Cadmium Telluride (CdTe) Thin-Film Panels are a type of solar panel that uses a thin layer of cadmium telluride deposited on a substrate material, such as glass or stainless steel, as the semiconductor material. Not only lightweight and easy to install, they also has high energy production in low-light conditions, which means that they can generate electricity even in cloudy or overcast weather. It is estimated that CdTe thin-film solar panels reached a 19% efficiency under Standard Testing Conditions (STC), but single solar cells have achieved efficiencies of 22.1%. However, there are some concerns about the toxicity of cadmium, since it is a heavy metal that can cause environmental damage if not disposed of properly.
l Copper Indium Gallium Selenide (CIGS) Thin-Film Panels are manufactured by placing a molybdenum (Mo) electrode layer over the substrate through a sputtering process. Compared to other PV technologies,they have high efficiency and can achieve a theoretical efficiency of 33% in the future. In addition, they are less prone to cracking or breaking and easily-operated. However, despite these advantages, the cost is relatively more expensive than for other technologies, which may hamper their further development.
l Amorphous Silicon (a-Si) Thin-Film Panels are manufactured by processing glass plates or flexible substrates, along with a p-i-n or n-i-p configuration. Advantages of a-Si thin-film panels include their flexibility and lightweight construction, which makes them ideal for use in portable applications, such as camping or powering remote sensors. However, since the conductive glass for these panels is expensive and the process is slow, its price is relatively expensive of nearly $0.69/W.
l Gallium Arsenide (GaAs) Thin-Film Panels are more complex than for regular thin-film solar cells of the manufacturing process. It is worth mentioning that they achieve high efficiencies of up to 39.2% and are more resistant to heat and moisture. Nevertheless, the manufacturing time, cost for the materials, and high growth materials, make it a less viable choice .
5.The Applications of Thin-film Solar Panels
As an emerging class of alternatives to silicon photovoltaics, thin-film solar panels are mainly used in the following fields.
l Building-Integrated Photovoltaics(BIPV)
Since thin film PV panels can be up to 90 % lighter than silicon panels, one application starting to become widely popular worldwide is BIPV, where the solar panels are attached to the roof tiles, window, weak structures and so on. Additionally, some types of thin film PV can be made semi-transparent, which help to keep aesthetics for homes and buildings while allowing the possibility of solar power generation.
l Space applications
Due to the advantages of lightweight, highly efficient, a wide temperature of operation range, and even the damage resistance against radiation, thin-film solar panels, especially CIGS and GaAs solar panels, have been an ideal for space applications.
l Vehicles and marine applications
One common application of thin-film solar panels is the installation of flexible PV modules on vehicle rooftops (especially RVs or buses) and the decks of boats and other vessels, which can be used to power electricity while at the same time keeping aesthetics.
l Portable applications
Its portability and size have provided it a sustainable development in small self-powered electronics and Internet of Things (IoT) sector, which is expected to grow substantially in the coming years. And with its advancement, it may be further applied in remote locations with foldable solar panels, solar power banks, solar-powered laptops and so on.
6.The Development Trends of Thin-film Solar Panels
With the incresing acceptance of solar energy worldwide, the implementation of strict energy restrictionsand the increasing government efforts to integrate green sources into the grid, thin-film solar panels is expected to hit around USD 27.11 billion by 2030 with a remarkable CAGR of 8.29% from 2022 to 2030. The increase is drove by its advantages and R&D, since they are extremely economical and easily-created, utilize less material and produce less waste. And the R&D to enhance solar cell endurance and performance will also create new opportunities for market growth.
However, opportunities come together with challenge. The high levels of competition,a changing regulatory environment as well as the availability of scarce finances and resources means at present they may not be able to take a sizable chunk of the global market share.
7. The Investment Analysis of Thin-film Solar Panels
The market for thin-film solar cells appears to develop in recent years, which is drove by several factors.
l Product Type Analysis
In 2018, CdTe produced electricity at a price that was significantly lower than or on par with that of conventional fossil fuel sources of energy. Because of its non-toxic, cheap operation and production costs, at present the cadmium telluride category dominated the worldwide thin-film solar cell market, and it is anticipated that it will continue to grow at the quickest rate throughout the prediction period.
l End-User Analysis
The rising development and research to lower installation and maintenance costs may boost consumer needs.In 2022, the utility market dominated the worldwide thin-film solar cell market, and it is predicted that it would continue to develop at the quickest rate throughout the forecast period. Since thin-film solar panels degrade at a much slower pace, they offer a potential alternative to the traditional c-Si solar panels.
l Regional Analysis
Asia-Pacific was the largest region in the world for thin-film solar cells in 2022, and it is anticipated that it will continue to expand at the highest rate, which is drove by many factors. For example, as the largest solar PV markets around the world, China will raise the target for renewable energy from 20% to 35% by 2030. And utility-scale solar Photovoltaic facilities in China mostly employ thin-film technology. Moreover, Japan has also declared its intention to use only sustainable power in the further.
8. Things to Consider for High-quality Thin-film Solar Panels
When buying solar panels, not only the price and quality must be considered, other factors should also be kept in mind.
l Effiency: High effiency can convert more of the sun's energy into electricity. Generlly having a higher concentration of charge carriers can increase the efficiency of the solar cell by increasing the conductivity. The addition of a concentrator to a solar cell is not only help to increase efficiency, but can also reduce the space, materials, and cost needed to produce the cell.
l Durability and lifetime: Some thin-film modules also have issues with degradation under various conditions. Among all materials, CdTe displaying the best resistance to performance degradation with temperature. And unlike other thin-film materials, CdTe tends to be fairly resilient to environmental conditions like temperature and moisture, but flexible CdTe panels may experience performance degradation under applied stresses or strains.
l Weight: It refers to the density of the thin-film solar panel. In general, thin-film solar panel are lightly weighted so you should not be scared of applying dead weight on your roof. Nonetheless, the weight still need to be considered when selecting ones so as to ensure it won’t be overloaded for installation.
l Temperature: This means the minimum and maximum temperature in which the Thin Film solar panel can function. In general, all the best thin film solar panels are considered to have a minimum temperature of -40°C and a maximum temperature of 80°C.
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