ENVIRONMENTAL IMPACT OF SOLAR CELLS

Source: Downtoearth

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Context

• Researchers at the Indian Institute of Technology (IIT) Mandi have conducted a comprehensive study on the environmental impact of various solar cell technologies, focusing on the Indian context.
• This study aims to identify the most sustainable options for solar energy production.

Details

Key Findings

• Lowest Environmental Impact: Cadmium Telluride (CdTe) technology exhibits the least environmental impact among the solar cell technologies assessed. It has the lowest levels of carbon dioxide emissions, ozone depletion potential, human health effects, and particulate air pollution.
• Comparison with Other Technologies: The study compared five solar cell technologies:
  1. Mono-Silicon
  2. Polysilicon
  3. Copper Indium Gallium Selenide (CIGS)
  4. Passivated Emitter and Rear Contact (PERC)
  5. Cadmium Telluride (CdTe)

CdTe was found to be the most sustainable, closely followed by CIGS photovoltaic (PV) cells​​ .

Life Cycle Assessment (LCA)

• The researchers used the Life Cycle Assessment tool to perform a detailed analysis of 18 environmental impact categories. These categories included:
• Global warming potential
• Stratospheric ozone depletion
• Human carcinogenic and non-carcinogenic toxicity
• Fine particulate matter formation
• The LCA considered the entire life cycle of the solar cells, from raw material extraction to the manufacturing of the solar panels.
• However, it did not cover the recycling and end-of-life phases, which are planned for future research .

Context

• Between 2010 and 2020, India made significant progress in clean energy, driven by initiatives like the Jawaharlal Nehru National Solar Mission.
• However, the COVID-19 pandemic disrupted the solar supply chain, delaying numerous projects.
• Post-COP26, India's focus has shifted to green solar manufacturing to enhance supply chain reliability, energy security, and decarbonization, aligning with UN clean energy goals .

Cadmium Telluride (CdTe)

• Cadmium telluride (CdTe) is a semiconductor material widely used in photovoltaic (PV) applications.
• It has become a key material for solar cells due to its optimal bandgap, defect tolerance, and cost-effective manufacturing processes.
• CdTe solar cells are second only to silicon-based cells in terms of market share and have several unique properties that make them particularly suitable for large-scale solar energy production.

Material Properties

• CdTe is characterized by a direct bandgap of approximately 1.45 eV, which allows it to efficiently absorb and convert sunlight into electricity.
• This direct bandgap makes CdTe highly efficient at absorbing solar radiation compared to silicon, which has an indirect bandgap of 1.12 eV​.
• CdTe's defect tolerance simplifies the manufacturing process, reducing costs and enhancing the material's efficiency in converting sunlight to electricity.
• This defect tolerance means CdTe can perform well even when it has impurities or crystal defects that would severely impact other materials​.

Manufacturing Process

• CdTe solar cells are typically produced using a thin-film deposition process.
• This involves applying thin layers of CdTe and other materials onto substrates such as glass or flexible materials.
• Common methods for depositing CdTe include close-spaced sublimation, vapor transport deposition, and electrodeposition​.

Efficiency and Performance

• CdTe solar cells have demonstrated efficiencies up to 22% in laboratory settings, though commercial modules typically achieve efficiencies between 11% and 16%.
• While this is lower than the highest efficiencies seen in silicon-based cells, CdTe cells excel in specific conditions.
• They perform better at high temperatures and in low-light environments, making them suitable for regions with less consistent sunlight​​.

Advantages and Disadvantages

Advantages:

• Cost-Effective:Simplified manufacturing process leads to lower production costs.
• High Absorption Efficiency:Direct bandgap enables efficient sunlight absorption.
• Defect Tolerance:High tolerance for material defects allows for more straightforward production.
• Performance in Varied Conditions:Better performance in high temperatures and low-light environments.

Disadvantages:

• Lower Efficiency:Commercial CdTe cells are generally less efficient than silicon-based cells.
• Toxicity:Contains cadmium, which is toxic and poses environmental and health risks if not handled properly.
• Recyclability:More challenging to recycle compared to silicon, impacting long-term sustainability.

Solar Cells

• Solar cells, also known as photovoltaic (PV) cells, convert sunlight directly into electricity.
• This technology is central to the global shift toward renewable energy, offering a sustainable alternative to fossil fuels.
• Solar cells are categorized into three generations based on the materials and technologies used.

First Generation Solar Cells: Crystalline Silicon

• Monocrystalline Silicon (Mono c-Si): Made from a single continuous crystal structure, these cells are known for their high efficiency (up to 25%) and longevity (25-30 years). They are more efficient but also more expensive to produce.
• Polycrystalline Silicon (Poly c-Si): Composed of silicon crystals melted together, these cells are less efficient (around 20%) but cheaper to produce and have a shorter lifespan compared to monocrystalline cells.
• First-generation solar cells are well-established, widely used in residential and industrial applications, and have a proven track record for performance and reliability.

Second Generation Solar Cells: Thin-Film Technologies

• Cadmium Telluride (CdTe): Known for its low cost and relatively high efficiency (up to 22%), CdTe is easy to produce and performs well in low-light conditions. However, concerns about cadmium toxicity and long-term durability exist.
• Copper Indium Gallium Selenide (CIGS): Offers high efficiency (up to 23%) and flexibility, making it suitable for a variety of applications, including building-integrated photovoltaics (BIPV).
• Amorphous Silicon (a-Si): Less efficient (around 10-12%) but cheaper and flexible, often used in low-power devices like calculators and portable electronics.
• Thin-film solar cells use less material, making them lighter and potentially cheaper. They perform better in high-temperature environments but generally have lower efficiency and shorter lifespans compared to first-generation cells.

Third Generation Solar Cells: Emerging Technologies

• Perovskite Solar Cells: Show promise with high efficiencies (up to 29%) and potential for low-cost production. However, their commercial viability is currently limited by their short lifespan and stability issues.
• Organic Photovoltaics (OPV): Made from organic molecules or polymers, OPVs are flexible, lightweight, and potentially very low-cost. Current efficiencies are lower (around 20%), but ongoing research is rapidly improving their performance and stability.
• Quantum Dot Solar Cells: Utilize nanoscale semiconductor particles, or quantum dots, to offer tunable bandgaps and high theoretical efficiency. Still in the research phase with practical efficiencies lower than other technologies.
• Third-generation solar cells aim to combine high efficiency with low production costs, utilizing materials that are abundant and environmentally friendly.

Comparative Analysis

• Efficiency: Third-generation cells, especially perovskites, show the highest potential efficiency, surpassing traditional silicon and thin-film technologies.
• Cost: Thin-film and third-generation cells offer lower production costs, making solar power more accessible.
• Durability: First-generation silicon cells currently have the longest lifespan, making them reliable for long-term installations.

Sources:

Downtoearth

PRACTICE QUESTION Q: CdTe remains a critical material in the solar energy sector due to its unique properties and cost advantages, while it has some disadvantages compared to silicon. Discuss. (250 Words)