Improving solar cell performance

 

In news:

• Scientists have conducted an in-depth study on how carbon nanotubes with oxygen-containing groups can be used to greatly enhance the performance of perovskite solar cells.
•  The newly discovered self-recrystallization ability of perovskite could lead to improvement of low-cost and efficient perovskite solar cells.

 

What are perovskite solar cells?

• They represent the most exciting approach to build solar cells that are inexpensive and highly efficient.
• A perovskite solar cell is one that includes a perovskite-structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer.
•  The terms “perovskite” and “perovskite structure” are often used interchangeably.
• A perovskite structure is any compound that has the same structure as the perovskite mineral.
• A perovskite is a material that has the same crystal structure as the mineral calcium titanium oxide, also known as Perovskite.
• Perovskite compounds have a chemical formula ABX3, where ‘A’ and ‘B’ represent cations and X is an anion that bonds to both. Because of their unique crystal make-up, perovskites often display a number of interesting properties, including superconductivity, giant magnetoresistance, and ferroelectricity.
• It has only been recently that their applications to clean energy have drawn scientific attention.
• Within the last several years, perovskite solar cells have outpaced all other third-generation solar technologies in terms of efficiency.Technically, a perovskite is a type of mineral that was first found in the Ural Mountains and named after Lev Perovski who was the founder of the Russian Geographical Society.
• A perovskite solar cell (PSC) is a type of solar cell which includes a perovskite structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer.Perovskite materials, such as methylammonium lead halides and all-inorganic cesium lead halide, are cheap to produce and simple to manufacture.

 

Explain why these cells are more efficient that conventional silicon solar cells?

• Perovskites solar cells are more efficient in comparison to conventional silicon solar cells due to following reasons:

• Within the last several years, perovskite solar cells have outpaced all other third-generation solar technologies in terms of efficiency.
• Efficiency of a solar cell depends upon the mobility of atoms and molecules within the material used for its construction.
• A perovskite mineral have high mobility and respond to light within trillionths of a second, which is much faster than that by a silicon wafer. This property makes Perovskites solar cells highly efficient in converting light energy to electricity.
• Perovskite thin films are also lightweight and flexible in comparison to silicon solar cells.
• Unlike silicon solar cells, Perovskites solar cells are environment friendly (manufacturing and disposal process), cheap, and easy to install.

• Because of their unique crystal makeup, perovskites often display a number of interesting properties, including superconductivity, giant magnetoresistance, and ferroelectricity. 
• A large number of different elements can be combined together to form perovskite structures. This allows scientists lots of room to selectively design and optimize perovskite physical, optical and electrical characteristics.
• Within the last several years, perovskite solar cells have outpaced all other third-generation solar technologies in terms of efficiency.
• Perovskite solar cells aim to increase the efficiency and lower the cost of solar energy.
• PVs hold promise for high efficiences , as well as low potential material and reduced processing costs.
• A big advantage of PVs have over conventional solar technology is that they can react to various different wavelenghts of light, whch let them convert more of the sunlight that reaches them into electricity.
• These easily synthesized materials are considered the future of solar cells, as their distinctive structure makes them perfect for enabling low-cost, efficient photovoltaics. They are also predicted to play a role in next gener electric vehciles barriers, sensors, laser and much more.
• They are widely viewed as the next generation of solar cells, offering similar power convenson effienciency(PCE) performance, but at a much lower cost than the market dominant crystalline silicon based solar cells.

 

What is solar cells?

• A solar cell is a semiconductor device in which solar energy of certain wavelengths can be absorbed to generate free electrons (negative charges) on one side and holes (positive charges) on another.

• A solar cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon.
• It is a form of photoelectric cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance, vary when exposed to light.
• Solar cells are the building blocks of photovoltaic modules, otherwise known as solar panels.
• Solar cells are described as being photovoltaic irrespective of whether the source is sunlight or an artificial light.
• They are used as a photodetector (for example infrared detectors), detecting light or other electromagnetic radiation near the visible range, or measuring light intensity.

 

Photovoltaic Cell:

• Photovoltaic cells consist of two or more layers of  semiconductor with one layer containing positive charge and the other negative charge lined adjacent to each other.
• Sunlight, consisting of small packets of energy termed as photons, strikes the cell, where it is either reflected, transmitted or absorbed.
• When the photons are absorbed by the negative layer of the photovoltaic cell, the energy of the photon gets transferred to an electron in an atom of the cell.
• With the increase in energy, the electron escapes the outer shell of the atom. The freed electron naturally migrates to the positive layer creating a potential difference between the positive and the negative layer. When the two layers are connected to an external circuit, the electron flows through the circuit creating a current.

 

 

 

Advantages of Photovoltaic Cells:

• Environmental Sustainability: Photovoltaic cells generate clean and green energy as no harmful gases such as Co_x, NO_x etc are emitted. Also, they produce no noise pollution which makes them ideal for application in residential areas.
• Economically Viable: Operation and maintenance cost of cells are very low. The cost of solar panel incurred is only the initial cost i.e., purchase and installation.
• Accessible: Solar panels are easy to set up and can be made accessible in remote locations or sparsely inhabited areas at a lesser cost as compared to conventional transmission lines. They are easy to install without any interference to the residential lifestyle.
• Renewable: Energy is free and abundant in nature.
• Cost: Solar panels have no mechanically moving parts except in some highly advanced sunlight tracking mechanical bases. Consequently, the solar panel price for maintenance and repair is negligible.

 

Disadvantages of Photovoltaic Cells:

• The efficiency of solar panels is low compared to other renewable sources of energy.
• Energy from the sun is intermittent and unpredictable and can only be harnessed in the presence of sunlight. Also, the power generated gets reduced during cloudy weather.
• Long range transmission of solar energy is inefficient and difficult to carry. The current produced is DC in nature and the conversion of DC current to AC current involves the use of additional equipments such as inverters.
• Photovoltaic panels are fragile and can be damaged relatively easily. Additional insurance costs are required to ensure a safeguard to the investments.

 

India’s target towards solar energy:

• Recently, India achieved the third rank globally for solar installation capacity. Mercom India, a clean energy research organsation, has reported that the installed solar photovoltaic (PV) capacity has reached over 28 GW as of December 2018.
• India may have emerged as the third largest market for solar, but a comparison at the global front suggests that India has a long way to go in order to become a solar super power.
• India has a target of installing 100 GW of solar capacity by 2022 and is still 72 GW short of it. To achieve this ambitious goal, a ramping up of the yearly targets is the need of the hour. Yet, the challenges are immense.

 

Challenges in achieving above targets:

• To achieve the 100 GW target, India needs to invest $65 billion in the next four years. A major part of it has to be raised within the country, as the renewable sector could so far attract a foreign direct investment (FDI) worth only $7.5 billion in the last 18 years (2000-2018), according to a report by the India Brand Equity Foundation.
• The factors causing negative growth of the solar sector in CY 2018 — the confusion along the GST and the import duty on solar equipment — are yet to be resolved completely.
• On the domestic manufacturing front, India fares worse. Various efforts by the Solar Energy Corporation of India (SECI) to attract bids for the development of the Inter-state Transmission System (ISTS) connected Solar Photovoltaic (PV) Power Plant since May 2018 has been in vain.
• India needs a more comprehensive approach in order to achieve the targets of 2022 and beyond. Alternate demand has to be generated through open-access platforms in the situation when discoms are violating the Power Purchase Agreements.

Need of solar energy

• Energy security:
  • India energy demands are largely fulfilled by non-renewable source of energy.
  • The scarcity of these fossil resources stresses the need for renewable energy sources.
  • Abundance of solar energy can fulfill India clean energy demands.
  • India is dependent on imports to fulfill its energy demands, thereby incurring huge expenditure and uncertainty with regards to energy security.

 

• Economic development:

  • India being a developing economy needs proper electricity for industrial growth and agriculture.
  • India also needs self sufficiency and minimal cost in power generation, assured regular supply, which will boost industries and economy.

 

• Social development:

  • The problem of power cuts and unavailability of electricity especially in rural area, leads to improper human development.
  • Mostly energy demands are fulfilled by subsidised kerosene, leading to loss for exchequer.

 

• Environment concern:

  • India’s large part of energy demand is fulfilled by thermal energy largely dependent on fossil fuels.
  • It also causes environment pollution
  • Solar energy is clean form of energy resource, which can be a substitute.

 

Technology

• Solar Photovoltaic: Solar photovoltaic (SPV) cells convert solar radiation (sunlight) into electricity. A solar cell is a semi-conducting device made of silicon and/or other materials, which, when exposed to sunlight, generates electricity.
• Solar thermal: Solar Thermal Power systems, also known as Concentrating Solar Power systems, use concentrated solar radiation as a high temperature energy source to produce electricity using thermal route.

 

Government initiatives

• Ministry of new and renewable energy is the nodal agency to tackle India's renewable energy issues.
• National Solar Mission is a major initiative of the Government of India and State Governments to promote ecologically sustainable growth while addressing India's energy security challenge.
• The Indian Renewable Energy Development Agency (IREDA) is a Non-Banking Financial Institution under the administrative control of this Ministry for providing term loans for renewable energy and energy efficiency projects.
• National institute of solar energy is created as autonomous institution under MoNRE is apex body for R&D.
• Establishment of solar parks and ultra major solar power project and enhancing grid connectivity infrastructure.
• Promotion of canal bank and canal tank solar infrastructure.
• Sustainable rooftop implementation of Solar transfiguration of India (SRISTI) scheme to promote rooftop solar power projects in india.
• Suryamitra programme to prepare qualified workforce.
• Renewable purchase obligation for large energy consumer customers.
• National green energy programme and green energy corridor.

 

Source)

https://www.thehindu.com/todays-paper/tp-features/tp-sci-tech-and-agri/improving-solar-cell-performance/article29748094.ece