UNIT 2: Solar Energy

Rajasthan Polytechnic (BTER) March 07, 2025

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UNIT 2: Solar Energy

Solar energy is one of the most important and abundant renewable energy sources. It harnesses the power of the sun to generate electricity, provide heating, and drive various applications. Let's explore each topic in detail, breaking down the key concepts related to solar energy.

2.1 Solar Radiation

Solar radiation is the energy emitted by the sun in the form of electromagnetic waves. This radiation is the primary source of energy for life on Earth and is crucial for solar power generation.

  • Sunlight Spectrum: Solar radiation consists of visible light, ultraviolet (UV), and infrared (IR) radiation.

    • Visible Light: The portion of the electromagnetic spectrum that can be seen by the human eye.
    • Infrared Radiation: Responsible for heating.
    • Ultraviolet Radiation: Can cause damage to living organisms but also helps in Vitamin D production.

  • Solar Constant: The amount of solar energy that reaches the Earth's outer atmosphere is approximately 1361 W/m². This value is called the solar constant.

  • Solar Energy on Earth: Only a fraction of the solar radiation that reaches the Earth’s surface is used for energy generation, as it is influenced by factors like the Earth's atmosphere, cloud cover, and latitude.

Diagram: A simple graph showing the solar spectrum with the intensity of various types of radiation (visible, infrared, UV).

2.2 Measurements of Solar Radiation

To harness solar energy effectively, it is essential to measure solar radiation accurately. There are different instruments used to measure solar radiation.

  • Pyranometer: Measures the global solar radiation received on a flat surface. It gives data about both direct and diffuse solar radiation.

  • Pyrheliometer: Measures only the direct solar radiation from the sun. It is used to assess the intensity of sunlight that hits a surface.

  • Sunshine Recorder: Measures the duration of sunlight over a given period. It helps in understanding the total sunshine hours available.

  • Solar Radiation Sensors: These sensors are used in solar power plants to monitor the intensity of sunlight and adjust the power generation accordingly.

Diagram: Illustration showing different instruments like Pyranometer and Pyrheliometer.

2.3 Flat Plate and Concentrating Collectors

In solar thermal systems, collectors are used to capture solar energy and convert it into heat.

  • Flat Plate Collectors: These are the most commonly used collectors in solar water heating systems.

    • Structure: They consist of a flat, dark-colored plate that absorbs sunlight, which is then transferred to a fluid (water or air).
    • Advantages: Simple, cost-effective, and reliable for heating water and air.
    • Applications: Residential water heating, space heating, etc.

  • Concentrating Solar Collectors: These systems use mirrors or lenses to concentrate sunlight onto a small area, increasing the intensity of sunlight to produce high-temperature heat.

    • Types: Parabolic troughs, heliostats, and dish collectors.
    • Applications: Power plants for large-scale electricity generation.

Diagram: Comparison of flat plate collector vs. concentrating collector.

2.4 Solar Direct Thermal Applications

Solar direct thermal applications use the heat from the sun directly for various heating purposes without converting it into electricity.

  • Solar Water Heating: Flat plate and evacuated tube collectors are commonly used for domestic and industrial hot water production.

  • Solar Space Heating: Solar energy is used to heat homes or commercial buildings, reducing the need for conventional heating systems like gas or electricity.

  • Solar Cooking: Solar cookers use concentrated sunlight to cook food. These are used in rural areas and regions with abundant sunlight.

  • Solar Drying: Drying food, clothes, and other materials using solar heat is an energy-efficient way to dry items without using electricity.

Example: Solar water heaters used in homes, swimming pools, and industries to reduce energy consumption.

2.5 Solar Thermal Power Generation

Solar thermal power generation involves using solar energy to produce electricity through the conversion of solar heat into mechanical energy, which drives a generator.

  • Working Principle: Solar thermal power plants use mirrors or lenses to concentrate sunlight onto a receiver, where it heats a fluid (often oil or molten salt). The heated fluid then drives a steam turbine connected to an electricity generator.

  • Types of Solar Thermal Power Plants:

    • Parabolic Trough Systems: Large, curved mirrors concentrate sunlight onto a receiver tube.
    • Solar Power Towers: A large field of mirrors (heliostats) focuses sunlight onto a central receiver.
    • Dish Stirling Systems: Parabolic dishes concentrate sunlight onto a Stirling engine for electricity generation.

  • Advantages:

    • Can be integrated with thermal storage to provide electricity even when the sun isn't shining.
    • High efficiency for large-scale power generation.

Diagram: Flow diagram showing the process of solar thermal power generation using parabolic troughs or solar power towers.

2.6 Fundamentals of Solar Photovoltaic Conversion

Photovoltaic (PV) conversion refers to the process of converting sunlight directly into electricity using solar cells made of semiconductor materials.

  • Working Principle: When sunlight strikes the surface of a solar cell, it excites electrons in the semiconductor material, creating an electric current.

    • Semiconductor Material: Silicon is the most commonly used material in solar cells.
    • Photons from sunlight excite electrons, causing them to flow through the semiconductor and generate electricity.

  • Efficiency: The efficiency of PV cells depends on factors like the type of material used, the angle of the panel, and the intensity of sunlight.

Example: A typical solar calculator works using the principle of photovoltaic conversion to generate power directly from sunlight.

2.7 Solar Cells

Solar cells are the basic building blocks of photovoltaic systems, designed to convert solar radiation into electrical energy.

  • Structure: A solar cell is made of a semiconductor layer (typically silicon), with a positive and negative layer, creating an electric field.

  • Types of Solar Cells:

    • Monocrystalline: Made from a single silicon crystal. They are highly efficient but expensive.
    • Polycrystalline: Made from silicon crystals melted together. They are less efficient but cheaper.
    • Thin-Film Solar Cells: Made by depositing thin layers of semiconductor materials onto a surface. They are flexible and lightweight but less efficient.

  • Efficiency: Monocrystalline cells have the highest efficiency (~18-22%), while thin-film cells have the lowest (~10-12%).

Diagram: Structure of a typical silicon solar cell showing the positive, negative layers, and the electric field.

2.8 Solar PV Power Generation

Solar Photovoltaic (PV) power generation refers to generating electricity by converting sunlight directly into electricity using solar cells connected in series and parallel to form solar panels.

  • System Components:

    • Solar Panels: Multiple solar cells connected together to form a panel.
    • Inverters: Convert DC (Direct Current) electricity from the panels into AC (Alternating Current) electricity for home and grid use.
    • Battery Storage: Store excess electricity for use when sunlight is not available (optional).

  • Grid-connected Systems: PV systems are often connected to the electricity grid to supply power during the day and draw power at night.

  • Off-grid Systems: Solar power is used independently in remote areas where there is no electricity grid connection.

Example: Rooftop solar panels on homes and offices to generate electricity for domestic use.

2.9 Solar PV Applications

Solar photovoltaic technology has a wide range of applications, from residential to commercial to industrial.

  • Residential Applications:

    • Solar Home Systems: Provide electricity for lighting, appliances, and other domestic needs.
    • Solar Water Pumping Systems: Used in rural and agricultural sectors for water supply.

  • Commercial Applications:

    • Solar Roofs and Solar Farms: Large commercial buildings and farms use solar panels to generate electricity.

  • Industrial Applications:

    • Solar-Powered Factories: Solar energy can power factories, reducing dependence on the grid and lowering electricity costs.
    • Off-grid Applications: Solar panels are used in remote areas for powering water pumps, communication towers, and other essential services.

Example: A large solar farm in the desert generating electricity for a city or an off-grid solar-powered water pumping system for irrigation.

Conclusion

Solar energy is a highly promising renewable energy source that is widely used for both direct thermal applications and photovoltaic electricity generation. It offers a clean, sustainable solution to many of the world's energy challenges. By understanding the fundamentals of solar radiation, solar cells, thermal power generation, and photovoltaic systems, we can effectively harness solar energy to power homes, industries, and entire cities.

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Rajasthan Polytechnic (BTER)

Posted by Rajasthan Polytechnic (BTER)

Hi! I’m Garima Kanwar, founder of Rajasthan Polytechnic (BTER). This platform provides notes, PDFs, and video lectures for all Polytechnic branches (ME, CS, EE) and semesters to make learning easy .I ensure exam-focused, updated, and simple-to-understand content, along with academic updates and career guidance.

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