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Overview of Unit–I: Solar Radiation. Sun as Energy Source. 

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• Nuclear fusion processes
• Solar radiation spectrum

• Pyrheliometer & Pyranometer
• Sunshine recorders

• Forecasting models
• AI & machine learning

• Thermal & battery systems
• Green hydrogen technology

• Working principles
• Applications & types

The Sun as a Source of Energy. Primary Energy Driver. 

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• Sustains Earth's oceans, atmosphere,
land, and biosphere

• Continuous electromagnetic radiation
emission

• Powers climate systems and weather
patterns

Solar Energy Origin: Nuclear Fusion. Fusion Process Location. 

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• Sun's core - extreme conditions
• Temperature: ~15 million Kelvin
• Pressure: 250 billion × Earth's atmosphere

• Hydrogen nuclei (protons) combine
• Form helium atoms
• Releases enormous energy

• Gamma rays
• Neutrinos
• Kinetic energy of particles

41H -+ 4He + 2e+ + 2ve + 2M + 26.7 MeV. The Proton-Proton (p-p) Chain Reaction. 

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• Temperature: ~15 million Kelvin
• Pressure: 250 billion × Earth's atmosphere
• Energy contribution: 99% of Sun's total output

• Four hydrogen nuclei (protons) fuse together
• Forms one helium-4 nucleus plus particles
• Releases gamma rays, neutrinos, and kinetic energy
• Net energy release: 26.7 MeV per reaction

The CNO Cycle and Energy Output. CNO Cycle Process. 

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Earth maintains stable energy balance through equilibrium between
incoming solar radiation and outgoing thermal radiation

• Secondary fusion process in the Sun
• Uses carbon, nitrogen, oxygen as catalysts
• Accounts for less than 2% of solar energy
• More dominant in massive stars
• Converts hydrogen to helium like p-p chain

• Sun's total power: 3.8 × 10²⁶ watts
• Earth receives: 342 W/m² at atmosphere
• Total Earth input: 4.4 × 10¹⁶ watts
• Equivalent to 44 million power plants
• Dynamic energy equilibrium maintained

The Solar Radiation Spectrum. Ultraviolet (UV). Visible Light. 

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Peak wavelength: ~500 nm (green light)
Sun's surface temperature: ~5,778 K

• Wavelength: 100-400 nm
• Energy: ~10%
• Absorbed by ozone layer

• Wavelength: 400-700 nm
• Energy: ~40%
• Drives photosynthesis

• Wavelength: 700 nm - 1 mm
• Energy: ~50%
• Thermal heating

Aphelion perihelion. Extraterrestrial Solar Radiation. 

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Total Solar Irradiance (TSI) at top of Earth's
atmosphere

• ±0.1% variation due to Earth's elliptical orbit
• Maximum at perihelion (early January)
• Minimum at aphelion (early July)

• ±0.3% variations from solar cycles
• Linked to 11-year sunspot cycle
• Affects long-term climate patterns

Atmospheric Effects: Scattering. Rayleigh Scattering. 

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• Affects shorter wavelengths (blue
and violet light)

• Caused by interaction with small
molecules

• Responsible for blue color of the
sky

• Caused by larger particles (dust,
water droplets)

• Responsible for white appearance
of clouds

• Increases diffuse radiation at
surface

Both scattering processes increase diffuse radiation and contribute to
the ~30% reduction in total solar radiation reaching Earth's surface

Atmospheric Effects: Absorption and Reflection. Key Absorbing Components. 

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Atmospheric Effects: Absorption and Reflection

Net Effect: ~30% reduction in solar
radiation reaching Earth's surface

• Ozone (O₃): Absorbs UV radiation
(200-300 nm)

• Water Vapor (H₂O): Absorbs infrared
(600-800 nm, 1200-1800 nm)

• Carbon Dioxide (CO₂): Absorbs at
1400-1600 nm, 2000-2500 nm

• Oxygen (O₂): Absorbs at 760 nm and
1270 nm regions

• Clouds: Reflect up to 90% of incoming
radiation

• Aerosols: Reflect or absorb based on
composition

• Earth's Surface: Variable albedo effects

Direct Beam Radiation Diffuse Sky Radiation Global Horizontal Irradiance (GHI). 

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Direct Beam
Radiation
Diffuse Sky
Radiation
Global Horizontal
Irradiance (GHI)

Solar radiation reaching Earth's surface
consists of three distinct components:

Solar rays traveling directly from the sun in
straight lines without atmospheric scattering

Scattered solar radiation from molecules,
aerosols, and clouds in the atmosphere

Total solar radiation received on a horizontal
surface - combination of direct beam and diffuse
radiation

Measurement of Solar Radiation:
Overview. Key Applications. 

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Accurate solar radiation measurement is essential
for scientific research and practical applications

• Meteorology & climate
science
• Solar energy system design
• Weather prediction models

• Direct beam radiation
• Global horizontal irradiance
• Sunshine duration

• Optimize energy generation
• Grid integration planning
• Resource assessment

Instrument: The Pyrheliometer. Key Features & Function. 

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• Measures direct normal solar irradiance
• Uses thermopile sensor technology
• Requires sun-tracking mount alignment
• Essential for CSP system assessment
• Output calibrated in W/m²

• Solar radiation enters through quartz window
• Absorbed by blackened sensor surface
• Temperature difference generates voltage
• Voltage proportional to solar irradiance

Output Voltage. Instrument: The Pyranometer. Function & Purpose. 

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• Measures global horizontal irradiance (GHI)
• Captures direct beam + diffuse sky radiation
• Used in meteorology & solar energy assessment

• Thermopile sensor under glass dome
• Blackened sensor surface for heat absorption
• Reference surface for temperature comparison

• Spectral range: 0.3–3.0 µm
• Output: Voltage proportional to irradiance
• Requires level installation & regular cleaning

Instrument: The Sunshine Recorder. Traditional Types. 

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Measures duration of sunshine when direct solar irradiance exceeds 120 W/m²

• Glass sphere focuses sunlight onto
recording card
• Creates burn trace indicating sunshine
duration

• Small aperture projects sunlight onto
photosensitive paper

• Three photovoltaic cells (one shaded,
two on southeast/southwest faces)

• Calculates direct irradiance by
comparing outputs

Planning Prediction Optimization. Prediction of Available Solar Radiation. 

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• Enables efficient energy planning and operational control
• Critical for grid integration of variable solar resources

• Supports better economic decision-making
• Optimizes solar power generation schedules

• Improves reliability of solar energy supply
• Facilitates maintenance and resource allocation

Forecasting Models: Statistical and Physical. Statistical Models. 

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Forecasting Models: Statistical and Physical

• ARIMA (AutoRegressive Integrated Moving
Average)

• Struggle with non-linear solar irradiance

Advanced Forecasting:
AI and Machine Learning. Key AI/ML Technologies. 

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Advanced Forecasting:
AI and Machine Learning

• Artificial Neural Networks (ANN) & Support Vector
Machines (SVM)

• Convolutional Neural Networks (CNN) for spatial features

• Long Short-Term Memory (LSTM) for temporal sequences

• CNN-LSTM hybrids with attention mechanisms

Traditional Models: 0.12-0.18
AI/ML Models: 0.08-0.12
Deep Learning: 0.07-0.09
CNN-LSTM Hybrid: 0.076

• Reduce prediction errors by up to 50%

• Excel at non-linear pattern recognition

• Capture temporal dependencies effectively

Data Integration and Hybrid Approaches. Satellite Imagery. 

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• CNN-A-LSTM model:
nRMSE = 0.076
• 25% error reduction in
cloudy conditions
• Enhanced accuracy
and robustness

• Data assimilation
techniques
• Big data analytics
• Cloud computing
integration

Example: National Solar Radiation Database (NSRDB)

Importance of Solar Energy: Environmental Impact. 

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Importance of Solar Energy: Environmental Impact

• Produces no greenhouse gases during operation
• Most effective technology for reducing CO₂ emissions in
electricity sector

• IPCC projects solar could supply over 30% of global
electricity by 2050
• Critical for limiting global warming to 1.5°C (Paris Agreement)

• Significantly reduces air pollution from fossil fuel combustion
• Mitigates health and environmental impacts of coal and gas

Solar Energy: Energy Access and Economics. Energy Access for Off-Grid
Communities. 

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Solar Energy: Energy Access and Economics

Solar energy has transformed from an expensive alternative to
one of the most cost-effective electricity sources globally

• Bangladesh Solar Home Systems: 4
million households

• Kenya M-KOPA systems: 1 million
homes

• Improved lighting, communication,
and healthcare

• Global solar jobs: 4.9 million (2022)

Solar Collection Molten Salt Storage Power Generation. 

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Solar
Collection
Molten Salt
Storage
Power
Generation

• Sodium nitrate &
potassium nitrate
mixtures

PptxGenJS Presentation

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