Lecture 4 Notes: Solar Resources and Photovoltaic Systems Fundamentals

The Sun and Its Radiation

  • Composed of mainly Hydrogen and Helium, with various other elements.

  • Core temperature: nearly 2727 million ºF (15 million ºC).

  • Nuclear fusion occurs in the core, where Hydrogen converts to Helium.

Radiation Spectrum

  • Solar radiation includes:

    • 6.6%6.6\% UV rays (less than 380380 nm)

    • 44.7%44.7\% visible light (380380–780780 nm)

    • 48.7%48.7\% infrared (IR) rays (more than 780780 nm)

Global Insolation

  • Solar Irradiance: Power of solar radiation per unit area (W/m²).

  • Solar Irradiation: Energy over time (kWh/m²).

  • Insolation: Average daily solar radiation (kWh/m²/day).

Direct and Diffused Radiation

  • Direct Radiation: Unobstructed sunlight reaching Earth.

  • Diffused Radiation: Sunlight scattered by the atmosphere.

  • Total solar radiation = Direct + Diffused.

Solar Resources Definitions

  • GHI: Global Horizontal Irradiance – total rays on a horizontal surface.

  • DNI: Direct Normal Irradiance.

  • DHI: Diffused Horizontal Irradiance.

  • Ground-reflected radiation: from Earth's surface, measured via albedo.

  • GTI: Global Tilted Irradiance – total on a tilted surface.

Atmospheric Effects

  • Solar output variability due to weather conditions (rain, dust, etc.).

Earth's Radiative Equilibrium

  • Condition when energy entering = energy exiting Earth, known as the energy budget.

Air Mass Index

  • Air Mass: Volume of air with uniform temperature and moisture.

  • Air Mass Index (AM): Path length of sunlight through the atmosphere.

  • Calculated by AM=1/cos(z)AM = 1/cos(z), where zz is the zenith angle.

Solar Constant

  • Solar energy received per unit area at 1 AU: 1.3661.366 kW/m².

Peak Sun Hour (PSH)

  • Number of hours when average GHI =1000= 1000 W/m², measured in kWh/m² per day.

Sun Angles

  • Zenith Angle (z): From the zenith to the sun.

  • Solar Elevation Angle (α): From the horizon to the sun.

Sun Path Diagrams

  • Used to represent sun position at various times; crucial for PV design.

  • Unique for each geographical location.

PV Module Orientation

  • Optimal facing: South (Northern hemisphere) or North (Southern hemisphere)

  • Tilt angle equals the geographical latitude; adjust for seasons.

Site Assessment Requirements

  • Ensure adequate sunlight exposure, no shading, pollution control.

  • Considerations for residential and commercial systems vary.

  • For solar farm: Comprehensive surveys, resource availability, and feasibility studies are critical.