Solar Radiation and Irradiance

• Radiation originates from the Latin word "radiare," meaning "to emit rays."
• Solar radiation refers to electromagnetic waves of light from the Sun.
• The three major types of solar radiation are visible light, infrared light, and ultraviolet light.

Understanding Solar Irradiance

• Solar irradiance is the amount of energy from the Sun that enters the Earth as radiation or sunlight.
• Solar irradiance is measured in watts per square meter (W/m²) or kilowatt hours per square meter (kWh/m²).
• A solar irradiance map shows the amount of incoming solar radiation absorbed over a year, measured in kilowatt hours per square meter.

Sun Spectrum

• The electromagnetic spectrum consists of radio waves, microwaves, infrared, visible light, ultraviolet light, X-rays, and gamma rays, ordered from lowest to highest frequency.
• Solar radiation includes infrared, visible, and ultraviolet light.
• Visible light is the portion of solar radiation most perceptible to humans.
• Visible light ranges from red (lowest frequency) to violet (highest frequency).
• Infrared light is below red light, while ultraviolet light is beyond violet light; both are invisible to the human eye, though some animals can see them.

Types of Solar Radiation

• Solar radiation types are categorized by frequencies and wavelengths.
• The sun emits mostly visible light.
• The sun emits ultraviolet (UV) light, which is partially blocked by the atmosphere.
• The sun emits infrared light, much of which reaches Earth's surface, except for specific wavelengths absorbed by the atmosphere.

Infrared Rays

• Infrared rays have lower frequencies than visible light and higher frequencies than microwaves.
• Infrared light wavelengths range from 2.5 micrometers (um) to 750 nanometers (nm).
• Infrared light is felt as warmth.

Visible Rays

• Visible light is detectable by the human eye.
• Visible light has higher frequencies than infrared light and lower frequencies than ultraviolet light.
• Visible light wavelengths range from approximately 400-750 nanometers.
• Red light has a wavelength of around 700 nm, orange around 600 nm, yellow around 550 nm, green around 500 nm, blue around 450 nm, and purple around 400 nm.

Ultraviolet Rays

• Ultraviolet (UV) rays have higher frequencies than visible light.
• UV light wavelengths range from about 1-400 nanometers.
• UV-A (above 300 nm) is generally harmless.
• UV-B and UV-C (below 300 nm) can damage human cells, causing sunburns and skin cancer.

Effect on Earth

• Solar emissions are the radiation that leaves the Sun, while incoming solar radiation is what enters the Earth's atmosphere.
• Incoming solar radiation warms the planet and maintains livable temperatures.
• Without the Sun, Earth's temperature would be approximately 300 degrees Celsius colder.
• Earth's seasons are due to its tilt, not variations in sunlight amount or distance from the Sun.
• The angle at which sunlight strikes the ground affects its potency and energy density, influencing the seasons.
• The "greenhouse effect," where the atmosphere absorbs outgoing infrared radiation, also affects Earth's temperature.
• Increased greenhouse gases in the atmosphere trap extra energy, leading to a warmer Earth.