Alternative Energy Chapter 9

Chapter 9: Alternative Use of Energy

• Alternative energy sources are non-depleting or renewable energy sources.
• Examples of alternative energy sources include solar and wind power, while conventional energy sources like natural gas, coal, and oil are considered alternative at different times in history.
• Government funding and tax incentives for alternative energy research and development (R&D) decreased significantly in the 1980s and early 1990s.

9.1 Solar Thermal Systems

• This section covers solar thermal systems, including:
  • Introduction
  • Solar Irradiance
  • Solar Thermal Collectors
  • Thermal Storage Systems

Solar Irradiance (Distribution)

• The Middle East and North Africa (MENA) region receives the highest solar irradiance globally.
• Mapping of solar irradiance is used to visualize the variation of solar energy.

Solar Irradiance (Orientation)

• To maximize solar energy collection, the orientation of collectors should be perpendicular to the solar radiation.
• The angle of the sun's path over the course of a day and throughout the year affects the angle at which solar panels need to face the sun to be most effective.

Solar Irradiance (Numerical Facts)

• Solar energy arrives at Earth's atmosphere at a rate of approximately 1353 W/m² (428 Btu/hr ft²).
• This value is known as the solar constant.
• Only about two-thirds of solar radiation reaches Earth's surface due to atmospheric reflection, absorption, and scattering.
• Noontime solar radiation at 40° north latitude is typically approximately 946 W/m² (300 Btu/hr ft²) on a clear day.

Solar Thermal Collectors

• Solar Thermal Collectors are categorized into two types:
  • Non-concentrating collectors:
    • Flat plate collectors
    • Evacuated tube collectors
    • Volumetric air collectors
  • Concentrating collectors:
    • Parabolic Trough
    • Compound Parabolic Concentrator (CPC)
    • Fresnel
    • Solar Power Tower
    • Solar Dish Stirling Engine

Flat Plate Collectors

• Typically used for applications requiring relatively low temperatures (below 120°C).
• The collector is usually oriented towards the south to maximize solar energy capture.
• The collector heats a fluid (like air or water) which can be used for various applications.

Evacuated Tubes (Vacuum Tubes)

• Similar in concept to flat plate collectors.
• The glass tube allows solar radiation and traps heat generated from solar radiation, preventing loss through convection.

Volumetric Air Collectors

• Offers benefits over liquid collectors, including:
  • Resistance to freezing
  • Less damage from leaks
  • Decreased likelihood of corrosion

Parabolic Trough

• Collectors operate within a temperature range of 250–450°C.
• They use concentrating collectors that capture relatively high temperatures for applications like power generation.
• The systems need to track the precise movement of the sun to optimize radiation capture.

Compound Parabolic Concentrator (CPC)

• Uses multiple smaller flat mirrors arrayed in a specific shape to concentrate solar radiation.
• Is simpler and less costly than parabolic troughs

Fresnel collectors

• Similar to parabolic trough collectors, they use numerous flat mirrors
• A less sophisticated design, easier to maintain and cheaper than parabolic systems

Solar Power Tower

• The system uses multiple two-axis tracking mirrors to direct sunlight towards a central receiver.
• Molten salt is used as a coolant for the heat storage.

Solar Dish Concentrator

• Direct solar energy conversion occurs at the receiver.
• Uses a generator that directly produces AC power

Thermal Storage Systems

• The demand for solar energy is typically inconsistent throughout the day and throughout the year.
• System components store the captured and processed or heated solar energy output.
• Heat storage systems are an essential part of solar heating and cooling systems.
• Air-type collectors use rock beds, while water tanks are more common in liquid systems.
• Systems may need antifreeze in the event of freezing temperatures.

Solar Cells (Photovoltaics)

• Solar cells use semiconductor materials to convert sunlight directly into electricity.
• Most solar cells are made up of p-n junctions which are large areas composed of very large area of p-n junction diodes.
• Different solar cell types exist, with varying efficiencies and characteristics

Wind Energy

• Wind is a form of solar energy arising from the uneven heating of the atmosphere, irregularities of the earth, and rotation of the earth.
• Wind energy is "harvested" by modern wind turbines for electricity generation

Wind Calculations

• Factors affecting wind energy include:
  • Air density: Affected by altitude and temperature
  • Swept area of turbine: A = πr2 (r=rotor blade length). Larger swept areas capture more energy.
  • "Cube" of wind speed: Wind power potential scales with the cube of wind speed.

Wind Turbine Types

• Modern wind turbines are categorized into:
  • Horizontal-axis turbines: Propeller-like blades. The most common type.
  • Vertical-axis turbines: Eggbeater-like design.

Turbine Components

• Components of wind turbines include:
  • Blade or rotor: Converts wind energy to rotational energy
  • Drive train: Gearbox and generator
  • Tower: Supports the rotor and drive train
  • Other equipment: Controls and interconnection equipment