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Comprehensive Notes on Solar Power

Solar Power by Dr. E. Melchiorre, CSUSB

Introduction to Solar Energy

  • Solar power is the most abundant energy source on Earth's surface.
  • Solar energy availability significantly exceeds hydrocarbon availability.
  • Photovoltaic (PV) systems, also known as solar cells, convert light energy into electricity.
  • PV systems power small devices like calculators and watches.
  • More complex systems provide electricity for:
    • Pumping water
    • Powering communications equipment
    • Lighting homes
    • Running appliances
  • PV power is often the cheapest form of electricity for certain tasks.

Challenges and Advantages of Solar Energy

  • Challenges:
    • Solar energy is diffuse, requiring collection and conversion.
    • Energy and materials are needed for manufacturing PV systems.
  • Advantages:
    • Produces no CO_2 emissions.
    • Requires no fuel.
    • Panels are recyclable.

How Photovoltaic Cells Work

  • Photovoltaic cells convert light to direct current (DC) electricity at the atomic level.
  • The process was first discovered in 1839, but the underlying principles weren't understood for over a century.
  • The term "photovoltaic" originates from:
    • "Phos": Greek for light
    • "Volt": Named after Alessandro Volta (1745-1827), a pioneer in electricity study.

History and Reliability

  • The modern photovoltaic cell was developed in 1954.
  • By 1958, PV cells were powering U.S. spacecraft.
  • Some early space-based systems are still operational, demonstrating the technology's reliability and durability exceeding 30 years.

Applications of Photovoltaics

  • Military applications, such as recharging radios, night-vision goggles, and remote sensors using solar panels.
  • Rigid and flexible solar panels exist to suit various needs.

PV Cell Components and Materials

  • A typical solar cell consists of:
    • Cover glass: Protects against weather.
    • Anti-reflective layer: Reduces light reflection.
    • Front contact: Collects electrons and transfers them to the external load.
    • Semiconductor layers: Where electron current is generated.
  • Various materials are used for the semiconducting layers, each with pros and cons.
  • Expected lifespan of PV modules exceeds 30 years.

Silicon in Solar Cells

  • Most solar cells are made of silicon semiconductor material.
  • Silicon-related terms:
    • Silicon: The element.
    • Silica: Silicon and oxygen compound.
    • Silicate: Group of minerals based on silica tetrahedra.
    • Silicone: Organic polymer used for caulking and prosthetics.
  • Silicon in solar cells undergoes doping.

Doping Silicon for Conductivity

  • N-type Silicon:
    • Doped with phosphorus, which has extra free electrons.
    • "N" stands for negative, referring to the prevalence of negative charge carriers (electrons).
    • N-type silicon is a much better conductor than pure silicon.
  • P-type Silicon:
    • Doped with boron, which has only three electrons in its outer shell instead of four, creating “holes”.
    • "P" stands for positive, referring to the prevalence of positive charge carriers (holes).
  • When N-type and P-type silicon are joined, an electric field is generated.
    • Free electrons from the N side migrate to fill the holes on the P side.

Types of Silicon Solar Cells

  • Single Crystal:
    • Oldest and most expensive.
    • Most efficient.
    • Made from large, single synthetic crystals.
    • Uniform blue color.
  • Multicrystalline:
    • Cheaper to make than single crystal cells.
    • Less efficient, requiring more cells to produce the same power.
    • Patchwork blue colors.
  • Amorphous:
    • Cheapest type.
    • Least efficient.
    • Silicon vapor is plated on glass or steel.
    • Black color.

Photovoltaic Systems

  • PV modules only produce electricity when the sun is shining.
  • Storage batteries are often required for applications needing electricity at night.
  • A PV system consists of:
    • PV modules
    • Wiring
    • Charge controllers
    • Switches
    • Electrical protective components
  • If the load requires alternating current (AC), an inverter is used to convert direct current (DC) power to AC.

PV Mounts and Tracking

  • PV cells can be mounted on:
    • Fixed mounts: Point in one direction for maximum solar exposure.
    • Tracking mounts: Follow the sun throughout the day.
  • Tracking mounts can yield:
    • 40% more energy in the summer
    • 15% more energy in the winter
  • Tracking systems reduce the number of solar cells needed but increase system cost.
  • Fixed mounts can be placed on south-facing roofs, on the ground, or on poles.

Real-World Example: The Navajo Nation

  • The Navajo Nation covers 25,000 square miles across Arizona, New Mexico, and Utah.
  • Photovoltaic (PV) systems have been used by the Navajo Nation since 1978.
  • Over 1000 systems have been installed.
  • The Navajo Tribal Utility Authority (NTUA) provides power to residents.
  • NTUA uses PV systems to electrify remote residences where extending utility lines is not economical due to the reliability and low maintenance requirements of PV systems.

Innovative Solar Applications

  • Camel Fridge: Solar-powered refrigerator to transport vaccines to remote villages.
  • SolaRoad: Bike path in Krommenie, Netherlands that converts sunlight into electricity.
    • 75 feet of bike path can provide all the electricity needed for a home.
    • Households, schools, and businesses can become co-owners of a SolaRoad section, contributing to sustainable energy.
    • SolaRoad produces sustainable power for street lighting.
    • Can charge electric bikes along the road. Every square meter provides enough energy to annually charge 100 (500 kwh) batteries.
    • SolaRoad produces electricity for electric cars and buses and may eventually charge cars while driving.

Global Solar Production

  • Top 5 Countries by Solar Energy Production (2019):
    • China: 306.9 GWh
    • United States: 95.9 GWh
    • Japan: 74.2 GWh
    • Germany: 58.5 GWh
    • India: 49.7 GWh
  • Refer to the Global Solar Atlas for detailed solar resource data.

Passive Solar Design

  • Passive solar buildings are "climate responsive" buildings.
  • Concepts are relatively simple.
  • A properly sized array of insulating, south-facing windows can add significant solar energy.
  • Skylights and specially designed openings can provide daylighting.

Types of Passive Solar Design

  • The four principal types are:
    1. Direct gain systems
    2. Mass-wall systems
    3. Solar greenhouse systems
    4. Daylighting systems

Direct Gain Systems

  • Utilize south-facing windows of appropriate size.
  • Interior surfaces contain materials with extra heat storage capacity, such as:
    • Block
    • Brick
    • Concrete
    • Water containers
  • Sunlight is directly admitted to and stored in indoor spaces for later heating.

Mass-Wall Systems

  • Employ indirect solar gain.
  • Utilize a concrete block or brick wall behind south-facing insulating glass.
  • Sunlight transmits through the glazing, heating the mass-wall.
  • Stored heat is used later.
  • Mass-walls are typically designed with windows to provide natural light to rooms behind them.

Solar Greenhouse Systems

  • Use many large windows for maximum solar gain.
  • Can be fitted to a building's exterior or integrated into the design as a room.
  • Should have sufficient heat storage mass to reduce overheating, provided by an insulated floor slab.

Daylighting

  • Can reduce electric lighting demand by up to 90%.
  • Rooftop skylights and "sun pipes" are designed to admit light without irritating glare or unwanted solar heat.
  • Daylighting can reduce cooling demand by minimizing the byproduct heat of electric lighting.
  • Skylights admit light to interior rooms lacking exterior walls for windows.

Green Strategies - Rocky Mountain Institute (Snowmass, Colorado)

  • Ground-coupled Systems: Use earth sheltering.
  • Solar Cooling Loads: Properly orient the building.
  • Daylighting for Energy Efficiency: Use south-facing windows for daylighting.
  • Hot Water Loads: Use water-efficient showerheads.
  • Water Heaters: Use solar water heaters.
  • Lamp Ballasts: Use automatic-dimming electronic fluorescent lamp ballasts in conjunction with daylighting.
  • High-performance Windows and Doors: Optimize energy performance of glazing systems.
    • Use superwindows with a whole-unit U-factor less than 0.25 (greater than R-4.0).
  • Heating Systems: Use sunspace passive solar heating.
  • Air Infiltration: Use air lock entries.
  • Refrigerators and Freezers: Use a high-efficiency refrigerator.