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.