Renewable Energy Quiz: Solar & Wind Power

Fossil Fuel Problems

• Burning fossil fuels causes air pollution, water pollution, and soil pollution.

Solar Radiation

• The sun is the source of all forms of energy.
• Sunlight intensity at the Earth's surface is approximately one thousand watts per square meter.

Solar Energy

• Solar energy refers to energy produced by the sun.
• It is also known as solar power and is radiant energy.
• Solar energy can be directly or indirectly converted into other forms of energy, such as heat and electricity.
• Solar energy is divided into two classes:
  • Direct thermal applications (e.g., heli-electrical, heli-thermal processes)
  • Indirect thermal applications (e.g., biomass energy, wind energy, tidal energy, ocean thermal energy, etc.)

Helio-Electrical Process

• Solar cells convert sunlight into electricity using the photovoltaic effect.
• Solar cells are semiconductor devices that release electric charges which flow through an electric load (like a light bulb).
• The photovoltaic effect is a physical and chemical phenomenon.
• A light-sensitive semiconductor in a solar cell converts visible light into voltage or direct current.

Silicon Doping

• Silicon is a tetravalent material with four valence electrons.
• Doping silicon with pentavalent materials (like arsenic, phosphorus) creates N-type semiconductors.
• Doping silicon with trivalent materials (like boron) creates P-type semiconductors.
• When a P-N junction of semiconductor is exposed to sunlight, a voltage around 0.5 volts is created and current is produced.
• Current production depends on the exposed area of the cell.

Photovoltaic Cells

• Photovoltaic cells are devices whose electrical characteristics such as current, voltage, and resistance vary when exposed to light.
• Silicon solar cells are important for converting photon radiation into electrical power, particularly in space programs.

Solar Photovoltaic Conversion

• Solar cells convert solar radiation directly into DC electricity.
• Solar cells have advantages like needing few moving parts, low maintenance, and satisfactorily working with beam or diffuse radiation, adaptable to varying power requirements.
• Limitations include low efficiency, intermittent solar energy, and cost.
• Most commercial solar cells are single crystal or multi-crystalline silicon cells.

PV Technology Applications

• PV technology is used in space satellites, remote radio communication booster stations, marine warning lights, lighting purposes, powering household appliances, powering handheld devices, water pumping (irrigation), streetlights, and solar powered vehicles and battery charging.

Flat Plate Collectors

• Flat plate collectors transform solar energy into thermal energy using fluids such as water, air, or ethylene glycol.
• They are simple in construction and do not require tracking.
• These collectors are usually installed outside and are exposed to atmospheric disturbances.

Flat Plate Collector Components

The construction of a flat plate collector has these five principal parts:

• Absorber plate (usually metal with a high absorptance coating).
• Tubes fixed to absorber plate.
• Transparent cover (glazing).
• Collector box (metal enclosure).
• Insulation (on the container sides to reduce heat losses).

Flat Plate Collector Operation

• Incident radiation on the collector is not fully absorbed; part is reflected back to the glass cover.

Flat Plate Collector Characteristics

• A typical flat plate collector is a metal box with a glass or plastic cover (glazing) atop a dark-colored absorber plate.
• The sides and bottom are insulated to minimize heat loss.

Absorber Plate Role

• Absorbs as much incident solar radiation as possible.
• Minimizes heat loss from the absorber to the atmosphere.
• Transfers maximum heat to the fluid.

Cover System

• The cover should be transparent to incoming solar radiation and opaque to re-radiated infrared energy.
• Commonly made of toughened glass (4-5mm thick).

Insulation and Collector Box

• Bottom and sides are insulated with mineral wool, rock wool, or glass wool coated with aluminum foil (thickness 2.5 to 8cm).
• Usually a box shape, tilted at a suitable angle.
• Collector boxes are frequently made of aluminum, with an epoxy coating for protection.
• The collectors are generally around 2m² with a length longer than the width.

Flow Passages

• Working fluids (liquid or air) flow through passages in the collector.
• For liquid, tubes attach directly to the heat absorber plate.
• For air, passage configurations may vary.

Cover Plate (Glazing)

• One or two transparent covers (glazing) are usually placed above the absorber plate.
• This reduces convective and radiative heat losses from the absorber.
• Commonly made from glass or plastic.

Insulation

• Materials like fiberglass are placed on the back and sides of the collector to decrease heat losses.

Enclosure

• The enclosure is a box that holds all components together and protects them from weather, facilitating convenient roof- or frame-based installations.

Water Heating Applications

• Flat plate collectors are used in water heating systems, along with a solar heat exchanger, an automatic controller, an existing pump and filter, and, optionally, a gas heater or heat pump.

Wind Energy

• Wind power (or wind energy) is the use of wind to generate mechanical power through wind turbines.
• Wind power is a sustainable and renewable energy source, utilizing wind's kinetic energy.

Wind Generation

• Wind results from atmospheric pressure gradients, causing wind to move from high-pressure to low-pressure regions.
• Wind's strength is directly related to the atmospheric pressure gradient.
• Wind energy-converting machinery captures wind power.

Wind Turbine Structure and Function

• Wind turbines consist of multiple blades radiating from a central hub or axis.
• When the wind blows against the blades, they spin, converting wind's kinetic energy into mechanical work.
• The mechanical energy drives a generator to create electricity.
• Amount of power depends on rotor size and wind speed.
• Blades of FRP (GFRP/CFRP) material.

Wind Turbine Function

• The wind turbine rotor spins, driving the shaft, and converts kinetic energy into mechanical energy.
• The energy is then converted into electrical energy by a generator.

Wind Turbine Components

• Blades, hub, rotor, gearbox, generator, control system, yaw drive, tower, foundation, cover plate, and insulation.
• The automatic yaw mechanism ensures the rotor always faces the wind.

Types of Wind Turbines

• Horizontal axis wind turbines (HAWTs) have the rotor and generator at the top of a tower, needing to be pointed into the wind.
• Vertical axis wind turbines (VAWTs) don't require pointing into the wind, which is suitable for variable wind directions, and the generator and gearbox can be situated near the base.

Offshore Wind Turbines

• Advantages include stronger turbine capabilities, longer operational lifetimes, higher energy output (50%), greater wind speeds, and more constant wind conditions.
• Disadvantages are more costly to build and maintain, and more challenging and expensive to access.

Hydroelectric Power Plant

• Hydropower, also known as hydroelectric power or hydroelectricity, converts hydraulic potential energy from water into electricity.
• Hydroelectric power plants are often located in mountainous regions with damnable locations.

Hydropower Components

• Dams, spillways, headworks, surge tanks, penstocks, and power stations are major components of a hydroelectric power plant.

Hydropower Working

• Water flows from a reservoir through a penstock to a turbine.
• Conversion to mechanical energy occurs within the turbine which drives the alternator converting it into electrical energy.

Hydropower Advantages

• Environmentally friendly (non-polluting).
• Robust turbine operation due to low speeds.
• Reservoirs aid agriculture and flood control.
• Lower operating and maintenance costs.

Hydropower Limitations

• Deforestation and relocation can result.
• Significant quantities of water are needed.
• Rainfall can impact power delivery.
• Dam construction is costly.
• High transmission costs due often-remote locations.