Solar, Wind, Geothermal, and Biomass Energy: A Comprehensive Overview
Solar Energy
Nuclear Fusion Reactions
At the core of the Sun, nuclear fusion reactions continually produce energy, converting approximately 4 million tons of mass into radiation. This solar energy reaches Earth’s surface directly (direct radiation) or indirectly after being reflected by atmospheric dust and water vapor (diffuse radiation).
Harvesting Systems
There are two main methods for harvesting solar energy: the thermal route, which transforms solar radiation into heat, and photovoltaic conversion, which converts radiation directly into electricity.
Thermal Route
Heat can be generated through active systems, with or without radiation sensors and solar thermal power concentration. Passive use involves designing buildings with architecture adapted to the surrounding environment and climate. Active systems can be low, medium, or high temperature.
Low-Temperature Systems
Low-temperature systems utilize flat-plate collectors based on the greenhouse effect.
Medium and High-Temperature Systems
Medium and high-temperature systems can indirectly generate power for solar thermal applications. A crucial application is the high-temperature solar oven used in high-tech materials research. This involves a large parabolic area of mirrors that reflect and concentrate radiation onto a small focal point, generating extremely high temperatures.
Distributed Collector Systems (DCS)
DCS concentrates solar radiation onto a small collector area, achieving temperatures up to 300°C, sufficient for producing high-temperature steam for electricity generation or industrial processes.
Central Receiver Systems (CRS)
CRS harnesses solar energy at high temperatures. A field of heliostat mirrors concentrates solar radiation onto a receiver atop a tower. The heliostats track the sun’s trajectory, maximizing direct radiation capture.
Photovoltaic Conversion
Photovoltaic conversion directly transforms solar radiation into electricity using solar cells. These cells consist of a semiconductor material layer that produces electricity when impacted by photons (the photovoltaic effect).
Applications
Photovoltaic conversion is used in isolated facilities and grid-connected commercial installations.
Low-Temperature Solar Energy Systems
Greenhouses
Greenhouses trap infrared radiation emitted by heated objects, increasing the enclosed space’s temperature.
Usage Systems
Bioclimatic Architecture
Bioclimatic architecture focuses on housing comfort by optimizing architectural elements for solar energy utilization and natural ventilation. Key elements include windows, thermal mass, protective elements, and reflectors.
Active Systems
Active systems use solar energy to heat fluids (typically water or air) for domestic hot water and heating. They comprise:
- Catchment Subsystem: Includes solar collectors and connecting elements.
- Storage Subsystem: Mediates between capture and consumption.
- Consuming Subsystem: Connects storage to demand points (showers, taps, etc.).
Installations can operate in open or closed circuits, with natural or forced circulation. Open circuits use the heated water directly, while closed circuits use a heat exchanger.
Collectors/Sensors
The collector/sensor captures solar radiation and transfers it as heat to a fluid. Its operation is based on the greenhouse effect. Key components include:
- Absorber Plate: Absorbs solar radiation and transfers heat to the fluid.
- Transparent Cover: Reduces losses, protects the absorber plate, and creates the greenhouse effect.
- Insulation: Minimizes heat loss.
- Casing: Houses all collector elements.
Wind Power
Wind power harnesses wind energy using aeroturbines (windmills).
Types of Aeroturbines
Aeromotors
Slow machines with 12-24 blades and diameters up to 8m. They have low performance but require low wind speeds.
Turbines
Fast machines with 2-3 blades and variable diameters. They have high performance but require higher wind speeds.
Parts of an Aeroturbine
- Rotor/Turbine: Transforms wind energy into mechanical energy.
- Regulation System: Positions the rotor perpendicular to the wind and controls speed.
- Energy Converter: Transmits mechanical energy from the rotor axis.
- Nacelle: Supports and protects the power converter, regulation system, and typically the guidance system.
- Tower/Support: Elevates the rotor and absorbs vibrations.
Turbine Types
Vertical-Axis Wind Turbines
The generator is located near the base, simplifying operations.
Horizontal-Axis Wind Turbines
The most common type, used for both small and large generators. Classified by rotor position:
- Downwind Rotor: No guidance system required.
- Upwind Rotor: Requires a guidance system (tail, side helix, or automatic mechanisms).
Rotor blades can be fixed-pitch or variable-pitch. Variable pitch allows for greater energy production.
Wind Farms
Facilities using multiple wind turbines. Classified as:
- Off-Grid: Used in rural electrification, agriculture, signaling, and communications.
- Grid-Connected (Support): Reduce energy costs.
- Grid-Connected (Generating): Provide electricity to the grid.
Geothermal Energy
Geothermal energy utilizes Earth’s internal heat.
Types of Plants
- Condensation Plants: Steam from the turbine is condensed and reused.
- Non-Condensation Plants: Steam is released into the atmosphere.
Tidal Power
Tides are cyclical rises and falls in sea level caused by the gravitational pull of the Moon and Sun. Tidal amplitude (height difference between high and low tide) varies with lunar proximity.
Biomass Energy
Biomass encompasses all living material on Earth. From an energy perspective, it refers to organic matter of plant or animal origin, used for energy production. Photosynthesis is the origin of all biomass.
Physical Processes
- Refinement/Homogenization: Adapting biomass particle size, composition, or moisture content.
- Densification: Improving biomass properties for briquette and pellet production.
Thermochemical Processes
- Pyrolysis/Dry Distillation: Thermal degradation of biomass molecules in the absence of oxygen.
- Gasification: Incomplete combustion of biomass with limited oxygen, producing a gas mixture (CO, H2, CH4, etc.).
Biochemical Processes
- Anaerobic Digestion: Fermentation of biomass to produce biogas.
- Aerobic Fermentation: Used to produce bioalcohol (ethanol) from sugar- or starch-rich materials.
Biofuels
Liquid fuels derived from biomass, used as fossil fuel replacements.
Types
- Biodiesel: Obtained from vegetable oils (pure or used).
- Bioalcohol: Methanol and ethanol. Methanol is now derived from natural gas or petroleum. Ethanol is produced from aerobic fermentation and used as fuel or additive.
Municipal Solid Waste (MSW)
Waste generated by domestic activity. Current disposal methods include:
- Landfilling: Burying waste.
- Composting: Aerobic fermentation of organic waste.
- Recycling: Reprocessing waste materials.
- Incineration: Burning waste and treating the resulting gases.
Ecoparks
Facilities that generate energy and fertilizer from MSW and garden waste. They have two treatment lines: organic fraction treatment and remaining fraction treatment.
Biogas Recovery in Landfills
Biogas from landfill waste decomposition is extracted through degassing and extraction wells to mitigate environmental risks.