Conventional & Non-Conventional Energy Sources: Advantages, Disadvantages, and Applications
Conventional Energy Sources
Conventional energy sources include coal, lignite, oil, natural gas, hydroelectric, and nuclear fuels. These sources are generally non-renewable, finite, and can cause pollution when used.
Examples:
- Coal
- Natural gas
- Petroleum
Non-Conventional Energy Sources
Non-conventional energy sources include solar, wind, geothermal, tidal, and biomass energy. These sources are renewable, inexhaustible, and environmentally friendly.
Examples:
- Solar energy
- Wind energy
- Geothermal energy
Advantages of Conventional Energy Sources
- High energy density: Conventional fuels pack a lot of energy per unit volume or mass.
- Reliable and consistent supply: Especially in established infrastructure, conventional sources offer a stable energy supply.
- Technologically mature and widely used: The technologies for utilizing conventional energy are well-developed and widely implemented.
Limitations of Conventional Energy Sources
- Pollution and environmental damage: Burning fossil fuels releases pollutants that harm the environment and human health.
- Finite resources: Conventional energy sources are limited and will eventually be depleted.
- Contribution to global warming and acid rain: Greenhouse gas emissions from fossil fuels contribute to climate change and acid rain.
Solar Energy Collectors
Flat Plate Collectors
Flat plate collectors have a large absorber area and a concentration ratio of 1. They operate at a low-temperature range, generally not exceeding 70°C. These collectors utilize both beam and diffuse radiation. They are simple in construction and maintenance, requiring no tracking system, and are less costly. However, their applications are limited to low-temperature uses and are suitable for all locations as they can function in both clear and cloudy conditions.
Focusing Collectors
Focusing collectors have a small absorber area and a high concentration ratio, varying from 4 to 3000. They can achieve high temperatures, up to 3000°C, and primarily use beam radiation. These collectors have a more complicated design, require difficult maintenance and a tracking system, and are more costly. They are suitable for high-temperature applications, such as power generation, and are best suited for locations with many clear days.
Photovoltaic (PV) Systems
Standalone PV System
Standalone PV systems include solar panels, a charge controller, batteries for energy storage, and an inverter. These systems are self-sufficient, supplying electricity directly to the load and storing excess energy in batteries. They are commonly used in remote areas where grid connectivity is not feasible.
Grid-Connected PV System
Grid-connected PV systems include solar panels, an inverter, and a connection to the electricity grid. Excess energy produced during the day is fed into the grid, and electricity can be drawn from the grid when solar power is insufficient. These systems do not require batteries, reducing costs, and are more efficient for continuous power supply.
Effect of Temperature and Insolation on Solar Cell Characteristics
Temperature
- An increase in temperature typically reduces the efficiency of a solar cell.
- Higher temperatures decrease the open-circuit voltage and can slightly increase the short-circuit current.
Insolation
- Insolation (solar radiation) directly affects the current output of the solar cell.
- Higher insolation increases the current output and, thus, the power generated by the solar cell.
- Maximum power output is achieved at optimal insolation levels, which corresponds to the maximum power point on the I-V curve.
Components of a Flat Plate Collector
- Absorber plate: Intercepts and absorbs incident solar radiation. It is usually a blackened heat-absorbing plate made of copper, aluminum, or steel, often with a coating to minimize heat emission.
- Transparent cover: Made of one or more transparent sheets of glass or plastic, placed above the absorber plate to allow radiation to reach the plate while preventing reradiation and convective heat loss.
- Fluid tubes or channels: Arranged in thermal contact with the absorber plate to transfer heat to the fluid.
- Thermal insulation: Provided under the absorber plate and fluid tubes to minimize heat loss by transmission or convection.
- Tight container or box: Protects all the components of the collector.
Characteristic Features of a Flat Plate Collector
- Absorbs both direct and diffuse solar radiation.
- Does not need a sun-tracking system, making it mechanically stronger than other collectors.
- Has simple construction requiring little maintenance.
Central Tower Collector
- The receiver is located at the top of a tower, and solar radiation is reflected onto it from many independently controlled flat mirrors called heliostats.
- Heliostats can be moved independently about two axes to direct reflected solar radiation towards the absorber.
- Heliostats are spread over a large area on the ground surrounding the tower.
- Thousands of heliostats simultaneously track the sun to reflect solar radiation from all sides onto the receiver.
- These heliostats act as a very large paraboloidal dish collector, achieving a concentration ratio as high as 3000.
- Solar radiation at the receiver is converted into heat, which is transported to a heat engine or other device for use.
Solar Cell Characteristics
Open Circuit Voltage (Voc): The maximum voltage available from a solar cell when there is no current flowing.
Short Circuit Current (Isc): The current through the solar cell when the voltage across the cell is zero.
Fill Factor (FF): A parameter that defines the maximum power output relative to the product of Voc and Isc.
Efficiency: The ratio of the electrical power output to the incident solar power, expressed as a percentage.
Standalone PV System
A standalone solar PV power station is located at the load center and designed to meet the electrical load of a remote area, village, or installation. Energy storage is essential to meet the requirement during non-sunshine hours.
The maximum power point tracker (MPPT) adjusts the operating point to obtain maximum power output from the solar array based on climatic conditions. The solar electric output in direct current is converted into alternating current and fed into the load. Excess power is stored by charging the battery or dumped in electric heaters. When solar radiation is unavailable, the batteries supply electricity through the converter.
Classification of Solar Cells Based on Material
- Single Crystal Silicon Cells: High efficiency and high cost, widely used in terrestrial applications.
- Multicrystalline Silicon Cells: Lower cost but also lower efficiency compared to single crystal.
- Amorphous Silicon Cells: Thin-film technology, less efficient but cheaper and flexible.
- Gallium Arsenide Cells: High efficiency, used in space applications.
- Copper Indium Diselenide (CIS) Cells: Thin-film technology, good efficiency and flexibility.
- Cadmium Telluride Cells: Thin-film, relatively low cost but environmental concerns due to cadmium.
- Organic Photovoltaic Cells: Emerging technology, based on organic materials, lower efficiency but potential for low-cost production.
Biofouling in OTEC
Biofouling refers to the accumulation of microorganisms, plants, algae, or small animals on the surfaces of heat exchangers in Ocean Thermal Energy Conversion (OTEC) systems. This accumulation creates thermal resistance, reducing heat transfer efficiency and the overall efficiency of the OTEC plant.
Effect on OTEC: Biofouling significantly reduces the efficiency of the OTEC system by creating a barrier to heat transfer, decreasing the plant’s power output.
Methods to avoid biofouling:
- Mechanical Cleaning: Regular cleaning of the heat exchanger surfaces to remove accumulated biofouling.
- Chemical Treatment: Chlorination or other chemical treatments to prevent biofouling growth.
Advantages and Disadvantages of Tidal Power Plants
Advantages
- Renewable Source: Tidal power is inexhaustible and renewable.
- Predictable: Tidal cycles are highly predictable, making energy generation reliable.
- No Greenhouse Gas Emissions: Tidal power generation does not produce greenhouse gases.
- Low Operating Costs: Once constructed, tidal power plants have low operating and maintenance costs.
- No Fuel Requirement: No fuel is needed, reducing dependency on fossil fuels.
Disadvantages
- High Initial Cost: Construction and installation of tidal power plants are expensive.
- Location Specific: Suitable sites are limited to coastal areas with high tidal ranges.
- Environmental Impact: Construction of tidal barrages can impact marine life.
- Intermittent Energy Production: Energy generation depends on tidal cycles.
- Potential Corrosion: Machinery may suffer from corrosion due to the saline environment.
Classification and Explanation of Tidal Power Plants
Classification
- Single-basin arrangement:
- Single-effect plant: Generates power during the ebb tide.
- Double-effect plant: Generates power during both ebb and flood tides.
- Double-basin arrangement:
- Double-basin linked-basin plant: A single basin divided into two with continuous power generation.
- Double-basin paired-basin plant: Two basins with supplementary paired basins, allowing continuous but irregular power output.
Explanation of Two Types
Single-basin Single-effect Plant: Generates power only during low tide. Water is stored in the basin during high tide and released during low tide to drive turbines.
Double-basin Linked-basin Plant: Two basins, a high basin and a low basin, with water flowing from the high basin to the low basin through turbines, allowing continuous power generation.
Tidal Range
Tidal Range is the difference in water level between high tide and low tide, denoted by “R.” It is crucial in determining the potential energy available for tidal power generation. The greater the tidal range, the more potential energy can be harnessed.
Site Selection Criteria for OTEC
- Thermal Gradient: A temperature difference of about 20°C between surface and deep water is ideal.
- Topography: The ocean floor should be suitable for laying pipes and constructing the plant.
- Seismic Activity: The site should have minimal seismic activity.
- Infrastructure: Availability of necessary infrastructure like airports and harbors.
- Proximity to Load Centers: Close to demand centers to reduce transmission losses.
Anderson Cycle (Closed Cycle OTEC)
Warm surface water vaporizes a working fluid (e.g., ammonia). The vapor drives a turbine to generate electricity and is then condensed by cold deep-sea water. The closed-loop system ensures continuous circulation of the working fluid.
