Renewable Energy Sources: A Comprehensive Guide to Solar, Tidal, and OTEC Technologies
Conventional and Non-Conventional Energy Sources
Conventional Energy Sources: Include coal, lignite, oil, natural gas, and hydroelectric and nuclear fuels. They are generally non-renewable, finite, and cause pollution when used. Examples: Coal, natural gas, petroleum.
Non-Conventional Energy Sources: Include solar, wind, geothermal, tidal, and biomass energy. These are renewable, inexhaustible, and environmentally friendly. Examples: Solar energy, wind energy, geothermal energy
Advantages of Conventional Energy Sources
- High energy density.
- Reliable and consistent supply, especially in established infrastructure.
- Technologically mature and widely used.
Limitations of Conventional Energy Sources
- Cause pollution and environmental damage.
- Finite resources, leading to depletion over time.
- Contribute to global warming and acid rain.
Solar Energy
Types of Solar Collectors
Flat Collectors
The absorber area is large. Concentration ratio is 1. Temperature range is low, generally not more than 70°C. It uses both beam and diffuse radiation. Simple in construction and maintenance, no tracking system is required. Less costly. Application limited to low temperature uses. Suitable for all places as it can work in clear and cloudy days.
Focusing Collectors
Absorber area is small. Concentration ratio is high varying from 4 to 3000. Temperature range is high, which is up to 3000°C. It uses mainly beam radiation. More complicated design and difficult maintenance, tracking system is required. More costly. High temperature applications such as power generation. Suitable where there are more clear days in a year.
Solar PV Systems
Standalone PV System
Includes solar panels, a charge controller, batteries for energy storage, and an inverter. The system is self-sufficient, supplying electricity directly to the load and storing excess energy in batteries. Used in remote areas where grid connectivity is not feasible.
Grid-Connected PV System
Includes 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. Does not require batteries, reducing costs, and is more efficient for continuous power supply.
Effect of Temperature and Insolation on Solar Cells
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. It is meant to intercept and absorb incident solar radiation. It is primarily a blackened heat-absorbing plate usually made of copper, aluminium or steel. It may also be given a coating to minimise the emission of heat from its surface.
- Transparent cover. It is made of one or more transparent sheets of glass or plastic. It is placed above the absorber plate. The cover allows radiation to reach the absorber plate but it prevents any reradiation and heat loss due to convection.
- Fluid tubes or channels. Fluid tubes or channels are arranged in thermal contact with the absorber plate so that heat can be transferred from the absorber plate to the fluid in the tubes or channels.
- Thermal insulation. The thermal insulation is provided under the absorber plate and fluid tubes to minimise any heat loss by transmission or convection from the absorber plate and fluid tubes.
- Tight container or box. All the above components of the collector are protected by a tight container or box.
Characteristics of a Flat Plate Collector
- It absorbs both direct and diffuse solar radiation.
- It does not need any sun tracking system. Hence, it is mechanically stronger than other collectors which require a tracking system.
- It has simple construction requiring little maintenance.
Central Tower Collector
– In this type of collectors, the receiver is located at the top of a tower and solar radiation is reflected on it from many independently controlled flat mirrors called heliostats.
– The heliostats can be moved independently about two axes so that the reflected solar radiation is always directed towards the absorber mounted on the tower
– The heliostats are spread over a large area on ground surrounding the absorber mounted on the tower.
– The number of heliostats can be as high as thousands, and they simultaneously track the sun to reflect the solar radiation from all sides on the receiver.
– These heliostats together act as a very large paraboloidal dish collector. The concentration ratio as high as 3000 can be obtained by this point-type concentrator called central tower receiver collector.
– The solar radiation at the receiver is converted into heat, which is transported to a heat engine or any other device for use.
Solar Cell Parameters
(b) Define:
- 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 Solar PV System
STAND ALONE SYSTEM
• Solar PV power station is planned and located at the load centre. Its complete electricity generation is meant to meet the electrical load of any remote area, village or installation. Energy storage is essential to meet the requirement during non-sunshine hours.
The solar electric output in direct current is converted into alternating current and it is fed
into the load.
The excess power is preferably stored by charging the battery and otherwise excess is
dumped in the electric heaters.
When the sun radiation is unavailable, the batteries supply the electricity through the
converter.
Classification of Solar Cells
Classify solar cells based on the type of material used:
- 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.
Tidal Energy
Biofouling in OTEC
What is meant by “biofouling” and what is its effect on OTEC? What are the methods used to avoid this problem?
Biofouling refers to the accumulation of microorganisms, plants, algae, or small animals on the surfaces of the heat exchangers in Ocean Thermal Energy Conversion (OTEC) systems. This accumulation creates thermal resistance, reducing the efficiency of heat transfer and thereby 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, which decreases the power output of the plant.
Methods to avoid biofouling:
- Mechanical Cleaning: Regular mechanical cleaning of the heat exchanger surfaces to remove accumulated biofouling.
- Chemical Treatment: Chlorination or other chemical treatments are used to prevent the growth of biofouling on the surfaces.
Advantages and Disadvantages of Tidal Power Plants
List out the advantages and disadvantages of a tidal power plant.
Advantages:
- Renewable Source: Tidal power is an inexhaustible and renewable source of energy.
- Predictable: Tidal cycles are highly predictable, making energy generation more 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, which reduces dependency on fossil fuels.
Disadvantages:
- High Initial Cost: The construction and installation of tidal power plants are expensive.
- Location Specific: Suitable sites for tidal power plants are limited to specific coastal areas with high tidal ranges.
- Environmental Impact: The construction of tidal barrages can have significant ecological impacts on marine life.
- Intermittent Energy Production: Energy generation is not continuous and depends on the tidal cycles.
- Potential Corrosion: The machinery may suffer from corrosion due to the saline environment.
Classification of Tidal Power Plants
3. Classify tidal power plants and briefly explain any two of them.
Classification of Tidal Power Plants:
- Single-basin arrangement:
- Single-effect plant: Generates power during the ebb tide (water flows out from the basin to the sea).
- Double-effect plant: Generates power during both the 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: This type of plant generates power only during the low tide. Water is stored in the basin during the high tide and then released during the low tide to drive turbines.
- Double-basin Linked-basin Plant: In this type, there are two basins: a high basin and a low basin. Water flows from the high basin to the low basin through turbines, allowing continuous power generation without waiting for tidal cycles.
Tidal Range
4. Explain the term Tidal Range with the help of a figure.
Tidal Range is the difference in water level between the high tide and the low tide. It is denoted by”” and is a crucial factor in determining the potential energy available for tidal power generation. The greater the tidal range, the more potential energy can be harnessed.
Ocean Thermal Energy Conversion (OTEC)
Site Selection Criteria for OTEC
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 is used to vaporize a working fluid (e.g., ammonia). The vapor drives a turbine to generate electricity, and the vapor is then condensed by cold deep-sea water. The closed-loop system ensures the working fluid circulates continuously.
