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Conventional Sources of Energy

Conventional Sources Of Energy

Conventional sources of energy are those energy sources that have been in widespread use for a long time and are generally well-established technologies for energy production. Historically, these have been the primary sources meeting global energy demands. They include fossil fuels (coal, petroleum, natural gas) and large-scale hydropower. These sources are often contrasted with non-conventional or renewable sources, which are more recently developed or are being increasingly adopted due to environmental concerns and sustainability goals.

In many parts of the world, including India, conventional sources still constitute a significant portion of the energy mix, although there is a growing emphasis on transitioning towards renewable alternatives. Their widespread use is due to factors like high energy density (especially fossil fuels), established infrastructure for extraction, transportation, and conversion, and relatively lower historical costs. However, they also come with significant environmental drawbacks, as discussed in the previous section.

Fossil Fuels (Coal, Petroleum, Natural Gas)

Fossil fuels are the most prominent example of conventional energy sources. They are formed from the remains of ancient plants and animals that were buried deep beneath the Earth's surface over millions of years and subjected to immense heat and pressure. These organic materials were transformed into energy-rich substances: coal, petroleum (crude oil), and natural gas.

Fossil fuels are non-renewable sources because their rate of formation is extremely slow compared to the rate at which we are consuming them. They represent stored solar energy from millions of years ago.

Types of Fossil Fuels:

  1. Coal: A solid fossil fuel primarily composed of carbon. It is extracted through mining. Coal is a major source of energy for electricity generation, especially in countries like India. It is relatively abundant and cheaper to extract than other fossil fuels but is also the most polluting when burned.
  2. Petroleum (Crude Oil): A liquid fossil fuel consisting of a mixture of hydrocarbons. It is extracted through drilling. Crude oil is refined to produce various fuels like petrol, diesel, kerosene, aviation fuel, and also serves as a raw material for petrochemicals. It is a primary source of energy for transportation.
  3. Natural Gas: A gaseous fossil fuel, primarily methane (CH$_4$). It is often found alongside petroleum deposits or in separate reservoirs. It is transported via pipelines or as liquefied natural gas (LNG). Natural gas is considered the cleanest burning fossil fuel, producing less CO$_2$ and pollutants than coal or oil for the same amount of energy. It is used for electricity generation, heating, cooking, and as a fuel for vehicles (CNG).

The combustion of fossil fuels releases chemical energy in the form of heat, which can then be converted into other forms of energy like electricity or mechanical work. Despite their environmental impacts, fossil fuels remain the backbone of the global energy system due to their high energy density, ease of transport (for liquids and gases), and established infrastructure.

Thermal Power Plant

A thermal power plant is a facility that generates electricity by converting heat energy into electrical energy. The heat energy is typically produced by burning fossil fuels, most commonly coal, but also oil and natural gas. In India, a large portion of the electricity generation capacity comes from coal-based thermal power plants.

Working Principle: Thermal power plants operate based on the principle of the steam cycle (Rankine cycle).

Diagram showing the basic layout of a thermal power plant

Basic diagram showing the energy conversion process in a thermal power plant.

  1. Fuel Combustion: Fuel (e.g., pulverised coal) is burned in a large furnace or boiler.
  2. Steam Generation: The heat produced from combustion is used to heat water in tubes running through the boiler, converting the water into high-pressure, high-temperature steam.
  3. Turbine: The high-pressure steam is directed onto the blades of a turbine (a large fan-like structure). The force of the steam causes the turbine to rotate. This is the conversion of thermal energy into mechanical energy.
  4. Generator: The rotating turbine is connected to the shaft of an electric generator. The generator, based on the principle of electromagnetic induction, converts the mechanical energy of the rotating turbine into electrical energy.
  5. Condenser: After passing through the turbine, the steam is cooled and condensed back into water in a condenser. This water is then pumped back to the boiler to complete the cycle. Cooling is often done using water from a river, lake, or cooling towers, leading to potential thermal pollution.

The efficiency of a thermal power plant is limited by the second law of thermodynamics (Carnot efficiency) and practical factors, typically ranging from 30% to 45%. Significant energy is lost as waste heat during the conversion process.

Thermal power plants, especially coal-based ones, are major contributors to air pollution (SO$_2$, NO$_x$, particulate matter, heavy metals) and greenhouse gas emissions (CO$_2$), making them a primary target for reducing environmental impact in the energy sector.

Hydro Power Plants

Hydro power plants generate electricity by harnessing the energy of flowing or falling water. They are a significant source of conventional renewable energy. Large-scale hydro power plants, typically involving the construction of dams, are considered conventional due to their long history of use and established technology, differentiating them from smaller-scale or newer hydro technologies.

Working Principle: Hydro power plants convert the potential energy of water stored at a height into kinetic energy, then into mechanical energy, and finally into electrical energy.

Diagram showing the basic layout of a hydroelectric power plant with a dam and reservoir

Basic diagram of a hydroelectric power plant.

  1. Dam and Reservoir: A dam is constructed across a river to create a reservoir of water at a significant height. The stored water in the reservoir possesses gravitational potential energy.
  2. Penstock: Water from the reservoir flows down through large pipes called penstocks to the turbine. As water flows down, its potential energy is converted into kinetic energy.
  3. Turbine: The high-speed flow of water strikes the blades of a hydro turbine, causing it to rotate. This is the conversion of kinetic energy into mechanical energy. Different types of turbines (e.g., Francis, Kaplan, Pelton) are used depending on the water head and flow rate.
  4. Generator: The rotating hydro turbine is connected to the shaft of an electric generator. The generator converts the mechanical energy of the turbine into electrical energy using electromagnetic induction.
  5. Tailrace: After passing through the turbine, the water is discharged into the river downstream.

The amount of power generated depends on the height of the water head (difference in water level between the reservoir and the turbine) and the volume flow rate of water through the turbine.

Simplified diagram of a hydro turbine and generator

Simplified view of a hydro turbine driving a generator.

Hydro power plants are considered renewable because they rely on the continuous natural water cycle. They do not produce air pollutants or greenhouse gas emissions during operation. However, as discussed in the previous section, they have significant environmental and social impacts related to dam construction, reservoir creation, and alteration of river ecosystems.

Improvements In The Technology For Using Conventional Sources Of Energy

While the shift towards renewable energy is gaining momentum, conventional energy sources, particularly fossil fuels, are expected to remain significant components of the global energy mix for some time. Therefore, technological advancements aimed at improving the efficiency and reducing the environmental impact of using these sources are crucial.

  1. Improved Efficiency in Thermal Power Plants:
    • Supercritical and Ultra-supercritical Technology: Operating thermal power plants at higher steam temperatures and pressures increases their thermal efficiency, meaning more electricity is generated from the same amount of fuel, leading to lower fuel consumption and emissions per unit of electricity. Modern plants are moving towards ultra-supercritical parameters ($> 600^\circ$C, $> 25$ MPa).
    • Combined Cycle Power Plants (for Natural Gas): These plants use a gas turbine (where hot combustion gases drive a turbine) and then use the waste heat from the gas turbine to produce steam to drive a separate steam turbine. This combination significantly increases overall efficiency (often exceeding 60%).
    • Cogeneration (Combined Heat and Power - CHP): Using the waste heat from electricity generation for other purposes like industrial processes or district heating further improves the overall energy utilisation efficiency.
  2. Pollution Control Technologies (for Fossil Fuels):
    • Flue Gas Desulfurization (FGD) / Scrubbers: Used to remove sulphur dioxide (SO$_2$) from power plant emissions, reducing acid rain.
    • Selective Catalytic Reduction (SCR): Used to reduce nitrogen oxides (NO$_x$) emissions.
    • Electrostatic Precipitators (ESPs) and Baghouses: Used to remove particulate matter (fly ash) from flue gases, improving air quality.
    • Carbon Capture, Utilisation, and Storage (CCUS): Technologies aimed at capturing CO$_2$ emissions from power plants and industrial facilities, transporting it, and storing it underground or using it for other purposes. While technically possible, CCUS is currently expensive and has limited large-scale deployment.
  3. Clean Coal Technologies: Term sometimes used to refer to technologies that improve the efficiency and reduce emissions from coal-fired power plants (e.g., gasification of coal before burning, integrated gasification combined cycle - IGCC plants, advanced combustion techniques).
  4. Improvements in Hydropower Technology: While large dam impacts remain, technologies like pumped-storage hydropower (using excess electricity to pump water to an upper reservoir for later generation) improve grid flexibility. Run-of-river hydro (generating power from flowing water without large reservoirs) minimizes some environmental impacts of large dams, though typically with lower power output.
  5. Efficient Extraction and Transport: Technologies to improve the efficiency of extracting oil and gas (e.g., directional drilling, hydraulic fracturing - though the latter has significant environmental concerns) and safer transportation methods aim to reduce costs and environmental risks (like pipeline leaks or oil spills).

These technological advancements help to mitigate some of the negative aspects of using conventional energy sources, making them cleaner and more efficient. However, they do not fundamentally address the finite nature of fossil fuels or eliminate all environmental risks associated with these sources.