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Alternative and Non-Conventional Sources of Energy

Alternative Or Non-Conventional Sources Of Energy

Alternative or Non-Conventional sources of energy refer to those energy sources that have been developed and adopted more recently compared to conventional sources like fossil fuels and large hydropower. These sources are typically renewable and are being increasingly explored and utilised to address environmental concerns related to climate change and air pollution from fossil fuels, and to ensure long-term energy sustainability.

The development and widespread adoption of these non-conventional sources are crucial for transitioning to a cleaner and more sustainable energy future. While some of these technologies have been around for a while (like wind mills), their large-scale deployment and integration into modern energy systems are relatively recent phenomena.

Solar Energy (Solar Cells, Solar Cookers)

Solar energy is the energy obtained from the Sun. It is the most abundant and freely available renewable energy source on Earth. It can be harnessed in various ways to produce heat or electricity.

Direct Harvesting Methods

Solar energy can be harnessed directly for various applications:

  1. Solar Cells (Photovoltaic Cells): These are semiconductor devices that convert sunlight directly into electricity through the photovoltaic effect. Solar cells are typically made from silicon or other semiconductor materials. When photons from sunlight strike the solar cell with sufficient energy, they excite electrons, creating electron-hole pairs. The built-in electric field at the p-n junction separates these carriers, generating a voltage and current. A single solar cell produces a small voltage (around 0.5-0.7 V); multiple cells are connected in series and parallel to form solar panels (or modules) to generate usable voltage and current.

    Diagram of a solar panel made of multiple solar cells

    A solar panel, consisting of multiple interconnected solar cells.

    Advantages: Clean energy generation (no emissions during operation), modular design, can be used in remote areas. Disadvantages: Intermittent source (only works when sunlight is available), relatively low conversion efficiency (typically 15-25% for commercial panels), high initial cost, requires significant land area for large-scale deployment.
  2. Solar Thermal Systems: These systems convert sunlight into heat.
    • Solar Cookers: Devices that use sunlight for cooking. Simple solar cookers often use reflectors to concentrate sunlight onto a cooking vessel. More advanced designs include box-type cookers and parabolic dish concentrators.

      Diagram of a simple box-type solar cooker

      A simple box-type solar cooker uses insulation and a cover to trap heat.

      Advantages: Save fuel, reduce indoor air pollution, environmentally friendly. Disadvantages: Cooking is slow, depends on sunlight, not suitable for all types of cooking, may not work on cloudy days or at night.
    • Solar Water Heaters: Systems that use solar collectors (e.g., flat-plate collectors or evacuated tube collectors) to absorb sunlight and heat water, which is then stored in an insulated tank for later use. Used for domestic or industrial hot water supply.
    • Concentrated Solar Power (CSP): Large-scale systems that use mirrors or lenses to concentrate sunlight onto a receiver, heating a fluid (e.g., molten salt) to a very high temperature. This heat is then used to generate steam to drive a turbine and produce electricity, similar to a thermal power plant. Some systems include thermal energy storage to generate power even after sunset.

Solar energy holds immense potential as a clean and sustainable energy source, and its technology is continuously improving, leading to cost reductions and increased efficiency.

Energy From The Sea (Tidal Energy, Wave Energy, OTEC)

The oceans and seas contain vast amounts of energy in various forms. Harnessing this ocean energy provides several non-conventional renewable energy options.

  1. Tidal Energy: Energy derived from the rise and fall of tides. Tides are caused by the gravitational interaction between the Earth, Moon, and Sun. Tidal energy is predictable.
    • Tidal Barrages: Dams built across estuaries or bays capture water at high tide and release it through turbines at low tide to generate electricity (similar to hydropower). Requires significant infrastructure and can impact estuary ecosystems.
    • Tidal Stream Generators: Use turbines placed in tidal currents to generate electricity from the kinetic energy of the flowing water (similar to underwater wind turbines). Less infrastructure is needed, and environmental impact is potentially lower than barrages.
    Advantages: Predictable energy source, high energy density compared to wind or solar for specific sites. Disadvantages: Limited suitable sites, high initial cost, potential impact on marine ecosystems, requires large tidal range.
  2. Wave Energy: Energy derived from the motion of ocean surface waves, which are generated by wind. Wave energy is less predictable than tidal energy but is a vast global resource. Various technologies are being developed to capture wave energy, including oscillating water columns, floating devices that generate electricity from their motion, and tapered channel systems. Advantages: Large potential resource, relatively environmentally friendly during operation (depending on technology). Disadvantages: Variable output, high stresses on devices from harsh ocean environment, potential visual impact, potential impact on marine life and navigation.
  3. Ocean Thermal Energy Conversion (OTEC): Energy derived from the temperature difference between warm surface water and cold deep ocean water in tropical regions. This temperature difference can be used to drive a heat engine and generate electricity. Principle: Uses the temperature difference (at least $20^\circ$C) to vaporise a working fluid (like ammonia), which drives a turbine. The vapour is then condensed using cold deep ocean water. Advantages: Large potential resource, can potentially produce desalinated water as a byproduct, base-load power capability (not intermittent). Disadvantages: Low conversion efficiency due to small temperature difference, high infrastructure costs, potential impact on marine life and deep-sea environment from pumping large volumes of water, scaling and biofouling issues.

Ocean energy technologies are still relatively less developed and have higher costs compared to other renewables, but they offer promising options, especially for coastal areas and islands.

Geothermal Energy

Geothermal energy is heat derived from the Earth's interior. This heat is a continuous resource, generated by the radioactive decay of isotopes in the Earth's crust and mantle and primordial heat from the Earth's formation.

Harvesting Geothermal Energy

Geothermal energy can be harnessed in different ways depending on the geological conditions:

  1. Dry Steam Power Plants: Use steam directly from underground reservoirs to drive turbines.
  2. Flash Steam Power Plants: Use hot water from underground reservoirs; as pressure is reduced, part of the water flashes into steam to drive turbines.
  3. Binary Cycle Power Plants: Use hot water (even at lower temperatures) to heat a secondary working fluid (like isopentane), which has a lower boiling point, to vaporise it and drive a turbine. This is used for lower temperature geothermal resources.
  4. Geothermal Heat Pumps: Use the stable temperature of the Earth near the surface to provide heating and cooling for buildings (different from electricity generation).

Diagram showing a geothermal power plant

Schematic diagram of a geothermal power plant (flash steam type shown).

Advantages: Renewable, provides base-load power (available 24/7, not intermittent), relatively low greenhouse gas emissions compared to fossil fuels (some CO$_2$ or H$_2$S might be released from underground fluids, but much lower than fossil fuels), efficient use of land area for power generation compared to large-scale solar/wind farms. Disadvantages: Suitable sites are geographically limited (usually near tectonic plate boundaries), potential release of underground gases (H$_2$S, CO$_2$), risk of inducing seismic activity (in Enhanced Geothermal Systems), potential for thermal pollution of local water bodies.

Nuclear Energy (Fission as a source)

While large-scale nuclear fission power plants are often considered conventional due to their long history of use in electricity generation, the energy source itself (nuclear reactions) and the fuel cycle technologies are distinct from fossil fuels and are sometimes discussed alongside other alternative energy sources because of their low greenhouse gas emissions during operation. However, nuclear fuel (Uranium) is a finite resource, making it a non-renewable source in the long term.

Nuclear fission power is generated in nuclear reactors, where controlled chain reactions of heavy atomic nuclei (like Uranium-235) release large amounts of energy (primarily heat), which is then converted into electricity. (See previous section on Nuclear Energy and Reactions for details on Fission and Nuclear Reactors).

Nuclear energy from fission is a major source of electricity globally and in India, contributing to grid stability as a base-load power source. It offers a low-carbon alternative to fossil fuels for electricity generation. However, the challenges of managing radioactive waste, the risk (albeit low) of severe accidents, security concerns regarding nuclear materials, and the finite nature of the fuel remain significant considerations in its role in the future energy landscape.

Research into advanced reactor designs (like breeder reactors and Small Modular Reactors - SMRs) and nuclear fusion power (the energy source of the Sun) aims to address some of the limitations of current nuclear fission technology and explore potentially more sustainable or cleaner nuclear options for the future.