Unit 5: Other Renewable Energy Sources

Rajasthan Polytechnic (BTER) March 07, 2025

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Unit 5: Other Renewable Energy Sources

In addition to solar, wind, and biomass energy, there are several other renewable energy sources that can play a vital role in the future energy landscape. These sources often rely on natural forces like the ocean, geothermal heat, and even hydrogen, which can be used for sustainable power generation. Below is a detailed explanation of these sources:

5.1 Tidal Energy

Tidal Energy is the form of energy that comes from the natural rise and fall of sea levels caused by the gravitational pull of the moon and the sun on Earth's oceans. This motion can be harnessed to generate electricity.

  • How It Works: Tidal energy can be captured using Tidal Stream Generators (similar to underwater wind turbines) or Tidal Barrages (dams built across tidal estuaries). As water flows in and out of the estuary with the tide, the turbines spin, generating electricity.

  • Advantages:

    • Predictable and reliable source of energy.
    • Minimal environmental impact compared to fossil fuels.

  • Disadvantages:

    • High installation and maintenance costs.
    • Limited to areas with significant tidal movements.

  • Example: The La Rance Tidal Power Station in France, which has been in operation since 1966, is one of the largest tidal power plants in the world.

5.2 Wave Energy

Wave Energy harnesses the energy created by the motion of surface waves on the ocean. The kinetic energy from the up-and-down motion of waves can be converted into mechanical power, which is then used to generate electricity.

  • How It Works: Wave energy devices are typically either floating buoys or submerged pressure systems. These devices move with the waves and drive turbines to generate electricity.

  • Advantages:

    • Consistent energy source in coastal areas.
    • High energy density.

  • Disadvantages:

    • Needs to be located offshore, making installation difficult.
    • Strong waves and storms can cause damage to the equipment.

  • Example: The Pelamis Wave Energy Converter is one of the most well-known wave energy systems, designed to operate offshore and convert the motion of waves into electricity.

5.3 Open and Closed OTEC Cycles

Ocean Thermal Energy Conversion (OTEC) is a process that uses the temperature differences between the warm surface waters and the cold deep ocean waters to generate electricity.

There are two main types of OTEC cycles:

  • Open Cycle OTEC:

    • Involves the direct use of warm surface seawater to produce steam that drives a turbine to generate electricity.
    • The steam is condensed using cold water from the deep ocean.
    • Advantages: No chemical fluids used, environmentally friendly.
    • Disadvantages: Requires very specific location conditions and large infrastructure.

  • Closed Cycle OTEC:

    • Uses a heat exchanger where warm surface water is used to vaporize a working fluid (like ammonia), which is then used to drive a turbine.
    • Cold deep ocean water is used to condense the vaporized fluid.
    • Advantages: More widely applicable compared to open cycle.
    • Disadvantages: More complex systems and use of synthetic fluids.

  • Example: The Nauru OTEC project is one of the ongoing pilot projects that use the ocean’s temperature differential to generate electricity.

5.4 Small Hydro and Geothermal Energy

  • Small Hydro Energy:

    • Refers to hydroelectric systems with a capacity of less than 25 MW.
    • These are typically used in smaller rivers or streams and are less invasive than large-scale hydropower plants.
    • Advantages: Less environmental impact, cost-effective for rural or remote areas.
    • Example: Run-of-the-river systems, which do not require large reservoirs, are commonly used for small hydro generation.

  • Geothermal Energy:

    • Geothermal energy is derived from the Earth's internal heat, which is harnessed by tapping into underground hot water reservoirs or steam fields.

    • How It Works: Wells are drilled into the Earth to access geothermal reservoirs. The steam or hot water is brought to the surface, and this heat is used to generate electricity through turbines.

    • Advantages: Constant and reliable energy source, minimal land use.

    • Disadvantages: Location-specific, expensive to build and maintain geothermal plants.

    • Example: The Geysers, located in California, is the largest geothermal power plant complex in the world.

5.5 Hydrogen and Storage

Hydrogen is a clean energy carrier that can be used in various forms, including for electricity generation, heating, and even in transportation (fuel cells). Hydrogen does not release pollutants when used as a fuel, making it an attractive option for a low-carbon future.

  • How It Works: Hydrogen is typically produced through electrolysis, a process that splits water into hydrogen and oxygen using electricity (which can be sourced from renewable energy). The hydrogen can then be stored in tanks and used as fuel or to generate electricity through a fuel cell.

  • Storage Methods:

    • High-pressure tanks
    • Cryogenic storage (storing hydrogen as a liquid at very low temperatures)

  • Advantages: Zero emissions at the point of use, versatile applications in various sectors.

  • Disadvantages: Expensive production methods, high energy consumption in storage and transportation.

  • Example: The Toyota Mirai is a hydrogen-powered vehicle, demonstrating hydrogen’s use in transportation.

5.6 Fuel Cell Systems

Fuel Cells are devices that convert chemical energy (typically hydrogen) directly into electrical energy. They work on the principle of electrochemical reactions and do not involve combustion.

  • How It Works: A fuel cell uses hydrogen (or another fuel) and oxygen to produce electricity, heat, and water. The hydrogen is supplied to the anode, and the oxygen is supplied to the cathode. An electrochemical reaction takes place, generating electrical energy.

  • Types of Fuel Cells:

    • Proton Exchange Membrane Fuel Cells (PEMFC): Used primarily in transportation (cars, buses).
    • Solid Oxide Fuel Cells (SOFC): Used for stationary power generation.

  • Advantages: High efficiency, low emissions, quiet operation.

  • Disadvantages: Expensive, requires a hydrogen infrastructure.

  • Example: Ballard Power Systems is one of the companies that produces hydrogen fuel cell systems for various applications.

5.7 Hybrid Systems

Hybrid Systems combine two or more renewable energy sources to optimize the generation and efficiency of power. These systems are designed to take advantage of different energy sources’ strengths and compensate for their weaknesses.

  • How They Work: A hybrid system might combine solar and wind energy, where solar power is available during the day and wind power is more efficient at night. Similarly, solar and battery storage systems can work together to provide power even when the sun is not shining.

  • Types of Hybrid Systems:

    • Solar-Wind Hybrid: Combining the variability of solar and wind to provide more stable energy generation.
    • Solar-Diesel Hybrid: Using solar power in conjunction with a diesel generator to reduce fuel consumption in off-grid areas.
    • Solar-Battery Hybrid: Solar energy charges batteries that can provide power when needed.

  • Advantages:

    • Increased reliability and power supply.
    • Optimized use of renewable resources.

  • Disadvantages:

    • Higher initial investment and maintenance costs.
    • Requires sophisticated management systems.

  • Example: Solar-Wind Hybrid systems used in remote off-grid locations to provide a continuous power supply by integrating solar and wind energy sources.

Conclusion

The world of renewable energy is vast, and there are many alternatives beyond the traditional solar and wind energy sources. Technologies such as tidal, wave, OTEC, hydrogen, and fuel cells are pushing the boundaries of how we generate and store clean energy. As these technologies continue to evolve and mature, they hold significant potential in combating climate change and transitioning to a sustainable energy future.

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Rajasthan Polytechnic (BTER)

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