Comprehensive Notes on Hydroelectric and Geothermal Power Generation

Geothermal Energy

• Energy derived from the Earth's internal heat, which is a renewable resource.

• Accessible by drilling water or steam wells.

• Can be used for heating and electricity generation.

• Geothermal power plants have low emissions if managed sustainably.

• High upfront costs for building geothermal plants.

• Geothermal Gradient:

  • The Earth's temperature increases with depth.

  • Gradients range from 15^oC/km to 50^oC/km.

  • High geothermal gradients mean hotter temperatures at shallower depths.

  • Areas with volcanic activity or tectonic plate boundaries often have higher geothermal gradients.

• Geothermal energy may produce waste brines, which contain dissolved minerals and salts.

• Proper disposal and management of waste brines are necessary to prevent environmental contamination.

• Geothermal energy produces no CO_2 during electricity generation.

• Minimal greenhouse gas emissions compared to fossil fuels.

• Utilization:

  • Hot water is pumped to heat buildings through direct-use applications.

  • Steam drives turbines for electricity generation in geothermal power plants.

  • Geothermal heat pumps can heat and cool buildings by utilizing shallow ground temperatures.

• Iceland relies heavily on geothermal energy for power and heating due to its volcanic activity and high geothermal potential.

• Other countries with significant geothermal energy use include the United States, Philippines, Indonesia, and New Zealand.

Hydroelectric Power

• Represents:

  • Up to 50% of West Coast electricity.

  • Up to 7% of US electricity.

  • Up to 20% of World’s electricity.

  • Hydroelectric power is a significant source of renewable energy worldwide.

• Involves:

  • Major environmental impacts, such as habitat destruction and altered river flow.

  • High construction costs for building dams and hydroelectric power plants.

• Relies on kinetic energy (KE) of running water to generate electricity.

• Dams convert KE to potential energy (PE) by storing water in reservoirs.

• Released water converts PE back to KE, turning turbines connected to generators for electricity generation.

• Tidal flux is used at some dams to generate electricity from the movement of tides.

Generating Electricity from Ocean Tides and Currents

• Ocean currents turn turbines or propellers to generate electricity.

• Tidal energy harnesses the energy of rising and falling tides.

• Rising tide: water accumulates on the seaward side of a barrier or dam.

• Falling tide: water is trapped on the landward side.

• Flowing water turns turbines in either scenario, generating electricity.

Small-Scale Hydroelectric Power Components

• Generator: Converts mechanical energy from the turbine into electrical energy.

• Control panel: Monitors and controls the operation of the hydroelectric system.

• Tailrace: Channel that carries water away from the turbine after it has passed through.

• Power canal: Channel that directs water from the reservoir to the penstock.

• Penstock: Pipe or tunnel that carries water from the reservoir to the turbine.

• Powerhouse: Building that houses the turbine, generator, and other equipment.

• Intake gates: Control the flow of water into the penstock.

• Turbine: Converts the kinetic energy of moving water into rotational mechanical energy.

• Draft tube: Helps to recover additional energy from the water leaving the turbine.

Large-Scale Hydroelectric Power Components

• Transmission lines conduct electricity to homes and businesses.

• Dam stores the water in a reservoir, creating a large water supply for power generation.

• Penstock carries water to the turbines.

• Generators are rotated by the turbines to generate electricity.

• Turbines are turned by the force of the water.

• Cross section of conventional hydropower facility that uses an impoundment dam.

Hydroelectric Power: Positive and Negative Aspects

• Positive Aspects:

  • Reduces flood risks by storing excess water in reservoirs.

  • Stores water for drinking, irrigation, and recreation.

  • Provides renewable energy without depleting fossil fuels.

  • Does not create hazardous waste or produce CO_2 during electricity generation.

• Negative Aspects:

  • Dams and reservoirs alter landscapes and ecosystems (e.g., 119 dams on Columbia River have caused a 94% drop in wild salmon).

  • Displaces millions of people worldwide as reservoirs flood traditional homelands.

  • No room for expansion in the US due to environmental concerns and limited suitable locations.

  • Filling of reservoirs often triggers seismicity due to increased pressure on underlying geological formations.

  • Reservoirs halt the downstream movement of sediment:

    • Downstream delta and beaches destabilized due to sediment starvation.

    • Reservoir loses capacity and must be dredged to remove accumulated sediment.

Impacts of Hydropower on People

• Dams can provide many human benefits but:

  • Disrupts ecological services rivers provide; e.g. 119 dams on Columbia River have caused a 94% drop in wild salmon; removing hydroelectric dams will restore native spawning grounds.

Impact of Hydropower on Fish

• Increased pollution from reservoir sedimentation and chemical runoff.

• Loss of biodiversity due to habitat destruction and altered river ecosystems.

• Invasive species can thrive in reservoirs, outcompeting native species.

Hydroelectric Power Generation By Country

• Canada.

• United States.

• Brazil.

• China.

• Russia.

• Norway.

• Japan.

• India.

• Sweden.

• France.

• These countries have significant hydroelectric power generation capacity due to their abundant water resources and suitable topography.

Hydroelectric Power Share of Total State Generation (Percent)

• Graphical representation of the percentage of hydroelectric share in the USA by state.

Hydroelectric Power Generation

• Graphical representation of the monthly net generation of hydroelectric power for Hoover dam and Folsom dam.

Three Gorges Dam (China)

• Purpose:

  • To produce energy for burgeoning Chinese population and reduce reliance on fossil fuels.

  • End disastrous floods along the Yangtze River.

  • 1998 Yangtze flood: 4,000 dead, 14 million left homeless and 24 billion in economic losses.

• Advantages:

  • Improved navigability on the river, allowing for increased shipping and trade.

  • Larger ships can sail as far as 2000 km upstream from the the sea, in the service of China's burgeoning domestic and export trade.

• Power Generation

  • 22.5 GW of electricity (or 11 San Onofre nuclear plants, or 34 Palm Springs Wind Farms!).

  • Created a reservoir 600 km (370 miles) long, and 1.1 km (0.68 miles) wide (on average).

  • Cost approx 26 billion (US).

• Disadvantages:

  • It inundated >1000 important archaeological sites, leading to the loss of cultural heritage.

  • Required the resettlement of 1.9 million people, causing significant social and economic disruption.

  • About 74,000 ha of good agricultural land has been flooded, reducing agricultural productivity.