Using Hydroelectric Power (College Board AP® Environmental Science): Study Guide

Hydroelectricity generation

• Hydroelectricity is the generation of electricity using the energy of moving water

• It is a renewable and sustainable source of energy

• The kinetic energy of flowing or falling water is converted into mechanical energy and then into electrical energy

A hydroelectric dam

How hydroelectricity generation works

• Water is stored in a reservoir created by building a dam across a river

• The dam controls water flow and creates a height difference (water head) to maximize potential energy

Turbines

• When water is released from the reservoir, it flows through turbines

• The force of the water turns the blades of the turbines, converting potential and kinetic energy into mechanical energy

Generators

• The turbines are connected to generators, which convert mechanical energy into electrical energy through electromagnetic induction

Transmission

• The electricity generated is transported via power lines to homes, industries, and other facilities

Types of hydroelectric power plants

Impoundment

• Impoundment is the most common type and uses a dam to store water in a reservoir

  • Water is released from the reservoir to flow through turbines and generate electricity

• Advantages of impoundment

  • Impoundment power stations are responsive because they can be turned on and off easily to meet changing demand

  • Impoundment power stations are cheap to run

  • Impoundment power stations can produce large amounts of electricity

• Disadvantages of impoundment

  • Valleys are flooded to create the reservoir used to store the water, which destroys habitats, towns and villages

  • Impoundment power stations are expensive to build because the land and properties need to be acquired in order to build the reservoir

Run-of-the-river

• Run-of-the-river uses the natural flow of the river to generate electricity by placing turbines in the channel flow

• The river's flow is captured and directed to the power plant via a headrace or penstock

  • Rest of the river water flows naturally

• After passing through the turbines, the water is returned to the river via a tailrace

  • This reduces environmental and natural flow impacts

• Advantages of run-of-the-river

  • Small, well-sited projects can be developed with minimal environmental impacts

  • Simple to operate, with fewer components and infrastructure than large dams

  • Low-carbon renewable energy

• Disadvantages of run-of-the-river

  • For fish-bearing rivers, a ladder may be needed for fish migration patterns

  • Dissolved gases downstream may affect aquatic ecosystems

  • Energy production varies depending on the river's flow and climate

• Pumped storage is where water from a lower reservoir is pumped to an upper reservoir during periods of low electricity demand

  • During peak demand, water is released back to the lower reservoir to generate electricity

• Advantages of pumped storage:

  • Large capacity: it can store energy from excess electricity generated

  • Reliable: provides quick response to sudden demand increases (known as peak-shaving)

  • Long lifespan: pumped storage plants can operate for decades with low maintenance, contributing to their sustainability

• Disadvantages of pumped storage:

  • Geographic limitations: requires specific landforms (mountains, valleys) and large reservoirs, limiting where it can be built

  • Environmental impact: constructing dams and reservoirs can damage ecosystems and disrupt local wildlife

  • Economic costs: can have very high initial costs to build

  • Pumping systems use fossil fuels, which release greenhouse gases and pollution into the atmosphere

Tidal energy

• A form of hydropower, also known as tidal energy, tidal power generates electricity by using the energy contained in the natural rise and fall of ocean tides

Basic principles

1. Gravitational forces: tidal energy is generated by the gravitational forces exerted by the moon and the sun, along with the rotation of the Earth

2. Tidal range is the difference in height between high tide and low tide. A larger tidal range results in more potential energy

3. Kinetic and potential energy: The movement of water during tidal changes contains both kinetic and potential energy that can be harnessed to generate electricity

Types of tidal power systems

Tidal barrages

• Tidal barrages store water at a height as the tide comes in and goes out

• Dams are built across the entrance of a tidal basin

• When the barrage is opened, water flows through a channel over a turbine

Tidal barrage

Tidal stream generators

• Underwater turbines are placed in fast-flowing tidal currents

• These turbines capture the kinetic energy of moving water to generate electricity

Tidal lagoons

• Enclosed areas capture high tide water and release it through turbines during low tide to generate electricity

Advantages of tidal power

• Renewable: Tidal energy is a renewable resource that is replenished by the natural tidal cycles

• Predictable: Tidal patterns are highly predictable, making it easier to forecast energy production

• Low emissions: Produces no direct greenhouse gas emissions during operation

• Long lifespan: Tidal power plants have a long operational lifespan, often exceeding 100 years

Disadvantages of tidal power

• Environmental impact: tidal power plants can disrupt marine ecosystems and affect local wildlife

• High initial costs: construction of tidal power plants requires significant investment

• Limited locations: suitable sites for tidal power plants are limited by geography and tidal range

• Intermittent: energy production is intermittent, depending on the tidal cycles