Sustainable Living Challenge Sustainability and Really Cool Technologies - Subject Supplement

Electricity – Innovative Technologies towards Sustainable Development

‘Learning-by-Notes’ Package for
Senior School - Physics

Lesson 7: Flowing Water

How Do We Make Electricity from Flowing Water?

Teaching Sustainability in High Schools:
Subject Supplement

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Prepared by The Natural Edge Project 2008 Page 1 of 47

Electricity – Innovative Technologies towards Sustainable Development
Lesson 7: Electricity from Water

© The Natural Edge Project(‘TNEP’) 2008

The material contained in this document is released under a Creative Commons Attribution 3.0 License. According to the License, this document may be copied, distributed, transmitted and adapted by others, providing the work is properly attributed as: ‘Desha, C., Hargroves, S., Smith, M., Stasinopoulos, P. (2008) ‘Sustainability Education for High Schools: Year 10-12 Subject Supplements. Module 2:Electricity – Innovative Technologies towards Sustainable Development’. The Natural Edge Project (TNEP), Australia.’ This document is freely available electronically.

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Acknowledgements

The development of the ‘Sustainability Education for High Schools: Year 10-12 Subject Supplements’ has been supported by a grant from the Port of Brisbane Corporation as part of the Sustainable Living Challenge. The Port of Brisbane Corporation is a Government Owned Corporation responsible for the operation and management of Australia’s third busiest container port. Its vision is, ‘To be Australia’s leading port: here for the future’. Sustainability for the Port of Brisbane Corporation means making economic progress, protecting the environment and being socially responsible. In response to the recent drought, and the wider global debate on climate change, the Port is committed to working with the port community to showcase the Port of Brisbane as a sustainable business precinct. Initiatives aimed at reducing the Port of Brisbane’s ecological footprint include energy efficiency, a green corporate fleet and constructing green buildings.

The development of this publication has been supported by the contribution of non-staff related on-costs and administrative support by the Centre for Environment and Systems Research (CESR) at GriffithUniversity; and the Fenner School of Environment and Society at the AustralianNationalUniversity. The material has been researched and developed by the team from The Natural Edge Project. Versions of the material have been peer reviewed by Cameron Mackenzie, Queensland Department of Education, and Ben Roche, National Manager, Sustainable Living Challenge, University of New South Wales.

Project Leader: Mr Karlson ‘Charlie’ Hargroves, TNEP Director

Principle Researcher: Ms Cheryl Desha, TNEP Education Director

TNEP Researchers: Mr Michael Smith, Mr Peter Stasinopoulos

Copy-Editor: Mrs Stacey Hargroves, TNEP Editor

The Natural Edge Project

The Natural Edge Project (TNEP) is an independent non-profit Sustainability Think-Tank based in Australia. TNEP operates as a partnership for education, research and policy development on innovation for sustainable development. TNEP's mission is to contribute to, and succinctly communicate, leading research, case studies, tools, policies and strategies for achieving sustainable development across government, business and civil society. Driven by a team of early career Australians, the Project receives mentoring and support from a range of experts and leading organisations in Australia and internationally, through a generational exchange model. TNEP’s initiatives are not-for-profit. Our main activities involve research, creating training and education material and producing publications. These projects are supported by grants, sponsorship (both in-kind and financial) and donations. Other activities involve delivering short courses, workshops, and working with our consulting associates as we seek to test and improve the material and to supplement the funds required to run the project. All support and revenue raised is invested directly into existing project work and the development of future initiatives.

Enquires should be directed to: Mr Karlson ‘Charlie’ Hargroves, Co-Founder and Director, The Natural Edge Project

Prepared by The Natural Edge Project 2008Page 1 of 21

Electricity – Innovative Technologies towards Sustainable Development
Lesson 7: Electricity from Water

Lesson 7: Flowing Water
How Do We Make Electricity fromFlowingWater?

Water covers more than 70 percent of the Earth's surface. Using environmentally responsible technologies, we have a tremendous opportunity to harness energy produced from ocean waves, tides or ocean currents, free flowing water in rivers, and other water resources to … provide clean and reliable power.

Andy Karsner, US Department of Energy
Assistant Secretary for Energy Efficiency and Renewable Energy, May 2008[1]

Educational Aim

The aim of this lesson is to describe the key components of hydroelectric power plants and ocean power plants, and the processesused by these technologies to generate electricity from flowingwater.

Key Words for Searching Online

Hydroelectric power plant,hydrologic cycle, dam, water turbine, ocean power, tidal power, current power, wave power, tide, ocean current, wind wave.

Key Learning Points

  1. Making electricity from flowingwater is generally a three step process:

1)harnessing or creating a water flow;

2)using the water flow in a water turbine to rotate the turbine shaft; and

3)using the rotating turbine shaft in an electric generator to generate electricity.

  1. While electricity from flowing water can be an excellent source of ‘renewable energy’, the generation of electricity in this way needs to be considered carefully for environmental and social implications. These including potentially significant impacts on fish and other species, and upstream and downstream human settlements. Depending on the method of making electricity, hydroelectric plants may have greenhouse gas emissions associated with decomposing vegetation that has been submerged in the process of creating dams, and energy used for pumping the water. Depending on their design, dams can have a high evaporation rate, they can become toxic for fish, and can also increase the likelihood of algal blooms.[2] Plants using ocean currents, tides and wind may also have environmental impacts in particular systems that harness energy at the junction between waterways and the ocean with potential impacts on estuary flows.
  2. With these considerations in mind, we will now consider how these systems work.

Hydroelectric Power Plant (Waterways – Natural Flows and Dams):

  1. Hydroelectric power plants generate electricity using the energy from flowing water, called ‘linear kinetic energy’, and energy from pressure, called ‘pressure potential energy’:

The water flow may be natural in an existing waterway, created by what we refer to as a ‘Water Cycle’, or ‘Hydrologic Cycle’, driven by the Sun’s energy.

The water flow may be created by releasing from water at pressure behind a dam. Dam walls are essentially barricades in waterways that slow or stop the water flow so that the water accumulates behind it, in a reservoir. Water flow is created by releasing water from the reservoir to a waterway, ocean or to another lower reservoir.

  1. Water Turbines convert water flow to mechanical rotation.Water flow (linear kinetic energy) at pressure (pressure potential energy) is channelled onto the turbine’s blades and forces them to move via either an impulse force or a reaction force, depending on the type of turbine. The blades are connected to the turbine shaft such that when the rotor blades move, the turbine shaft rotates (rotational kinetic energy). (Turbines are explained in Lesson 6).
  2. A water turbines’ power output depends on two main factors: the energy of the water flow and the volume of water.
  3. Impulse turbines are typically used where the energy of the water flow is high and the volume of water is moderate to low. Reaction turbines are typically used where the energy of the water flow is moderate to low and the volume of water is high.
  4. There are three main types of large-scale (greater than 30 megawatts) and small-scale (100 killowatts to 30 megawatts) hydroelectric power plants: 1) conventional,[3]2) pumped storage[4]and 3) diversion.[5] There are also very-small-scale (less than 100 kilowatts), or ‘microhydro’, plants.[6]

Ocean Power System (Tides, Currents and Wind):

  1. Electricity can be made from the ocean’s water by using the tides, waves or currents. Making electricity in tidal, current or wave power systems is similar to making electricity in a hydroelectric power plant or in a wind power system (see Lesson 5B).
  2. Tides are created by the pulling gravitational force applied by the moon and, to a lesser effect, the Sun. The ocean’s bulging sides are at high tide and the ocean’s flat sides are at low tide. The bulging and flat sides rotate once around the Earth every 24 hours and 50 minutes as the Earth rotates on its axis.
  3. Currents[7]occur in the ocean’s surface layer (the upper 200-400 metres). Cyclic currents, called gyres, are created by a combination of the Sun’s heat energy, wind forces, gravitational forces and Coriolis forces (which result from the Earth’s rotation).
  4. Wind waves[8] are the most common type of ocean wave. Wind waves are created by the force of wind over the water’s surface.
  5. Tidal power systems: Barrier systems use a type of dam, called a barrage, which stretches completely across the wide mouth (estuary) between a river basin and the ocean. The barrage has vertical sluice gates that are raised and lowered to control the water flow between the ocean and the river basin. Around high tide, water flows into the lagoon; and around low tide, that water ebbs back into the ocean. The turbine can be configured to operate with either the water flow or the water ebb; or with both. Tidal lagoon systems use a type of enclosed dam built from rubble mounds and are located up to 2km offshore. They operate similarly to barrier systems.
  6. Current power systems: Tidal fences, or tidal mills, use a fence structure, called a caisson, across a region of high current. The caisson has several vertical-axis turbines (usually impulse turbines), the blades of which are rotated by the current. Tidal turbines are similar to horizontal-axis wind turbines (see Lesson 5B).
  7. Wave power systems: There are two general types of wave power systems – fixed and floating. These systems are diverse in their operation. For example:

-The Oscillating Water Column and the Mighty Whale systems use waves to force an air flow in a fixed or floating column, which then rotates an air turbine.

-The TAPCHAN and Wave Dragon systems (which may be fixed or floating) use their geometry to force waves to increase in height and direct the water into an elevated reservoir. The reservoir is used in a similar arrangement to a reservoir in a hydroelectric power plant to rotate the turbine’s blades.

-The WaveRoller, Pelamis and Salter Duck use objects that are partially rotated by the force of the waves. The partial rotation is converted to full rotation by mechanisms such as piston pumps and hydraulic motors.

-The Archimedes Wave Swing uses a vertically expanding capsule that contains pressurised air. As waves above the capsule move through crests and troughs, the water pressure above the capsule varies relative to the air pressure in the capsule, which then forces the capsule to vertically expand and contract. This vertical motion is converted into electric current by an inbuilt linear electric generator.

Prepared by The Natural Edge Project 2008Page 1 of 21

Electricity – Innovative Technologies towards Sustainable Development
Lesson 7: Electricity from Water

Brief Background Information

Making electricity from water is generally a three step process:

  1. Harnessing or creating a water flow
  2. Using the water flow in a water turbine to rotate the turbine shaft
  3. Using the rotating turbine shaft in an electric generator to generate electricity

The two configurations to make electricity from water are the hydroelectric power plant and the ocean power system.

Hydroelectric Power

Water Flow

Hydroelectric power plants generate electricity using a water flow’s movement energy, called linearkinetic energy, and pressure energy, called pressure potential energy.Water flowis harnessed from either ariver or, more commonly, from water at pressurebehind adam.

Dams are like barricades in rivers that slow or stop the water flow such that the water accumulates in a reservoir (see Figure 7.1).

The water in the reservoir is at pressure, called hydrostatic pressure, which provides the water with pressure potential energy.

Hydrostatic pressure, and hence pressure potential energy,increase with the water depth. Water flow is created by releasing water from the reservoirto either the river, the ocean or a lower reservoir.

In creating the water flow, some of the pressure potential energy is converted to linear kinetic energy while the rest of the pressure potential energy is maintained.

Figure 7.1.Cross section ofa conventional hydroelectric power plant

Source:US Department of Energy[9]

A river’s natural water flow is created by the Water Cycle, or Hydrologic Cycle, which is a natural, global cycle as shown in Figure 7.2. In the Water Cycle, which is driven by the Sun’s energy, water evaporates from lakes and oceans, forms clouds, precipitates as rain or snow and flows back to lakes and oceans.[10]

Figure 7.2. The Water Cycle

Source:US Department of Energy[11]

Water Turbines

Water Turbines convert water flow to mechanical rotation.Specifically, they convert the combined input linear kinetic energy and pressure potential energy of water flow to output rotational kinetic energy of the turbine shaft in a process similar to that ofa steam turbine(see Lesson 6). In brief, water flow (linear kinetic energy)at pressure (pressure potential energy)is channelled onto the turbine’s blades and forces them to move via either an impulseforce ora reaction force, depending on the type of turbine.The blades are connected to the turbine shaft such that when the rotor blades move, the turbine shaft rotates (rotational kinetic energy).

Water turbines’ power output mainly depends on two factors:

  1. The energy of the water flow: which determines the force applied by the water on the blades. For many hydroelectric power plants, this energy depends on the hydrostatic pressure, and hence the water depth above the turbine.
  2. The volume of water: which determines either the blade areaover which the force acts or the duration for which the force acts.

These factors are optimised by locating hydroelectric power plants at the base of a valley, gorge or dam.[12]They also determine the type of turbine used in a hydroelectric power plant.[13]

Impulse turbines are typically used where the energy of the water flow is high and the volume of water is moderate to low.In impulse turbines, water is guided by stationary blades, or nozzles, onto moving blades, or buckets. The impulse force applied by the water on the buckets causes the buckets to move and the turbine shaft to rotate. A common type of impulse turbine is the Pelton Wheel turbine (see Figure 7.3).Other types of impulse turbinesare the Turgo Wheel and Cross-Flow turbine.[14]

Figure 7.3. Pelton Wheel water turbine in a hydroelectric power plant

Source: Western Power Corporation cited in Research Institute for Sustainable Energy (2006)[15]

Reaction turbines, or propeller turbines, are typically used where the energy of the water flow is moderate to low and the volume of water is high. In reaction turbines, water is guided by stationary blades, or guide vanes, onto moving blades, which are usually immersed in the water flow. The reaction force applied by the water on the moving bladeswhen the direction of the water flow changes causes the moving blades to move and the turbine shaft to rotate. Common types of reaction turbinesare theFrancis (see Figure 7.4) andKaplan turbines (see Figure 7.5). Other types of reaction turbinesare the Propeller,Bulb, Straflo,Tubeand Kinetic turbines.[16]

Figure 7.4.Francis water turbine in a hydroelectric power plant

Source: Western Power Corporation cited in Research Institute for Sustainable Energy (2006)[17]