Chapter 18: Renewable Energy Alternatives

Lesson 1: Biomass and Geothermal Energy

The Reasons for Alternative Energy Alternative energy resources are needed to replace

fossil fuels, reduce air pollution, and reduce the emission of greenhouse gases.

Benefits of renewable energy• Most of them are unlikely to run out• If renewable energy resources replace fossil fuels,

they will help decrease air pollution and greenhouse gas emissions• Become less dependent on other nations to supply us

with fuel• Will create jobs for people to design, build, and

maintain the needed technology

Renewable energy today• Fossil fuels supply 80% of our energy• Use of renewable energy sources is generally

growing much faster than use of nonrenewable energy• Currently renewable energy sources cannot yet

produce enough power to replace fossil fuels and nuclear energy

Biomass Energy Energy derived from biomass is used for cooking, heating,

powering motor vehicles, and generating electricity. Biomass is material that makes up living organisms or

comes from organisms. Biomass energy is energy that is produced from this

material More than 1 billion people still burn wood from trees as

their main energy source Wood, charcoal, and manure account for 35% of energy

use in developing nations Biomass energy can now power motor vehicles and

generate electricity

Biofuels• Liquid fuels from biomass sources are known as

biofuels• Ethanol

oProduced by the fermentation of starches or sugars

oUsed in gasoline enginesoIn the US it is mainly produced from cornoA blend of gasoline and alcohol called

gasohol is widely used in the US because it releases smaller amounts of many pollutants

• BiodieseloProduced from vegetable oiloCan be used in its pure form, but is usually

mixed with conventional petroleum-based diesel fuel

oCuts down on emissions

Biopower• Electricity that is generated by the combustion of

biomass is called biopower.• Many of the sources used for biopower are the

waste products of existing industries or processes such as sawdust and cornstalks.• The decomposition of biomass by microorganisms

produces gas that can be used to generate electricity.• The methane produced in landfills, called “landfill

gas,” is captured and sold as fuel.

Benefits of biomass energy• The carbon produced by the combustion of

biomass is the same amount of carbon that was removed from the atmosphere by photosynthesis to make the biomass in the first place.• Biomass is distributed worldwide• Help reduce dependence on imported fuels

Costs of biomass energy• Biofuel crops take up land that might be used for

growing food or left in its natural condition• Deforestation, soil erosion, and desertification can

result if wood is cut down too rapidly for fuel• Can cause indoor air pollution and increases the

risk of respiratory system problems.• Corn ethanol provides only a small amount more

energy than the energy needed to produce it.

Geothermal Energy Steam and hot water produced by geothermal

energy can be used for generating electricity and for heating

Deep beneath the surface of Earth, high pressure combined with the breakdown of radioactive elements produces heat – geothermal energy.

Hot springs and geysers are the result of geothermal energy

Harnessing geothermal energy• Steam from geysers at the surface is used to

supply energy• Usually wells must be drilled down hundreds or

thousands of meters toward heated rocks and water

Generating electricity1. Magma heats ground water2. Wells tap underground heated water or

steam 3. Steam turns turbines and generates power4. Steam is cooled and condensed5. Water is returned back into the aquifer• Some geothermal plants will pump cold water

deep underground where it reaches heated rocks and turns into steam

Hot groundwater can be used directly for heating homes, offices, and greenhouses

A ground source heat pump takes advantage of the fact that the temperature of soil a few feet underground stays the same all year.• In the winter, the water in the pipes picks up heat

from the ground and transfers it to a building• In the summer, the water in the pipes transfers

heat from the house to the ground.

Benefits and costs of geothermal energy• Can help replace the use of fossil fuels• Causes less air pollution• Releases smaller quantities of greenhouse gases• Sources may not always be truly sustainable• The water of many hot springs contains

chemicals that damage equipment and add to pollution• Some geothermal energy projects may trigger

earthquakes• Limited to areas where heated groundwater is

easily accessible

Lesson 2: Hydropower and Ocean Energy

Generating Electricity with Hydropower The movement of river water can be used

to generate electricity In hydropower, or hydroelectric power, we

use the kinetic energy of moving water to turn turbines and generate electricity.

In the US 6% of the electricity is generated by hydropower

Using water stored behind dams• A dam blocks a river and water is stored in a

reservoir behind the dam• As the river water passes through the dam, the

water turns the blades of a turbine which cause generators to produce electricity• Most hydropower is generated by dams

Using the natural flow of a river• Called the run-of-the-river approach• Some of the river water is diverted through a

pipe, which carries the water to the turbines.• This method does not disturb natural habitats

as much• When the river is low, little electricity is

produced

Benefits and Costs of Hydropower Hydropower is nonpolluting and relatively

inexpensive, but dams can harm ecosystems and disrupt people’s lives.

Most of the rivers that offer the best opportunity for hydropower are already dammed.

Benefits• Renewable resource• Considered “clean” because nothing is burned• Does not pollute the atmosphere or release

greenhouse gases• Relatively inexpensive• Dams can also control floods

Costs• Drastically change ecosystems• Interrupts the natural flow of water• Negative impact on fish populations• Dam construction can cause damages to the

landscape, erosion, and landslides• Dams can prevent important sediments and

nutrients from getting downstream

Three Gorges Dam• On China’s Yangtze River• Completed in 2008• Generates enough hydropower to replace dozens of large

coal and nuclear plants• Controls floods and enables boats to travel farther

upstream• Cost $26 billion to build• Flooded many cities, destroyed the homes of 1.3 million

people, and flooded 10,000 year-old archeological sites.• Rising water has destroyed farmlands and wildlife habitats.

Energy From the Ocean The movement of tides and ocean thermal

energy can be used to generate electricity Tidal Energy• The term tidal energy refers to using the

movement of tidal water to generate electricity• Twice a day, as ocean tides rise and fall, large

amounts of water move upward and then draw back

• In one method, a dam is built across a bay or tidal riveroAs the tide rises, water moves through the

dam and enters the bay and as the water from the receding tide passes through the dam it is channeled through a system of turbines.

• Harnessing tidal energy works best in long, narrow bays such as Alaska’s Cook Inlet or the Bay of Fundy in Canada because the differences in height between high and low tides are especially great.

• Tidal electricity stations have the benefit of releasing few or no pollutants• Can harm the ecology of the bay or river• There are few places where tidal energy can be

harnessed effectively

Thermal energy from the ocean• Each day, ocean water near the equator

absorbs radiation from the sun• Ocean thermal energy conversion (OTEC) is a

process that converts the thermal energy in ocean water to electrical energy that people can use.

• The natural temperature gradient in ocean water is used to generate electricityoWarm surface water circulates around pipes

that contain substances that boil at temperatures that are lower than the boiling point of water.

oThe heat from the water makes the substance evaporate and the gas spins turbines to generate electricity.

oCold water piped in from the ocean depths then condenses the gas so it can be used again.

• Costs remain high

Lesson 3: Solar and Wind Energy

Harnessing Solar Energy The sun’s energy can be used to heat buildings and

generate electricity The sun provides energy for almost all life processes

on Earth Using sunlight directly, without involving mechanical

or electrical devices is called passive solar heating• Involves designing a building to collect, store, and

distribute the sun’s energy naturally• Greenhouses and homes that are designed with windows

that face south and east to capture sunlight in winter are using passive solar heating

An active solar heating system uses technology to collect, move, and store heat derived from the sun.• A flat-plate solar collector generally consists of

a black, heat-absorbing metal plate in a flat box with a glass cover and has a long tube running through itoSunlight passes through the glass and heats

the metal plate and the fluid in the tube absorbs heat from the metal plate

• In a photovoltaic (PV) cell, solar energy is converted directly into electricity.oContain two plates typically made of siliconoOne plate is rich in electrons and when sunlight

strikes this plate it knocks some electrons loose which are then attracted to the other plate

oThe flow of electrons creates an electric current

oPV cells can be arranged in panels or contained in special roofing tiles

• Concentrating solar power (CSP) is a technology that uses mirrors to focus sunlight in order to generate electricity.oA “power tower” has hundreds of mirrors

positioned in a large area surrounding a tall tower that houses a receiver.o Heated fluid in the receiver is used to produce steam

which turns the blades of a turbine and powers a generator.

Benefits and Costs of Solar Power Solar power has many benefits, such as its

limitless supply, but it depends on weather and is currently expensive

Benefits• Endless source• Technology uses no fuel• Quiet and safe technology• No greenhouse gases released• Requires little maintenance• Reduces dependence on power plants• Possible to sell excess solar electricity to power

companies• Creating many new jobs

Costs• Manufacturing solar-energy devices creates

some pollution• Some regions are not sunny enough to provide

much solar power• Solar equipment is expensive

Harnessing Wind Power Wind turbines convert wind’s kinetic energy into

electrical energy People have used wind power for thousands of

years with windmills A wind turbine is a device that converts the

wind’s kinetic energy into electrical energy• Wind blowing into a turbine turns blades that

connect to a gearbox which connects to a generator that produces electricity.

Wind turbines are often built in groups called wind farms

Average wind speeds are approximately 20% greater over water than over land

Offshore wind turbines are becoming more common even though costs to erect and maintain wind turbines in water are higher.

Benefits and Costs of Wind Power Wind power is nonpolluting and efficient,

but its supply is unpredictable and it may damage the landscape and wildlife.

Benefits• Does not cause pollution• Highly efficient• Wind farms are less expensive than fossil fuel

power plants once they are up and running

Costs• Wind farm startup costs are generally higher than

those of fossil fuel power plants• We have no control over when wind will occur –

unpredictable• Some areas are windier than others• When wind farms are proposed near communities,

the people living in the area often oppose themoClutter the landscapeoToo noisy

• Birds and bats can be killed

Lesson 4: Energy From Hydrogen

Producing Hydrogen Fuel Hydrogen fuel can be produced from the

breakdown of water or other hydrogen-containing compounds

In electrolysis, water molecules are broken down into oxygen gas (O2) and hydrogen gas (H2) by an electric current that runs through the water• 2H2O → 2H2 + O2 • Does not emit greenhouse gases or pollutants• A costly process

Hydrogen can be extracted from the breakdown of methane in natural gas.• CH4 + H2O → 4H2 + CO2

• Less expensive• Produces a greenhouse gas

Scientists are investigating other ways to obtain hydrogen• The heat given off by a nuclear reactor may be

used to split water into hydrogen and oxygen• Algae may be used to produce hydrogen

Benefits • Hydrogen is the most abundant element in the

universe• Produces few greenhouse gases or pollutants• Water and heat may be the only waste

products generated• Can be stored and transported

Costs• Can catch fire if not stored properly• Requires energy inputs• Expensive to produce• To be useful in a motor vehicle, hydrogen needs

to be compressed

Fuel Cells Fuel cells are used to generate electricity Hydrogen gas can be used to produce

electricity within fuel cells A fuel cell has a positive electrode and a

negative electrode and reactions in a fuel cell result in an electric current • Uses the reverse of the reaction for electrolysis

o2H2 + O2 → 2H2O

• Hydrogen gas enters the side of the cell with the negative electrode and each molecule then splits into two positively charged hydrogen ions (H+)• Oxygen gas enters the cell on the side with the

positive electrode• A series of reactions cause an electric current to

flow from the negative terminal to the positive terminal and while this happens the oxygen and hydrogen ions combine to form molecules of water

A fuel cell can be used in many ways such as powering vehicles and producing electricity.