Chapter 19: Alternative Energy and the Environment

Introduction to Alternative Energy Sources

• Nonrenewable alternative energy– Nuclear because it requires a mineral fuel

mined from Earth– Geothermal because heat can be extracted faster

than it is replenished

• Renewable energy sources– Solar, fresh water, wind, ocean, and biofuels– All derive from the sun’s energy

Introduction to Alternative Energy Sources

• Total energy we are able to extract from alternative energy is enormous

Some Limitation of Renewable Energy

• May not be available when we need it.– Daily and seasonal variation– To smooth out supply need energy storage

systems

• Not equally available in all locations• Solar energy more expense

– Smaller subsidies

• Compete with other land use

More Benefits of Alternative Energy

• Associated with minimal environmental degradation– Do not increase atmospheric CO2

– Will not cause climate change or raise sea levels

– Lead time to build plants is short

Solar Energy

• Total amount of solar energy reaching Earth’s surface is tremendous– 10 weeks of solar energy equivalent to all

known fossil fuel reserves

Passive Solar Energy

• Promotes cooling in hot weather and retaining heat in cold weather

• Methods include– Overhangs that block summer sun but allow

winter sun in– Building a wall that absorbs heat during the day

and releases it at night– Plant deciduous trees

Active Solar

• Energy systems that require mechanical power– Electric pumps to circulate air, water or other

fluids from solar collectors to a location where heat is stored

– Then pumped to where the energy is used

Solar Collectors

• Provide space heating or hot water– Usually flat glass covered plates over a black

background where and absorbing fluid is circulating through tubes

– A second type is evacuated tube collector• Each tube along with absorbing fluid pass through a

larger tube

Photovoltaic

• Converts sunlight directly into electricity– Made from thin layers of semiconductors and a

solid-state electronic components with few or no moving parts

• World’s faster growing source of energy

Photovoltaic

• Off the grid emerging as a major contributor to developing countries– Don’t have ability to build a electrical grid– Systems can power lights and televisions in

small villages

Solar Thermal Generators

• Focus sunlight onto water-holding containers. – The water boils and is used to run conventional

steam-drive electrical generators– Being built with very large output – Traditionally towers more recently devices built

w/ many mirrors

Solar Energy and the Environment

• Generally low impact

• One concern– Variety of metals, glass plastics, and fluids used

in the manufacture and use of solar equipment.– Production and accidental spills could release

toxic materials

Converting Electricity from Renewable Energy to a Fuel that can be Burned and

can Power Vehicles

• Basically two choices:– Store electricity in batteries and use electrical

vehicles– Transfer the energy in the electricity to a

gaseous or liquid fuel.• hydrogen

Hydrogen Fuel

• An electrical current can be used to separate water in top the hydrogen and oxygen.

• Can be produced using solar and other renewable energy sources– Then transported in pipelines and held in tanks

• Combustion product is water

Water Power

• A form of stored solar energy.

• Long history– Waterwheels convert water power to

mechanical energy

• Today hydroelectric power plants use the water stored behind dams.– Also produced through the process of pump

storage

Small-Scale Systems

• The total amount of electrical power produced by running water from large dams will probably not increase in the coming years in the US.– Most dam sites already utilized– Small scale systems have potential in

mountainous areas along streams.

Water Power and the Environment

• Water power is clean and efficient power– No burning of fuel, no radioactive waste

• Impact– Flood large tracts of land– Block fish migration– Trap sediment that would replenish beaches– Evaporative loss of water from reservoirs

Ocean Energy

• A lot of energy is involved in the motion of waves, currents and tides in the ocean.– Difficult to harness

• Storms destructive and water corrosive

– Most successful tidal power– But very few areas w/ the right topography

Tidal Power

• To harness a dam built across the entrance to a bay or estuary– Water held in or out of bay until significant

difference in level will force water in or out running turbines

• Has environmental impacts– Changes hydrology of bay– Restricts passage of fish– Changes habitat for birds and other organisms

Wind Power

• Winds are produced when differential heating of Earth’s surface create air masses with differing heat contents and densities.– Potential energy from wind large– Problems w/ use because highly variable in

time, place, and intensity.• Wind velocity often increases over hill tops or

funneled through a mountain pass

Wind Power

• Wind energy is the cheapest form of alternate energy.– Less than natural gas and coal– Now used in many place including offshore

Wind Power and the Environment

• Wind energy does have a few disadvantages– Kills birds– Use large areas of land– May degrade area’s scenic resources

Future of Wind Power

• Growing at approximately 30% per year– Nearly 10 times the growth rate of oil use– Created thousands of jobs and investment

opportunities– Technology producing more efficient wind

turbines

Biofuels

• Energy recovered from biomass-organic matter– Three groups

• Firewood

• Organic wastes

• Crops grown to be converted into liquid fuels

Biofuels

• Are biofuels a net benefit or disbenefit?– Using waste as a fuel is a good way to dispose

of them– Firewood that regenerates naturally or in

plantations that require little energy input will continue to be important sources of energy

– Farming of crop to convert to liquid fuels is a poor source of energy

Biofuels and Human History

• Energy from biomass is the oldest fuel used by humans.– Until end of 19th century major fuel source in

the US– 1 billion people in the world still use wood as

primary source of energy for heat and cooking

• Includes: firewood, cattle dung, peat

Biofuels and the Environment

• Can pollute the air and degrade the land– World’s forests will decrease if our need for

forest products and forest biomass fuel exceeds the productivity of the forests.

– Combustion of biomass-derived fuel generally release fewer pollutants then combustion of coal/gasoline.

• But burning urban waste can release heavy metals

Geothermal Energy

• Natural heat from the interior of the Earth.– Mined and used to heat buildings and generate

electricity– May be considered nonrenewable when rates of

extraction are greater than rates of natural replenishment

Geothermal Systems

• Areas of high heat flow occur at plate boundaries– Divergent and convergent plate boundaries

• A common system, hydrothermal convection, transfers heat from depths to surface.– Using steam or hot water

Geothermal

• Most groundwater can be considered a source of geothermal energy– Groundwater at a depth of 100m is 13oC or

55oF– In summer heat can be transferred to the cool

water– In winter heat can be transferred from the water

to the air

Geothermal Energy and the Environment

• Problems include:– Considerable thermal pollution from hot

wastewaters• May be saline or highly corrosive

– On-site noise, emissions of gas and disturbance of land

Future of Geothermal Energy

• Could produce 10% of the electricity needed for the western US.

• Geohydrothermal could potentially provide four times that (10% of US total)