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Renewable Energy

“The use of solar energy has not been opened up because the oil industry does not own the sun.”- Ralph Nader

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Nonrenewable energy, including fossil fuels and nuclear power, make up the vast majority of the U.S. energy portfolio.

In the long-term, there are two major issues with this reliance on nonrenewable energy:Dwindling supplies.Environmental

pollution.

Nonrenewable Energy

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Nonrenewable resources, by definition, are finite and will eventually be used up.Most of the easily recoverable sources of coal,

oil, and natural gas have already been tapped.As supplies of these resources tighten, or they

become more expensive to extract, price will increase.

Dwindling Supplies

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Deep-ocean drilling of oil and hydraulic fracturing of natural gas are examples of resource extraction that would not have been economically viable in the past.

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The extraction, transport, and burning of fossil fuels is also a highly polluting process.

Pollution

Fossil fuels have a lot of modern applications. ElectricityFuel for

transportation

HeatThe strategies

for replacing them is going to vary for each. 6

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Electricity works by passing electrons from a power source through a series of wires, called a circuit. Within the circuit there are devices that use

the energy released by the electrons to do work (as light, heat, etc)

Electricity

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Electric power is measured in watts, the rate at which electrons moving through a circuit are doing work.

A standard incandescent light bulb consumes 60W of power.

A medium-sized car will consume about 100,000W.

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Electricity consumption is measured in kilowatt-hours.This includes both power and running-time.The charge per kilowatt-hour in this bill is 10.7

cents.

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At the rate shown in this bill, running a 60-watt light bulb for an hour would cost…60watts x 1 kilowatt/ 1000 watts = 0.06 kilowatts0.06 kilowatt-hours x $0.107/kwh = $0.00642 or 0.662 cents.

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The greatest renewable source of electricity production currently in use is hydroelectricity.

Renewable Electricity

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Hydroelectric power plants use running water to spin a turbine and generate electricity.Hydroelectricity is very economical, with costs

per kilowatt-hour similar to coal.No pollution is produced.

Hydropower

Trade-Offs: Large-Scale Hydropower, Advantages and Disadvantages

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The construction of the dam has major ecological impacts.Regular flooding downstream stops, preventing deposition of

silt and nutrients.The reservoir can experience sedimentation, where particles

of soil in the river settle to the bottom of the reservoir.The ecosystem immediately behind the dam becomes

flooded.River water, when stopped, warms faster and begins to

evaporate.Fish and other organisms can no longer move upstream.

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Any cities or villages in the area of the reservoir will have to be abandoned.

The Three Gorges Dam in China, completed in 2008, displaced 1.13 million people from the Yangtze River region.

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Another issue with dams is that they produce a constant, steady stream of electricity that cannot be easily adjusted to meet demand.Some dams have pumped storage, where water

will be sent and stored during low-demand times, then returned back through the dam’s turbines when demand is higher.

Kinzua Dam and

Seneca pumped storage

generating station,

Mead, PA

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Wind energy is similar to hydroelectricity, except that moving air provides the force to spin the generator.

Wind Energy

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Wind turbines are able to orient themselves to face the oncoming wind.

As the air passes through, the blades rotate. These are attached to a shaft, which connects to

the turbine.

Solutions: Wind Turbine and Wind Farms on Land and Offshore

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A single wind turbine can generate 1-7 megawatts of energy per year, not enough for a large population.Wind farms are large numbers of wind turbines

clustered together.

The Gansu Wind Farm in China produces 6 billion kilowatt-hours of electricity per year.

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Wind power is comparable in cost to coal.Possible negative impacts of wind turbines

include:Disruption of bird and bat migration pathways.Noise.Disruption of scenery.

Fig. 16-23, p. 421

TRADE-OFFSWind Power

Advantages DisadvantagesModerate to high net energy yield

Steady winds needed

High efficiencyBackup systems needed when winds are lowModerate capital

costLow electricity cost (and falling)

Plastic components produced from oil

Very low environmental impact

Environmental costs not included in market price

No CO2 emissions High land use for wind farm

Quick construction

Easily expandedVisual pollution

Can be located at seaNoise when located near populated areas

Land below turbines can be used to grow crops or graze livestock

Can kill birds and interfere with flights of migratory birds

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Geothermal power, like nuclear and coal, works by boiling water to steam.Naturally-occurring

heat from the Earth is used in place of fuel.

At a geothermal plant, two wells are drilled. One injects cold

water towards the underground heat.

The second directs steam to the turbine.

Geothermal Energy

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An enormous amount of energy (over 1,000 watts per square meter) hits the Earth every day.This energy is very diffuse, spread out across the

entire surface area of the planet.Two separate technologies have been

developed to convert solar energy into electricity.

Solar Energy

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Parabolic solar collection involves using curved reflective surfaces that collect light and focus it onto a concentrated point. The heat is absorbed and used to boil water into

steam, which spins a turbine.

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Photovoltaic cells capture solar energy and convert it directly to electrical current.

Solar electricity tends to be 1.5-2 times the cost of electricity from coal or other renewable sources.Not available on

overcast days or at night.

Fig. 16-11, p. 412

TRADE-OFFS

Passive or Active Solar Heating

Advantages Disadvantages

Energy is free Need access to sun 60% of time

Net energy is moderate (active) to high (passive)

Sun can be blocked by trees and other structures

Quick installation Environmental costs not included in market priceNo CO2 emissions

Very low air and water pollution

Need heat storage system

Very low land disturbance (built into roof or windows)

Active system needs maintenance and repair

High cost (active)

Active collectors unattractive

Moderate cost (passive)

Trade-Offs: Solar Energy for High-Temperature Heat and Electricity

Fig. 16-20, p. 417

TRADE-OFFS

Solar Cells

Advantages Disadvantages

Fairly high net energy yield

Need access to sun

Work on cloudy days

Low efficiency

Easily expanded or moved

Need electricity storage system or backupQuick installation

Environmental costs not included in market priceNo CO2 emissions

Low environmental impact

High costs (but should be competitive in 5–15 years)

Low land use (if on roof or built into walls or windows)

High land use (solar-cell power plants) could disrupt desert areas

Last 20–40 years

Reduces dependence on fossil fuels

DC current must be converted to AC

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Electricity generation by solar, wind, hydrokinetic, or geothermal plants is restricted by the natural geography of the United States.

Geography

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The Great Plains have the highest average wind speeds and the greatest potential for wind power.

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Areas with significant elevation differences and river courses are ideal for hydroelectricity generation.

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The western states are the most favorable for geothermal energy production.

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The deserts of the southwest are ideal for solar electricity generation.

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Besides electricity, significant amounts of fossil fuels are burned for heat, especially natural gas.

Heat

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Traditionally, humans have relied on burning biomass, such as wood, charcoal, and dung as a source of heat.These fuels will replenish, but produce similar

levels of pollution to fossil fuels.Excess demand can also lead to deforestation.

Biomass

Fig. 16-24, p. 422

TRADE-OFFSSolid Biomass

Advantages DisadvantagesLarge potential supply in some areas

Nonrenewable if harvested unsustainably

Moderate to high environmental impactModerate costs

No net CO2 increase if harvested, burned, and replanted sustainably

Environmental costs not included in market price

Increases CO2 emissions if harvested and burned unsustainably

Low photosynthetic efficiency

Plantation can be located on semiarid land not needed for crops Soil erosion, water

pollution, and loss of wildlife habitat

Can make use of agricultural, timber, and urban wastes

Often burned in inefficient and polluting open fires and stoves

Plantations could compete with cropland

Plantation can help restore degraded lands

Fig. 16-25, p. 424

TRADE-OFFS

Biodiesel

Advantages Disadvantages

Reduced CO emissions

Increased NOx emissions and more smog

Reduced CO2 emissions (78%)

Higher cost than regular diesel

High net energy yield for oil palm crops

Environmental costs not included in market price

Low net energy yield for soybean crops

Moderate net energy yield for rapeseed crops May compete with

growing food on cropland and raise food prices

Reduced hydrocarbon emissions

Loss and degradation of biodiversity from crop plantations

Better gas mileage (40%)

Potentially renewable

Can make engines hard to start in cold weather

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Energy from the sun can also be gathered to use as a source of heat.

Passive solar heat structures have no moving parts, but use south-facing windows to gather and absorb as much solar heat as possible.

Solar Heating

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Active solar heat structures pump water or another liquid through a collector.Can be used for

household radiant heating, or as a source of hot water for showers and cooking.

Image source: www.almeriaspas.com

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The third major energy need is fuel for transportation.

Most of the cars, planes, and ships of the world run on petroleum products – gasoline, diesel, etc.

Transportation

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Vehicles can be run on other fuels besides petroleum-based ones.

Biofuels, like ethanol, are generated from using bacteria or yeast to ferment plant matter.Currently, the biggest

source of this plant matter is corn. This can influence foodprices.

Alternative Fuels

Fig. 16-27, p. 426

TRADE-OFFS

Ethanol Fuel

Advantages DisadvantagesHigh octane Lower driving range

Low net energy yield (corn)

Some reduction in CO2 emissions (sugarcane bagasse)

Higher CO2 emissions (corn)Much higher cost

High net energy yield (bagasse and switchgrass)

Environmental costs not included in market price

May compete with growing food and raise food prices

Reduced CO emissions

Higher NOx emissions and more smog

Can be sold as E85 or pure ethanol

Corrosive

Can make engines hard to start in cold weather

Potentially renewable

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Hydrogen fuel cells use a chemical reaction between hydrogen and oxygen gas to generate an electric current.

H2 + O2 → H2O

Refueling is difficult, as pure hydrogen is a gas and difficult to store and transport safely.

No waste products are produced, except for water vapor.

Fig. 16-31, p. 430

TRADE-OFFSHydrogen

AdvantagesFuel cell

DisadvantagesCan be produced from plentiful water

Not found as H2 in natureEnergy is needed to produce fuelLow environmental

impact Negative net energyRenewable if produced from renewable energy resources

CO2 emissions if produced from carbon-containing compounds

No CO2 emissions if produced from water

Environmental costs not included in market price

Good substitute for oil Nonrenewable if

generated by fossil fuels or nuclear powerCompetitive price if

environmental and social costs are included in cost comparisons

High costs (that may eventually come down)

Easier to store than electricity

Will take 25 to 50 years to phase inShort driving range for current fuel-cell carsSafer than gasoline

and natural gas No fuel distribution system in place

Nontoxic

High efficiency (45–65%) in fuel cells

Excessive H2 leaks may deplete ozone in the atmosphere

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Cars could be indirectly run on renewable energy if they had powerful enough batteries to store a charge needed to run the car for long periods of time.Lead-acid batteries, currently in use, are too

large and do not hold enough energy.Nickel-Metal Hydride batteries, used in early

generation hybrid cars, have a higher storage capacity, but will quickly lose a stored charge when not in use.

Lithium-ion batteries are the smallest and have the best storage capacity, but are also expensive to produce.

The Tesla Model S runs on lithium-ion batteries, with a range of 265 miles.

Getting Energy from the Earth’s Internal Heat

Geothermal energy: heat stored inSoilUnderground rocksFluids in the earth’s mantle

Geothermal heat pump systemEnergy efficient and reliableEnvironmentally cleanCost effective to heat or cool a space

Fig. 16-28, p. 427

Basement heat pump

Fig. 16-29, p. 428

TRADE-OFFS

Advantages Disadvantages

Geothermal Energy

Very high efficiency Scarcity of suitable sites

Moderate net energy at accessible sites

Can be depleted if used too rapidly

Environmental costs not included in market priceLower CO2 emissions

than fossil fuelsCO2 emissions

Low cost at favorable sites

Moderate to high local air pollution

Low land use and disturbance Noise and odor (H2S)

Moderate environmental impact

High cost except at the most concentrated and accessible sources

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Energy Conversion EfficienciesIn addition to finding

alternative, renewable energy sources, it is also important to reduce energy consumption.

Energy Efficiency is a measure of the percentage of energy consumed that actually performs the desired work.Incandescent light bulbs: 5-

10% efficientCompact fluorescent: 20-33%

efficientLED: 40-60% efficient

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Promoting Renewable EnergyDistributional surcharges

are small charges levied on all utility customers to help finance research and development of renewable energy.

A renewable portfolio is a state mandated minimum percentage of energy that utilities must get from renewable sources.

Green pricing is the practice of some electricity suppliers offering plans (at a premium) that only use renewable sources for electricity.

California has enacted a 33 percent renewable portfolio standard set for 2020.

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Promoting Renewable Energy

The energy star program is a federal initiative to promote and provide incentives for purchasing more efficient devices and appliances.

Fig. 16-33, p. 432

SOLUTIONSMaking the Transition to a More Sustainable Energy Future

Improve Energy Efficiency More Renewable Energy

Increase fuel-efficiency standards for vehicles, buildings, and appliances

Greatly increase use of renewable energyProvide large subsidies and tax credits for use of renewable energy

Mandate government purchases of efficient vehicles and other devices

Include environmental costs in prices for all energy resourcesEncourage government purchase of renewable energy devices

Provide large tax credits or feebates for buying efficient cars, houses, and appliances

Greatly increase renewable energy research and development

Reduce Pollution and Health RiskOffer large tax credits for investments in energy efficiency

Cut coal use 50% by 2020

Phase out coal subsidiesReward utilities for reducing demand for electricity Levy taxes on coal and oil use

Greatly increase energy efficiency research and development

Phase out nuclear power subsidies, tax breaks, and loan guarantees

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Energy conservation tends to be highly tied to consumer prices.In response to 1970’s oil prices, average U.S.

automobile gas-mileage increased from 13 mpg in 1975 to 28.8 mpg in 1988.

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Falling fuel prices in the 1980s-early 2000s discouraged further improvements in fuel economy.

The recent popularity of smaller cars, hybrid cars, and electric cars has improved average MPG again.

Total Costs of Electricity from Different Sources in 2004

What Can you Do? Shifting to Sustainable Energy Use