Due May 6, 12:00pm CST

Maoxiaoying

Chapter12.pdf

Home >Environmental science homework help >Due May 6, 12:00pm CST

Environment Tenth Edition

Raven

Chapter 12

Renewable Energy and Nuclear Power

Overview of Chapter 12

• Direct Solar Energy

• Indirect Solar Energy

• Other Renewable Energy Sources

• Nuclear Energy

Africa’s Demand for Energy Met by Renewables? • Report from U of C Berkeley’s

Renewable and Appropriate Energy Lab o Meet energy demands with

relatively low cost with hybrid systems

o Smaller-scale hydroelectric dams, batteries, etc.

o Energy produced where it is used

• Repackage for fossil-fuel- dependent economies?

Direct Solar Energy

• Perpetually available

• Varies with latitude, season, time of day, and cloud cover

Passive Solar for Heating

• Passive solar energy o System of putting the sun’s

energy to use without requiring mechanical devices to distribute the collected heat

• Certain design features can enhance heating potential o South facing windows (in N.

hemisphere)

o Well insulated buildings

o Attic vents

o Overhangs and solar sunspaces

Passive Solar Heating Designs

• Design options

• How does passive solar heating reduce climate change?

Solar Sunspace

• Utilizes passive solar energy to heat and cool homes o Using sun’s energy

without mechanical devices to distribute heat

• Can be added to existing homes

Active Solar Energy

• System of putting the sun’s energy to use with collectors to absorb solar energy, and pumps or fans to distribute

• Typically used to heat water o 8% of energy in the U.S. is

used to heat water

Solar Thermal Electric Generation

• Means of producing electricity by using mirrors or lenses to concentrate sun’s energy to either heat a fluid-filled pipe or drive a Stirling engine

• More efficient than other solar technologies

o No air pollution

o No contribution to global warming or acid precipitation

Solar Thermal in Action

Photovoltaic Solar Cells

• Method of converting sunlight to electricity using layers of materials that either readily give up or absorb electrons

• No pollution and minimal maintenance

• Used on any scale o Lighted road signs

o Entire building

Economics of Photovoltaic

• More economical than running electrical lines to rural areas

• Can be incorporated into building materials o Roofing shingles

o Tile

o Window glass

Cost of Electrical Power Plants Alternative power sources are competitive with traditional power sources

Table 12.1 Generating Costs of Electric Power, 2016

Energy Source Generating Costs

(cents per kilowatt hour)*

Hydropower 6–7

Biomass 8–12

Geothermal 4–5

Wind 3–8

Solar thermal 5–13

Photovoltaics (PV) 4–14

Natural gas 5–8

Coal 5–8

Nuclear power 9–11

*Electricity production and consumption are measured in kilowatt-hours (kWh). As an example, one 50-watt light bulb that is on for 20 hours uses one kilowatt-hour of electricity (50 × 20 = 1000 watt-hours = 1 kWh).

Source: Energy Information Agency.

Indirect Solar Energy

• Biomass o Plant materials, such as wood, crop wastes, and animal

wastes, used as fuel

o Is the use of firewood always carbon-neutral? Why or why not?

• Wind energy o Electric or mechanical energy obtained from surface air

currents caused by solar warming of air

• Hydropower o Form of renewable energy reliant on flowing or falling water

to generate mechanical energy or electricity

Energy from Biomass

• Contains energy from sun via photo-synthesizing plants o Oldest known fuel to humans-

still used by half the world’s population

o Renewable when used no faster than it can be produced

• Can convert to biogas or liquids

o Ethanol and methanol

o Clean fuel

Biomass

• Advantages o Reduces dependence on fossil fuels

o Often uses waste materials

o If trees are planted at same rate biomass is combusted, no net increase in atmospheric CO2

• Disadvantages o Requires land, water, and fossil fuel energy

o Can result in bad air quality

o Can lead to: • Deforestation

• Desertification

• Soil erosion

Wind Energy

• World’s fastest growing source of energy

• Wind results from sun warming the atmosphere o Varies in direction and magnitude

• New wind turbines harness wind efficiently o Most profitable in rural areas with

constant wind

Wind Energy from Turbines

• Few environmental problems o Kills aerial wildlife: birds

and bats

• No waste - clean source of energy

• Biggest constraints: o Cost

o Public resistance

Hydropower

• Most efficient energy source (90%)

• Most widely used form o 19% of world’s energy

• Traditional hydropower o Suited only to large dams

• New technology o Utilize low flow systems

Advantages and Disadvantages of Hydropower (1 of 2)

• Three Gorges Dam on Yangze River, China o Huge electricity generation

o Displaced ~ 1.5 million people o Large environmental shift in area

Advantages and Disadvantages of Hydropower (2 of 2) Table 12.2 Advantages and Disadvantages of Dams

Reasons to Build Dams Problems with Dams

Electrical power Mechanical power Irrigation Navigation Flood control Commercial fishing Recreation • Fishing • Swimming • Boating

Ecological disruption downstream • Sediment stopped in dam • Water source diverted • Fish migration halted at dam Ecological disruption in reservoir • Habitat flooded • Sediment buildup • Pollution if toxic materials are submerged Displacement of people Loss of cultural resources Catastrophic failure Disease Seismicity Evaporation from reservoir

Other Forms of Indirect Solar Energy

• Ocean waves o Produced by winds

o Has potential to turn a turbine and create electricity

• Ocean Thermal Energy Conversion (OTEC) o Ocean Temperature Gradients

o Use difference in temperature of surface and deep water to create electricity

Other Renewable Energy Sources

• Geothermal energy o Energy from the Earth’s interior for either space heating or

generation of electricity

o Becoming an option in homes

• Tidal Energy o Form of renewable energy that relies on the ebb and flow

of the tides to generate electricity

o Location dependent

Geothermal Energy

• Enormous energy source o 1% of heat in upper 10 km

of Earth’s crust is equal to 500x the Earth’s fossil fuel sources

• From hydrothermal reservoirs o Created by volcanoes

o Reservoirs used directly for heat or to generate electricity

Geothermal Heat Pumps

• Use difference in temperature between surface and subsurface

• Great for heating buildings

• Expensive installation

• From hot, dry rock

Tidal Energy

• Typical difference between high and low tide is 1-2 ft. o Narrow bays may have greater variation

• Potential energy difference between low and high tide can be captured with: o A dam across a bay

o A turbine similar to a wind turbine

Nuclear Power

• Nuclear energy - energy released by nuclear fission or fusion

• Nuclear fission o Splitting of an atomic nucleus into two smaller fragments,

accompanied by the release of a large amount of energy

• Nuclear fusion o Joining of two lightweight atomic nuclei into a single, heavier

nucleus, accompanied by the release of a large amount of energy

• Radiation - energy in the form of electromagnetic waves or high-velocity subatomic particles

Atoms and Radioactivity

• Nucleus o Comprised of protons (+) and neutrons (neutral)

• Electrons (−) orbit around nucleus

• Neutral atoms o Same # of protons and electrons

Atomic Mass and Isotopes

• Atomic mass o Sum of the protons and neutrons in an atom

• Atomic number o Number of protons per atom

o Each element has its own atomic number

• Isotope o Atom where the number of neutrons is greater than the

number of protons

Nuclear Fission

1. Neutron bombardment

2. Nucleus splits into atomic fragments

3. And free neutrons

4. Free neutrons bombard U-235 nuclei

5. More free neutrons released in chain reaction

Nuclear Fuel Cycle

• Processes involved in producing the fuel used in nuclear reactors from mining to disposing of radioactive (nuclear) wastes

Nuclear Reactor

• Device that initiates and maintains a controlled nuclear fission chain reaction to produce energy

• Enrichment – refining of uranium ore to increase fissionable U-235 (isotope) o Uranium pellets and fuel rods

How Nuclear Produces Electricity

• How might this process be similar to a geothermal heat pump?

Comparison of Coal and Nuclear (1 of 2)

Impact Coal Nuclear (Conventional Fission)

Land use 17,000 acres 1900 acres

Daily fuel requirement 9000 tons/day 3 kg/day

Availability of fuel, based on present economics

A few hundred years 100 years, maybe longer (much longer with breeder fission)

Air pollution Moderate to severe, depending on pollution controls

Low**

Climate change risk (carbon dioxide emissions)

Severe Relatively small**

Radioactive emissions, routine 1 curie 28,000 curies

Table 12.3 Comparison of Environmental Impacts of 1000-MW Coal and Nuclear Power Plants*

Comparison of Coal and Nuclear (2 of 2)

[Table 12.3 continued]

Impact Coal Nuclear (Conventional Fission)

Water pollution Often severe at mines Potentially severe at nuclear waste disposal sites

Risk from catastrophic accidents Short-term local risk Long-term risk over large areas

Link to nuclear weapons No Yes

Annual occupational deaths 0.5 to 5 0.1 to 1

Certainty about risks Well known Highly uncertain

*Impacts include extraction, processing, transportation, and conversion. Assumes coal is strip-mined. (A 1000-MW utility, as a 60% load factor, produces enough electricity for a city of 1 million people.)

**While nuclear electricity generation does not generate air pollution and carbon dioxide directly, many of the steps (mining, construction, and waste disposal, for example) require fossil fuels.

Safety Issues in Nuclear Power Plants

• Meltdown o At high temperatures, the metal encasing the uranium fuel

can melt, releasing radiation

• Probability of meltdown is low

• Public perception is that nuclear power is not safe

• Sites of major accidents: o Three Mile Island, PA (1979)

o Chernobyl, Ukraine (1986)

o Fukushima Daiichi, Japan (2011)

Spread of Fallout - Chernobyl

• 170,000 people permanently abandoned their homes

• Fallout extensive o Mothers did not nurse because

milk was contaminated

o Frequency of birth defects and mental disabilities increased for several decades

o Exposed children experienced increased incidences of leukemia, cancer, and abnormalities of the immune system

Impacts from Fukushima Daiichi

• March 11, 2011 - caused by magnitude 9.0 earthquake and ensuing tsunami o Disrupted power systems that pumped cooling water to

reactor cores and spent fuel rods

• Caused increased radiation in local water and food supplies o May limit seafood catches for decades

Damaged Fukushima Daiichi Plant

Radioactive Waste

• Low-level radioactive waste o Radioactive solids, liquids, or gases that give off small

amounts of ionizing radiation

o Produced by power plants, research labs, hospitals, and industry

o States responsible for all waste they generate

• High-level radioactive waste o Radioactive solids, liquids, or gases that give off large amounts

of ionizing radiation

o Primarily spent fuel rods and assemblies

Storage of Radioactive Waste

• Temporary storage solutions o In nuclear plant facility

(require high security) • Underwater storage

• Aboveground concrete and steel casks

• Storage is biggest obstacle

• No belowground storage in U.S. currently (2017)

Dry cask storage

Decommissioning Nuclear Power Plants

• Power plants cannot be abandoned when they are shut down (put into storage mode) o Company guards it for 50-100 yrs.

• Three solutions o Storage

o Entombment

o Decommissioning (dismantling)- best option

• 141 power plants were retired as of 2016 o 31 retired plants are in U.S.; remaining plants are aging quickly

Storing Nuclear Waste

• Nuclear Waste Policy Act (1982) – government to ‘own’ nuclear waste by 1998 o Store waste from weapons, but not civilian waste

• Yucca Mountain identified as permanent storage (1987) o Could store amount produced until 2025

o DOE spent billions in feasibility studies

o U.S. federal courts demanded site meet EPA safety standards for 1 million years (2004)

Yucca Mountain

• Difficulty for science to meet million year mark o Remote possibility of volcanic

eruption (1 in 10,000 in next 10,000 years)

o Site near active fault lines and water table

• Currently not an active storage site

Section 117 of the 1976 United States Act without the express written permission of the

Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up

copies for his/her own use only and not for distribution or resale. The Publisher assumes

no responsibility for errors, omissions, or damages, caused by the use of these programs

or from the use of the information contained herein.