Chapter 16: Energy Efficiency and Renewable Energy

Core Case Study: The Astounding Potential for Wind Power in the U.S.

• Wind energy: wind farms convert to electrical energy
• Wind power is inexhaustible
• Could meet the electricity needs of the lower 48 states
  • Texas and California are top producers
• Net energy efficiency is how much useful energy we get from an energy resource after subtracting the energy used and wasted in making the energy available. Net energy efficiency includes the efficiency of each step in the process of making energy available for use. Two general principles for saving energy are:
  • Keep the number of steps in an energy conversion process as low as possible.
  • Strive to have the highest possible energy efficiency for each step in an energy conversion process.

16.1 Why Is Energy Efficiency an Important Energy Resource?

We Use Energy Inefficiently

• Energy efficiency: How much helpful work we get from each unit of energy
• Advantages of reducing energy waste
  • Usually, the cheapest way to provide more energy
  • Reduces pollution and degradation
  • Slows in global warming Increase economic and national security
• Four widely used devices that waste energy
  • Incandescent light bulb
  • A motor vehicle with an internal combustion engine
  • Nuclear power plant
  • Coal-fired power plant

Improving Energy Efficiency

• Prolongs fossil fuel supplies
• Reduces oil imports and improves energy security
• Very high net energy yield
• Low cost
• Reduces pollution and environmental degradation
• Buys time to phase in renewable energy
• Creates local jobs

We Can Improve Energy Efficiency in Industry and Utilities

• Cogeneration: Combined heat and power or two forms of energy from the same fuel source
• Recycle materials
• Switch from low-efficiency incandescent lighting to higher-efficiency fluorescent and LED lighting

We Can Design Buildings That Save Energy and Money

• Green architecture
• Living or green roofs: With specially designed soil and vegetation
• Superinsulation: No need for a heating system
• U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED)

We Can Use Renewable Energy to Provide Heat and Electricity

• Renewable energy
  • Solar energy
  • Geothermal energy
• Renewable energy will be cheaper if we eliminate
  • Inequitable subsidies
  • Inaccurate prices
  • Artificially low pricing of nonrenewable energy

16.2 What Are the Advantages and Disadvantages of Solar Energy?

• Large arrays of solar collectors in sunny deserts can produce high-temperature heat to spin turbines and produce electricity, but costs are high. Solar thermal systems can collect and transform radiant energy to high-temperature thermal energy (heat), which can be used directly or converted to electricity.
• Solar has two forms for heating, passive and active. We can heat buildings by orienting them toward the sun (passive solar heating) or by pumping a liquid such as water through rooftop collectors (active solar heating).

We Can Heat Buildings and Water with Solar Energy

• Passive solar heating system: Absorbs and stores heat from the sun directly within a well-insulated structure
• Active solar heating system: Captures energy from the sun in a heat-absorbing fluid

Passive or Active Solar Heating

• Advantages
  • Net energy is moderate (active) to high (passive)
  • Very low emissions of CO2 and other air pollutants
  • Very low land disturbance
  • Moderate cost (passive)
• Disadvantages
  • Need access to the sun 60% of the time during daylight
  • Sun can be blocked by trees and other structures
  • High installation and maintenance costs for active systems
  • Need a backup system for cloudy days

Solar Thermal Systems

• Advantages
  • High potential for growth
  • No direct emissions of CO2 and other air pollutants
  • Lower costs with natural gas turbine backup
  • Source of new jobs
• Disadvantages
  • Low net energy and high costs
  • Needs backup or storage systems on cloudy days
  • Can disrupt desert ecosystems

We Can Use Solar Cells to Produce Electricity

• Photovoltaic (PV) cells: Convert solar energy to electric energy
• Design of solar cells: Sunlight hits cells and releases electrons into wires

16.3 What Are the Advantages and Disadvantages of Using Hydropower

We Can Produce Electricity from Falling and Flowing Water

• Hydropower: Uses kinetic energy of moving water and is an indirect form of solar energy
  • World’s leading renewable energy source used to produce electricity
  • Micro-hydropower generators: floating turbines

Large Scale Hydropower

• Advantages
  • High net energy yield
  • Large untapped potential
  • Low-cost electricity
  • Low emissions of CO2 and other air pollutants in temperate areas
• Disadvantages
  • Large land disturbance and displacement of people
  • High CH4 emissions from rapid biomass decay in shallow tropical reservoirs
  • Disrupts downstream aquatic ecosystems

16.4 What Are the Advantages and Disadvantages of Using Wind Power?

Advantages

• High net energy yield
• Widely available
• Low electricity cost
• Little or no direct emissions of CO2 and other air pollutants
• Easy to build and expand

Disadvantages

• Needs backup or storage system when winds die down
• Visual pollution for some people
• Low-level noise bothers some people
• Can kill birds if not properly designed and located

16.5 Advantages and Disadvantages of Using Biomass as an Energy Source

We Can Produce Energy by Burning Solid Biomass

• Biomass: Plant materials and animal waste we can burn or turn into biofuels
• Production of solid mass fuel: Plant fast-growing trees; biomass plantations Collect crop residues and animal manure

Solid Biomass

• Advantages
  • Widely is available in some areas
  • Moderate costs
  • Medium net energy yield
  • No net CO2 increase if harvested, burned and replanted sustainably
  • Plantation can help restore degraded lands
• Disadvantages
  • Contributes to deforestation
  • Clear-cutting can cause soil erosion, water pollution, and loss of wildlife habitat
  • Can open ecosystems to invasive species
  • Increases CO2 emissions if harvested and burned unsustainably

Case Study: Is Biodiesel the Answer?

• Biodiesel: Produced from vegetable oil
  • European Union countries produce 95% of the world’s biodiesel
• Crops require large amounts of land
• Production requires fossil fuels

Case Study: Is Ethanol the Answer?

• Ethanol: Can be made from sugarcane, corn, switchgrass, and various wastes.
  • United States’ largest producer
  • Made from corn; low net energy yield
  • Brazil second
  • Sugarcane has a medium net energy yield
• Cellulosic ethanol: Produced from cellulose

Liquid Biofuels

• Advantages
  • Reduced CO2 emissions for some crops
  • Medium net energy yield for biodiesel from oil palms
  • Medium net energy yield for ethanol from sugarcane
• Disadvantages
  • Fuel crops can compete with food crops for land and raise food prices
  • Fuel crops can be invasive species
  • Low net energy yield for corn ethanol and for biodiesel from soybeans
  • Higher CO2 emissions from corn ethanol

16.6 What Are the Advantages and Disadvantages of Geothermal Energy?

We Can Get Energy by Tapping the Earth’s Internal Heat

• Geothermal Energy Heat Storage: Soil, underground rocks, and fluids in the earth’s mantle
• Geothermal heat pump system: Energy efficient and reliable, environmentally clean, and cost-effective to heat or cool a space
• Hydrothermal reservoirs: Drill wells and extract various streams
  • The U.S. is the world’s largest producer
• Geothermal energy problems
  • High cost of tapping hydrothermal reservoirs
  • Dry- or wet-steam geothermal reservoirs could be depleted
  • Could create earthquakes

Geothermal Energy

• Advantages
  • Medium net energy yield and high efficiency at accessible sites
  • Lower CO2 emissions than fossil fuels
  • Low cost at favorable sites
• Disadvantages
  • High cost except at concentrated and accessible sites
  • Scarcity of suitable sites
  • Noise and some CO2 emissions

16.7 The Advantages and Disadvantages of Using Hydrogen as an Energy Source

Will Hydrogen Save Us?

• Hydrogen: Eliminates most of the air pollution problems and reduces global warming threat.
• Some challenges
  • Chemically locked in water and organic compounds - net negative energy yield
  • Expensive fuel cells are the best way to use hydrogen
  • CO2 levels dependent on method of hydrogen production

Hydrogen

• Advantages
  • Can be produced from plentiful water at some sites
  • No CO2 emissions if produced with use of renewables
  • Good substitute for oil
  • High efficiency in fuel cells
• Disadvantages
  • Negative net energy yield
  • CO2 emissions if produced from carbon
  • containing compounds
  • High costs create need for subsidies
  • Needs H2 storage and distribution system

16.8 How Can We Make the Transition to a More Sustainable Energy Future?

Economics, Politics, Education, and Sustainable Energy Resources

• Government strategies
  • Keep the prices of selected energy resources artificially low to encourage their use
  • Keep energy prices artificially high for selected resources to discourage their use
  • Consumer education

Three Big Ideas

• We should evaluate energy resources on the basis of
  • Their potential supplies
  • Their net energy yields
  • Environmental and health impacts of using them
• Making the transition to a more sustainable energy future will require
  • Sharply increasing energy efficiency
  • Using a mix of environmentally friendly renewable energy resources
  • Including the harmful environmental and health costs of energy resources in their market prices

Tying It All Together: Wind Power and Sustainability

• Relying on a diversity of direct and indirect forms of solar energy
  • Would implement three principles of sustainability
  • Recycle and reuse materials to reduce the consumption of energy
  • Mimic nature’s reliance on biodiversity by diversifying energy sources