Chapter 8 Energy Efficiency and Renewable Energy 能源有效性与可再生能源

Key Concepts  Energy  Evaluating energy resources  Improving energy efficiency  Energy  Evaluating energy resources  Improving energy efficiency  Types and uses of solar energy  Types and uses of flowing water  Uses of wind energy  Types and uses of biomass  Use of hydrogen as a fuel  Use of geothermal energy  Decentralized power systems

Glossary  energy efficiency Percentage of the total energy input that does useful work and is not converted into low-quality, usually useless heat in an energy conversion system or process. See energy quality, net energy. Compare material efficiency.  geothermal energy Heat transferred from the earth's underground concentrations of (1) dry steam (steam with no water droplets), (2) wet steam (a mixture of steam and water droplets), or (3) hot water trapped in fractured or porous rock.

Energy: Forms  Kinetic energy  Potential energy  Heat

Glossary  kinetic energy Energy that matter has because of its mass and speed or velocity. Compare potential energy.  potential energy Energy stored in an object because of its position or the position of its parts. Compare kinetic energy

Transfer of Heat Energy ConvectionConductionRadiation Heat from a stove burner causes atoms or molecules in the pan’s bottom to vibrate faster. The vibrating atoms or molecules then collide with nearby atoms or molecules, causing them to vibrate faster. Eventually, molecules or atoms in the pan’s handle are vibrating so fast it becomes too hot to touch. As the water boils, heat from the hot stove burner and pan radiate into the surrounding air, even though air conducts very little heat. Heating water in the bottom of a pan causes some of the water to vaporize into bubbles. Because they are lighter than the surrounding water, they rise. Water then sinks from the top to replace the rising bubbles.This up and down movement (convection) eventually heats all of the water.

Energy: Quality  High-quality energy  Low-quality energy

Evaluating Energy Resources  Renewable energy  Non-renewable energy  Future availability  Net energy yield  Cost  Environmental effects

Glossary  nonrenewable resource Resource that exists in a fixed amount (stock) in various places in the earth's crust and has the potential for renewal by geological, physical, and chemical processes taking place over hundreds of millions to billions of years. Examples are copper, aluminum, coal, and oil. We classify these resources as exhaustible because we are extracting and using them at a much faster rate than they were formed. Compare renewable resource.  net energy Total amount of useful energy available from an energy resource or energy system over its lifetime, minus the amount of energy (1) used (the first law of thermodynamics), (2) automatically wasted (the second law of thermodynamics), and (3) unnecessarily wasted in finding, processing, concentrating, and transporting it to users.

Important Nonrenewable Energy Sources

Nuclear Energy  Fission reactors  Uranium-235  Potentially dangerous  Radioactive wastes

Glossary  nuclear energy Energy released when atomic nuclei undergo a nuclear reaction such as the spontaneous emission of radioactivity, nuclear fission, or nuclear fusion.

The Importance of Improving Energy Efficiency  Net useful energy ( 净有用能源 )  Net useful energy ( 净有用能源 )  Life cycle cost Least Efficient  Incandescent lights  Internal combustion engine  Nuclear power plants

Efficiencies

Ways to Improve Energy Efficiency  Insulation  Elimination of air leaks  Air to air heat exchangers  Cogeneration  Efficient electric motors  High-efficiency lighting  Increasing fuel economy

Glossary  cogeneration Production of two useful forms of energy, such as hightemperature heat or steam and electricity, from the same fuel source.

Electric and Hybrid Cars  Rechargeable battery systems  Hybrid electric-internal combustion engine  Fuel cells

Using Solar Energy to Provide Heat and Electricity  Passive solar heating  Active solar heating

Glossary  active solar heating system System that uses solar collectors to capture energy from the sun and store it as heat for space heating and water heating. Liquid or air pumped through the collectors transfers the captured heat to a storage system such as an insulated water tank or rock bed. Pumps or fans then distribute the stored heat or hot water throughout a dwelling as needed. Compare passive solar heating system.  passive solar heating system System that captures sunlight directly within a structure and converts it into low-temperature heat for space heating or for heating water for domestic use without the use of mechanical devices. Compare active solar heating system.

Using Solar Energy to Provide High- Temperature Heat and Electricity  Solar thermal systems  Photovoltaic (PV) cells

Glossary  solar cell See photovoltaic cell.  photovoltaic cell (solar cell) Device which converts radiant (solar) energy directly into electrical energy.  solar collector Device for collecting radiant energy from the sun and converting it into heat. See active solar heating system, passive solar heating system.

Producing Electricity from Moving Water  Large-scale hydropower  Small-scale hydropower  Pumped-storage hydropower  Tidal power plant  Wave power plant

Producing Electricity from Heat Stored in Water  Ocean thermal energy conversion (OTEC)  Saline solar ponds  Freshwater solar ponds

Producing Electricity from Wind

Producing Energy from Biomass  Biofuels  Biomass plantations  Crop residues  Animal manure  Biogas  Ethanol  Methanol

Glossary  biofuel Gas or liquid fuel (such as ethyl alcohol) made from plant material (biomass).

The Solar-Hydrogen Revolution  Extracting hydrogen efficiently  Storing hydrogen  Fuel cells

Geothermal Energy  Geothermal reservoirs  Dry steam  Wet steam  Hot water  Molten rock  Hot dry-rock zones

Entering the Age of Decentralized Micropower  Centralized power systems  Decentralized power systems  Micropower systems

Glossary  micropower systems Systems of small-scale decentralized units that generate 1-10,000 kilowatts of electricity. Examples include (1) microturbines, (2) fuel cells, and (3) household solar panels and solar roofs.

Solutions: A Sustainable Energy Strategy