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AP Environmental Science
Net Energy &
Energy Efficiency
© Brooks/Cole Publishing Company / ITP
What is Net Energy?
© Brooks/Cole Publishing Company / ITP
NET ENERGY: the total useful energy available from a resource over its lifetime minus the amount of energy used, automatically wasted, and unnecessarily wasted to find, process, and transport it
• Example: if 8 units of energy are wasted for every 10 units extracted, then there is a net energy of 2 units
• Net energy ratio--ratio of useful energy produced to the useful energy used to produce it
• higher ratios = greater the net energy yield
• 10/8 = 1.25
Net Energy Ratios
© Brooks/Cole Publishing Company / ITP
Net energy ratios for various energy systems used for space heating:
Net Energy Ratios
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Net energy ratios for various energy systems used for industry:
Fig.15–3b
Net Energy Ratios
© Brooks/Cole Publishing Company / ITP
Net energy ratios for various energy systems used for transportation:
Fig.15–3c
Energy Efficiency
What is it?
Energy efficiency – the percentage of total energy input that does useful work in an energy conversion system
Energy efficiency of common energy conversion devices
Efficiency of Some Common Devices
Device Efficiency (%) Dry-cell flashlight battery 90 Home gas furnace 85 Storage battery 70 Home oil furnace 65 Small electric motor 62 Steam power plant 38 Diesel engine 38 High-intensity lamp 32
Automobile engine 25 Fluorescent lamp 22 Incandescent lamp 4
Energy EfficiencyNet energy efficiency – the net efficiency of the entire energy delivery process is determined by the efficiency of each step in the energy conversion process
© Brooks/Cole Publishing Company / ITP
Energy Efficiency
Energy waste
43% of the energy used in the U.S. is unnecessarily wasted by using inefficient methods to produce electricity, heat our homes, and drive our cars
Energy Efficiency
The importance of reducing energy waste• Nonrenewable fuels last longer
• Time to phase in renewable energy resources
• Decrease dependence on oil imports
• Reduce local and global environmental damage
• Slow climate change
• Create new jobs
• Save money
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You don’t have to freeze in the winter or make huge personals sacrifices.
Energy conservation is implemented by using existing technologies and developing new ones
Improving Energy Efficiency
Improving energy efficiency is the easiest way to make big changes in our consumption• Cogeneration
• Fuel efficiency of motor vehicles or use of alternative fuel vehicles Slideshow: 23 Electric Cars Driving the Revolution
• Lighting and appliances
• Better insulated homes
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Cogeneration• Cogeneration – the production of two useful forms
of energy from the same fuel source-use energy converted to low energy heat to generate electricity
Fuel EfficiencyFirst step in conservation is to increase the fuel
efficiency of internal combustion cars! Hybrid-electric internal combustion engine – internal
combustion engine recharges electric battery Fuel-cell cars – combines H2 and O to produce water vapor
and electricity
Heat Houses More Efficiently! Most energy efficient –
Superinsulation with passive solar heat and high-efficiency (85-98%) gas furnace
Most expensive – Electric heaters!!!!
Least efficient – Electric heat supplied from nuclear power
Heat Water More Efficiently! Tankless water heaters
Lighting and Appliance Efficiency
Old tank water heaterTankless water heater
Lighting and Appliance Efficiency
Use Energy Efficient Appliances Use Energy Efficient Bulbs!
¼ of US electricity budget spent on lighting. 50% could be saved by changing to CFL’s
CFL’s use 1/3 the wattage of an incandescent bulb
Not all CFL’s created equal If each house replaced ONE
incan with a CFL, enough energy would be conserved to light 3 million homes and save $600 million annually
Cut Off Electrical Devices When Not In Use!—Vampire Draws
Better Insulated Homes Insulate & Plug Leaks – 1/3 of heated air in the US
leaks through closed windows, holes, and cracks in houses
Use Energy Efficient Windows – buy superinsulating glass and low-E (low-emissivity) windows that cut down on heat loss. More $ but pay for themselves as they save money.
Add more insulation to walls and ceilings Strict Energy-Efficiency Standards for New Buildings!
Sweden has stricter standards so homes use 1/3 as much energy
A sustainable energy strategy
(see Fig.16–23)
© Brooks/Cole Publishing Company / ITP
•Drive a car that gets at least 15 kilometers per liter (35 miles per gallon) and join a carpool.
•Use mass transit, walking, and bicycling.
•Superinsulate your house and plug all air leaks.
•Turn off lights, TV sets, computers, and other electronic equipment when they are not in use.
•Wash laundry in warm or cold water.
•Use passive solar heating.
•For cooling, open windows and use ceiling fans or whole-house attic or window fans.
•Turn thermostats down in winter and up in summer.
•Buy the most energy-efficient homes, lights, cars, and appliances available.
•Turn down the thermostat on water heaters to 43-49ºC (110-120ºF) and insulate hot water heaters and pipes.
What Can You Do?
Energy Use and Waste
