Transcript EE80S-4.F08 - ucsc.edu) and Media Services

Microphone!
Energy: What it is, how we
use it, how we waste it
Which would you prefer to do?
Stick your hand in boiling water or steam?
What is “Energy?”
Energy is the amount of work a physical system is
capable of performing so energy can be defined
as that which changes the position, physical
composition or temperature of an object
Energy comes in many flavors
Form
What it is or does
Example
Mechanical
Motion: kinetic or
potential
Moving car, coyote
poised to fall
Chemical
Potential energy in
molecular bonds
Fossil fuels, food,
explosions
Thermal
Internal temp. of
substances
Hot water, steam,
body temperature
Electrical
Electrons moving
across potentials
Electric circuits,
batteries, fuel cells
Radiant
Electromagnetic
light, heat
Sunlight, heat
emitted by objects
Nuclear
Potential energy in
atomic nucleus
Nuclear fission &
fusion
Gravitational
Energy of place or
position
Hydroelectricity,
falling coyote
We tend to transform energy in order to
make it usable
• We burn fossil fuels to generate usable heat
energy to make steam to turn electrical turbines
•We split atomic nuclei to do the same thing
•We burn gasoline to create energetic gases that
push pistons in internal combustion engines
•We transform liquids and gases moving at high
velocities into rotational kinetic energy that turns
shafts for various purposes
Energy is measured in many different units
BTUs
Kilowatt-hours
Therms
Barrels
Calories
Gallons
Kilocalories (equals one
food calorie
Energy densities vary a great deal
1 milllion BTU equals approximately:
•90 lbs of butuminous coal and lignite production
•125 lbs of oven-dried wood
•8 gallons of gasoline (enough to move an average
passenger car ~150-200 miles)
•10 therms of dry natural gas
•11 gallons of propane
•2 months of dietary intake of a laborer
•20 cases (240 cases) of table wine
You are a lightbulb (not a walrus), and as
much as 10 “C” batteries
Power is a measure of the rate of energy production and
consumption
A typical 100 watt light bulb consumes 100 watts
of energy per hour (0.1 kWh)
A standard 1 GWe (gigawatt)
nuclear power plant generates a
billion watts of electrical energy
per hour (1 million kilowatt-hrs)
A 150 horsepower car that
gets 30 mpg, driven at 60 mph,
consumes 2 gal/hr of gasoline;
2 gallons of gasoline contain
about 73 kWh or 98 hp-hr of
energy.
To use energy more efficiently, it helps to
match power rates to requirements
Because an automobile has highly variable power requirements—
from 1 mph to bursts of 80 mph, it requires a high peak power
capacity—which is difficult to provide with electricity and which
tends to lower the efficiency of energy use
By contrast, a vehicle that only needs a maximum speed of 30 mph
also requires much variability in velocity and acceleration rates, and
less peak power capacity (that is why hybrids rely much more on
electric power system for local travel)
Meanwhile, we value energy for the services it
can provide, not for its specific form
We burn fuel at 1,000+
degrees to boil water at
212° to make a hot drink
at 120° which we radiate
as body heat at 98.6°
Basic principle of energy use:
we take high quality energy sources, use them to do
work for us, and degrade them into lower-quality heat
Someday, all energy sources in the
universe will probably dissipate as
very low quality “heat”
House as an energy
eco-system: energy
goes in, does work,
becomes heat, and
escapes at <70°
Houses are only one type of
“energy ecosystem”
There are various ways to
increase the efficiency of energy
use on both supply and demand
sides:
•in the generation process;
•in matching source to need (e.g.,
solar for heating water & space);
•in more efficient combustion &
distribution systems;
•in demand reduction through
more efficient appliances,
insulation, leak reduction, etc.
Saving energy in the
household
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Set your thermostat lower
Don’t heat the whole house
Wash cloths with the Cold/Cold setting and use full loads
Unplug computers, TV’s, Cable boxes, and other “energy vampire”
appliances when not in use
Turn off the lights when you leave the room
Take shorter showers
Trim those bushes on the south side of your home and open the
shades
Adjust water heaters down to 126 degrees
Clean heater and refrigerator filters & vents to maximize
performance
Cook more efficiently
What is your consumption profile?