Earth’s Changing Environment
Energy Options
Review of Concepts
Reducing fossil fuel consumption
alleviates environmental problems
Conserve fossil fuel
resources
Reduce air pollution
Reduce CO2 emissions
Reduce extraction
impacts
Reduce use of water
and other resources.
US Residential Energy Consumption
(21 Quad)
Electricity
67%
Natural Gas
21%
Oil
7%
US Commercial Energy Consumption
(17 Quad)
Electricity
76%
Natural Gas
18%
Oil
4%
US Industrial Energy Consumption
(32 Quad)
Electricity
33%
Natural Gas
23%
Oil
28%
US Transportation Energy
(27 Quad)
Oil
100%
US Electricity Generation
(38 Quad)
Coal
52%
Nuclear
21%
Gas
15%
Renewable
10%
Ways to reduce fossil fuel consumption.
Increase energy
efficiency.
Use renewable
energy.
Alter lifestyle to
lower energy
needs.
Energy Efficiency
Energy Efficiency = Useful Energy Output / Energy Input
Power Plant Capacity
Consider a 1000 MW
Capacity Plant
W = Watt = unit of
power
So, a 1000 MW plant
could provide a
maximum of 1000
million watts of power
or 1,000,000 kW of
power
Power Plant Energy Output
Energy = power x time
Express power in kilowatts
(kW) and time in hours; so,
energy will be in kWh or
“kilowatt hours”
During a 24 hour day, a
1000 MW plant could provide
1 million kW x 24 hours =
24 million kWh
Power Plant Annual Output
A typical coal-burning plant will operate at 70%
capacity.
Energy produced by a 1,000 MW plant =:
0.70 x 1x106 kW x 24 hours/day x 365 days =
6.13 billion kWh (annual)
A typical residential customer consumes 12,000 kWh
annually; so a 1000 MW plant can supply 0.5 million
customers.
Power Plant Energy Efficiency
A typical 1000 MW plant burns
enough fuel to release 3333 MW
of thermal power.
Efficiency
= output power / input power
= 1000 MW / 3333 MW
= 30 %
First Law of Thermodynamics
Energy must be conserved; so, the other 2,333 MW
is dumped as waste heat.
Second Law of Thermodynamics
Efficiency is always less than
100%.
Some energy is always dumped
as waste heat.
Typically coal plant efficiency
is 30%, but new plants may be
50% efficient.
High efficiency plants conserve
energy and reduce CO2
emissions.
Power
Power (watts) = I (amps) V (volts)
Compact Fluorescent Bulbs
Efficiency is 4X
incandescent bulb.
14 W bulb produces
light level
corresponding to 60 W
bulb
Last 10X longer,
10,000 hours
Space Heating
The amount of heat that flows through a wall or
window may be calculated by the following formula:
Heat Loss (Btu/hour) =
Wall Area • (Tin - Tout)  R-value
R-value of insulation indicates its resistance to the
flow of heat.
R-20 has twice the resistance to heat loss as R-10.
How do we lower energy
consumption for space heating?
Increase R-value of walls, ceiling, and
windows.
Increase efficiency of furnace.
Use heat pump.
Use natural gas rather than electric heater.
Better home design and construction.
Lower Tin. (Easy lifestyle change)
Decrease wall size. (Major lifestyle change)
How do we lower energy
consumption for Air-Conditioning?
Increase R-value of walls, ceiling, and
windows.
Increase efficiency of Air-Conditioner. Use
heat pump.
Better home design and construction.
Raise Tin. (Easy lifestyle change)
Decrease wall size. (Major lifestyle change)
Air-Conditioner Efficiency
Regulated by the U.S. DOE.
Efficiency rating -SEER (seasonal
energy efficiency).
SEER is defined as the annual cooling
output (Btus) divided by its total energy
input (Watt-hours) during the same
period.
Air-Conditioner Efficiency - SEER
The minimum SEER allowed for a central A/C is 9.7.
The best available SEER is 18.
Older units have SEER ratings of 6 or less.
Consumers should look for a SEER of 12 or higher
when buying a new A/C system.
Cars and Drivers
210 million cars and
light trucks
191 million licensed
drivers
140 billion gallons
gasoline/year
2.7 trillion vehicle
miles
US Automobile Culture
Transportation
consumes18% of
Household Expenses
91% travel by private
vehicles vs. 2% by
mass transit
76% rides to work are
solo
2.7 trillion vehicle
miles per year
Carbon Emissions
US Automobiles add
1.3 billion metric tons
of CO2 to atmosphere
annually. (23% of US
total emission)
Efficiency of cars is 20
miles/gallon
Drivers travel 14,000
miles annually
How do we reduce global impact of
US transportation?
Raise CAFE Standards
Reduce Miles Traveled
New Technologies
Raise CAFE Standards
• Corporate Average
Fuel Economy
• Established in 1975
to set U.S. mileage
standards.
Current CAFE Standards
• 27.5 mpg for
passenger
automobiles
• 20.7 mpg for light
trucks & SUVs
How can cars be more efficient?
• Smaller & more streamlined (wind
resistance)
• Lighter (starting & stopping)
• Less powerful (lower acceleration)
Internal Combustion Engine
Engine – 20%
efficient
Highway driving –
Energy lost to air
drag.
City driving –
Energy lost during
braking
Electric Car
Batteries are heavy
and limit range to
100 miles.
Vehicles don’t have
enough acceleration
for traffic.
Not a practical
solution.
Why do hybrids get better mileage?
Smaller engine. Electric
motor boosts gas engine for
acceleration.
Regenerative braking.
Electric motor runs at low
speed where gas engine is
very inefficient.
Electric motor shuts off when
stopped.
Fuel Cells and the Hydrogen
Economy
Fuels Cells use
hydrogen to produce
electrical energy
2H2 +O2  2H2O +
energy
Fuel cells could be used
to power cars with
hydrogen as the fuel.
Clean fuel
Barriers to Hydrogen Cars
Availability of
hydrogen fuel.
Storage of
hydrogen fuel.
Expensive.
Infrastructure
Fuel Cells
In development
stage.
Currently very
expensive.
Are not a source of
energy.
Hydrogen must be
supplied.
Hydrogen Sources
Steam reforming of natural
gas:
CH4 +2H2O  CO2 + 4H2
Electrolysis:
2H2O + energy  2H2 + O2
Energy Source for Electrolyzer
Electrolysis requires
energy.
Energy could come from
Solar, Nuclear, or Wind.
In the short term, it
would probably come
from coal.
Nucleus
Composed of protons
and neutrons
239Pu
94 or Pu – 239
94 protons
145 neutrons
Isotope of Plutonium
Radioactivity
Some isotopes are
unstable
Spontaneously Decay
Decaying isotopes
emit particles
Half-life
Pu-239 decays to U235 with the
emission of an alpha
particle:
The time for half of
the Pu-239 nuclei to
decay is called the
half-life.
24,000 years is halflife for Pu-239 decay
Fission
By bombarding a
nucleus with neutrons, a
stable isotope can be
induced to fission or
split.
U-235 is an example of a
fissionable material.
The release of neutrons
in this reaction means
that we can set up a
chain reaction
Fission Releases Energy
When the fission is
controlled, as in a
nuclear reactor, it can
be a practical source
of power.
When the fission is
uncontrolled it can be
the basis for weapons
of mass destruction.
Fusion
Two light nuclei combine
to form a heavier
nucleus.
The fusion of deuterium
(a hydrogen isotope)
with tritium (another
hydrogen isotope) to
form a helium nucleus
can release a great deal
of energy.
Nuclear Reactors:
Boiling Water Reactor (BWR)
Similar to coal plant:
boils water, makes
steam, steam drives
turbine, turbine turns
electrical generator
Fissioning of U-235 is
the fuel.
BWR Components
Containment
building prevents
release of radiation
Water is needed as
coolant and to
prevent meltdown.
Nuclear Reactor is a Heat Engine
Efficiency is
similar to a coal
burning plant,
about 33%
So, 2/3 of the
released energy is
waste heat.
Uranium Fuel
Only 0.7% of natural
U is U-235.
U-238 is not
fissionable.
U must be enriched to
2.8% U-235.
Uranium Fuel Supply
Worldwide U-235
resource does not offer
a long-term energy
solution.
Breeder reactor
consuming U-235 can
convert U-238 into
Pu-239.
Plutonium Economy
Breeder reactors
would greatly increase
the availability of
weapons-grade
Plutonium.
Nuclear Power in the US
104 nuclear plants
Produce 20% US
Electricity
No new plants since
1973
Why?
Nuclear Accidents
1979 Three Mile
Island partially core
melt
1986 Chernobyl
explosion and fire,
release of radiation
Waste Disposal
WIPP near Carlsbad,
NM. Stores hi-level
waste associated with
nuclear weapons
Yucca Mountain,
Nevada. High-level
waste from
commercial reactors.
Three forms of solar energy.
Passive Solar
Active Solar
Photovoltaic
Passive Solar Energy
Sensible architectural design
Use sun in the winter
Avoid in the summer.
Cold climates- large glazing which
may be insulated at night and
opened during the day.
Hot climates - blocking the sun and
providing good ventilation.
Passive Design
Another interesting
design.
The wall is down and the
passive collector is
collecting solar energy
Passive Design
In this mode, the wall is
up and the building is
storing solar energy or
blocking summer heat
gain.
Active Solar Energy
Use pumps and solar collectors to provide
energy.
Two types of solar collectors:
flat plate
 concentrating

Flat Plate Collector
Made of a black absorbing plate with water
running through it or air blowing past it.
Usually a flat plate collector has a glazing
to stop heat from escaping.
Efficiency 50% or better.
Flat Plate Collector
Hot Water Heater
Solar water heater
system has four
components:
Collector
Tank
Pump
Controller
Concentrating Collector
A concentrating collector includes some
kind of lens or mirror.
Tracks the sun.
High temperature.
Efficiency near 50%.
Concentrating Collector
Components:
Optics
Glazing
Absorber
Insulation
Tracking
Photovoltaics
Photovoltaic systems convert solar energy
directly into electricity. They have
efficiencies near 10%.
Photovoltaics
A complete system has
an array, a battery, an
inverter and a load.
The system can supply
either DC or AC loads.