Download Renewable Energy and Conservation

Renewable Energy
and Conservation
Chapter 12
Direct Solar Energy
I. Direct Solar Energy
A. Availability:
Solar energy is dispersed over
the Earth’s surface, but varies in
intensity depending on latitude,
season, time of day and degree
of cloud cover; for solar energy
to be useful, we must collect it
B. Cost:
Although initial costs associated
with converting to solar power
are high, the long-term savings
may offset the high start-up
costs; efficiency of collecting
systems is also increasing,
making it a more cost effective
alternative
Direct Solar Energy
C. Uses:
1. Passive solar heating
a.. Uses infrared
radiation (waves of heat energy) to
heat buildings without the need for
pumps or fans to distribute the
collected heat
b. May utilize southfacing windows, floors of concrete
or stone, and excellent insulation
2. Active solar heating
a. Uses a series of
collection devices mounted on a
roof or in a field to gather solar
energy
b. Used primarily for
heating water – heat absorbed is
transferred to a liquid inside the
panel which is then pumped to a
heat exchanger, where the heat is
transferred to water that will be
stored in a hot water tank
Direct Solar Energy
3. Solar thermal electric
generation
a. Systems that collect
incident sunlight and concentrate it,
using mirrors or lenses, to heat a
working fluid to high temperatures;
water is converted to steam, which
turns a turbine to generate
electricity
b. Usually have a backup
(such as natural gas) that is
available to generate electricity at
night and on cloudy days
c. With improved
engineering, manufacturing, and
construction methods, solar thermal
energy may become costcompetitive with fossil fuels
Direct Solar Energy
4. Photovoltaic solar cells
a. Wafers or thin films of
solid state materials that are treated
with certain metals in such a way that
they generate electricity (a flow of
electrons) when solar energy is
absorbed
b. Can be used on any scale
– small, portable modules to large
power plants
c. Produce no pollution,
require minimal maintenance
Direct Solar Energy
d. Only about 1015% efficient at converting
solar energy to electricity,
but efficiencies are
improving
e. Future
technological progress
may make PVs
economically competitive
with electricity produced by
conventional sources
Direct Solar Energy
5. Solar-Generated Hydrogen
a. Electricity generated by PVs
(or any energy source) can
be used to split water into
oxygen and hydrogen
b. Hydrogen is a clean fuel,
producing very little air
pollution (minimal amounts
of nitrogen oxides are
produced)
c. Hydrogen offers a convenient
way to store solar energy
as chemical energy; can be
easily transported by
pipeline
d. Hydrogen fuel cells (similar to
batteries) may be used to
power automobiles
Indirect Solar Energy
II. Indirect Solar Energy
A. Biomass
1. Consists of wood,
crop wastes, and
animal dung
containing
chemical energy
that can be traced
to the sun (radiant
energy used by
photosynthetic
organisms to form
the organic
molecules of
biomass)
Indirect Solar Energy
2. Availability:
a. A renewable
source of energy,
as long as it is
managed
properly
b. At least ½ of the
world’s
population relies
on biomass as
their main source
of energy
3. Cost:
Converting biomass to
liquid fuels is expensive
and overall efficiency is low
Indirect Solar Energy
4. Types:
a. Combustion of wood
b. Biogas – a mixture of
gases produced by
biomass, mostly animal
waste; easy to store
and transport, and
burns cleanly
c. Liquid fuels such as
ethanol and methanol
can also be produced
from corn, sugar cane
or even agricultural
wastes and used in
internal combustion
engines (gasohol –
alcohol mixed with
gasoline)
Indirect Solar Energy
5. Advantages:
a. Reduces dependence on fossil
fuels
b. Often makes use of wastes,
reducing our waste disposal
problem
c. Reduced air pollution problems
(as compared to fossil fuels)
6. Environmental Impact:
a. Requires land and water, shifting
its use from food production
b. Intensive use of wood as fuel
contributes to deforestation,
erosion, and desertification
c. Removal of crop residues for
biomass fuel exposes soil to
erosion and deprives the land of
nutrient enrichment from
decomposition
Indirect Solar Energy
B. Wind Energy
1. Wind results from the warming
of the atmosphere by the sun;
radiant energy of the sun is
transformed into mechanical
energy
2. Availability:
Wind is sporadic over the
surface of the Earth, and varies in
direction and magnitude; must be
harnessed to be useful
3. Cost:
As turbines have become
larger and more efficient, costs for
wind power have declined rapidly;
currently the most cost-competitive
of all forms of renewable energy
4. Mechanism:
Wind turbines spin a drive
shaft, powering a generator that
sends electricity to nearby utilities
Indirect Solar Energy
5. Advantages:
Produces no waste /
emissions – a clean
source of energy
6. Environmental impact:
a. Birds collide with the
turbines; should be located
away from migratory
routes
b. Aesthetically displeasing;
may be combined with
pasture land, or located
offshore to utilize ocean
winds
Indirect Solar Energy
C. Hydropower
1. The sun’s energy drives the
hydrologic cycle; as water
flows from higher
elevations back to sea level,
we can harness its energy
2. Availability:
a. Currently, hydropower
generates ~19% of the
world’s electricity (9% of
the US’s energy)
b. Highly developed
countries have already
built dams at most of
their potential sites, but
still represents a great
potential source of
electricity in the
developing world
3. Cost:
Dams cost a great deal to build
but are relatively inexpensive to
operate; also have a limited
lifespan (50-200 years) due to
Indirect Solar Energy
4. Mechanism:
The potential energy of water held
back by a dam is converted to kinetic energy as
water falls down a penstock, where it turns a
turbine to generate electricity
5. Advantages:
Produces no waste/emissions – a
clean source of energy
6. Environmental Impact:
a. Formation of a reservoir (by damming a
river) destroys plant and animal
habitats and displaces people
b. Alteration of the river affects native
fishes, especially migratory species
c. Seismic activity may be induced by
filling a reservoir
d. Dams trap silt carried by the river,
preventing nutrient-enrichment of
agricultural land downstream and
decreasing productivity
Indirect Solar Energy
D. Ocean Waves and Temperature
Gradients
1. Ocean waves are produced by
winds, which are caused by the
sun
a. A concrete, hollow
power plant box is sunk into a gulley
off the coast to catch waves; as each
new wave enters the chamber, the
rising water in the chamber pushes air
into a vent that contains a turbine,
causing the turbine to spin
b. More testing and
improvements in design are needed
before this technology can be widely
implemented
Indirect Solar Energy
2. Ocean Thermal Energy
Conversion (OTEC) involves the
generation of electricity by using
the differences in temperature at
various ocean depths (temperature
gradients)
a. Warm surface water is
pumped into a power plant where it
heats a liquid (such as ammonia)
to the boiling point; the ammonia
steam drives a turbine to generate
electricity as ammonia is cooled by
the very cold water brought up
from the ocean depths
b. Only about 3-4% efficient,
costly, and may have extreme
consequences on marine
ecosystems
Other Renewable Energy
Sources
III. Other Renewable Energy Sources
A. Tidal energy
1. In areas where the difference in
water level between high and
low tides is great enough, it is
possible to build a dam across
a bay and harness this energy
2. Availability:
Cannot become a significant
resource worldwide because
few geographical locations
have a large enough difference
between high and low tides
3. Cost:
Very expensive to build, but
relatively low operating costs
Other Renewable Energy
Sources
4. Mechanism:
The dam’s floodgates are
opened as high tide raises the
water on the bay side, then the
floodgates are closed; as the tide
falls, water flowing back out to the
ocean over the dam’s spillway is
used to turn a turbine and generate
electricity
5. Advantages:
No waste products / emissions;
a clean source of energy
6. Environmental Impact:
Building a dam across the
mouth of an estuary would prevent
many ocean organisms from
reaching their breeding grounds
Other Renewable Energy
Sources
B. Geothermal Energy
1. Large, underground
reservoirs of heat exist in
areas of geologically
recent volcanism;
hydrothermal reservoirs
(formed when heated
groundwater is trapped by
impermeable layers in the
Earth’s crust) contain hot
water and possibly steam
Other Renewable Energy
Sources
2. Availability:
a. The US is the world’s largest
producer of geothermal
electricity from hydrothermal
reservoirs, but other countries
(such as Iceland) also use this
type of electricity to power
many homes
b. Scientists are also studying
how to extract some of the
geothermal energy found in
hot, dry rocks of the Earth;
would make this form of energy
production more widely
available
Other Renewable Energy
Sources
3. Cost:
Installation of different types of
geothermal systems may be
expensive, but have low operating
costs and high efficiency
4. Types:
a. Geothermal wells – hot fluid
is brought to the surface
and the resulting steam is
expanded through a turbine
to spin a generator, creating
electricity
b. Geothermal heat pumps –
use an underground
arrangement of pipes
containing circulating fluids
to extract natural heat in
winter and transfer excess
heat in summer
Other Renewable Energy
Sources
5. Advantages:
Emits a fraction of air
pollutants of fossil fuel
based technologies, and
entails minimal land use
6. Environmental Impact:
a. The water used to
transfer
geothermal heat
to the surface is
not inexhaustible
– must be
recirculated to
ensure renewable
energy
b. May emit hydrogen
sulfide gas
Energy Solutions: Conservation
and Efficiency
IV. Energy Solutions: Conservation and
Efficiency
A. Conservation vs. Efficiency
1. Conservation – moderating or
eliminating wasteful or
unnecessary energy-consuming
activities
Ex. carpooling, lowering driving
speeds
2. Efficiency – using technology to
accomplish a particular task with
less energy
Ex. designing and
manufacturing more fuelefficient automobiles
Energy Solutions:
Conservation and Efficiency
B. Energy intensity – a country’s or
region’s total energy
consumption divided by is
GDP
a. In developed countries,
energy intensity is
considerably higher in the
US and Canada than in
Japan and Europe
b. Energy intensity in
developing countries is
substantially less than it is
in industrialized countries,
but the greatest increase in
energy consumption is in
developing nations (as
countries boost their
economic development,
energy demands increase)
Energy Solutions:
Conservation and Efficiency
C. Energy-efficient technologies
1. Homes, Cars, and
Industries:
a. Compact fluorescent
lightbulbs require
25% of the energy
used by incandescent
lightbulbs and last 9x
longer
b. “Superinsulated”
homes use 70-90%
less heat than those
insulated by standard
methods
Energy Solutions:
Conservation and Efficiency
C. Appliances:
i) National Appliance Energy
Conservation Act
(NAECA) sets national
appliance standards
for major home
appliances
ii) Requires manufacturers to
provide Energy Guide
labels on all new
appliances to provide
estimates of annual
operating costs
Energy Solutions:
Conservation and Efficiency
d. Automobile efficiency has
improved dramatically as a
result of the use of lighter
materials and designs that
reduce air drag
e. New aircraft are much more fuelefficient than older models
f. Technological improvements in
the paper making industry
translates to increased profits
for manufacturers
2. Cogeneration / Combined Heat and
Power (CHP) - involves the
production of two useful forms of
energy from the same fuel;
typically involves the generation of
electricity, and then the steam
produced during the process is
used rather than wasted
Energy Solutions:
Conservation and Efficiency
3. Commercial Buildings – energy
costs usually account for ~30%
of a company’s operating budget
but those housed in older
buildings don’t have the benefit
of new technologies; energyservices companies assess how
to improve energy efficiency,
provide funding for
improvements, then are paid by
energy savings
D. Electric Power Companies and Energy
Efficiency
1. Demand-side Management electric companies help
consumers save energy; may
offer cash awards for installation
of energy-efficient technologies
or may give consumers compact
fluorescent lightbulbs, air
conditioners, or other appliances
in exchange for a slightly higher
rate
Energy Solutions:
Conservation and Efficiency
2. Electricity Deregulation –
competitive utilities are
more likely than regulated
monopolies to adopt
technological advances that
increase energy efficiency
and thereby lower costs
E. Energy Conservation at the
Individual Level
1. Lower thermostat in winter
and raise it in summer
2. Turn off lights when you leave
a room
3. Drive more slowly
4. Utilize carpooling or public
transportation