Renewable
Energy
What parts of nature can
we harness to generate
renewable energy?
Renewable Energy
 Renewable
energy, is energy that
originates from a replenishable source.
 Renewable energy is important because
it does NOT require the existence of
limited resources, and because it does
not lead to significant pollution.
Solar Energy
 The
sun’s rays can
be harnessed for
the purposes of
heating and
electricity.
 Both passive and
active uses of solar
energy occur.
Solar Energy
 Passive
solar heating refers to using the
sun’s energy for direct heating purposes.
This allows buildings to avoid expending
fossil fuels for the purpose of heating and
cooling.
 Since the sun’s energy is not constant
over time, these buildings need quality
insulation to maintain their temperature.
Solar Energy
 Buildings
that use passive solar heating
are designed to take advantage of the
sun’s position in the sky.


During summer, the sun takes a high arc in
the sky; these buildings have an
overhanging roof to help stay cool.
During winter, the sun takes a low arc in the
sky; these buildings have large windows to
collect added sunlight.
Solar Energy
 In
the Northern Hemisphere, south-facing
windows receive the most sunlight, so
these windows will be the largest.
 These windows are also double-paned, so
they function as additional insulation
during nights.
Solar Energy
Solar Energy
 Solar
energy can also be directly
collected and converted to thermal
energy. This is active solar heating.
 During active solar heating, solar energy is
collected with roof-mounted collectors,
and used to heat liquid. This liquid is later
used to heat the building’s water supply.

8% of all energy spent in the U.S. is used to
heat water, so this can help conserve other
fuel sources.
Solar Energy
 Photovoltaic
cells are used to collect solar
energy and convert it to electrical
energy.
 Individual solar cells can only produce a
small electrical current. Solar panels are
formed by lining up multiple solar cells
together, but supplying all the energy for
a small city would still require hundreds of
acres of solar panels.
Solar Energy
 Despite
this drawback, research
continues to make solar cells more
efficient and less expensive.
 Solar cells are useful for providing energy
throughout the developing world, where
energy consumption is low and
distribution networks quite limited.
Wind Energy
 The
sun’s energy heats the Earth’s surface
unevenly. This produces air masses in the
atmosphere, otherwise known as wind.
 We can harness wind to generate
electrical energy. Windmills are essentially
a mounted turbine and generator; the
turbine collects the wind’s kinetic energy
and converts it to electrical energy.
Wind Energy
 Wind
farms are large arrays of wind
turbines laid out over a large area.
 Wind farms can small, consisting of 20
turbines in small rural areas. They can also
be large, and capable of supplying
energy to over 500,000 homes.
Wind Energy
 The
cost of wind energy has fallen as
technology has become more efficient.
Wind energy is currently the fastestgrowing energy source in the world.
 The greatest drawback to wind energy is
figuring out how to transport windgenerated energy from the turbine to
cities where it will be used – in an efficient
manner.
Biomass
 Any
natural material – such as plant
material or manure – is considered a
biomass fuel.
 Biomass fuels are organic and renewable.
Contrast with fossil fuels!
 Renewable biomass fuels are heavily used
for heating and cooking in the developed
world.

Wood and dung are common examples.
Biomass

However, biomass
fuels produce air
pollution, and
acquiring these
sources can also
cause ecological
damage.

This is especially true
of wood/timber and
dung!
Biomass
 Methane
is one of several byproducts
made during the decomposition of
organic wastes.
 Methane can be burned as a fuel for
heating, cooking and electricity.


In China, more than 30 million households
use biogas digesters to produce methane.
In the U.S., several landfills use methane
from decomposing waste for electricity.
Hydroelectric Energy
 Recall
the water cycle – precipitation
forms streams and rivers that run back to
the ocean. The kinetic motion of these
waterways can be harnessed to make
electrical energy.
 Hydroelectric energy is the process of
converting this kinetic energy to
electricity.
Hydroelectric Energy

20% of the world’s
energy comes from
hydroelectric
generators.

China, Canada,
Brazil, the U.S. and
Russia are the
world’s top countries
in using
hydroelectric
energy.
Hydroelectric Energy
 Hydroelectric
dams are used to block
natural water flow. This creates a
reservoir, or large lake for energy use.
 The reservoir will be slowly released,
converting the reservoir’s potential energy
to kinetic energy.
 Much like coal and wind power, a turbine
is used to collect this kinetic energy, and a
generator produces electrical energy.
Hydroelectric Energy
Hydroelectric Energy
 Hydroelectric
dams are expensive, but
are also very cheap to maintain. Contrast
with nuclear energy.
 Hydroelectric dams never release
airborne pollutants. They also last longer
than a typical fossil fuel power plant.
 Dams can also provide other benefits,
such as drinking water, irrigation and flood
control.
Hydroelectric Energy
 Large
hydroelectric dams block a river’s
natural flow. This can have serious
ecological consequences.


Flooding created by the reservoir causes
mass displacement of communities.
Decaying plant matter that gets trapped
within the reservoirs releases large amounts
of methane and other greenhouse gases.
Hydroelectric Energy
 Large
hydroelectric dams block a river’s
natural flow. This can have serious
ecological consequences.


The dam blocks further deposition of rich
sediment, which makes farmland downriver
less productive.
Cutting off different parts of the river can
disrupt established food webs and habitats.
Hydroelectric Energy
 Micro-hydropower
uses a small turbine to
collect energy from a stream, WITHOUT
having to construct a dam.
 This operation is cheaper and less
destructive than large-scale hydroelectric
energy. It is best suited for providing
energy to small isolated areas.
Bell Ringer
1.
2.
Identify two
benefits and two
drawbacks to
hydroelectric
dams.
Describe two
ways the home to
the left keeps
warm in winter.
Geothermal Energy
 Some
parts of Earth have underground
reservoirs of water, reservoirs that are
being heated up by energy from the
Earth’s mantle.
 In geothermal energy, these reservoirs are
drawn to provide kinetic energy for a
turbine, which allows a generator to
convert the kinetic energy to electric.

These reservoirs must be managed, to
avoid overuse.
Geothermal Energy
 The
U.S. is the world’s largest user of
geothermal energy, and the world’s
largest geothermal plant in the Geysers in
California (725,000 households).
 The Philippines, Iceland, Japan, Mexico,
Italy and New Zealand also make use of
geothermal energy.
Geothermal Energy
 Geothermal
heat
pumps are used in
over 600,000
households in the
U.S. These heat
pumps circulate
fluid from deep
underground to
surface level, and
back again.
Geothermal Energy
 The
ground’s temperature is constant
throughout the year. As such, it is warmer
than the air in winter, and cooler than the
air in summer.
 Geothermal pumps are useful for
moderating household temperatures.
Developing
Energy Tech.
What energy sources are
we looking at for the future?
Alternative Energy
 Alternative
energy refers to energy
sources that are currently in
development.


Perhaps the energy source is still in the
theoretical stage…
…or perhaps it still needs to be made
practical.
Tidal Energy
 Tidal
energy works very similarly to a
hydroelectric dam. Instead of using
running water, a tidal power plant traps
sea water behind a gate during high tide.
 Then, the water is released during low
tide. The trapped water returns to the sea.
In the process, a turbine is used to collect
kinetic energy, and convert it to electrical
energy.
Tidal Energy
OTEC
 Recall
that the sun’s energy only
penetrates the ocean to a certain depth.
Because of this, surface and deep waters
have a significant temperature
difference.
 Ocean thermal energy conversion (OTEC)
seeks to use this difference for the
purposes of electricity.
OTEC
 First,
warm surface water is drawn into a
vacuum chamber. Given low pressure,
water boils at low temperatures, so the
warm water is boiled using very low levels
of energy.
 The evaporated water becomes steam,
which spins a turbine. This converts kinetic
energy to electrical energy.
OTEC
 Next,
cold water from the deep ocean is
used to cool the steam, condensing it
back to water, so it can be used again.
 The cold water heats up in the process, so
it is returned to the surface as warm
water.

Fresh water is made as a byproduct of this
process.
OTEC
OTEC
 OTEC
remains impractical today, as
pumping deep water to the surfaces uses
about one-third of the energy that would
be produced.
 Also, the ecological consequences of
continually pumping deep water to the
surface remains unknown.
Hydrogen Fuels
 Hydrogen
gas (H2) can be burned as a
fuel, much more cleanly than fossil fuels.
 While hydrogen is the most abundant
element in the universe, H2 does NOT exist
naturally on Earth.
 This means we have to extract it from
other compounds, such as H2O or CH4.
Hydrogen Fuels
 As
such, hydrogen fuels require an input
of energy at some point before they can
be produced.

This energy may come from renewable or
non-renewable sources!
 Hydrogen
fuel cannot be made very
efficiently today. Furthermore, it is not very
efficient, and so must be compressed
before it can be a viable fuel.