Transcript 7. Renewable Energy: Solar and Thermal

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The then and now guide to solar energy
How has the use of solar energy changed over time?
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How much energy comes from the Sun?
The Sun is a huge sphere of very hot
gas and has been producing energy
for millions of years.
Even though it is about 150 million
kilometres away, the Sun is our
closest star and sustains all life.
Solar energy is the radiation from the Sun that reaches Earth.
It powers photosynthesis in green plants and is ultimately the
source of all food and fuel.
The amount of solar energy that strikes the Earth each day is
10,000 to 15,000 times greater than our daily energy needs.
In fact, the Sun is so powerful, that every minute, enough
solar energy reaches Earth to meet our needs for one year!
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How do we use solar energy?
Mankind has been using solar energy
for thousands of years. The Greeks
and the Romans designed and built
houses to maximize use of the Sun.
The Romans also made glass and knew
that it could trap solar energy. Sunlight
was so important that the Roman legal
system actually included the right to have access to the Sun!
In modern times, there are three main
ways of using solar energy:
passive solar heating
solar power stations
solar cells.
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What is passive solar heating?
Passive solar heating involves any system that can capture
the Sun’s energy directly. This can be done using a simple
solar collector or by the design of a building.
For example, the heat of the Sun
can be focused on one spot
using a curved mirror.
Solar cookers work on this
principle and so require no fuel.
Other examples of passive solar
heating include a greenhouse or
a south-facing window.
What do you think are the advantages and disadvantages
of passive solar heating?
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How can the Sun heat buildings?
Buildings can be designed to allow in as much light as
possible, by incorporating glass walls instead of solid walls.
The building is then heated by utilizing the greenhouse effect,
which reduces additional energy needs and costs.
This low energy house not
only has a photovoltaic roof
but also has been designed
so that it requires only a
minimum amount of energy
for heating and lighting.
The house is orientated in
an east-west direction and
the rear is south-facing to
maximize access to the Sun.
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How does a greenhouse capture solar energy?
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Greenhouse effect – ordering activity
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What is a solar power station?
Solar power stations use the Sun’s energy to heat water and
make steam, which then drives a turbine to produce electricity.
Some solar power
stations use a series
of mirrors, called
heliostats, to reflect
light onto a boiler.
© Sandia National Laboratory/NREL
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This solar power
station in California
consists of about
1800 heliostats, with
an electrical output
of 10 megawatts.
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More solar power stations
Some solar power stations
use curved mirrors, which
focus solar energy onto pipes
containing water. This heats
the water and forms the steam
needed to drive a turbine.
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Making solar power stations effective
Solar power stations are most
effectively located in areas with
high light intensity.
This test design is located in
Arizona where the sunlight is
intense and the air temperature
is high.
The mirrors must track the Sun
as it moves across the sky, to
be as efficient as possible.
Would this sort of power station
be effective in the UK?
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Why use solar cells to power satellites?
Solar cells (or photocells) turn light energy from the Sun
directly into direct current electricity.
Manufacturing solar cells is very expensive and requires the
use of highly toxic materials. However, once the solar cell is
built it produces no pollution and requires little maintenance.
Solar cells are ideal for use
in remote locations where
maintenance is difficult and
other sources of electricity
would be expensive.
Satellites have been
powered using solar
cells since the 1950s.
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How do solar cells work?
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How well do solar cells work?
Solar cells suffer from a low efficiency. This is because only
light with enough energy causes electrons to be released,
which is only about 25% of all sunlight.
The amount of electricity a solar panel can produce depends
on two factors: its surface area and the light intensity.
Producing enough
electricity to power a
town would require a
very large area of solar
panels but covering the
roof of a house can
meet the annual
electricity needs of the
household.
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What are the problems with solar cells?
One obvious problem with solar cells is that they do not
produce electricity at night.
If more electricity is produced during the day than is used,
the excess can be used to charge a battery. This can then
provide power during the night.
Scientists are working
to develop improved
solar cells, which
require less polluting
chemicals in their
manufacture, cost less
to produce and are
more efficient than the
current technology.
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What are solar cells used for?
Solar cells are very useful
where the light intensity is
highest.
These solar panels are in a
remote part of Morocco
where they are used by a
local utility company.
Solar cells are also useful
where low amounts of power
are needed.
Calculators only require a small
amount of electricity, so most
calculators now use solar cells
in place of batteries .
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Where are solar cells used effectively?
Solar cells can be used very
effectively in the right situation.
The robust nature of solar panels
can be exploited in areas where
maintenance is difficult.
The Dangling Rope Marina on
Lake Powell in Utah, USA, is only
accessible by water. It previously
depended on more than 246,000
litres of diesel to fuel its generators.
A photovoltaic energy system has
now been installed. It will reduce
the cost of providing electricity and
is clean, quiet and dependable.
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Why use solar cells in remote areas?
Solar cells are very useful
for remote locations where
supplying mains electricity
would be expensive.
This solar-powered street
light is in a remote part of
mid-Wales with no mains
electricity supply close by.
The use of solar power in
this way removes the need
to lay electricity cables to
the light, which is another
benefit to the environment.
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Pros and cons of solar cells
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Solar cells – true or false?
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The then and now guide to biomass
Has the use of biomass fuels changed over time?
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What is biomass?
Biomass, also known as biofuels
or bioenergy, is material from
living sources. The simplest
biomass energy sources are
plants, which can be burned to
produce steam to turn a turbine.
Traditionally, wood is burned to
give heat but trees grow slowly
and require a lot of land. Other
materials, such as poultry farm
waste, can also be burned.
Biomass fuels are renewable
as more plants can be grown,
producing yet more biomass.
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The carbon dioxide
released during burning
biomass is absorbed by
the replacement plants.
Biomass is said to be
‘carbon neutral’ and does
not add to global warming.
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How can waste create biofuel?
Methane is a biogas, which can be used a replacement for
natural gas. This biofuel can be produced by making use of
the natural decomposition of organic waste material.
Methane can be produced
from concentrations of
rotting sewage or manure
stored in containers called
anaerobic digesters.
These can be readily used
in remote places, such as
this digester on a pig farm.
Another source of methane is the rotting organic waste
buried underground in landfill sites. The gas can be drawn
up through pipes to generate electricity or provide heat.
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How else can biofuel be made?
Some sources of biomass
energy can be processed to
produce biofuels that are
even more useful.
Certain plants can be
fermented to form ethanol,
a biofuel, which can be used
instead of petrol or even
aviation fuel, as in this plane!
Sugar cane and beet are the most efficient sources of this
‘bioethanol’ but potatoes, corn, wheat and barley can also
be used.
Another biofuel is ‘biodiesel’ which can be made from
vegetable oils, animal fats or recycled cooking oils.
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What are the pros and cons of biofuels?
Some advantages of using biofuels are:
 Biofuels are made from plant materials which makes
them completely renewable.
 They are biodegradable, so do not cause as much
pollution if spilled.
 They produce less pollution, when burnt, than fossil fuels.
Some disadvantages of using biofuels are:
 Vehicles need to be adapted to run on pure biofuel.
 Large areas of land are needed to grow crops, which
could lead to loss of habitats.
 Biomass is ‘carbon neutral’ but the environmental impact of
using fertilizers to grow sources of bioenergy and the
energy used in transportation must also be considered.
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Using biofuels – true or false?
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What is geothermal energy?
Geothermal energy involves harnessing the thermal energy
stored within the Earth.
This thermal energy comes
from the decay of radioactive
elements, such as uranium,
in rocks under the ground.
The heat released by this
radioactive decay warms
the surrounding rocks and
nearby water.
© Joel Renner - DOE/NREL
In some areas, where the hot rocks are near the surface,
hot water and steam rise to the surface. This creates features
such as steam vents, geysers and hot mid springs.
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How can hot rocks generate electricity?
A geothermal power plant can be built to utilize steam and
hot water that rise naturally to the Earth’s surface.
The steam and hot water
provide a way of turning a
generator, which then
produces electricity.
© David Parsons/NREL
This is the largest producer
of geothermal power in the
world. It is in California and
has an output of 750 MW
of electricity.
Sometimes, the hot water is trapped in natural underground
reservoirs and does not reach the Earth’s surface. This water
can be reached by drilling to depths of several kilometres.
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Can deeper hot rocks be used?
In some areas, the geothermal rocks are deep underground
where there is no water.
Where this occurs, wells can
be drilled down to the hot rocks
and cold water is pumped
down. The water is heated by
the rocks and returns to the
surface as steam.
This geothermal power plant
in California has 57 wells and
produces 52 MW of electricity.
Geothermal power plants can only be developed in suitable
locations. At the moment, there is only one geothermal power
plant working in the UK, in Southampton.
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Pros and cons of geothermal energy
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Glossary
 biofuel – Biomass that has been processed to produce a
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more useful fuel, such as ethanol.
biogas – Methane gas that has been produced by rotting
biomass waste.
biomass energy – Energy from living matter, which can
be used as fuel.
geothermal energy – Heat from radioactive decay in
rocks deep below the Earth’s surface.
passive solar heating – A system that can capture the
Sun’s energy directly, such as a simple solar collector or the
design of a building.
solar cooker – A curved mirror that focuses radiation
from the Sun onto one spot to heat food.
solar energy – Energy from the Sun, which is converted
into thermal or electrical energy.
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Anagrams
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Solar and thermal renewable energy
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Multiple-choice quiz
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