Unit-4

Environmental Science

Renewable and Non Renewable Energy Sources

Renewable Energy

• Renewable energy resources can be replaced or regenerated and will never run out (at least not for a very long time).

• Examples: wind and solar.

Solar Power Wind Power Water Power Thermal power

Solar cells

• 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.

• This makes solar cells ideal for use in remote locations where maintenance is difficult and other sources of electricity would be expensive.

Solar cells suffer from a low efficiency. This is because only light with enough energy causes an electron 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.

Efficiency of a solar cell

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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 which 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.

Problems with solar cells

© Warren Gretz/NREL

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Solar cells can be used very effectively in the right situation.

Effective use of solar cells

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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Effective use of solar cells

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 .

© Courtesy of BP Solarex/NREL

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Using the wind as a source of energy is not a new idea.

Sailing ships, powered by the wind, have been around for thousands of years.

Windmills which used the wind’s power to grind corn were once a common landmark across Britain.

Wind power

5

Wind turbines (or aero-generators) use large blades to capture the kinetic energy of the wind. This kinetic energy is used to directly turn a turbine and produce electricity.

Wind turbines do not produce any polluting waste, however, some people consider them to be an noisy and an eyesore. There is also concern that, if poorly located, they could kill migrating birds.

Wind turbines

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One problem with wind turbines is that individually they do not generate a lot of electricity. They are usually needed in large numbers to have an impact on electricity production. A group of wind turbines is called a wind farm.

Wind farms require large amounts of space in open areas, but the land can also be used for farming at the same time.

Offshore wind farms are located at sea. This wind farm is located 10 kilometres from the south-east coast of Ireland

Wind farms

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© Robert Thresher/NREL

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The energy produced by a wind turbine depends on the wind speed. If it is not windy, electricity is not produced, so wind turbines are not a reliable source of electricity.

Wind power can be used effectively in remote locations to charge batteries which can then be used to provide a constant supply of electricity.

To be effective, wind turbines need to be located in windy areas. Unfortunately, these are usually upland areas of natural beauty and some people object to the building of wind farms in these areas.

Effective use of wind turbines

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The power of flowing water has been used for hundreds of years to operate machinery. This power can also be used to generate electricity.

Water power 1: hydroelectric power

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Large scale hydroelectric schemes involve building a dam across the end of a river valley to create a reservoir. This is done high up in a mountainous area.

Hydroelectric power stations are able to start up electricity production quickly.

Hydroelectric power is also very reliable.

Hydroelectric power

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Hydroelectric power stations need to be situated in high mountainous areas such as North Wales or Scotland.

Damming the river causes the river valley to flood which could mean that houses and villages are destroyed.

Hydroelectric power schemes also cost a lot of money and take a long time to build. However, they do last a long time and they are able to produce large amounts of electricity.

Once they are built, hydroelectric schemes provide a cheap and reliable source of electricity.

Effective use of hydroelectric power

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The rise and fall of waves is a renewable source of energy. Effective sites for harnessing wave energy need to have strong waves most of the time, to ensure that enough electricity will be produced.

The “Limpet” (land-installed marine-powered energy transformer) on Islay, Scotland, is the world’s first commercial wave energy device. Its low profile is designed so that it does not effect coastal views.

Water power 2: wave power

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Tidal power involves building a dam across a river estuary.

Water can only flow in and out of the estuary through turbines in the dam, which harness the tidal energy.

When a tidal barrage is built, it results in some of the estuary being flooded. This can mean the loss of important habits for wading birds.

Water power 3: tidal power

Tidal power is able to provide a lot of electricity, however building a tidal barrage is very expensive.

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Tidal power provides a regular source of electricity. Exactly when this electricity will be produced is governed by the tides, which depend on the Moon.

The passage of ships past the tidal barrier and the effect on wildlife also complicate the construction of tidal barrage schemes.

Effective use of tidal power

Monthly variations in the tidal range will also affect how much electricity can be produced.

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In rocks under the ground, radioactive decay of elements, such as uranium, releases heat energy that warm the rocks.

In some areas, hot water and steam rise to the surface.

The steam and hot water which rises naturally to the surface can be harnessed to generate electricity.

The largest geothermal power plant is in California and has an output of 750 megawatts.

Geothermal energy

© Joel Renner - DOE/NREL

© David Parsons/NREL

15

Geothermal energy

In some areas, the warm rocks are very deep underground.

This geothermal power plant in California has 57 wells and produces 52 MW of electricity.

Where this occurs, wells are 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.

© Warren Gretz/NREL16

Non Renewable Energy Sources

Non-renewable energy resources will eventually run out – once used they cannot be used again.

Examples: coal and oil.

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What are fossil fuels? Industrial societies need a lot of energy and, at the moment, rely on fossil fuels as the main source of this energy.

Coal, oil and natural gas are fossil fuels. They are carbon-based materials that formed over millions of years from the remains of ancient plants and animals.

Fossil fuels are so useful because they contain stored chemical energy, which is converted into large amounts of useful heat energy when the fuels are burned.

The total amount of fossil fuels available is limited and so they are classed as non-renewable energy resources.

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What waste do fossil fuels produce?

Burning fossil fuels creates waste products that can act as pollutants and have harmful environmental effects.

Carbon dioxide – This greenhouse gas is the main waste product of burning fossil fuels. Increased levels of carbon dioxide due to human activities are thought to be connected with global warming.

Sulfur dioxide and nitric oxides – These gaseous pollutants contribute to the formation of smog and acid rain.

Ash – This waste solid is disposed of in landfill sites.

What can be done to reduce the problems caused by burning fossil fuels? 18

Nuclear fuel is used to generate electricity but, unlike fossil fuels, it does not burn.

In a nuclear fuel, such as uranium, reactions take place that split the atoms and release huge amounts of heat energy.

This is called nuclear fission.

In a nuclear power station, the heat released from nuclear fission reactions is used to change water into steam. As in other types of power station, the steam then turns a turbine, which turns a generator and produces electricity.

Nuclear power stations do not release any greenhouse gases such as carbon dioxide or gases which cause acid rain.

What is nuclear fuel?

19

What waste does nuclear power produce?

Nuclear power stations produce radioactive waste.

The used nuclear fuel contains some uranium, which can be separated from the waste and reused.

It also contains plutonium, which is a highly-radioactive product of the fission reactions that occur in uranium nuclear fuel.

New reactors that use this waste product as a fuel have been built.

However, plutonium is also used in the construction of

nuclear bombs and poses a very serious threat if it

gets into the wrong hands.

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Nuclear waste that cannot be reused poses serious problems as it can remain radioactive for thousands of years.

Highly radioactive waste can be turned into glass to help stabilize it and prevent leaks during storage. One solution is to bury the waste deep underground. This must be in a geologically stable environment, so there are few suitable sites.

Another suggested solution is to dump radioactive waste at the bottom of the sea. Dealing with nuclear waste is expensive and any solution has to be long term.

Where can nuclear waste be stored?

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Book/Web Resources

Environment & Ecology by Dr Gourkrishna Dasmohapatra

Thank You