GCSE Physics

Energy Resources

RENEWABLE AND NON-RENEWABLE ENERGY (RE)SOURCES

The Sun is ultimately the source of all our energy supplies, though mostly in stored form.

Renewable (sometimes called alternative) energy sources	Non-renewable energy sources
wind water - hydroelectric (running water) - tidal (sea) - waves (sea) - other possibilities solar (sunlight) geothermal (heat from centre of Earth) biomass (biological materials such as wood)	fossil - coal - oil - gas nuclear - uranium - plutonium
Can quickly and continually be replaced (i.e. replenished or regenerated) by nature or humans. They can be managed. They will not run out (i.e. they cannot be exhausted or depleted). However, if forests are cut down too quickly, there's not enough time for them to be replanted and grow - so not enough timber.	Can't be replenished. They are being exploited by humans and are steadily being depleted It will take millions of years for nature to replace the fossil fuels we have used. Nuclear fuels can't be replaced.
Use of renewable energy sources does not create environmental damage. But some people feel that windfarms spoil the view and are a bit noisy. Also, if forests are cut down too quickly, there's not enough time for them to be replanted and grow - so too few trees, which are important to environment.	Exploitation of these energy reserves creates considerable environmental damage
Not much of our electrical energy comes from renewable sources	Most of our electrical energy comes from non-renewable fuels - mainly from fossil fuels

TIMESCALES OVER WHICH ENERGY IS ACCUMULATED IN THIS PLANETS ENERGY RESOURCES

rainfall and wind power	biomass	coal, oil and gas	nuclear
hours	months (straw) or years (wood)	many thousands of years	billions of years
Renewable		Non-renewable

MORE ON RENEWABLE ENERGY SOURCES

Renewable energy is derived:

(1) directly from the sun's rays - a tiny, tiny, tiny fraction of the Sun's energy that hits the Earth is enough to meet all our power requirements. Solar / photovoltaic / photoelectric cells, solar water panels, solar furnaces.

(2) indirectly from the sun, e.g. wind, waves, hydroelectric, and biomass (plants), biogases, landfill gas, sewage treatment plant gas. The main type of hydropower is hydroelectric power.

(3) from other natural movements and mechanisms of the environment, e.g. the Earth's heat (geothermal energy) and tidal energy.

This renewable energy can be used to generate electricity as well as for other applications. For example, biomass may be used as boiler fuel to generate steam heat; solar energy may be used to heat water or for passive space heating; and landfill methane gas can be used for heating or cooking.

Biomass is organic non-fossilised material. For example, plants and animals are biomass, as are the materials they produce, such as animal droppings and wood. (Interesting facts though no need to learn: (a) microbes make up over a half of all Earth's biomass; (b) the animal species with the greatest biomass, is the Antarctic krill, with a biomass of probably over 500 million tonnes - roughly twice the total biomass of humans.)

Biomass used for fuel is called biofuel. Biofuel is sometimes burned as fuel for cooking and to produce electricity and heat. Biomass used as fuel often consists of 'leftovers' like chaff and animal waste. Central heating units supplied by food grade wheat or maize are available. This type of alternative energy causes a fair amount of pollution.

Biofuels do not increase the net carbon dioxide in the atmosphere - which is good from the global warning point of view. However they do produce methane: recent evidence suggests that methane may perhaps be a factor in increasing global warming.

Geothermal power is electricity generated by using naturally occurring geological heat sources. It is harnessed in areas near geysers or hot springs usually by using superheated ground water. When underground water under high pressure is allowed to expand, it forms steam which is used to drive turbines. In some areas there is more steam than water coming up, so the steam can be used directly. Other ways of tapping geothermal energy also exist.

Renewable energy resources may be used directly or used to create other more convenient forms of energy.

Direct use	Indirect use
solar ovens geothermal heating water-mills windmills	electricity generation through wind turbines or electricity generation through photovoltaic cells production of fuels such as ethanol from biomass.

MORE ON NON-RENEWABLE ENERGY SOURCES

(1) Fossil fuels are hydrocarbon-containing natural resources such as coal, petroleum and natural gas. The use of fossil fuels (which are non renewable) has fuelled industrial development and largely supplanted water-driven mills and the burning of wood or peat (which are renewable sources of energy).

When generating electricity, energy from the combustion (i.e. burning) of fossil fuels is often used to power a turbine:

Older generators used steam turbines (the steam produced from water that is heated by the burning fuel produces steam which drives the turbines).
Newer power plants use gas turbines (the gases produced by burning of the fuel drive the turbine directly).

The burning of fossil fuels is the main source of human-produced emission of carbon dioxide, which is one of the greenhouse gases that is believed to contribute to global warming.

(2) Nuclear fuels include uranium and plutonium. These undergo fission in a nuclear reactor, producing heat which is used to indirectly produce electricity.

ELECTRICITY AND TURBINES

Electricity is a very convenient and widely used energy source. Except in the case of solar cells, electricity is generated in power stations by using rotating turbines.

Renewable energy sources that drive turbines directly include:

the wind;
the rise and fall of water due to waves;
the flow of water from a higher level to a lower level from behind tidal barrages or the dams of hydro-electric schemes.
geysers. In some volcanic areas, hot water and steam rise to the surface. The steam can be tapped and used to drive turbines producing geothermal energy. The energy released in volcanic areas originally come from the decay of radioactive elements, including uranium, within the Earth.

Geothermal energy is can also be tapped in a more indirect way in situations where using naturally-occuring water in the form of geysers is not possible. Water pipes are laid deep in the rocks: the water heats up producing steam wich drives turbines.

Non-renewable energy sources that drive turbines indirectly include:

In Britain, most power stations burn fossil fuels.
Most of the remaining power stations use nuclear fuel - mainly uranium and plutonium.

Fossil fuels are hydrocarbon-containing natural resources such as coal, petroleum and natural gas. The use of fossil fuels has fuelled industrial development and largely supplanted water-driven mills and the burning of wood or peat.

When generating electricity, energy from the combustion of fossil fuels is often used to power a turbine. Older generators used steam generated by the burning of the fuel to turn the turbine, but in newer power plants the gases produced by burning of the fuel turn a gas turbine directly.

The burning of fossil fuels is the main source of human-produced emission of carbon dioxide, which is one of the greenhouse gases that is believed to contribute to global warming.

ENVIRONMENTAL CONSIDERATIONS

Pros and cons of different methods of large-scale electricity production:

Burning fossil fuels releases carbon dioxide, which increases the greenhouse effect and so contributes to global warming. For the same amount of energy released, coal produces more carbon dioxide than oil and oil produces more carbon dioxide than natural gas. There is no feasible way of preventing the very large amounts of carbon dioxide produced from entering the atmosphere.
Burning most types of coal and oil also releases sulphur dioxide, a gas that helps to produce acid rain, which destroys the foliage of trees and shrubs. The fuel's sulphur content and the waste gases' sulphur dioxide contet can be removed from the waste gases before they enter the atmosphere, though this increases the cost of the electricity that is generated.
Nuclear fuels do not produce gases that increase the greenhouse effect or acid rain. When nuclear power stations are running normally, very little radiation or radioactive material escapes into the surroundings. If there is an accident, however, large amounts of very dangerous radioactive material may be released over a wide area. Nuclear power stations also produce waste, some of which stays dangerously radioactive for thousands of years and which has to be stored safely.
Groups of large wind generators (wind farms) are usually sited on hills and/or coasts and are considered unsightly by some people. They can also be noisy for people living nearby. In other words, wind farms cause visual pollution and noise pollution.
Using tidal energy involves building barrages across river estuaries. This destroys the habitat of many organisms e.g. wading birds and the mud-living organisms on which they feed
Hydroelectricity schemes involve damming upland river valleys. This means flooding land that may have previously been used for farming or forestry.
Solar cells are very clean, though they have a very high cost per Unit of electricity produced over their lifetime compared to all other sources of electricity except nonrechargeable batteries. Despite their cost, they are often the best energy source for producing electricity in remote locations (e.g. on satellites) or where only small amounts of electricity are needed (e.g. for watches or calculators).

AVAILABILITY OF ENERGY SOURCES FOR ENERGY PRODUCTION

Energy sources also differ in when they are available for generating electricity.

Power stations which use fuels can produce electricity at any time (of the day or of the year); they are reliable energy sources. The time it takes to start them up varies considerably: nuclear longest time; gas shortest time.
The amount of electricity produced by wind generators depends on the strength of the wind which varies considerably.
The amount of electricity produced by tidal barrages depends on the state of the tide, which varies during each day, and the height of the tide, which varies both on a monthly and yearly cycle. The amount of electricity produced by solar cells depends on the intensity of light that falls on them. Each of these energy sources can generate electricity only at certain times; they are all to some extent unreliable.
Hydroelectric schemes are generally very reliable. They can also be started up very quickly to meet sudden increases in the demand for electricity. They can also be operated in reverse using surplus electricity from other power stations to pump water from a lower reservoir to a higher one. This means that most of the energy from the surplus electricity is stored rather than being wasted.

ADDITIONAL LINKS

http://www.darvill.clara.net/altenerg/index.htm

http://www.iee.org/Policy/Areas/EnvEnergy/renew_water.pdf