Sustainable Energy

Efficency = useful output energy transfer / total input energy transfer

OR

Efficencey = useful power output / total power input

EXAMPLE:

A steam engine uses coal, when the chemical energy in the energy is reduced by 150kj, the engine does 18kj of useful work against resistance force. Calculate the efficency

ANSWER:

Efficency = useful output energy transfer / total input energy transfer

                  = 18 / 150

                = 0.12 OR 12%

There are four main stages:

1. Fuel is burned to boil water to make steam
2. Steam makes a turbine spin
3. Spinning turbine turns a generator which produces electricity
4. Electricity goes to the transformers to produce the correct voltage.

The National grid uses power lines to connect power stations to the consumers. These include homes, factories, offices and farms.

Some examples of everyday energy stores are:

• gravitational potential ‐ the energy stored in water at the top of a mountain is used for hydroelectric power
• kinetic ‐ the energy stored in a flywheel is used as an alternative to traditional batteries in a hybrid car
• thermal ‐ the energy stored in the concrete blocks of a night storage heater is released during the day
• nuclear ‐ the energy stored in the nucleus of an atom of uranium is released when the atom undergoes nuclear fission
• chemical ‐ the energy stored in the chemicals of a battery or in the fuel at a power station is transferred as an electric current to do work on domestic appliances

Energy transferred = power x time

This is when:

Energy transferred is measured in joules, J

Power is measured in watts, W

Time is measured in seconds, S

Example:

A 250W computer s used for 10mins. Calculate the energy transferred

Answer:

10minutes = 10 x 60 = 600s

energy transferred = 250 x 600

energy transferred = 150KJ

Power = energy transferred / time

This is when:

Power is measured in watts, W

Energy transferred is measured in joules, J

Time is measured in seconds, S

Example:

An electric lamp tranfers 1,200J in 2 minutes. Calculate its power

Answer:

2 minutes = 2 x 60 = 120 s

Power = 1,200 / 120

Power = 10W

Sankey diagrams show the energy transfers in a system:

• The total energy transferred into the system is shown as an arrow
• This arrow splits into narrower arrows showing other transfers

The width of the arrow is drawn to scale to show the amount of energy. Sankey diagrams show that the total energy transferred into a system is equal to the useful energy transferred plus the energy dissipated or 'wasted'. This confirms that energy is conserved.

Energy Resource                   Energy Store          Power Input                Impact on environment

Fossil Fuels                             Chemical                  High                             Releases CO2(global                                                                                                                                 warming)

Nuclear Fuels                         Nuclear                   Very High                    Radioactive waste needs                                                                                                                      to be disposed of safely

Bio-Fuels                               Chemical                Medium                        'Carbon Neutral' so low                                                                                                                                    impact.   

Wind Power                           Kinetic                  Very Low                       May 'spoil the view'

Hydroelctricity                      Gravitational         Medium                           Loca habitats are affected        

Geothermal                       Thermal                        Medium                       Very Low

Water Waves                      Kinetic                            Low                             Very Low

Power stations that use fossil fuels or nuclear fuel are very reliable sources of energy. These two types of stations provide most of the country's electricity. They operate almost continuously. When additional power is needed, gas power stations or hydroelectric power stations are usually used because they will come on very quickly and start generating electricity almost immediately.

The fuel for nuclear power stations is relatively cheap but the power stations themselves are expensive to build. It is also very expensive to dismantle, or decommission, old nuclear power stations at the end of their useful life and the highly radioactive waste needs to be stored for millions of years before the natural activity will reduce to a safe level.

Water power, eg tidal and hydroelectricity, are reliable and predictable because of the Moon causing the tides and rainfall filling reservoirs. These two can also be used to supply additional demand. But many of the renewable sources are unreliable, including wind and solar energy, and cannot respond to increased demand - sunny and windy weather cannot be guaranteed.

Electricity is generated in power stations and transported across the UK via the National Grid

To move power around the National Grid:

• Before electrical power leaves a power station it is transferred at high voltages by using 'step-up' transformers to increase the voltage to 275,000 V or 400,000 V
• Before electrical power enters homes and factories the voltages are decreased by 'step-down' transformers to 33,000 V (large factories), 11,000 V (medium factories), 230 V (homes, shops, small factories and offices)

Nuclear power stations use fuel containing uranium.

1. Uranium atoms split releasing energy so fuel becomes hot. This heats the water turning it into steam.
2. The steam turns the turbine.
3. The turbine turns a generator and electricity is produced.
4. The electricity goes to the transformers to produce the correct voltage.

The fuel used eventually becomes solid nuclear waste. This waste is radioactive and emits ionising radiation.

ADVANTAGES:

Geographical limitations - nuclear power plants don't require a lot of space; they do not need a large plot like a wind farm. But they have to be built near a large body of water for cooling purposes - using the water as a heat sink. They are usually found on the coast so there is no risk to drinking water sources. Nuclear power stations do not contribute to carbon emissions - no CO₂ is given out - it therefore does not contribute to global warming. Nuclear power stations do not produce smoke particles to pollute the atmosphere or emit gases that contibute to acid rain. Nuclear energy is by far the most concentrated form of energy - a lot of energy is produced from a small mass of fuel. This reduces transport costs - (although the fuel is radioactive and therefore each transport that does occur is expensive because of security implications).  Nuclear power is reliable. It does not depend on the weather.

DISADVANTAGES:

Disposal of nuclear waste is very expensive. As it is radioactive it has to be disposed of in such a way as it will not pollute the environment. Decommissioning of nuclear power stations is expensive and takes a long time.  Nuclear accidents can spread 'radiation producing particles' over a wide area, This radiation harms the cells of the body which can make humans sick or even cause death.