P3: Sustainable Energy

• Electricity is called a secondary energy source because it is generated from another energy source, e.g. coal, nuclear, wind, etc.
• During the generation process some energy is always lost to the surroundings. This makes electricity less efficient than when compared with using the primary resource directly.
• However, the convenience of electricity makes it very useful. It can be easily transmitted over long distances and used in a variety of ways. 
• To generate electricity, fuel (either fossil fuel or nuclear) is used to release energy as heat.
• The heat is used to boil water which produces steam and the steam is then used to drive the turbines that power the generators.
• The electricity produced in the generators is sent to a transformer and then to the National Grid. The voltage is then reduced to a safer level of 230V, after which we can access it in our homes.
• In a fossil fuel power station the fuel is burned to release the chemical energy it contains as heat. As they are burning carbon fuels, the power stations also produce carbon dioxide.
• In a nuclear power station the energy is released due to changes in the nucleus of radioactive substances. Nuclear power stations do not produce carbon dioxide, but they do produce radioactive waste.

Nuclear waste emits ionising radiation and this can cause a number of health-related issues:

• Irradiation means exposure to radiation. This can happen naturally through background radiation from sources such as the Earth or space. It could also happen by exposure during medical treatments such as x-rays. In such cases the cells may become damaged, but the person does not become radioactive. Increased exposure may eventually lead to cancer and death.
• Contamination involves a radioactive material being placed inside a person. This can be far more damaging than irradiation, yet it is often used in medical treatments where the risk is considered worth the benefit, such as tumour suppression.

• Coal, oil and gas are energy sources that are formed over millions of years from the remains of plants and animals. They are called fossil fuels and are responsible for most of the energy that we use. However, because they cannot be replaced within a lifetime, they will eventually run out. They are therefore called non-renewable energy sources.
• Nuclear fuels such as uranium and plutonium are also non-renewable. Nuclear fission is the splitting of a nucleus that generates thousands of times more heat energy than burning the same mass of fossil fuel.
• However, nuclear fuel is not burned like coal, oil or gas to release energy and is not classed as a fossil fuel.
• Nuclear Fuel - A nuclear reactor is used to generate heat by nuclear fission. A heat exchanger is used to transfer the heat energy from the reactor to the water, which turns to steam and drives the turbines.

• As the demand for electricity continually increases, other sources of energy are needed. Renewable energy sources are those that will not run out because they are continually being replaced. Many of them are caused by the Sun or Moon. The gravitational pull of the Moon creates tides and the Sun causes evaporation (which results in rain and flowing water) and convection currents (which result in winds, that in turn create waves).
• Renewable energy sources can be used to drive turbines or generators directly. In other words, no fuel needs to be burned to produce heat.
• Wind Turbines - Wind can be used to drive huge turbines which, in turn, drive generators. Wind turbines are positioned in exposed places were there is a lot of wind, such as the tops of hills or offshore.
• Tidal Barrage - As the tide comes in, water flows freely through a valve in the barrage. This water then becomes trapped. At low tide, the water is released from behind the barrage through a gap which has a turbine in it. This drives a generator.
• Wood - Although burned for energy, wood is not a fossil fuel, nor is it non-renewable. It is classed as a renewable energy source since trees can be grown relatively quickly to replace those that are burned to provide energy for heating.

• Gas Advantages: Enough natural gas left for the short to medium term. Can be found as easily as oil. No sulfur dioxide is produced. Gas-fired power stations are flexible in meeting demand and have a quicker start-up time than nuclear, coal and oil-fired reactors.
• Gas Disadvantages: Burning produces carbon dioxide, although it produces less than coal and oil per unit of energy (global warming). Expensive pipelines and networks are often required to transport it to the point of use.
• Coal Advantages: Relatively cheap and easy to obtain. Coal-fired power stations are flexible in meeting demand and have a quicker start-up time than their nuclear equivalents. Estimates suggest that there may be over a century's worth of coal left.
• Coal Disadvantages: Burning produces carbon dioxide and sulfur dioxide. Produces more carbon dioxide per unit of energy than oil or gas does. Sulfur dioxide causes acid rain unless the sulfur is removed before burning or the sulfur dioxide is removed from the waste gases. Both of these add to the cost of electricity.
• Oil Advantages: Enough oil left for the short to medium term. Relatively easy to find, though the price is variable. Oil-fired power stations are flexible in meeting demand and have a quicker start-up time than both nuclear-powered and coal-fired reactors.

• Oil Disadvantages: Burning produces carbon dioxide and sulfur dioxide. Produces more carbon dioxide than gas per unit of energy. Often carried between continents on tankers leading to the risk of spillage and pollution.
• Nuclear Advantages: Cost of fuel is relatively low. Nuclear power stations are flexible in meeting demand. No carbon dioxide or sulfur dioxide produced.
• Nuclear Disadvantages: Although there is very little escape of radioactive material in normal use, radioactive waste can stay dangerously radioactive for thousands of years and safe storage is expensive. Building and decommissioning is costly. Longest comparative start-up time.
• Summary of Advantages: Produces huge amounts of energy. Reliable. Flexible in meeting demand. Do not take up much space (relatively).
• Summary of Disadvantages: Pollute the environment. Cause global warming and acid rain (fossil fuels only). Will eventually run out. Fuels often have to be transported over long distances.

• Wind Advantages: No fuel and little maintenance required. No pollutant gases produced. Once built, wind turbines provide 'free' energy when the wind is blowing. Can be built offshore.
• Wind Disadvantages: Need a lot to produce a sizeable amount of electricity, which means noise and visual pollution. Electricity output depends on the wind. Not very flexible in meeting demand. Capital outlay can be high to build turbines.
• Tidal and Waves Advantages: No fuel required. No pollutant gases produced. Once built, installations provide 'free' energy. Barrage water can be released when demand for electricity is high.
• Tidal and Waves Disadvantages: Tidal barrages across estuaries are unsightly, a hazard to shipping, and destroy the habitats of wading birds, etc. Daily variations of tides and waves affect output. High initial capital outlay to build barrages.
• Hydro-electric Advantages: No fuel required unless storing energy to meet future demand. Fast start-up time to meet growing demand. Produces a lot of clean, reliable electricity. No pollutant gases produced. Water can be pumped back up to the reservoir when demand for electricity is low, e.g. in the night.

• Hydro-electric Disadvantages: Location is critical and often involves damming upland valleys, which means flooding farms, forests and natural habitats. To achieve a net output there must be adequate rainfall in the region where the reservoir is. Very high initial capital outlay (though worth the investment in the end.
• Solar Advantages: Ideal for producing electrcity in remote locations. Excellent energy source for small amounts. Produces free, clean electricity. No pollutant gases produced.
• Solar Disadvantages: Dependent on the light intensity. High cost per unit of electricity produced, compared to all other sources except non-rechargable batteries.
• Bio-fuels Advantages: Contain no sulfur. Can use many readily available waste materials. Could be considered carbon neutral.
• Bio-fuels Disadvantages: Have lower energy output than traditional fuels. Could lead to competition of land use between fuel and food.
• Geo-thermal Advantages: Minimal fuel costs. Long life span and varying size of power output     Geo-thermal Disadvantages: High initial capital costs. Possible environmental damage from harmful gases escaping from deep within the Earth.
• Summary of Advantages: No fuel costs during operation. Generally no chemical pollution. Often low maintenance.      Summary of Disadvantages: Some produce small amounts of electricity. Can be unreliable. High initial capital outlay for most. 

• Mains electricity is produced by generators. Generators use the principle of electromagnetic induction to generate electricity by rotating a magnet inside a coil.
• When charge flows through a component, energy is transferred to the component. Power, measured in watts, is a measure of how much energy is transferred every second. 
• Power is therefore the rate of energy transfer. Electrical power can be calculated using the following formula:
• Power = Voltage X Current

• Energy is measured in joules (J). A joule is a very small amount of energy, so a domestic electricity meter measures the energy transfer in a much larger unit, the kilowatt hour (kWh).
• The amount of energy transferred for either joules or kilowatt hours can be calculated by the following equation: 
• Energy transferred = Power X Time

• The cost of the electrical energy used can be calculated if the power, time and cost per kilowatt hour are known. The formula for the cost of energy is as follows:
• Total cost = Number of kWh X Cost per kWh

• The greater the proportion of energy that is usefully transferred, the more efficient we say an appliance is. Efficiency can be calculated using the following formula:
• Efficiency (%) = Energy usefully transferred / Total energy supplied X 100

• Energy is lost at every stage of the process of electricity generation. Sankey diagrams can be used to show the generation and distribution of electricity, including the efficiency of energy transfers. 

• The greater the power supplied by a generator, the more of the primary fuel (coal, oil, etc.) it uses every second. Depending on the type of power station, voltages of between 1000 and 25000 V can be produced. 
• Due to the inefficiency of electrical energy transfer through cables, the National Grid uses extremely high voltages through its network of pylons. Over half a million volts is often used, meaning a low current is needed and less energy is lost due to heat. The voltages are then reduced to 230V by transformers in local substations before safely entering the home.

• Energy Saving in the home can be done in a variety of ways. These include loft insulation, double glazing, draught proofing, lagging the hot water tank and the use of efficient light bulbs.
• When considering which methods to employ, the homeowner needs to weigh up the economic effectiveness of any changes.

• When it comes to saving energy, choices are being made on a national scale as well as domestically. Reducing a country's carbon emissions is quickly becoming a global issue with international agreements such as the Kyoto Protocol.
• The need to reduce energy usage is important, but so is the need to maintain a secure supply of energy. This is done by using a wide mix of energy sources.
• You can save energy by replacing old houses with new efficient ones, increased use of public transport, more efficient trains and buses, encourage more widespread recycling and encourage car sharing and fewer journeys.

• As well as energy loss through the physical infrastructure of a building, a large amount of energy can be saved by following a few simple steps in the workplace.
• Turning off computers at the end of the working day, turning down an office radiator by just one degree Celsius or designing spaces to use more natural light can save money and help to reduce the business's carbon footprint.
• You can save energy by cleaning air conditioner filters, using low-energy light bulbs, roof insulation / cavity wall insulation in modern buildings, use of efficient modern, low-energy machinery and use of modern, efficient vehicles for transport of goods.