ENERGY. 1. Non-renewable or finite energy resources are. 2. Renewable or infinite energy resources are source of

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1 Energy is the ability to do work. Energy cannot be created or destroyed: it can only be transformed, from one type into another. Energy can be either potential or kinetic. Kinetic energy is found in anything that is moving. That includes the smallest atom that is moving around fast because it is hot (heat energy) to the biggest boulder rolling down a hill or an elephant pushing down trees. Potential energy is stored or latent. It is energy that is not being used now, but could be used in the future. FORMS OF Both kinetic and potential energy can be found in several d i f f e r e n t f o r m s. F o r e x a m p l e : Heat energy is the result of the particles in a substance moving around. It is measured as temperature. Electrical energy is the result of the movement of electrons through a conductor, causing an electrical charge. Chemical energy is the energy stored in the chemical bonds between a substance's molecules, which can be released through a chemical reaction such as combustion. Nuclear or atomic energy stored in the nucleus of atoms. The energy is released through processes called nuclear fission (splitting the atom), fusion (combining two atoms) or radioactive decay. PUTTING TO WORK Humans often turn energy into electricity before turning that into yet another form of energy which we can use. For example, coal (potential energy) is burnt in a power station, releasing chemical energy as its chemical bonds are broken. The power station uses this to generate electricity (electrical energy), which in turn is used to power domestic cookers (heat energy). The sources of the energy put to work by humans fall into two categories: 1. Non-renewable or finite energy resources are sources of power that cannot be replaced once they are used, because the energy source has taken millions of years to form (e.g. coal and oil). 2. Renewable or infinite energy resources are source of power that quickly replenish themselves and can be used again and again. Some resources can be thought of as both renewable and non-renewable. Wood can be used for fuel and is renewable if trees are replanted. Biomass, which is material from living things, can be renewable if plants are replanted. Non-renewable energy Over the last 200 years an ever-increasing proportion of our energy has come from non-renewable sources such as oil and coal. The table below explains the advantages and disadvantages of non-renewable energy resources. Renewable energy sources Renewable energy sources are sources of power that quickly replenish themselves and can be used again and again. For this reason they are sometimes called infinite energy resources. The table below explains the advantages and disadvantages of the main renewable energy sources. ENVIRONMENTAL ISSUES AND CONSERVATION The growing global demand for energy - especially energy from fossil fuels - has major environmental impacts. Two examples are the problem of acid rain, and the (much more serious) problem of global warming. Acid Rain is rain that has a higher than normal acid level (that is, a low ph). Acid rain may contain weak solutions of sulphuric, carbonic and nitric acids. Where it falls over a prolonged period it can cause damage to the environment. Effects of acid rain Some of the problems attributed to acid rain include: Trees lose some of the protection in their leaves, leaving them more at risk from frost and diseases. Tree roots may also become stunted, so they can't take up as many nutrients. Soils lose some of their nutrients. Increasing acid levels may cause problems for aquatic animals and plants. Some fish may have trouble breathing for example. Acid rain may dissolve the stonework and mortar of buildings causing structural problems of buildings. The greenhouse effect When fossil fuels are burnt - by industry, in power stations and in vehicles and planes - the gases enter the atmosphere. Although these gasses have always been present in the world's atmosphere, their concentration is gradually increasing as more and more fossil fuels are burnt. Scientists believe that the build-up of these so-called greenhouse gases in the atmosphere acts like a blanket or greenhouse around the planet; heat is trapped inside the earth's atmosphere. This is the greenhouse effect, and the resulting increase in global temperatures is called global warming. Energy generation from fossil fuels also produces a build-up of gases - principally carbon dioxide and methane - which is thought to be a major cause of global warming. Another group of greenhouse gases includes the chlorofluorocarbons (CFCs for short). CFCs have been responsible for depleting the ozone layer as they attack and destroy ozone molecules. Whatever the causes and timescale, the implications of global warming are very serious. 27

2 non-renewable energy Type of fuel Where it is from Advantages Disadvantages Coal (fossil fuel) Formed from fossilised plants and consisting of carbon with various organic and some inorganic compounds. Must be mined from seams of coal which are found sandwiched between other types of rock in the earth. Burnt to provide heat or electricity. Coal is a ready-made fuel. It is relatively cheap to mine and to convert into energy. Coal supplies will last longer than oil or gas. When burnt coal gives off atmospheric Oil (fossil fuel) A carbon-based liquid formed from fossilised animals. Lakes of oil are found under land or sea, sandwiched between seams of rock in the earth (land or sea). Pipes are sunk down to the reservoirs to pump the oil out. Used a lot in industry and transport. Oil is a ready-made fuel. Relatively cheap to mine and to convert into energy. Only a limited supply. When burnt, it gives of atmospheric Natural gas (fossil fuel) Methane gases trapped between seams of rock under the earth's surface (land or sea). Pipes are sunk into ground to release the gas. Often used in houses for heating and cooking. Gas is a ready-made fuel. It is a relatively cheap form of energy. It's a slightly cleaner fuel than coal and oil. Only limited supply of gas. Nuclear Biomass Radioactive minerals such as uranium are obtained by mining. Electricity is generated from the energy that is released when the atoms of these minerals are split (fission) or joined together (fusion) in nuclear reactors. This is decaying plant or animal waste. An organic material which can be burnt to provide energy, e.g. heat or electricity. An example of biomass energy is oilseed rape (the fields of yellow flowers you see in the UK in summer) which produces oil. After treatment with chemicals it can be used as a fuel in diesel engines. A small amount of radioactive material produces a lot of energy. Raw materials are relatively cheap and can last quite a long time. It doesn't give off atmospheric pollutants. It is a cheap and readily available If the crops are replaced, biomass can be a long-term, sustainable energy source. Nuclear reactors are expensive to run. Nuclear waste is highly toxic, and needs to be safely stored for 100s or 1000s of years (extremely expensive) Accidental leakage of nuclear materials can have a devastating impact on people and the environment. The worst nuclear reactor accident was at Chernobyl, Ukraine in If crops are not replanted, biomass is a non-renewable resource. Wood Obtained from felling trees, burnt to generate heat and light. A cheap and readily available source of energy. If the trees are replaced, wood burning can be a long-term, sustainable energy source. When burnt it gives off atmospheric If trees are not replanted wood is a non-renewable resource. 28

3 renewable energy Type of energy Where it is from Advantages Disadvantages Solar Energy from sunlight is captured in solar cells and converted into electricity Single dwellings can have own electricity supply Manufacture and implementation of solar cells can be costly. Wind Wind turbines (modern windmills) turn wind energy into electricity. Can be found singularly, but usually many together in wind farms. Manufacture and implementation of wind farms can be costly. Some local people object to on-shore wind farms, arguing that it spoils countryside. Tidal Wave The movement of sea water in and out drives turbines. A tidal barrage (a kind of dam) is built across estuaries, forcing water through gaps. In future underwater turbines may be possible out at sea and without dam. The movement of sea water in and out of a cavity on the shore compresses trapped air, driving a turbine. Should be ideal for an island country such as the UK. Potential to generate a lot of energy this way. Tidal barrage can double as bridge, and help prevent flooding. Should be ideal for an island country. These are more likely to be small local operations, rather than done on a national scale. Construction of barrage is very costly. Only a few estuaries are suitable. Opposed by some environmental groups as having a negative impact on wildlife. May reduce tidal flow and impede flow of sewage out to sea. Construction can be costly. May be opposed by local or environmental groups. Geothermal It is possible to use the heat of under the earth in volcanic regions. Cold water is pumped into earth and comes out as steam. Steam can be used for heating or to power turbines creating electricity. Is used successfully in some countries, such as New Zealand. Can be expensive to set up. Only works in areas of volcanic activity. Geothermal activity might calm down, leaving power station redundant. Dangerous underground gasses have to be disposed of carefully. Hydrological or Hydroelectric Power (HEP) Energy harnessed from the movement of water through rivers, lakes and dams. Creates water reserves as well as energy supplies. Costly to build. Can cause the flooding of surrounding communities and landscapes. Dams have major ecological impacts on local hydrology. Biomass This is decaying plant or animal waste. An organic material which can be burnt to provide energy, e.g. heat or electricity. An example of biomass energy is oilseed rape (the fields of yellow flowers you see in the UK in summer) which produces oil. After treatment with chemicals it can be used as a fuel in diesel engines. It is a cheap and readily available If replaced, biomass can be a long-term, sustainable energy source. Biomass is only a renewable resource if crops are replanted. Wood Obtained from felling trees, burnt to generate heat and light. A cheap and readily available If the trees are replaced, wood burning can be a long-term, sustainable energy source. When burnt it gives off atmospheric If trees are not replanted then wood is a non-renewable resource. 29

4 CALCULATIONS OF As stated earlier Kinetic energy is the energy of movement. It is the name given to the energy a body possesses due to its motion. where m, is the mass of the object (in kg) and v its velocity (in m/s). Potential energy can be best thought of as energy stored in a static object. It can be due to how high the object is above a datum (starting point), or due to the fact that work has already been done on the object and the energy is stored in it (for example in a spring). where m is the mass of the object, g is the acceleration of gravity acting on the object and h is the height the object is above the ground or datum. Exam tips Kinetic energy is proportional to mass. But it's proportional to the square of the velocity. This means that for instance, doubling an object's velocity has much more effect on the kinetic energy than doubling its mass. E K 1 mv Don't confuse weight (in N) and mass (in kg). Calculations at higher level will be harder than the calculations for foundation level. For instance, you might have to transpose (change the subject of) a formula at higher level. You should also be familiar with the equations to do with work and power. Electrical energy is one of the most convenient and commonly used forms of energy since it can be transported easily from place to place (along electrical cables) and can be easily changed into other forms of energy. where V is the voltage of the circuit, I is the current flowing through the circuit and t is the time (in seconds) that the circuit has been operating. Heat energy is the energy transferred to a body that results in a change in the body s temperature. where m is the mass of the material in kg, DT is the change in temperature in degrees (Celsius or Kelvin) and c is the specific heat capacity of the material being heated. The specific heat capacity of a substance is the amount of energy required to raise the temperature of 1 kg of the material by 1 K. 2 2 E P mgh E h E e ItV mct POWER AND WORK DONE Work is a kind of energy transfer. When a force moves something the energy transfer is called work. Work isn't a form of energy - it's one of the ways that energy can be transferred. The amount of work done is the same as the amount of energy transferred. The amount of work is measured in joules (J). The distance is measured in the direction of the force. work = force x distance moved W= F x s Force is normally measured in newtons (N) and distance in metres (m). The unit for measuring work is therefore newton metres (Nm), or Joules (J). Power means how fast energy is transferred, that is, it gives an indication of how quickly the energy is changed from one form to another. Power = energy transferred / the time taken P = E/t P is the power in watts (W), E is the energy transfer in joules (J). t is the time in seconds (s) t must be in seconds. CONSERVATION OF In everyday usage, the term energy conservation has come to mean conserving energy in the sense of using less of it to do the same amount of work. Examples include improving the heat insulation of houses and other buildings, improvements in the efficiency of lighting and other electrical devices, making cars which use fuel more efficiently, etc. In technology and science conservation of energy has an older and different meaning. It is looked upon as a rule. The rule states that energy cannot be created or destroyed but can only be changed from one form to another - transformed or converted. This rule is also termed a natural law. The Law of Conservation of Energy The law of conservation of energy asserts that for a closed system, where no energy goes in or out, the total energy within the system must always be the same, although its form may change. On the other hand, in an open system such as a power station, this rule leads to the conclusion that the total energy input to the system must be exactly equal to the total energy output. The extent to which the output energy is able to do useful work - that is, of the desired type - is called the efficiency of the system. We calculate this by comparing the useful output from the system with its energy input. 30

5 Energy Transformation How energy can be converted or transformed is of prime importance to the technologist. Some forms of energy are directly interchangeable (for example potential and kinetic) but others need to go through several changes to arrive at the final desired form (for example chemical,heat,kinetic,electrical). LOSSES DURING TRANSFORMATIONS Although we have stated that energy cannot be destroyed and that the energy output from a system is equal to the energy input to the system, not all the energy in the system is used efficiently. When an energy conversion takes place there is always an energy change that we do not desire - usually a loss in the form of heat, sound or friction from the moving parts of a mechanism. As part of the course you should be able to understand the energy transformations in systems such as a wind turbine, geothermal power station, nuclear power station, hydro-electric dam, etc. The following components might be included in the description of these energy systems: You can also think of it in terms of power: Efficiency = useful power output / total power input This will give you a decimal number between 0 and 1, but efficiency looks better as a percentage. Multiply the efficiency by 100 to get this. Percentage Efficiency = Useful Energy Output 100% Total Energy Input AUDITS During an energy transformation, all the energy going IN to the system must come OUT and appear as other forms. It is not possible to destroy energy: it must go somewhere! Unfortunately, not all of the energy being put into a system appears as useful energy at the output. For example, a generator is designed to convert kinetic energy into electrical energy; however, due to the frictional forces, some heat energy will also be produced. Turbine this transfers steam, wind or water (hydraulic) energy into rotary motion, i.e. from Kinetic Energy to Mechanical Energy. KINETIC GENERATOR ELECTRIC HEAT Generator this converts the mechanical energy from a turbine into electrical energy. Motor this does the opposite of a generator converting electrical energy into mechanical energy. CALCULATING TRANSFERS During an energy transformation, therefore, the total energy contained within any closed system must remain constant. Knowing the total amount of energy at the start (or end) of any energy transformation tells us the total energy at any given time during the transformation. Energy Efficiency It was stated earlier that it was very important to try and conserve energy and to waste as little as possible. It is possible to look at how well an energy system is operating by calculating the efficiency of the system. Calculating efficiency The efficiency of an energy transformation is a measure of how much of the input energy appears as useful output energy. Efficiency = useful energy output / total energy input Since this heat energy is useless in terms of generating electricity, it is sometimes referred to as waste energy or (confusingly) as lost energy. Even systems that are designed to produce heat will have some energy losses. For example, the element of a kettle is designed to heat up water, but not all of the energy will go into heating up the water. Some of the energy is used to heat up the kettle; some heat will be lost to the room, etc. Since we know, however, that the total energy in any closed system must be constant, we can still carry out meaningful calculations if we remember to take all types of input and output energy into account. In the generator example above: the input energy is in the form of kinetic energy (E K ) the total output energy will be electrical energy plus the heat energy (E e + E h ). Hence, through conservation of energy, E K = E e + E h In order to ensure that we have taken all energies into account, it is useful to carry out an energy audit. An energy audit is a list of all the energies coming IN and going OUT of a system. The total for the energies IN must be the same as the totals for the energies OUT. 31