Unit 2 Energy Basics, Energy Services and Demand Introduction 3 1. Energy: 2. Forms of energy 3. 4. 3 3 Units of energy Power 4.1 Conversion between units 5. 6. What is it? Temperature 5 6 10 and heat 11 Energy conversion 6.1 Conservation of energy - the first law of thermodynamics 6.2 Efficiency 6.3 Primary and end use energy 6.4 Maximising energy efficiency 6.4.1 6.4.2 13 13 14 15 18 Energy conservation Energy efficient appliances 18 19 6.5 The second law of thermodynamics 7. Energy services 7.1 Matching the energy source to the service 20 23 25 8. 27 Home energy audit Identify all energy services and their energy sources Obtain historical records of energy usage Determine the energy consumption for each service 8.1 8.2 8.3 8.3.1 8.3.2 Estimating electrical energy consumption Electrical energy consumption for a battery charging stand-alone power system Estimating energy for hot water 8.3.3 8.4 Analyse the information, draw conclusions and make recommendations 8.4.1 8.4.2 8.4.3 8.5 8.6 8.7 9. 28 28 31 32 34 35 36 Calculating primary energy Major energy use areas Identifying ways to reduce energy use 36 39 40 Implementing the Recommendations Analyse the result of the improvement. Do it all again! 43 43 43 Summary Summary of quantities, units and their symbols used in this unit: Standard metric prefixes 9.3 Summary of equations used in this unit: 44 46 46 47 9.1 9.2 1O. Glossa ry 48 11. Bibliography 50 Home Energy Audit - Sample Worksheets © TAFE QUEensland Renewable Energy Centre 51 Unit 2, 1 Resource Book In the natural world, as well as in our constructed energy systems, energy is constantly being converted from one form to another. For example, plants convert light energy from the sun into chemical energy which it uses to grow. When we turn on a light switch, we allow the conversion of electricity into useful energy as light. There are two laws which describe what happens in every energy conversion process, regardless of what kind it is. These laws are called the Laws of Thermodynamics. Thermodynamics is simply a branch of science which looks at how heat and other forms of energy are related. In tlle case of turning on the electric light, the electrical energy is converted to light, but some of it is also being converted into heat. This heat constitutes an energy "loss" in tlle conversion process. Note that the energy tllat is "lost" does not actually disappear, but it is no longer available to do the task we wanted. It is no longer in a useful form. 6.1 Conservation of energy - the first law of thermodynamics The First Law of Thermodynamics is also known as the Law of "Conservation of Energy". It causes us to examine the proportions of useful eJlergy output and eJler:?'J losses in any energy conversion process. The First Law states: Energy cannot be created or destroyed; whenever energy is transformed from one form to another, the total quantity of energy remains the same. This is shown in the Figure 2 below. In a light bulb, the input eJlergy is the electricity. The useful energy output is light energy (tllis is also called the "useful work"). The energy loss is the heat given off from the bulb. / Input Energy ~ ~ Useful Energy Output (Light) (Electrical) ~ Energy Loss (Heat) Figure 2 A light bulb provides a simple example of what happens in every energy conversion process. This can be represented mathematically by the following equation: input energtJ = useful energy output + energtJ lasses © TAFE QUEellS/and Renewable EnErgy Cenhoe Unit 2, 13 Introduction to Renewable Energy Ted1llologies or Eour + Ewss EIN where EIN ............................................................. (Eq 6.1) the total energy input Goules, watt-hours, etc.) the useful energy output Goules, watt-hours, etc.) the energy losses from the conversion process Goules, watthours, etc.) Eour Ewss Energy losses can take a number of forms. Heat is always one form, others examples are air movement (e.g. from a built in cooling fan), noise and vibration. The fact that the First Law operates with every energy conversion that has ever been witnessed (as far as tlie author knows) is why perpetual motion machines never work! Perpetual motion machines are supposed to prOduce more energy---outpUt than what goes into them. - 6.2 Return to Learning Guide - Efficiency The effidellctj of an energy conversion process is the proportion of input energy which is converted to useful energy output. It is defined mathematically as: useful eneI'm output input energy efficiency Using symbols, this equation is written as: Eour 1] where .......................................................... EIN 17 (Eq 6.2a) efficiency (no units, but is often expressed as a percentage). is the Greek letter" eta". the useful energy output Goules, watt-hours, etc.) the total energy input Goules, watt-hours, etc.) 11 Eoul' EIN 14, Unit 2 Renewable Energy Centre © TAFE Queensland Resource Book TI1e definition of efficiency given above relates to Energy efficiency i.e. it relates to the total amount of energy into and out of a process over a period of time. It is also useful to define an instantaneous efficiency i.e. Pawer efficiency. This has exactly the same form, but applies to the input and output power flowing at any instant. Pour 1] ......................................................... PIN where 1] (Eq 6.2b) efficiency (no units, but is often expressed as a percentage). the useful pawer output (watts, kilowatts, etc.) the total pawer input (watts, kilowatts, etc.) Pour PIN Note that the same symbol has been used here for power efficiency and energy efficiency. They will be the same, unless the efficiency changes over time. Where there are a number of steps in an energy conversion process, the total efficiency of the process is equal to the product of the efficiencies of each step. Mathematically: 1]TOT = .......................................................... 1]1 X 1]2 X ••. X 1]n Where (Eq 6.2c) the total efficiency of the process the efficiency of the first step the efficiency of the second step the efficiency of the n th (last) step. - 6.3 Return to Learning Guide - Primary and end use energy e1lergy is the energy that we collect from our original energy source. The energy sources shown in Table 1 of Unit 1 (e.g. solar, wind, oil, coal etc.) are all primary energy sources. E1ld-use energJ} is the energy at the point of use - the energy finally consumed by the appliance. This distinction is important because of the significant inefficiencies in our energy systems. Primary End-use energy is the energy consumed by an appliance at the point of use e.g. in the home, office or work-site. In most energy systems, energy is converted from one form to another several times. The efficiency of each energy conversion step can be assessed. The overall efficiency of the complete system is then the multiplication of the efficiencies of all energy conversion steps. © TAFE Queensland Renewable Energy Cenb-e Unit 2, 15 Intraductial1 to Renewable Energy Tedmalagies o0°0 [l]~~. _",A ~ '~?~~,r:;TD/ Pr,XjuctiDn of C::>al Tran:.portalion of Coal ~ BOllef powe~n~tatjon TurLJinc Auxiliaries Tr~~~~~on Primary Energy End Us. Energy Energy less Energy loss Energy used Figure 3 Energy losses in the production of electricity from coal. Note that these figures will vary from state to state, with total cumulative efficiency in the range 0.27 to 0.32. In the above example, the energy in the coal is the primary energy. The electrical energy being used in our home is the end use energy. For our purposes we wi1l refer to electricity as an end-use energy source. (It is sometimes referred to as a secondary energJj source). The cumulative efficiency is simply the product of the efficiency of all the previous steps multiplied together. Note that energy "losses" in the first two steps represent the amount of energy used for production and transportation. This energy does not actually come from the coal itself. 16, Unit 2 Renewable EnErgy Centre © TAFE Queensland Resource Book Only about 28 percent (0.28) of the energy content of the coal is being delivered to the point of use in our home, factory, or business. The remaining 72 percent represents energy losses in waste heat. There will be further energy losses depending on the efficiency of the appliance or machine that is driven by the electricity to perform work for us. It is important to note that while the amount of energy that we pay for on our electricity and gas bills is the end use energtj, the pollution and depletion of resources that we cause is related to the amount of primary energy* consumed. The two quantities are related by a form of the efficiency equation: EENDUSE ............................................................ 17PR-EU where (Eq 6.3) primary energy Goules, watt-hours, etc.) end use energy Goules, watt-hours, etc.) efficiency of conversion from primary to end use energy. EpRlMARY EENDUSE 17PR-EU *It is common to refer to a fuel such as coal as the primary energy source, though U1isis not stricUy correct The sun is really the primary source of energy. The efficiency of U1ewide range of energy conversions required to convert plant matter to coal are NOT taken into account (e.g. U1Camount of solar radiation converted in photosynthesis; the gravitational and heat energy required to compress U1eplant matter and convert it to coal over millions of years ... ) It is important to keep this point in nLind when making comparisons between electricity generated from coal and electricity generated directly from U1esun! Some typical efficiency factors (T)m-ill) End-use Energy Source electricity (from coal) electricity (from diesel genset) Comments T)m-ill 0.27 0.32 - for various fuels are provided below. Depends on coal type, power station technology and transmission distance. 0.05 - Small genset efficiencies are 15-20% under 0.10 optimum conditions, and when supplying household loads directly (often including dummy loads), the efficiency is very low. Natural gas 0.9 Takes into account extraction, transport or piped** transnussion, processing and leakage. 8. petrol, diesel 0.9 as for gas LPG (for cars and 0.87 Lower eff. than natural gas because it needs to bottles) be compressed for storage in bottles/ tanks kerosene 0.9 as for gas wood 0.9 Accounts for energy in collection and transport. **Natural gas (boWed and for cars) = 0.7 due to high pressures required for bottling. Table 3 Energy conversion efficiencies for various end-use energy forms. Note: If fuel is transported over long distances, T)PR-EU will be lower. - © TAFE Queensland Return to Learning Guide - Renewable Energy Centre Unit 2, 17 Introdllctiml 6.4 to Renewable Enelgy Tedlllologies Maximising energy efficiency In order to improve the overall efficiency of an energy system, we need to: Minimise the number of energy conversion steps Maximise the efficiency of each energy conversion step For example, consider the provision of hot water to a home. Two possible choices of technology are: an electric hot water system, and a gas hot water system. For the electric system, the overall efficiency of energy conversion from coal to hot water is about 25%. For a gas system, the overall efficiency is about 54% (or higher). The efficiency of the electric hot water system alone is fairly high - around 75 % (better insulation could improve this considerably), but the efficiency of conversion from coal to electricity is low because of the number of steps involved, and the large inefficiency in some steps. The overall efficiency of the gas system is much better because the fuel is burnt directly at the appliance, so there is only one major energy conversion step. The use of a gas hot water system will result in a primary energy consumption of less than half that of the electric system. The use of a solar hot water system would reduce fossil fuel consumption even further, and has other advantages which are discussed in the following section. 6.4.1 Energyconservation Energy conservation means using only as much energy as necessary. For example, turn off lights when you leave a room; put on an extra jumper instead of turning up the heater. There is another important side to energy conservation. As you've seen in Example 13, you could waste over 72 % of the energy of brown coal before you get electrical energy to your house. Therefore, saving a little energy at the house results in a far greater saving at the energy source. 18, Unit 2 Renewable Energy Centre © TAFE Queensland Resource Book When you use 100 Wh of energy at home (the amount a standard light globe requires) we must produce 340 Wh of generation at the power station to supply this lOOWh. 100Wh < 340 Wh I Using 20 Wh at home (the incandescent light that gives the same light output as the standard globe) requires 70 Wh of generation at the power station. 20 Wh < o o o o 70 Vv'h I The simple act of using a different light bulb in one room of your house results in the power station needing to generate 270 Wh LESS! Figure 4 energy. 6.4.2 Small savings in end-use energy create much larger savings in primary Equation 6.3 is used to calculate the primary energy. A conversion efficiency of .29 is assumed. Energy efficient appliances Part of an overall approach to energy conservation is the use of energy efficient appliances. Many electrical appliances wiI1 have an ellergJj star rati1lg based on the energy consumption of the appliance under standard test conditions. Quite simply, the more stars, the more energy efficient the appliance. The star rating as well as the total predicted yearly energy consumption is usua]]y prominently displayed on the appliance. Carefully note the settings at which each appliance is rated as these can vary considerably between appliances. For instance, one washing machine may be rated on a heavy duty cycle, whereas anotl1er at a less energy consuming setting. If possible, note the predicted energy consumption at the setting you would be using most often. © TAFE QUEensland RenEwable Energy Centre Unit 2, 19 Introduction to Renewable Ene1gy Tedl11ologies Figure 5 Example of appliance energy star rating labels. - 6.5 Return to Learning Guide - The second law of thermodynamics The Second Law of Thermodynamics has significant implications for the way our soc.iety uses energy. TI1e depletion of our energy resources in the next few years is of great concern, yet from the First Law, we know that we are not running out of energy as such: it can neither be created nor destroyed. The problem lies in the way we use energy. The Second Law relates to the quality of an energy source: its potential for useful conversion. \ The First Law talks about the quantihj of energy that we may have. The Second Law Ienergy talks about ellergtj quality. Energy quality depends on the degree of order in the form. (An inverse measure of the quality of an energy source is ClltfOp1j, which I is a measure of the randomness or state of chaos of an energy form). High quality energy can be easily converted into other forms, and may be used for many useful purposes. Low quality energy is much more limited in its usefulness. For example, the gravitational potential energy of stored water in a dam, and the chemical energy which bonds the atoms in coal are both examples of energy in a highly ordered state: i.e. high quality energy. 20, Unit 2 Renewable EnergtJ Centre © TAFE Queensland