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Need to know G621

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**Explain what is meant by efficiency. **

Sample Assignment A (AO1): Report on an organisation’s energy policy and usage. Investigate energy policies and energy saving practices of non-domestic consumers of electricity. Explain what is meant by efficiency. Explain why actual efficiency will always be less than the theoretical maximum. Investigate steps that could be taken by a non-domestic consumer to maximise efficiency of energy use.

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**Assignment A - Assessment:**

A detailed description of the energy policy of a non-domestic consumer of energy, with ways in which they limit their energy consumption. Note that the chosen organisation should be a consumer rather than a producer of electricity. The environmental impacts considered should focus on the effects of the energy usage of the company NOT other aspects such as their waste products

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**Sample Assignment B: Generation of electricity**

Students should choose two types of energy source and compare large and small scale electrical production for each. For example a candidate might choose to compare: (i) a large-scale oil-fired power station with a small diesel generator such as those used to power electrical tools where no mains supply is available. (ii) a large-scale off-shore wind farm with a small wind-powered generator used to supply electricity to an individual dwelling. Research data on the energy values of fuels per kg, per litre (l), per m3 or per kWh as appropriate. Calculate the cost per joule for each fuel researched. Compare the relative cost per joule of different fuels.

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**Resources (assignment B)**

Current fuel costs can be found from local suppliers such as petrol stations and coal merchants. Many petrol stations supply coal and bottled gas as well as petrol & diesel. Some also supply LPG. Mains gas and electricity costs can be obtained from domestic bills if available, or from suppliers’ websites. Energy values (also called calorific values) are given on the Kaye and Laby website: _11/3_11_4.html The Nottingham Energy Partnership website also includes a useful table of energy value and cost data: The BWEA website gives data on wind energy costs. Websites such as elltecsolar.co.uk/ give some useful information about

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**Some other resources for Assignment B:**

The Centre for Alternative Technology, Machynlleth, Powys, Mid Wales, SY20 9AZ vision%20list.htm Electrical generation and supply companies: • • • • • Various energy companies might help

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**Fuel cost calculations:**

1. Assignment B – Task 3 Fuel cost calculations: To compare fuel costs from different fuels you must convert each fuel to the same unit. The SI unit of energy – the joule (J) or megajoules (MJ) is the best choice. Alternatively the kWh can be used. Electricity: Usually measured in kWh and prices are stated as pence per KWh. On top of that there is a standing charge for the electrical meter and variable tariffs. Conversion is:- joules = watts × seconds so 1kWh = 1000W (1kW) x 3600s (1 h) = J or 3.6MJ 1kWh = J or 3.6MJ So if 1kW of electricity cost 10p 1MJ costs 10/3.6 = 2.78p This is not the whole story because – you have to consider the cost of the fuel used to generate the electricity and heat output (calorific value for the fuel).

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**Fuel cost calculations:**

2. Assignment B – Task 3 Fuel cost calculations: Gas: Gas is supplied in volumes m3. However, prices to consumers are charged in pence per kWh. So cost is calculated in similar way to electricity. So you calculate cost per MJ in the same way. If the gas is bottled it is usually costed per kg and calculations are done as per a solid fuel. Liquid fuels: Petrol and diesel are priced per litre at the pump. Heating oils are delivered in prices for 500l or 900l. The more you buy the cheaper it is because of reduced transport costs. If 500l costs £200, 1l costs p/500 = 40p The calorific value is 47MJkg-1 density of kerosene = 817kg m-3 So calorific value = 47 X 817 = MJl-1

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**Fuel cost calculations:**

3. Assignment B – Task 3 Fuel cost calculations: 1 m3 = 1000l; so calorific value = /1000 = 38.4 MJl-1 1MJ costs : cost per l/calorific value per l = 40/38.4 = 1.04p Solid fuels: A 25kg bag of coal costs £7.05 = 705p (delivery cost may add to this) If caloric value is 36MJkg-1 1MJ costs = cost per kg/calorific value per kg = (705 /25)/36 = 0.78p Wind energy: You can calculate the cost of wind energy per MJ as for general electricity prices using the costs per kWh given in BWEA website

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**Fuel cost calculations:**

4. Assignment B – Task 3 Fuel cost calculations: Biofuels: Lots of different types and they all have different calorific values. Suppose 1 m3 of logs costs £100. However 1m3 supplied will not be solid wood. There will spaces between the logs. So you have to make an assumption for that. 70% of the volume is wood. 0.7m3 of wood costs £ m3 of wood costs £ Calorific value = 15MJ kg-1 Densities of wood vary. Assume density = 600 kg m-3. So calorific value = 15 X 600 = 9000 MJ m-3. 1MJ costs = cost per m3/ calorific value per m3 = 14286/9000 = 1.959p

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**Wind energy: Thanet array contains 100 turbines, each one is 3MW.**

5. Assignment B – Task 3 Wind energy: Thanet array contains 100 turbines, each one is 3MW. Total MW for the whole array = 300MW. Each of these turbines will run for 8760 hours/yr This is an overestimate and does not take into account the wind not blowing, breakdowns and servicing. The capacity factor for offshore wind turbines has been set by the Government/industry at 35% (0.35). Average UK home uses about 4,478 KWh /Yr. To work out number of UK homes supplied:- (hours run X MW capacity X capacity factor (0.35) ) X 1000 = KWh KWh / average UK household use = 205,404 number of homes. If you are using wind energy, work out number of homes provided with power by the Kentish flats array.

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6. Assignment B – Task 3 Task: For your assignment you need to include some calculations of fuel/energy costs used in generation of electricity. Advise you not to try and calculate for solar panels it is very complicated because of buy back tariffs. Follow one of the examples but include up to date figures/data you have found on websites and rework calculations. Various energy companies might help

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**The following slides may be helpful for experiment write ups – see slide on precision v accuracy!!**

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**Titration calculation example**

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**Metric prefixes in everyday use**

Text Symbol Factor tera T giga G mega M kilo k 1000 hecto h 100 deca da 10 (none) 1 deci d 0.1 centi c 0.01 milli m 0.001 micro μ nano n pico p

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**Accuracy and Precision:**

Accuracy refers to the closeness of a measured value to a standard or known value. For example, if in lab you obtain a weight measurement of 3.2 kg for a given substance, but the actual or known weight is 10 kg, then your measurement is not accurate. In this case, your measurement is not close to the known value. Precision refers to the closeness of two or more measurements to each other. Using the example above, if you weigh a given substance five times, and get 3.2 kg each time, then your measurement is very precise. Precision is independent of accuracy. You can be very precise but inaccurate, as described above. You can also be accurate but imprecise. For example, if on average, your measurements for a given substance are close to the known value, but the measurements are far from each other, then you have accuracy without precision. A good analogy for understanding accuracy and precision is to imagine a basketball player shooting baskets. If the player shoots with accuracy, his aim will always take the ball close to or into the basket. If the player shoots with precision, his aim will always take the ball to the same location which may or may not be close to the basket. A good player will be both accurate and precise by shooting the ball the same way each time and each time making it in the basket.

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