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<title>Pegs on which to hang your learning</title>
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<h1>Pegs on which to hang your learning</h1>
<h2>Four facts</h2>
<ol>
<li>Energy is bigger than electricity: Less than a fifth of the energy we consume is electricity.<div class='note'> Source: Dukes 2011 Chart 1.4: UK 2010 final energy consumption by fuel, electricity is 17.5%.</span></li>
<li>The UK uses about 2500 TWh of energy a year. <div class='note'> Source: Dukes 2011 Table 1.1: UK 2010 total primary demand. Exact figure is 2646 TWh.</div></li>
<li>The maximum speed at which energy is used by the UK is about 400 GW, the minimum speed is about 100 GW. <div class='note'> Source: see spreadsheet of workings.</div></li>
<li>The UK spends 125 billion pounds on energy each year. <div class='note'> Source: Dukes 2011 paragraph 1.20: UK 2010 spend on energy by final consumers; does not include spend on energy using equipment like cars, boilers or kettles.</div></li>
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<h2>Four conversions</h2>
<ol>
<li>A TWh (tera-watt-hour) is a billion kWh (kilo-watt-hours). A kWh is the unit on your electricity bill. <div class='note'>In general: T means tera- which means trillion; G means giga- which means billion; M means mega- which means million; k means kilo- which means thousand.</div></li>
<li>A GW (giga-watt) is a million kW (kilo-watts). A kW is the rate at which a small fan heater produces heat.</li>
<li>A GW (giga-watt) of power, running non-stop for an hour, produces a GWh (giga-watt hour) of energy. <div class='note'>If a 1 kilo-watt solar panel ran flat out, non-stop, all year it would produce 1 kW x 24 hours x 365 days = 8760 kWh of electricty. It doesn't run non-stop, nor flat out. Darkness and clounds mean that, on average, it runs for 10% of the time, so it produces 1 kW x 24 hours x 365 days x 10% = 876 kWh of electricty. Almost nothing runs flat-out, non-stop, all year.</div></li>
<li>A billion pounds is &pound;15 for each man, woman and child in the UK. <div class='note'>Exact figure: &pound;d 16.06/person. Source: Office for National Statistics UK mid-2010 population of 62.3 million.</div></li>
</ol>
<h2>A caution</h2>
<div>Don't trust claims that something is better because it is more efficient. You need to understand exactly what is meant. Get help.
<div class='note'>For instance: the same device can be claimed to be more or less efficienct depending on whether its efficiency is 'gross' or 'net'; even though turning natural gas into heat is almost 100% efficient, while turning gas into electricity is only 60% efficient, turning gas into electricity isn't always wasteful; perpetual motion machines are impossible, but it is possible say a machine is more than 100% efficient.</div>
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<div id='citation'>This is version 0.1 written on 10 May 2012 by Thomas Counsell (<a href='mailto:tom.counsell@decc.gsi.gov.uk'>tom.counsell@decc.gsi.gov.uk</a>). The latest version is available from <a href="http:github.com/decc/numbers-for-decc/short.html">http:github.com/decc/numbers-for-decc/short.html</a>.
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