A little knowledge

In my daily life at DECC, I find it useful to bear these facts in mind.

Four facts

  1. Energy is more than just electricity: Less than a fifth of the energy we consume is electricity.
    Source: Dukes 2012 Chart 1.5: UK 2011 final energy consumption by fuel, electricity is 18.5%.
  2. The UK uses about 2500 TWh of energy per year.
    Source: Dukes 2012 Table 1.1: UK 2011 total primary demand. Exact figure is 2469 TWh.
  3. The maximum rate at which energy is used by the UK is about 400 GW, the minimum rate is about 100 GW.
    This is pretty approximate. See spreadsheet of workings.
  4. The UK spends £130 billion on energy each year.
    Source: Dukes 2012 paragraph 1.22: UK 2011 £134 billion spend on energy by final consumers; does not include spend on energy using equipment like cars, boilers or kettles.

Four conversions

  1. A TWh (terawatt-hour) is a billion kWh (kilowatt-hours). A kWh is the unit on my electricity bill.
    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.
  2. A GW (gigawatt) is a million kW (kilowatts). A kW is the rate at which my small fan heater produces heat.
  3. A GW (gigawatt) of power, running non-stop for an hour, produces a GWh (gigawatt-hour) of energy. Running non-stop for a year, it would produce just under 10 TWh (terawatt-hours) of energy.
    If a 1 kW solar panel ran flat out, non-stop, all year it would produce 1 kW × 24 hours × 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 × 24 hours × 365 days × 10% = 876 kWh of electricty. Almost nothing runs flat-out, non-stop, all year.
  4. A billion pounds is £16 for each man, woman and child in the UK.
    Exact figure: £15.82/person. Source: Office for National Statistics UK census night 2011 population estimate of 63.2 million.

Units

There are surprisingly many commonly-used units for energy.
You may see: kilowatt-hours (kWh), tonnes of oil equivalent (toe), tonnes of coal equivalent (tce), therms, British Thermal Units (BTUs), and joules (J). All of these may occur with the usual prefixes, eg, Mtoe (million tonnes of oil equivalent), or PJ (petajoules).

Hint:

If you given told a number in units other than TWh (or kWh) ask for it to be converted. Wait until the conversion is done: otherwise the number will be meaningless to you.

A caution

I don't trust claims that something is better because it is more efficient — I need to understand exactly what is going on to be sure.
For instance: The same device can be claimed to be more or less efficient 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 to say a machine is more than 100% efficient.
This is version 0.3 updated on 19 June 2013 by Thomas Counsell and James Geddes (tom.counsell@decc.gsi.gov.uk). The latest version is available from http://decc.github.io/numbers-for-decc/short.html. If you want to report bugs or propose fixes, you can do so at http://github.com/decc/numbers-for-decc