Common terms and units

Energy
energy is the capacity to do work. There are several different forms of energy, and energy can be transformed from one form into another more useful form. For example, chemical energy is the energy stored in the molecules of a fuel such as coal or wood, and is converted into thermal energy or heat by combustion. The kinetic energy of the wind is converted into mechanical energy of a wind turbine, and then into electrical energy. The basic unit of energy is the joule (abbreviated as J).
Power
power is the rate at which energy is converted or transmitted. Thus,
     energy = power x time, or power = energy / time.
Power is measured in watts (abbreviated as W). 1 watt is defined as the power produced when converting 1 joule of energy per second, which can be written as 1 J/s (or 1 J s-1)
1 joule and 1 watt are very small quantities compared to the amounts of energy and power typically considered, especially when we look at national energy use. So it more more common to use multiples of ten for both quantities (for example 1 megajoule (MJ) = 106 joules, ie 1 million joules, and 1 kilowatt (kW) = 103 watts).
The standard prefixes used are:

kilo (k) = 103 (thousand)
mega (M) = 106 (million)
giga (G) = 109 (billion)
tera (T) = 1012  
peta (P) = 1015  

Electrical power consumption is often expressed in units of kilowatt-hours (kWh). A 1 kilowatt device running for one hour uses 1 kilowatt-hour (kWh) of energy; this is equal to 3.6 megajoules.
1 Gg per GWh is equivalent to 1 kg per kWh
1 Gg per PJ is equivalent to 1 g per MJ


Energy and Power in Perspective
75 to 250 W Output from human pedal-powered generator
1 - 3 kW Power generated by typical roof-top photovoltaic system
600 kW - 2 MW Power generated by a wind turbine
   
 
100 kJ energy used by a 100 W bulb in just under 17 minutes
900 MJ = 250 kWh Daily amount of solar energy falling on a roof (50 sq.m) in Armidale (annual average)
648 PJ = 180 TWh Total electricity generation in Australia 1998 - 1999
2046 PJ Energy used for electricity generation in Australia 1998 - 1999


Useful Conversions




Greenhouse Gases:

CO2 Equivalent
The term CO2 equivalent (CO2e) emissions from combustion of a fuel source refers to the sum of the carbon dioxide emitted plus the equivalent global warming potential of associated emissions of other greenhouse gases, usually only methane and nitrous oxide.
CO2e is computed by scaling greenhouse gas emissions according to their global warming potential (GWP), and adding. CO2 is defined to have a GWP of 1, methane (CH4) has a GWP of 21, and nitrous oxide (N2O) has a GWP of 310.

Thermal efficiency of power stations.
Thermal efficiency is the energy supplied in electricity expressed as a percentage of the energy contained in the fuel used to produce the electricity - typical value around 35% (Delta Electricity 2001).

'Polycyclic Aromatic Hydrocarbons' is an aggregate substance group made up of the 16 US EPA Priority Pollutant PAHs (or the subset of those for which data is available) and reported as 'total' PAHs. This list of PAHs and CASR number is provided below.