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MAKING THE MODERN WORLD
Stories about the lives we've made

module:Geography of energy

page:Energy efficiency


'SunPipe' lighting system, Wroughton, June 2003. picture zoom © Science Museum/Science & Society Picture Library

Whatever choice of energy mix a country adopts, the fact remains that most countries are highly dependent on fossil fuels for their energy needs – oil to power transport and coal or gas to produce electricity. We depend on converting energy from one form (such as coal) to another (such as electricity), which proves inefficient. The more inefficient we are with fossil fuels, the more carbon emissions will be produced needlessly and the more we will influence unwelcome climate changes.

It is very difficult to convert energy from one form to another without a loss of energy in the process. For example, a typical coal fired power station converts 3.45Mw of chemical energy from coal into only 1.2Mw of electrical energy. The difference (2.2Mw) is lost as heat. In reality it would be more accurate to describe a power station as a generator of heat rather than a generator of electricity!


A Combined Heat and Power (CHP) station. picture zoom © Photofusion

The low efficiency (around 35%) can be improved if the ‘waste’ heat is re-used - for example, by pumping hot water round local housing for space-heating. Used this way, the power station becomes a Combined Heat and Power (CHP) station and the energy efficiency rises to 70-80% because the heat is no longer wasted but provides an important service.

The greatest efficiencies are produced when there are fewest conversions. For example, a water mill changes the kinetic energy of water to kinetic energy of machinery in an extremely efficient way (greater than 95% efficiency) because there is only one conversion. The missing 5% is energy used in overcoming the friction on the bearings of the waterwheel and on every piston or beam in the machinery, which produces heat in the process. This high efficiency is one reason water mills overlapped steam technology for a long time.

You can read more about the Newcomen and Watt inventions in the following scenes:


STORY: Power
SCENE: The Newcomen engine
launch scene


STORY: Power
SCENE: The Watt engine
launch scene


STORY: Power
SCENE: The steam turbine
launch scene

By contrast, if we wished to heat a room with an electric fire we would need 5 conversions (assuming the electricity came from a gas-fired power station):

  • the chemical energy of gas produces heat (but some heat escapes with exhaust gases)
  • heat energy turns water to steam (but some heat escapes through boiler walls and pipework)
  • the kinetic energy of expanding steam turns a turbine (but some energy is lost as friction, heat and noise)
  • the kinetic energy of the turbine generates electrical energy (but some is lost as heat in the cabling and in the pylon lines)
  • finally, the electrical energy is converted to heat energy in the electric fire (but some is wasted as visible light)

Added all together, this has been a very wasteful way to produce heat. Far better to have a gas fire directly producing heat with only one energy conversion required! But there is an even more efficient way - insulating the room so well that it is heated from the body heat of the occupants. From these examples it is clear that energy efficiency is not simply about technological improvements.

Technology plays an important part, but energy choices are more influenced by consumer expectations and interests of multinational industries.


Wood burning stove. picture zoom © Photofusion


Resource Descriptions

'SunPipe' lighting system, Wroughton, June 2003.
A Combined Heat and Power (CHP) station.
Wood burning stove.
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