Thursday, 17 September 2009


I came across the word and concept 'Exergy' the other day. Perhaps I have led a sheltered life but I had never heard of it before. I found it an interesting and useful concept.

As I understand it, the term was coined (in 1956) because the term 'energy' (the potential to do work) has some disadvantages. Those who remember their thermodynamics will remember that energy cannot be created or destroyed, only converted from one form to another. So when oil is burnt, the world's supply of energy is the same ... the energy now happens to be in a form that is less useful to us.

Hence the term exergy. When oil is in the ground it has energy (and by definition exergy). When it is burnt, the exergy has gone (but the energy has simply been converted into another form).

Exergy is useful when talking about sustainability and alternative energy forms. we cannot afford to use up the world's exergy resources - otherwise we cannot have that potential to do work back again. Exergy disappears and with it goes our potential well-being.

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