Combined heat and power

The standard view of conventional big centralised power stations is that

they are terribly inefficient, chucking heat willy-nilly up chimneys and

cooling towers. A more sophisticated view recognizes that to turn thermal

energy into electricity, we inevitably have to dump heat in a cold place (figure

21.8). That is how heat engines work. There has to be a cold place. But

surely, it’s argued, we could use buildings as the dumping place for this

“waste” heat instead of cooling towers or sea water? This idea is called

“combined heat and power” (CHP) or cogeneration, and it’s been widely

used in continental Europe for decades – in many cities, a big power station

is integrated with a district heating system. Proponents of the modern

incarnation of combined heat and power, “micro-CHP,” suggest that tiny

power stations should be created within single buildings or small collections

of buildings, delivering heat and electricity to those buildings, and

exporting some electricity to the grid.



There’s certainly some truth in the view that Britain is rather backward

when it comes to district heating and combined heat and power, but dis-

cussion is hampered by a general lack of numbers, and by two particular

errors. First, when comparing different ways of using fuel, the wrong mea-

sure of “efficiency” is used, namely one that weights electricity as having

equal value to heat. The truth is, electricity is more valuable than heat.

Second, it’s widely assumed that the “waste” heat in a traditional power



Figure 21.8 . How a power station works. There has to be a cold place to condense the steam to make the turbine go round. The cold place is usually a cooling tower or river.