station could be captured for a useful purpose without impairing the power
station’s electricity production
. This sadly is not true, as the numbers will
show. Delivering useful heat to a customer always reduces the electricity
produced to some degree. The true net gains from combined heat and
power are often much smaller than the hype would lead you to believe.

A final impediment to rational discussion of combined heat and power
is a myth that has grown up recently, that decentralizing a technology
somehow makes it greener. So whereas big centralized fossil fuel power
stations are “bad,” flocks of local micro-power stations are imbued with
goodness. But if decentralization is actually a good idea then “small is
beautiful” should be evident in the numbers. Decentralization should be
able to stand on its own two feet. And what the numbers actually show is
that centralized electricity generation has many benefits in both economic
and energy terms. Only in large buildings is there any benefit to local
generation, and usually that benefit is only about 10% or 20%.

The government has a target for growth of combined heat and power
to 10 GW of electrical capacity by 2010, but I think that growth of gas-
powered combined heat and power would be a mistake. Such combined
heat and power is not green: it uses fossil fuel, and it locks us into continued
use of fossil fuel. Given that heat pumps are a better technology,
I believe we should leapfrog over gas-powered combined heat and power
and go directly for heat pumps.

Heat pumps

Like district heating and combined heat and power, heat pumps are already
widely used in continental Europe, but strangely rare in Britain.
Heat pumps are back-to-front refrigerators. Feel the back of your refrigerator:
it’s warm. A refrigerator moves heat from one place (its inside) to

Figure 21.10. Heat pumps.