Energy options

Electricity is the ultimate convenience source of energy which disguises the fact that, with present methods of production and the fuel mix, it is highly energy inefficient. At its point of use, that is, as delivered energy, it is around 30 per cent efficient. Energy is defined as 'primary' and 'delivered'. Primary energy is that which is contained in the fuel in its natural state; delivered energy is that which is in the fuel at the point of use.

At present fossil-based energy is relatively cheap because, as indicated earlier, it does not carry its external costs such as the damage to health, to forests, to buildings and above all to climate. It may soon become politically necessary to incorporate these costs into the price of fossil fuels which will have huge economic consequences. Meanwhile the biggest carbon dioxide (CO2) abatement gains are to be realised in cutting demand especially in buildings. Even at the current price of energy green buildings can be cost effective.

It is worth noting the relative CO2 emissions between different forms of fossil-based energy:

Much has been made of the UK's switch to gas fired electricity generation, yet still electricity accounts for 750 grams of CO2 in the atmosphere for every kilowatt hour.

An increasingly popular way of servicing commercial and institutional buildings is by combine heat and power (CHP). It can be one of the more efficient ways of using energy. A typical distribution of total energy output from a CHP system is

Electricity 25%

High grade heat 55%

Medium grade heat 10%

Low grade heat 10%

kg/kWh delivered

Electricity

Coal Fuel oil Gas

This is called the 'energy balance' of CHP and it is attractive for two main reasons:

• Most of the energy of the fuel is useful.

• It can be adapted to low to zero carbon applications.

A CHP system is flexible. At present most CHP installations operate with gas or diesel reciprocating engines or turbines for larger installations. However, even relatively small installations will soon be able to switch to gas fired micro-turbines. Later in the decade there will probably be a considerable rise in the use of fuel cells. This is the technology of the future.

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