Understanding Power Distribution

Power is one of those things we all tend to take for granted – and it’s not until you flick a light-switch during a power cut that you begin to realise just how much.

We’ve all know that the electricity that drives so much of modern life is generated and then delivered to our homes, but few of us ever stop to think much about how it actually happens.

However, a little understanding of how power supplies are distributed can go a long way towards helping make sense of a lot of the issues surrounding energy efficiency.

Power Transmission

With conventional power generation taking place at centralised power stations, delivering electricity to homes and businesses requires an extensive transmission system. Typically this involves the network of over-head cables and pylons that are such a familiar part of the landscape, with the more expensive underground transmission being almost entirely reserved for heavily populated areas.

Generally, power is transmitted from the power station to substations located in or near population centres – which can often be some considerable distance apart. This fact brings both benefits and drawbacks.

On the one hand, it means that remote sources of energy, such as hydro-electric power or low grade fuels that would be uneconomic to transport, can be harnessed and used to meet the needs of people in towns miles away.

However, on the other, the distances involved means that an appreciable proportion of the energy generated is lost, although since there is less energy loss at high voltages, transmitting the electricity at 275kV and 400kV helps reduce this.

To make this possible, transformers are used to step the voltage up from the usual 25kV at the power station and then further transformers at the substation drop it down to 240V for domestic supply.

Embedded Power

An alternative solution – and one that most renewable energy generation systems use – is to connect smaller local generators to a local distribution network, rather than hooking them up to the National Grid.

Since the electricity is generated close to the eventual point of use – and sometimes in the same building – this approach reduces the transmission losses to an absolute minimum. It also avoids the need for large numbers of pylons and lengthy power lines.

This is “embedded generation” – an approach also called “on-site”, “dispersed” or “distributed” generation – and relies on the production of electricity from many individual sources, rather than a centralised power station.

Distributed energy resources offer fairly small-scale power generation – typically between 3kW and 10,000kW – which provide useful alternative or supplementary power supplies. Embedded power often comes at a relatively high price on the basis of the cost-per-kW-supplied – especially compared with the excellent economies of scale achieved by traditional centralised power stations.

However, for many domestic installations using the likes of photovoltaic solar panels and small-scale wind turbines, this may not be a major limiting factor.

With a government target to meet 10 per cent of Britain’s energy requirements from renewable sources by 2010, the issue of power distribution is likely to gain increasing importance as that target date approaches.

For many community energy initiatives, distributed energy power supplies seem to hold the key, while for others, the prospect of grid connection – and thus the opportunity to sell any surplus electricity generated – provides a major incentive for the project. For anyone involved in energy saving, whether as an individual or as part of a larger scheme, it can often be useful to understand something about the difference.