How is it possible to save CO₂ by running a diesel generator or making small changes to electricity consumption patterns? The answer lies in the way supply and demand are balanced in the national electricity system.

The need for reserve

Electricity consumers don’t ask permission every time they turn on a light; large power stations can trip suddenly and wind turbines can only generate in accordance with the wind. For these reasons, the national utilities must always keep something in reserve, second by second and hour by hour the reserve is required in order to cope with unexpected changes in both supply and demand and keep the system in perfect balance.

The environmental cost of reserve

A large volume of reserve comes from part-loaded fossil fuelled power stations even though it is inefficient to burn gas and coal at part load.  Although hydro and pumped storage generators can provide reserve at low carbon cost, there is insufficient capacity to meet reserve requirements.

Additional reserve is provided by warming older coal and oil power stations, which can take twelve hours or more. Often, this reserve is not needed in the event and the stations are switched off without generating anything. 

Our notes on balancing supply and demand give more information.

Demand-side flexibility

In 2006, Flexitricity participated in a UK government supported investigation into the environmental effect of electricity consumers providing reserve services in place of large power stations. Consumers can do this by running generators, or turning down load, for short periods. In the UK system, each megawatt of reserve capacity provided by consumers can save between 300 and 750 tonnes of CO₂ annually.  The full report is available for download from our resources page.

The results are similar for both standby generators and load management. This is partly because diesel generators produce less CO₂ than coal. However, the biggest saving is obtained simply by making the capacity available. By giving the electricity system an alternative balancing option, consumers allow fossil fuelled power stations to stay closer to their best efficiency point, or better still, to stay off completely.

Flexitricity isn’t just about revenue; by bringing electricity consumers into the electricity system, Flexitricity allows them to support the renewable energy revolution, reduce national CO₂ emissions and help to secure the national electricity supply.