Turning equipment off may not reduce CO₂ emissions

The Politician's View

The British Government keeps asking its citizens to switch off audio and other equipment to save electrical energy. As most of this electrical energy is produced by burning fossil fuels, reducing electrical energy also reduces the fossil fuels used to produce it. By reducing the fossil fuels burnt reduces the CO₂ put into the atmosphere and, therefore, reduces the CO₂ emissions of a household. Or does it? Could the simplified political view overlook some crucial elements that greatly overstate the potential savings?

The Engineer's View

The First Law of Thermodynamics suggests that energy is neither created nor destroyed. The first law of thermodynamics is often called the Law of Conservation of Energy. This law suggests that energy can be transferred from one system to another in many forms. Thus, the total amount of energy available in the Universe is constant. Einstein's described the relationship between energy and matter in his famous equation:

E = Mc²

where energy (E) is equal to matter (M) times the square of a constant (C) - the speed of light. Einstein suggested that energy and matter are interchangeable. His equation also suggests that the quantity of energy and matter in the Universe is fixed.

Put simply, in a closed system, the amount of energy in it is constant. For most of us, the only closed system that we encounter is the universe!

Our homes and offices are not closed systems. The reason we have to heat them is because they loose heat to the atmosphere through the walls, windows, roof, floors and draughts. If they were a closed system they would not loose heat and would, therefore not need heating.

When equipment is left on standby, almost all of the electrical energy consumed is converted to heat. This small amount of heat will, to a very small extent, heat the home or office. Most heating systems are controlled by thermostats so when the room temperature reaches the desired temperature, the thermostat will switch off the heating system. The room will them begin to cool and when the temperature has dropped sufficiently, the thermostat will switch on the heating system. If there is equipment on standby in the room, then the time from the room to cool sufficiently will be extended. In other words, the CO₂ emissions used to create the electricity to power equipment on standby will be offset by the CO₂ emissions saved by the heating system not switching on so often.

Our Advice

A typical British home will need heating for around 10 months of the year. Homes in Scotland may need heating more than average and a home in Cornwall may need heating less. While the heating system is on there is no great benefit to switching equipment off. When the heating system is off, then switch off equipment when not in use. It may make you feel that you are helping the planet but in reality, the saving is so small as to not be worth doing as the next section shows.

CO₂ Emissions Saved

The British Government have issued figures that suggest that around 8% of domestic electricity (see note 1) use is by equipment on standby. However, if we switched off such equipment, a typical home would only be saving CO₂ emissions for 2 months (1/6th) of the year. So a typical household would only reduce their CO₂ emissions by 1/6th of 8% of the electricity they use. Or to put it another way, the reduction of CO₂ emissions due to electrically usage would be around 1.3%.

However, most of the CO₂ emissions in a typical house comes from gas. When the gas usage is taken into the equation (see note 2), the saving in CO₂ emissions is only 0.34% of the total CO₂ emissions for a typical house.

Notes

1

In a news release by DEFRA in March 2006 the British Government claims that "These smaller appliances emit 1MtC a year when on standby, costing each household around £25 a year". At March 2005 prices, this equates to around 280kWh of energy. EDF estimates the average household to use 3,300kWh, so 280kWh is about 8.49% of a typical household usage.

2

According to EDF, typical UK household uses 3,300 kWh of electricity and 20,500 kWh of gas each year which, using our calculator, causes 1.4 tonnes and 3.9 tonnes of CO₂, respectively, to be emitted into the atmosphere. A 1% saving in electricity usage (0.014 tonnes of CO₂) corresponds to 0.26% (0.014/(1.4+3.9)) reduction of the total CO₂ emissions of a typical house.