Energy switching 

To put it simply, coal can be expressed as CH (one carbon atom and one hydrogen atom), oil as CH2 (one carbon, two hydrogen) and natural gas as CH4 (one carbon, four hydrogen). When burnt the carbon in the fuel is oxidised into carbon dioxide – CO2 – while hydrogen is oxidised to H2O (water).  Both of these reactions release useful energy. 

Energy chains from the point of production (i.e. an oil field or a coal mine) to final consumption will produce some emissions along the way, since energy is used for extraction and for transport to the consumer.

Converting coal, oil and natural gas to suitable energy carriers uses differing approaches. While natural gas and some types of oil can be fired in highly efficient gas turbine power plants, coal is mostly burnt in less efficient boilers due to the high content of ashes and other impurities.

Important to assess the effects

For the reasons above, the emissions from one kWh of electricity produced in Europe may vary greatly. While brown coal-based electricity may generate 1.2 kilograms of CO2 emissions per kWh of electricity, the emissions from a modern gas-fired power plant may be as low as 0.35 kg/kWh. Power stations fuelled by high quality coal will have lower CO2 emissions, but even so their emissions will be 2 – 2.5 times higher than natural gas fuelled plants.

Renewable energy sources, such as hydropower, wind mills and solar photovoltaic panels will typically not generate any CO2 emissions at all, but there may nevertheless be CO2 emissions associated with the production of materials, construction and transportation.

Electricity, hydrogen and hot water or steam are energy carriers that do not carry the carbon atom to the final consumer to become CO2. When considering switching from one fuel to another, it is important not only to look at the impact at the point of end-use, but to also consider impacts underway in the process.