Power plants use two types of coal: lignite and hard coal. Lignite evolved from former bog forests under high pressure 15 to 20 million years ago. Hard coal developed the same way, but was exposed to additional pressure and heat for 300 to 350 million years deep within the Earth. This explains the difference in carbon content - about 30 per cent for lignite and 80 per cent for hard coal.
In supplying society with energy, a balance must be struck between three key dimensions: competitiveness, security of supply, and the environment and climate. No single energy source is optimal from all dimensions. This energy triangle illustrates the pros and cons of coal power.
Security of supply: Coal power plants provide stable and large-scale electricity generation. Of the Earth's fossil fuels, coal is the most abundant and widely dispersed, meaning that supplies are readily available and not subject to disruption.
Competitiveness: Coal power has a competitive production cost. Fuel costs are low and coal markets are well-functioning. However, technologies to reduce coal power plant CO2 emissions are expensive.
Climate and environment: Coal power plants emit high levels of CO2. Coal mining also impacts significantly with the landscape and infrastructure. Former open-cast mines have to be re-cultivated. Major efforts - including the development of clean coal technologies to reduce CO2 emissions - are being made to manage the climate impact of coal power plants.