Evolution of Energy Sources

The economic and technological development of societies is linked with shifts in sources of energy. The tendency has been the adoption of denser energy sources, as the shift from coal (solid) to oil (liquid) and natural gas (gas) indicates. This shift can be simplified into 5 major phases, one being speculative:

• From the beginning of history up to the industrial revolution (18th century), mankind's use of energy relied only on muscular and biomass sources. Most work was provided by manual labor and animals, while the biomass (mainly wood) provided for heating and cooking energy needs. Other sources of energy, such as windmills and watermills were present but their overall contribution was marginal.
• By the mid 19th century, the industrial revolution brought a major shift in energy sources with the usage of coal, mainly for steam engines, but increasingly for power plants.
• As the 20th century began, the major reliance was on coal, but a gradual shift towards higher energy content sources like oil began. This second major shift inaugurated the era of the internal combustion engine and of oil-powered ships.
• In the late 20th century, the emphasis on petroleum products as the main provider of energy reached the point where the world economy highly depends on the internal combustion engine and supporting industries. As its level of technical expertise increased, mankind was able to tap on more efficient sources of fossil fuels, mainly natural gas, and energy released by matter itself (nuclear fission).
• The 21st century will be characterized by major shifts in energy sources with a gradual obsolescence of fossil fuels, like coal and oil, for more efficient fossil fuels such as natural gas. There may also be substantial clean coal technology potential. Advances in biotechnologies let anticipate the growing usage of biofuels. Nuclear energy, if nuclear fusion becomes commercially possible, may also play a significant role. A very important change in energy sources is likely to be the usage of hydrogen, mainly for fuel cells powering vehicles, small energy generators and numerous portable devices.