Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. The energy extracted from water depends on the volume and on the difference in height between the source and the water's outflow. Pumped storage hydroelectricity schemes produce electricity to supply high peak demands by moving water between reservoirs at different elevations. They currently provide the only commercially important means of grid energy storage. At times of low electrical demand, excess generation capacity is used to pump water back into the higher reservoir, from where it can be released through the turbines at short notice. Less common types of hydroelectricity include run-of-the-river, waterwheels, and tidal power schemes.

A major advantage of hydroelectricity is the elimination of fuel costs and the associated carbon emissions although, in tropical regions, decaying plant material behind the dam can sometimes result in greater greenhouse gas emissions than a conventional power station. Other issues include the need to relocate people from areas to be flooded and disruption caused to aquatic ecosystems.

• The Power of Community: How Cuba Survived Peak Oil is a documentary film which details Cuba's efforts to recover from the 1990s economic crisis known as the Special Period?

• The Geysers (pictured), north of San Francisco, California, is the largest geothermal power development in the world?

• The International Energy Agency was founded in 1974 by the Organisation for Economic Co-operation and Development (OECD) in the wake of the 1973 oil crisis?

• Indian Railways has started to use Jatropha oil, blended with diesel fuel in various ratios, to power its Diesel locomotives?

• The South Wales Gas Pipeline is the largest high pressure gas pipeline in the United Kingdom?

• The Presbyterian Church (USA) was the first major religious denomination in the world to call on its followers to become carbon neutral?

• There was partial meltdown at the Three Mile Island nuclear power plant in 1979?

• A hybrid electric vehicle achieves better fuel economy than a conventional vehicle without being hampered by the limited range of an electric vehicle?

Fermi was well-known for his simplicity in solving problems. Whenever possible, he avoided complicated mathematics and obtained quick results based on order of magnitude estimates. Fermi also meticulously recorded his calculations in notebooks, and later used to solve many new problems that he encountered based on these earlier known problems.

After accepting the 1938 Nobel Prize in Stockholm, Fermi immigrated to New York with his family to escape the anti-Semitic laws of Fascist Italy, as his wife Laura was Jewish.

After working at Columbia University, Fermi went to the University of Chicago and began studies that led to the construction of the world's first nuclear reactor Chicago Pile-1 (CP-1). The first artificial, self-sustaining, nuclear chain reaction was initiated within CP-1, on December 2, 1942.