Renewable energy sources are called such because they can be replenished by natural processes within a timescale that humans find useful. However, despite the great need for alternatives to fossil fuels, solar, wind, and geothermal plants produce only 3% of the world's electricity. Hydropower, on the other hand, contributes 16%.
The energy of the sun is used in two ways: direct heating of water, and photovoltaic electricity production.
Rooves can be fitted with a system of pipes filled with water, and these are heated by the sun to provide the hot water a house needs. Rooves can also be fitted with rows of photovoltaic panels to produce electricity during the day.
This electricity can be used directly, stored in batteries, or sold to the mains network of the city. Solar is still very expensive, but the price is decreasing as more people use it.
Governments often subsidise the installations to encourage it as a green energy.
The energy of the air used to turn a turbine and generate electricity. Wind turbines work very well at sea (off-shore wind 'farms') as well as in coastal areas.
Wind energy is now cheaper than nuclear, oil and coal, and is a large and rapidly growing industry. However, they can cause annoyance to local residents because of noise and visibility, and can be a hazard for birds.
The energy of moving water. In mountainous areas, such as Switzerland, dams store water in reservoirs and release it to turn a turbine. These reservoirs can also be used to store 'energy' from other sources.
Other hydro resources are tidal movements in and out of bays, and river flow. The largest hydropower dam in the world is on the Yangtze River in China, and generates power equivalent to more than 20 nuclear power stations.
Hydropower produces 16% of the world's electricity, but expansion of hydropower is limited by the availability of usable water resources.
The heat of the Earth provides a source of power. Water is pumped down into the crust, where it is heated by the hot rocks, and the resulting steam turns a turbine on the surface.
Energy from organic matter. Wood can be burnt directly, or plant material, such as sugar cane and corn, can be converted chemically into an alcohol fuel, which substitutes oil. Biomass is renewable because its inputs and outputs are part of the natural cycle. Nature does the rest.
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1918 - 2013
Frederick Sanger is one of three scientists to have been awarded the Nobel Prize twice, in 1958 and 1980, both times for chemistry.
He was a pioneer in the techniques for sequencing proteins, starting with insulin in the 1940s and 1950s. He moved on to peptides, RNA and finally DNA.
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