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.
Non-Renewable energy sources are those which have been created by natural processes over a long period of time, and which will not be replenished within a timescale that humans find useful.
Solid carbon residues of long-dead organic matter. Available in many places of the world in large quantities. It is a very dirty fuel, causing of the world's worst air pollution, and contributing very much to the Greenhouse Effect, responsible for climate change. Coal is used to produce 41% of the world's electricity.
In one second, a coal-burning power station burns 2 GJ of energy. This is about 80 tonnes of coal per second! The 3.4 billion tonnes of coal burnt in the world in 2002 produced 23% of the world's total energy needs.
It takes about 500 kg of coal to power a computer for one year. Google alone uses the equivalent electrical output of a whole power station to power its network of servers around the world.
A liquid hydrocarbon, which provides many fuel products, and is the base material for plastic. It is being phased out as a fuel for electricity production, due to its decreasing availability and increasing price.
Oil causes serious damage to sensitive ecosystems when it is accidentally released, from ships or undersea wells. Oil is a major contributor to city smog, acid rain, and global warming. The use of shale oil from rock strata will increase the environmental damage caused by oil even more.
Oil is used to produce 5% of the world's electricity.
A hydrocarbon gas, methane, which is used for heating and cooking. This is the cleanest and most efficient of the fossil fuels, but, like oil, its reserves are being depleted rapidly. Europe imports nearly all of its gas from Russia and North Africa via enormous pipeline networks. Gas is used to produce 21% of the world's electricity.
The biggest problem with fossil fuels is the emission of pollutants. Along with sulphur and nitrous oxide, which produce acid rain, and several other nasties, all fossil fuels produce CO2 in large quantities. CO2 is responsible for global warming and the loss of stable climate around the world.
CO2 emissions: 0.963 kg CO2/kWh for coal power, 0.881 kg CO2/kWh for oil, or 0.569 kg CO2/kWh for natural gas. From these statistics, you can see that coal is much less efficient than the other fossil fuels, and methane gas is the most efficient.
Uranium can be caused to decay at higher than natural rates in nuclear reactors. This releases huge amounts of heat which can be used to generate electricity. Uranium does not release pollution of the type fossil fuels do.
But nuclear power is expensive and its waste product, depleted uranium fuel, must be stored for tens of thousands of years till it is 'safe'. Accidents can cause leaks of radiative material which leave large areas of land uninhabitable due to contamination, as well as spreading through the groundwater and sea, entering the human foodchain through fish.
Ticino, Switzerland, received a lot of radiation from the Chernobyl nuclear accident in 1986, from a contaminated raincloud. Japan, Russia, Ukraine, and the USA have all suffered serious nuclear accidents, releasing deadly radiation which will contaminate land, water, and food for thousands of years.
It is being phased out in Germany and Switzerland, but France still makes 75% of its electricity from nuclear power. Italy does not use nuclear power at all. Nuclear reactors produce 13% of the world's electricity.
Content © Andrew Bone. All rights reserved. Created : August 30, 2014 Last updated :June 23, 2015
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1862 - 1943
David Hilbert, 1862 - 1943, was German, and is considered one of the greatest mathematicians ever, leaving a broad legacy in mathematics, physics and philosophy.
"To be a scholar," said Galileo, "you have got to publish papers - and the best papers have something written on them."
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