Energy is released by splitting the nuclei of uranium alone; a process called nuclear fission.
This method could probably produce enough energy for our needs for several thousand years. There is, however, increasing concern over the possible safety risks, particularly after the 1986 disaster in Chernobyl, USSR and the tsunami hit Fukushima nuclear plant in Japan which both sent radiation around the world.
One way to use tidal energy would be the dam an estuary. The rising tide fills a reservoir from where water falls through turbines to produce electricity. This method could meet 0.5 percent of the worlds energy needs.
The heat energy in the Earths core is released as volcanoes, geysers and hot springs. The latter provide heating for the city of Reykjavik, Iceland. Use of this energy source has been increasing at more than 15 percent each year. To make any great use of geothermal energy, however, it will be necessary to dig deep for it. In Cornwall, an experimental powers station will shortly be dug, with two wells each 6km deep. Cold water will be pumped in, heated by the hot rocks at that depth, and pumped out again, where the heat will be used to generate electricity.
The sun has an almost endless supply of energy. Plants trap it in photosynthesis to make carbohydrates; we can convert light into energy.
Solar energy may be used directly; in the Californian Mojave Desert solar panels produce power for 2000 homes. Even in Britain we can use solar panels in houses to reduce our need for fossil fuels. Solar power is probably only of use on a large scale in very sunny countries.
We can use other fuels than coal, including waste, dung, special crops and wood. These are collectively referred to as biomass. Some cities burn household waste in incinerators. In Coventry the heat is used by the Peugeot factory but in most other cities this heat is wasted. Heat could be harvested from the cooling towers of power stations. Brazil grows sugar cane and other crops to produce alcohol (ethanol) to fuel cars. In china waste and sewage are converted to bio gas which is used to light and heat homes in villages.
Wind turbines could provide 20 percent of our energy needs. Wind energy is endlessly renewable and does not cause pollution, but can be noisy and do require a large amount of space.
Wind turbines already provide an important source of power and can be positioned either on land or off shore in the sea. California has created great windmill farms in the desert. Each wind turbine has sails with a diameter of 20 metres, and generates a significant proportion of energy from the wind.
Burnt to produce heat or light, wood is the main energy source for some 70 percent of people in developing countries. The UK could grow enough wood to heat 700,000 homes - not nearly enough for today's population.
In many areas wood is being burnt faster than it can be replanted. Greenbelts help to slow this reduction of woodland but wood cannot be considered a renewable source of energy.
The power of water flowing down through a river or dam can be harnessed to generate electricity. Scotland, Scandinavia and many African countries already produce much of their power in this way.
There are drawbacks to hydro-electric power, not least the high initial costing of damming a suitable river. Agricultural land and homes may be flooded. Furthermore, the soil washed into the dammed lake makes it increasingly shallow, limiting the dam to a maximum 40 years effective use. This problem is particularly common in tropical countries.
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