Alternative Sources of EnergyPrior to the Industrial Revolution, the sun was the only source of energy widely available to humankind. Wood has been used since prehistory. Sails to use the sun-created wind were first raised 5,000 years ago, windmills 2,000 years later, and water-wheels 2,000 years after that. Coal came into general use just 300 years ago, and oil and gas only in the last 100 years. Not until the 20th century did non-solar energy arrive in the form of nuclear power. The natural flows of energy that have been used for millennia are known as renewable resources. The amount of energy fossil fuels can supply is ultimately limited by geology. These are known as non-renewable sources. As global energy demand grows and non-renewable sources begin to run out, so attention is turning back to the renewables. Biomass Biomass energy is plant or animal matter that can be converted into fuel. Nearly half the world’s population relies on biomass, mostly in the form of wood which is the principal fuel for 80% of people in developing countries. Hydropower Falling water generates 25% of the world’s electricity, about 5% of total energy demand. Although the most mature of the renewable technologies (over 30% of the developed world’s hydro potential is harnessed), it is still underexploited. Solar The sun already contributes significantly to the energy needs of buildings through the walls and windows, but because this energy is free, it is not counted in official statistics. Recent years have seen a massive increase in investment in technologies to make use of the sun’s energy.
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