What is Renewable Energy?

  In contrast to the fossil fuels, renewable energy, as the name suggests, exists perpetually and in abundant quantity in the environment. Renewable energy is ready to be harnessed, inexhaustible, and more importantly, it is a clean alternative to fossil fuels.
The term “renewable energy” has no official or commonly accepted definition. As an example, the Renewable Energy Working Party of the International Energy Agency defines renewable energy as “energy that is derived from natural processes that are replenished constantly”.

Typical renewable energy sources are:

Geothermal Energy
Energy generated from waste is termed as one kind of renewable energy sources in some countries. Others regard it as a waste disposal process rather than a renewable source, since there are pollutants generated as by-products, although modern technology has significantly reduced the pollutant emission to a very low level.

Solar Energy
Adopt modern technologies in capturing energy from the sun (solar energy) to produce hot water, steam or electricity.
Photovoltaic cells, made from semiconductor materials, such as silicon, can convert sunlight directly into electricity. The simplest and most common type of photovoltaic cells provide power to watches and calculators, while the more sophisticated “state-of-the-art” photovoltaic system can generate electricity to supplement local consumption in a building or a designated system, and the excess power can even be fed to the city electrical grid.
Solar hot water heaters can be installed on the roof to absorb solar energy and produce hot water.
Appropriate features can be incorporated into the design of buildings in cold countries so as to make the best use of solar energy. Materials that absorb and store the Sun’s heat can be built into the walls. The walls will then be heated up during the day and release heat at night.

Wind Power
• Wind energy has been used for thousands of years for milling grain, pumping water and driving other mechanical devices.
• Nowadays wind farm commonly employs groups of wind turbines, located either on land, near-shore and offshore, to harness wind energy for mass production of electricity.
A wind turbine is a device fitted with blades which converts kinetic energy of the wind into rotational motion to turn an electrical generator and produce electricity.
Wind power is commonly used in many countries including Germany, Denmark, Spain and United States. For example, over 15% of Denmark’s electricity demand is met by wind power.

Energy From Waste
• Household and commercial waste, commonly termed as municipal solid waste (MSW), can be used to produce heat for generating electricity and for district heating in cold countries.
• In general, there are three basic processes to convert MSW to useful heat and electricity, namely the thermal process, biological process and landfill gas utilization.
• Thermal process is the combustion of MSW to produce heat. Heat can then be used to produce steam to drive the turbine for production of electricity.
• Biological process means decomposing the organic fraction of MSW through bacterial action in the absence of oxygen, to form a biogas rich in methane which can be used as fuel for power generation. This process takes place under a controlled environment in a specially designed facility to allow biogas to be produced in a more rapid manner.
• After MSW have been deposited in a landfill for a period of time, a methane-rich-gas will be produced. This gas is known as the landfill gas (LFG), which can be used as fuel for power generation.
• Without undergoing any of these three processes, the organic materials will be decomposed naturally into methane or carbon dioxide which are greenhouse gases and thus are considered as undesirable by-products.

Other Forms of Renewable Energy Technology
• Other forms of renewable energy technology, such as hydroelectric power, wave power, geothermal energy and energy from vegetation, are also used in power generation worldwide.
• Hydroelectric power plant uses a dam built across a river to store water in a reservoir. Water released from the reservoir flows through turbine, which in turn activates a generator to produce electricity.
Wave power system generates electricity from the wave-driven rise and fall of water in a cylindrical shaft or caisson. The rising and falling water column drives air into and out of the top of the shaft and in turn power an air-driven turbine, which can drive a generator to produce electricity.
Geothermal energy is the natural heat extracted from the Earth’s crust. Geothermal power plant uses steam produced from reservoirs of hot water found below the Earth’s surface to drive electric generators.
Since the exploitation of these forms of renewable energy is very often dictated by geographical conditions, and thus the extent of their application usually has a wide variation among different countries.

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