Renewable energy comes from the sources that can theoretically be renewed as quickly as they are consumed. If used at a sustainable rate, these sources will be available for consumption for thousands of years or longer. Unfortunately, some potentially renewable energy sources, such as biomass and geothermal, are being depleted in some areas because the usage rate exceeds the renewal rate.
Solar Energy: Solar energy is the ultimate source of energy available on the earth. Though only a small fraction of the solar energy reaches on the earth’s surface, it is sufficient to meet the world’s energy requirements. The process of directly converting solar energy to heat or electricity is considered as renewable energy source. Solar energy has been used to heat homes and water, and modern technology such as photovoltaic cells has provided a way to produce electricity from sunlight.
There are two basic forms of radiant solar energy use: passive and active. Passive solar energy systems are static and do not require the input of energy in the form of moving parts or pumping fluids to utilize the sun’s energy. Buildings can be designed to capture and collect the sun’s energy directly. A southern exposure greenhouse with glass windows and a concrete floor is an example of a passive solar heating system.
Active solar energy systems require the input of some energy to drive mechanical devices such as solar panel, which collect the energy and pump fluids used to store and distribute the energy. Solar panels are generally mounted on a south or west-facing roof. A solar panel usually consists of a glass-faced, sealed, insulated box with a black matte interior finish. Inside are coils full of a heat collecting medium such as water. The sun heats the water in the coils, which is pumped to coils in a heat transfer tank containing water. The water in the tank is heated and then either stored or pumped through the building to heat rooms or supply hot water to taps in the building.
Photovoltaic Cells: A group of cells are linked together to provide the required flow of current. The electricity can be used directly or stored in storage batteries. Because photovoltaic cells have no moving parts, they are clean, quiet, and durable. The recent development of inexpensive semiconductor materials has helped greatly to lower the cost to the point where solar electric panels can compete much well cost wise with traditionally produced electricity.
Hydroelectric Energy: Hydroelectric power is generated by converting the kinetic and/or pressure energy of water into shaft power (mechanical work) producing electricity with the help of generator. Hydroelectric power is generated with the help of dams across the rivers. A dam built across river creates a reservoir. The head of the water behind the dam is greater than that below the dam, representing stored potential energy. When water flows down through the penstock of the dam, the potential energy is converted into electricity driving the turbines coupled with generator.
Wind Power: Wind is the result of the sun’s uneven heating of the atmosphere. Warm air expands and rises, and cool air contracts and sinks. This movement of the air is called wind. Wind has been used as an energy source for long time. It has been used to pump water, to power ships and to mill grains. Areas with constant and strong winds can be used by wind turbines to generate electricity. The major drawbacks of wind-powered generators are they require lots of open lands and a fairly constant wind supply. Windmills are also noisy, and some people consider them aesthetically unappealing and label them as visual pollution.
Biomass Energy: Biomass energy is the oldest source of energy used by human beings. It is the organic matter that composes the tissues of plants and animals. It can be burned for heating and cooking, and even generating electricity. The most common source of biomass energy is from the burning of wood, but energy can also be generated by burning animal manure, herbaceous plant material, peat or converted biomass such as charcoal. Biomass can also be converted into a liquid biofuel such as ethanol or methanol. Biomass is a potentially renewable energy source. Unfortunately, trees that are cut for firewood are frequently not replanted.
The use of biomass as a fuel source has serious environmental effects. When harvested trees are not replanted, soil erosion can occur. The loss of trees results in increased amounts of carbon dioxide in the atmosphere and contributes to global warming.
Geothermal Energy: Geothermal energy uses heat from the earth’s internal geological processes in order to produce electricity or provide heating. One source of geothermal energy is steam. Groundwater percolates down through cracks in the subsurface rocks until it reaches rocks heated by underlying magma, and the heat converts the water to steam. Sometimes this steam makes its way back to the surface in the form of a geyser or hot spring. Wells can be dug to tap the steam reservoir and bring it to the surface to drive generating turbines, and produce electricity. Hot water can be circulated to heat buildings. Regions near tectonic plate boundaries have the best potential for geothermal activity.
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