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Renewable energy
In contrast to non-renewable energy, such as fossil fuels, renewable energy resources are constantly being replenished and will not run out. Much research is being done to investigate how we may tap into these resources in the future.
WIND
Wind energy uses the energy in the wind for practical purposes like generating electricity, charging batteries, pumping water or grinding grain. Turbines capture the wind’s energy with two or three propeller-like blades, which are mounted on a rotor, to generate electricity.
Wind Energy
Wind turbines, like aircraft propeller blades, turn in the moving air and power an electric generator that supplies an electric current. Wind speeds typically need to be sustained at a minimum of 10 miles per hour to turn the turbine fast enough to generate electricity. The turbines usually produce about 50 to 300 kilowatts of electricity each. Turbines are often grouped together, also known as a wind farm, and generate bulk electrical power. Electricity from these turbines is fed into the local utility grid and distributed to customers just as it is with conventional power plants.
BIOENERGY
Bioenergy, energy derived from organic matter, has been used for thousands of years, ever since people started burning wood to cook food or to keep warm. There are many other sources of biomass besides wood including plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes.
Biomass Energy
Bioenergy technologies use renewable organic resources, called biomass, to produce many energy related products including electricity, liquid, solid and gaseous fuels, heat, chemicals and other materials. Bioenergy ranks second – to hydropower – in renewable U.S. primary energy production and accounts for 3 percent of the primary energy production in the United States.
HYDROPOWER
Flowing water creates energy that can be captured and turned into electricity. This is called hydropower. The most common type of hydropower plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which powers a generator to produce electricity.
Hydropower Energy
Hydropower uses flowing water to create energy that can be captured and turned into electricity. Hydropower provides the largest source of renewable energy in the United States. The most common type of hydropower plant uses a dam on a river to store water in a reservoir; this is called Impoundment hydropower. Water released from the reservoir flows through a turbine, spinning it, which activates a generator to produce electricity.
1. Dam
A barrier built across a watercourse to hold back the flow of water and create a reservoir. The reservoir that is formed is, in effect, stored energy.
2. Penstock
A pipeline used to convey water, under pressure, from the reservoir to the turbines of a hydroelectric plant.
3. Turbine
A machine that is turned by the force of the fast moving water pushing against its blades. Turbines convert the kinetic energy of the water to mechanical energy.
4. Generator
Connects to the turbine and rotates to produce the electrical energy
5. Transformer
Converts electricity from the generator to usable voltage levels.
6. Transmission lines
Conduct electricity from the hydropower plant to the electric distribution system. Transmission line voltages are normally 115 kilovolt or larger.
GEOTHERMAL
Geothermal energy technologies use the heat of the earth for direct-use applications, geothermal heat pumps and electrical power production. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of magma.
Geothermal Energy
Geothermal energy technologies use the heat of the earth for direct-use applications, geothermal heat pumps, and electrical power production. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface and down even deeper to the extremely high temperatures of molten rock called magma.
Three power plant technologies are being used to convert hydrothermal fluids to electricity. The type of conversion used depends on whether the fluid is steam or water and its temperature.
SOLAR
Solar technologies use the sun’s energy and light to provide heat, light, hot water, electricity and even cooling, for homes, businesses and industry. There are three kinds of concentrating solar power systems that are classified by how they collect solar energy: the photovoltaic system, the water heating system and the concentrating solar power system.
Solar Energy
Solar energy can be harnessed and used to generate electricity, provide hot water and to heat, cool and light buildings. There are three types of systems that tap into solar energy: concentrating solar power system, the photovoltaic system and the water heating system.
1. Concentrating Solar Power System
Concentrating solar power plants produce electric power by converting the sun’s energy into high-temperature heat using mirror configurations. The sunlight is concentrated by parabolically curved mirrors onto a receiver pipe that runs along the inside of the curved surface. The sun’s reflected energy heats oil flowing through the pipe and the heat energy is then used to generate electricity in a conventional generator. A collector field comprises many troughs in parallel rows aligned on a north-south axis to track the sun from east to west during the day. Individual trough systems currently can generate about 80 megawatts of electricity. Some systems use thermal storage during cloudy periods or at night to continue electricity production.
2. Solar Cell System (Photovoltaic)
Photovoltaic cells convert sunlight directly into electricity. When energy from the sun comes in contact with the cell, electrons in the two different semiconductors absorb the energy and use it to move around, creating an electrical current. Photovoltaic cells that are linked together to create a useful energy flow are called modules, which hold about 40 cells. About 10 of these modules can be mounted together to form a large array. Arrays can be used to generate electricity for a single building or, in large numbers, for a power plant.
3. Collector
The energy emitted from the sun is used to heat water. Solar water heating systems for buildings have two main parts: a solar collector and a storage tank. Typically, a flat-plate collector – a thin, flat, rectangular box with a transparent cover – is mounted on the roof, facing the sun. The sun heats an absorber plate in the collector, which, in turn, heats the water running through tubes within the collector.
4. Water Pump and Tank
To move the heated water between the collector and the storage tank, a system either uses a pump or gravity, as water has a tendency to naturally circulate as it is heated. Systems that use fluids other than water in the collector’s tubes usually heat the water by passing it through a coil of tubing in the tank. Solar water heating systems can be used to provide more than just hot water – they can actually be used to heat or cool a building. A solar ventilation system can be used to heat air or to provide energy for cooling a building.
OCEAN
The ocean harbors two types of renewable energy sources that can be harnessed in very different ways. Oceans cover more than 70 percent of Earth’s surface, making them the world’s largest solar collectors. Ocean thermal energy can be used to power a turbine, producing energy for many applications. Tides and waves are intermittent sources of energy. Tidal energy can be used to make electricity by forcing the water through turbines, activating a generator. Wave energy conversion can be done through one of three basic systems: channel systems that funnel the waves into reservoirs; float systems that drive hydraulic pumps; and oscillating water column systems that use the waves to compress air within a container. The mechanical power created from these systems either directly activates a generator or transfers energy to a working fluid – water or air – which then drives a generator.
HYDROGEN
Hydrogen is a simple element – an atom with only one proton and one electron. It is also the most plentiful element in the universe. Despite its simplicity and abundance, hydrogen doesn’t occur naturally as a gas on the Earth – it is always combined with other elements. Water, for example, is a combination of hydrogen and oxygen. Hydrogen can be separated from hydrocarbons by applying heat, a process known as “reforming” hydrogen. Hydrogen is high in energy, yet an engine that burns pure hydrogen produces almost no pollution. NASA has used liquid hydrogen since the 1970s to propel the space shuttle into orbit. Hydrogen fuel cells produce a clean byproduct: pure water.
http://www.cbsnews.com/stories/2004/06/29/tech/main626647.shtml