ALTERNATIVE ENERGY
by Mark Ringland , Year 9
SOLAR ENERGY
The Earth receives a tremendous amount of energy from the sun every day, but we don't use much of it. Space vehicles and satellites use solar cells, which convert sunlight into electricity. Calculators can also be powered by solar cells. We could cover part of the Sahara Desert with solar cells would produce electrical energy but the making of the cells and the installation would cost too much.
This is part of a solar energy display near Los Christianos, Tenerife. The large circular dish collects the solar energy and reflects it to a focus. The concentration of solar energy at the focus gives sufficiently high temperatures to cook food. The long tubes alongside the dish show another way to absorb solar energy. The black tube will absorb energy at a greater rate than the white tube. This is because dull, black surfaces are the best absorbers of radiation. Normally a set of these tubes would be filled with water , and form part of a heating system for a building. A typical solar heating system installed on to roofs of many houses in the Mediteranean countries is shown on the left. Notice the storage tank above the black solar collector.
BIOMASS
Some of the sunlight arriving at the surface of Earth is absorbed by plants. The process of photosynthesis converts the solar energy into carboydrates (food) for the plants. We then use this biomass, when we burn wood and when we eat plants and fruits. Rotting plants can produce a poisonous gas called methane, which is the same natural gas we use for cooking. An advantage of biomass occurs in Brazil where they grow sugar cane to produce alcohol. This alcohol is used for the fuel in cars instead of petrol.
WIND ENERGY
Wind Energy also comes from the Sun, this is because the Earth is heated unequally in different places aroind the world . This uneven heating causes air movement, and air movement is wind ! The modern windmills are extremely efficient but about 2000 wind turbines would be needed to provide as much power as one of the modern power stations
This shows a number of turbines in Tenerife, one of the Canary Islands
WAVE ENERGY
Waves are caused by wind blown across the sea's surface. The wind blowing across the sea contain lots of kinetic energy, which can be absorbed by devices which rock up and down in the sea.
One method of getting this free energy is to use huge floats which float up and down with the waves. The movement of this float convert the free energy into electricity. The comparison between 1 power station and a float is 1 power station to 20 kilometers of floats.
HYDRO-ELECTRICITY
Dams collect rain water. The water is then allowed to go through a turbine, where the kinetic energy of the water is converted to rotational kinetic energy. The roational kinteci energy of the turbine is then used to drive generators. The rotation of coils within a magnetic field generates electricity. This method is very clean and useful source of energy for mountainous regions. At night when the demand for electricity is low, the water can then be pumped to where it started using spare electricity so it can be used again to produce energy .
The Hoover Dam. on the Arizona/Nevada border. First started generating electricity in 1936. By 1961 the final generating unit, N-8, started to operate . This gave the total installed generating capacity of the powerplant as 1,334,800 kilowatts. The water to the right of the dam forms the start of Lake Mead, which is over 120 miles long. The project gave new hope and promise for those living in nearby desert conditions, and gave them valuable water supplies throughout the year. The control of the water resulted in an elimination of drought and flood conditions. The Colorado River levels changed dramatically before the installation of the Hoover Dam. Now, Arizona and Nevada could have a more controlled and regular supply of water, and water to irrigate the land for the growth of crops. Lake Mead is now a haven for all those interested in the outdoor life, and offers numerous recreational and sporting opportunities, through the provision of tourist centres, camping sites and small towns that now thrive around the lake.
TIDAL ENERGY
As the moon circles the Earth it pulls on the seas causing a regular variation on tide heights. If a dam is built across a estuary it traps the water at high tide. Then when the water is at low tide it is allowed to fall back through the dam generating electricity. The kinetic energy of the water is converted into electrical energy.
GEOTHERMAL
The inside of the Earth is very hot. In certain places the heat is easy to obtain ,since the hot rocks are near the surace . In some parts of the world hot water comes to the surface naturally. In other countries cold water is pumped down deep holes and the hot rocks heat the water. The water heats rapidly under pressure, and hot steam comes back to the surface. The steam is then used to drive turbines. The turbines drive generators, where the kinetic energy is converted into electrical energy.