The vertical distance through which the water falls.
This is called the "head"Hydro-electric power plants take the kinetic energy from falling water and convert it into electriaity. The energy in water comes from the sun and so is always being renewed. The energy that is in the sun's rays evaporates water from rivers, lakes, streams and oceans and this falls on the land in the form of rain. Land elevations result in rainfall runoff and allow the original solar energy to be used as hydro-electric power. (Figure 1)
Hydro power accounts for around 15% of the world's electricity, and is the worlds largest renewable energy source. In Canada, hydro supplies over 60% of our energy needs. Thought of as a clean, cheap source of energy, hydro plants being planned are coming up againts great opposition from various environmental groups.
Early hydro power plants were much more efficient then the fossile fuel plants. For this reason, many small to medium sized hydro plants started to spring up anywhere there was a supply of moving water and a need for energy. As the demand for more and more energy soared in this century and the efficienicy of fossile fuels grew, these small plants started to die out. Today, hydro power focuses on large mega-plants.
These plants involve the daming of water sources casuing flooding of vast areas of land to provide water storage. In the last few years the impacts of these large hydro projects have become a cause for concern. Opposition from envirnmentalists and the people living on the land being flooded have made it next to impossible to build new dams.
Hydro-electric power plants take the energy from water falling through a vertical distance, and turn this energy into electricty. The falling water is brought through a turbin that converts the water's energy into mechanical power. The turning of the water turbins is transferred to a generator which makes the electricity. Two factors determine the amount of electricity that can be made at a hydro plant.
The vertical distance through which the water falls.
This is called the "head"
The flow rate, measured in volume per unit time.The electricty produced is shown by the equation:
In this equation, FLOW is in cubic meters per second and HEAD is measured in meters.
With this, hydro power plants can be divided into two categories. The most common are the "high head" power plants, these use a dam to store the water at a high elevation. The dam also provides the ability of storing water during rainy peeriods and giving it out during dry periods. All this results in a reliable production of electricity that can meet energy demands. The heard for this kind of plant can be over 1000 m.
The other type are "low head" hyrdo plants, that usetilze heads of only a few meters or less. These types may use a low dam to channel water, or no dam at all and use the "run of the river". However, run of the river hydro plants cannot store water and so their output can vary with the flows of the water.
Hydro electric plants have many environmental effects. However, these must be compared against the impacts from burning coal or oil or other tradinational forms of energy. Hydro plants do not give off any of the "greenhouse gases" and there is no risk of radioactive contamination.
Recent studies of large reservious made from hydro dams have suggested that the decaying vegeation submerged by water, may give off gases equivalent to the gases from tridational forms of electricity. If this is true, hydro facilities could be large contributors to global warming and acid rain.
One environmental impact of hydro-electirc plants is the flooding of large areas of land to form reserviors for water. Much of this land is forested before it is submerged. These large reserviros can be used for adequat water, irrigation, and recreation, but they also flood the homes of native peoples and threaten rare ecosystems.
Hydro-electric power plants have played a major role in the world's energy supply. Hydro power is inexpensive, reliable, and has environmental impacts which are not as devestating as those from fossile fuels. Whatever lies ahead for the future of alternitive energy, hyrdo-electric power will play an important part.
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