Moving water contains a lot of energy that can be used to generate electricty - this if often called hydro-power or hydro-electricty.
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Using rivers to generate electricity
Using oceans to generate electricity Using rivers to generate electricity
The energy within rivers is harnessed by building hydro-electric dams. A hydro-electric dam is constructed to create a reservoir of water high above sea level.
The water then flows downhill and is channelled to turn a turbine at a lower height. The turbine drives a generator to produce electricity.
Electricity cannot be stored permanently and must be used quickly after it is generated. Hydro-electric dams solve this problem by controlling the flow of water and generating electricity only when it is needed.
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Using oceans and seas to generate electricity
Waves, tidal surges and the heat collected by oceans from sunlight are sources of renewable energy. They are increasingly being used to generate electricity.
Wave energy
Wind blowing across the ocean surface creates waves. Waves move up and down in deep areas of the ocean and result in surges near the shore. In recent times different technologies have been developed to capture the energy produced by waves. While these technologies work in different ways, they all use the energy of waves to drive turbines and generate electricity.
Tidal energy
Tides are the result of the gravitational pull of the moon. Tidal sizes are different depending on the time of the year and the place they happen. A tide can rise for fifteen meters or more depending on seasons, shape of the coastline and the ocean floor.
Capturing water in an enclosure at high tide and using its energy to turn a turbine when it recedes at low tide is a way of generating electricity. Daily changes in the tidal energy make this method a less reliable way of generating renewable energy.
Ocean heat energy
Oceans are the largest collectors of the sun’s heat on earth. At the tropics, surface temperatures can reach 26C while a few hundred meters below, temperatures are near freezing. This difference in temperature can be used to generate electricity.
Warmer water is used to vaporise a working fluid such as ammonia and the vapour drives a turbine. The cold water pumped from the lower layers then condenses the vapour back to a liquid and the cycle continues.
Because of small temperature differences in the water, a large amount of water needs to be moved to do this. This can decrease the efficiency of the process.
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