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4.3 Water

Hydro power :

Hydroelectricity is from converting the potential energy of water to mechanical energy in order to generate electricity. It is the most widely used renewable energy in the world, with 26% of the Worlds electrical energy.

There are three main types of hydro plants.

  • Impoundment facilities are the most common technology which uses a dam to create a large reservoir of water. Electricity is made when water passes through turbines in the dam.
  • Pumped storage facilities are similar but have a second reservoir below the dam. Water can be pumped from the lower reservoir to the upper reservoir, storing energy for use at a later time.
  • Run-of-river facilities rely more on natural water flow rates, diverting just a portion of river water through turbines, sometimes without the use of a dam or reservoirs. Since run-of-river hydro is subject to natural water variability, it is more intermittent than dammed hydro.

How Hydroelectricity works?

(Source : https://www.studentenergy.org/topics/hydro-power Links to an external site.)

For the basic theories of generators please check Chapter 3.3 Electromagnetic Theory


Types of turbines

There are two main types of hydro turbines: impulse and reaction. The type of hydropower turbine selected for a project is based on the height of standing water—referred to as "head"—and the flow, or volume of water, at the site. Other deciding factors include how deep the turbine must be set, efficiency, and cost.

  • Impulse turbine
    The impulse turbine generally uses the velocity of the water to move the runner and discharges to atmospheric pressure. The water stream hits each bucket on the runner. There is no suction on the down side of the turbine, and the water flows out the bottom of the turbine housing after hitting the runner. An impulse turbine is generally suitable for high head, low flow applications. Types of impulse turbine include Pelton and Cross-flow.

  • Reaction turbine
    A reaction turbine develops power from the combined action of pressure and moving water. The runner is placed directly in the water stream flowing over the blades rather than striking each individually. Reaction turbines are generally used for sites with lower head and higher flows than compared with the impulse turbines.Types of reaction turbine include Propeller, Francis, and Kinetic. 
    (Source : http://energy.gov/eere/water/types-hydropower-turbines Links to an external site.)

 

Tidal/Wave power :

Tidal energy is one of the oldest way of energy generation. It is a form of energy that converts the vertical rise and fall of the tides or fast flow of water to electricity. Tides are created by the effects of gravitational forces exerted by the Sun, the Moon and the rotation of the Earth.

Tidal power can only be installed along coastlines, which often have two high tides and two low tides a day. The difference in water levels must be more than 5 meters high to produce electricity.

There are 2 main types of tidal power:

  • Tidal barrages are the most efficient source of tidal energy. A tidal barrage is a dam that utilizes the potential energy generated by the change in height between high and low tides. This energy turns a turbine or compresses air, which generates electricity.
  • Tidal fences are similar to wind turbines under water. Electricity is generated when the mechanical energy of tidal currents turns turbines connected to a generator. Since ocean water is 832 times more dense than air, ocean currents generate relatively more energy than air currents and therefore applies greater force on the turbines.

How tidal power works?

(Source : https://www.studentenergy.org/topics/tidal-power Links to an external site.)

 

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