Water Power

Thousands of years ago, long before the invention of the Periodic Table, the Ancient Greeks believed that there were four elements: earth, air, fire, and water. Everything was made from the four elements.

Modern science has moved on, but we can still liken those elements to renewable Energy Resources.

• The earth element corresponds to geothermal energy.

• The air element corresponds to wind energy.

• The fire element corresponds to solar energy.

So, the water element must correspond to water energy! How can we use Earth's water to generate power?

The Definition of Water Power

Hydropower, sometimes referred to as water power, is one of the oldest renewable energy sources. It uses the natural flow of water to produce power.

This unusual liquid has excellent potential as an energy resource. Let's explore why?

• Abundance

71% of the Earth's surface is covered by water. It can also be found underground, in the atmosphere, in rivers and lakes, in glaciers, and even in your body!

• Density

Water is 800 times denser than air. As a result, it has a high energy density.

• Movement

Water is constantly moving. Think about rainfall, flowing rivers, and tides. Constant movement results in a large amount of kinetic energy, which can be harnessed and used to generate electricity.

Fig. 1 – Oceans constantly moving: tides, waves, precipitation, and evaporation, unsplash.com.

Examples of Water Power

There are three main methods of generating electricity using power from moving water: Hydroelectric Power, Tidal Power, and Wave Energy.

Hydroelectric Power

When an object is raised, it gains gravitational potential energy. Water in upland areas has gravitational potential energy, converting it to kinetic energy when it flows downhill.

Hydroelectric dams are a popular method of generating electricity. In fact, 71% of the world's renewable energy is generated using hydroelectric technologies.

Tidal Power

The positions of the Sun and the Moon control the Earth's tides. High tides occur when the Earth is parallel to the Moon, and low tides occur when the Earth is parallel to the Sun. It takes approximately 6 hours and 12 minutes for the tides to change from high to low or vice versa.

Wave Energy

Winds blow across oceans, transferring their energy to the water. This causes the water particles to move in a circular pattern, creating waves. The energy of a wave is dependent on its height.

Water Power Plants

A power plant sometimes referred to as a power station, is generally connected to an electrical grid. Mechanical power is converted into electricity. In this case, the kinetic energy comes from the motion of water and is, therefore, a low-carbon, renewable power source.

Let's go into further detail about how hydroelectric, tidal and wave energy are harnessed so that they can generate power.

Hydroelectric Power Plants

Most hydroelectric power plants are impoundment facilities. These plants use a dam to control the flow of river water downhill. When energy is needed, water is released from the dam. The water flows downwards due to the force of gravity, where it travels through turbine blades. The movement of the turbine blades drives an electrical generator, converting the kinetic energy into electricity.

Hydroelectric power can be harnessed to meet fluctuations in energy demands. Water stored above the dam in an upper reservoir holds a large amount of potential energy, which can be rapidly converted to electricity when required by releasing the stored water. The hydroelectric power plant then operates in the same way, generating electricity during peak times such as the weekend or evenings.

Fig. 2 – The Srisailam Dam, India. The water of the Krishna River is trapped behind the dam and forced through turbines to generate electricity, unsplash.com.

Tidal Power Plants

Tidal power plants harness the energy produced by the surge of ocean waters. There are three kinds of tidal power plants. All three types force water through turbines. The movement of the turbines powers generators that convert their kinetic energy into electrical energy.

• The first kind of power plant is a tidal barrage. These are large, dam-like structures built across bays and estuaries. Barrage gates trap water at high tide, forcing it through turbines to return to the sea.

• Another kind is tidal lagoons. These are bodies of water partly enclosed by a barrier, which can be natural or artificial. They function like a tidal barrage, Trapping water and controlling its release through turbines.

• The final kind of tidal power plant is an in-stream turbine. These are placed directly into a tidal stream (a fast-flowing current created by tides). These currents often occur in straits or inlets, where land masses funnel the water.

Tidal barrages and tidal lagoons control the flow of water through turbines. This enables the power plant to respond to surges in energy demand by releasing water.

Wave Energy Plants

There are five main types of technology used to generate power from waves.

1. Absorbers are floating structures that extract energy from movements on the surface. The kinetic energy is converted to electricity using linear or rotary generators.
2. Oscillating water columns are partially submerged structures. When waves travel in and out, it forces air through turbines at the top of the structure. Movement of the turbines powers a generator, converting their kinetic energy into electricity.
3. Attenuators have hinged 'arms', extracting energy from their relative movements. They are connected to hydraulic pumps, which convert the kinetic energy into electricity.
4. Overtopping devices function like tidal barrages, Trapping water and releasing it through turbines. Movement of the turbines powers a generator, converting their kinetic energy into electricity.
5. Oscillating wave surge converters have a hinged paddle, extracting energy from its relative movement. The paddle's motion drives hydraulic pumps, which power generators to convert kinetic energy into electricity.

Advantages of Water Power

Water power can be generated in different ways, but all three water power technologies have similar advantages.

Disadvantages of Water Power

No form of energy generation is perfect. Water power is no exception, below are the drawbacks to this renewable source of energy.

^{1. Emilio F. Moran, Sustainable hydropower in the 21st century, Proceedings of the National Academy of Sciences, 2018}

^{2. Lynn Laymon, Water World, Dive Training, 1998}

^{3. Water Science School, How Much Water is There on Earth?, USGS, 2019}