Hydroelectric power: What is it and how does it work?

Perhaps one of the most visible renewables, the operation of hydroelectric energy and its role in energy storage are as interesting as they are unknown

Contemporary to the great Greek thinkers such as Plato and Aristotle and a fundamental instrument for the growth of the Roman Empire, hydraulic energy has been of great use to humanity for millennia. However, it was not until the rise of the industrial revolution and electrical energy that hydraulic energy took a leap of importance to position itself as a key, already converted into hydroelectric energy, in the development of societies in the 19th and 20th centuries. Today we will take a look at the past, but also at the future of this type of renewable energy; in addition to delving into how it works. Will you join us on this journey through the power of water to discover how hydroelectric energy works?

Controlling the force of nature and harnessing it to our advantage has been one of the greatest endeavors of humankind. Thus, generation after generation, we have been modifying our environment for our own benefit, primarily to ensure our survival and secondarily to improve our quality of life. The great civilizations of antiquity shaped their world to exploit natural resources to their advantage and grow thanks to them. The power of water, one of the basic elements of our planet, is no stranger to this; rather, it is the main protagonist. The Greek waterwheel, the Roman mill, or the Egyptian saqia are just a few examples of how hydraulic power was essential for tasks such as pumping water or grinding grain. While its role was important then, it became crucial with the technological and scientific explosion experienced during the Industrial Revolution of the 19th century, a time when electricity became the backbone of the development of cities and, therefore, of the economies of industrialized countries. This is when the hydroelectric energy we know today emerged.

Boosted by the development of the electric generator and the sophistication of turbines, hydroelectric power plants began to multiply in the most developed countries. Terms like “dam” and “reservoir” began to spread in citizens’ vocabulary, and plans to build large hydraulic civil works to meet the growing need for electricity emerged in Europe and America at a dizzying speed, changing the landscape of our nature. By then, a significant portion of all electrical energy came from harnessing the power of water.

Coexisting with other types of renewable generation such as wind and solar, hydroelectric power has survived to this day and remains fundamental. It is not in vain that nearly a quarter of the world’s electricity is produced thanks to their operation, with this share being tremendously higher in countries such as Norway (99%), the Democratic Republic of the Congo (97%), Brazil (96%) or Canada (60%). An example of the great importance of this technology is that some of the great civil works of our time are hydroelectric power plants such as the Three Gorges Dam (China 22,500 MW) or the Itaipu Dam (Brazil and Paraguay 14,000 MW). But do we know how hydroelectric power works?

How does hydroelectric power work?

Let’s focus on a more or less standard hydroelectric power plant. Any power plant of this type is made up of several main elements for its operation. Let’s look at them one by one:

Hydroelectric energy: Parts of a hydroelectric generation plant

Dam: It is the civil construction, mainly made of concrete, that allows the volume of water to be maintained retained for use at the disposal of the central operator. Some of the most impressive waterfalls rise hundreds of meters.
Reservoir: This is the water storage area that houses the facility and collects the water that runs through the tributaries.
Filter gates or grids: These are the moving elements that open and close to allow water to pass through them.
Passage pipes: The main arteries through which water is conducted on its way to electricity generation.
Turbines: These are the motors that power the water as it passes through, allowing mechanical energy to be generated.
Electric generators: These are the elements responsible for converting the mechanical energy of the turbines into electrical energy.
Power lines: Transport the newly generated electricity to the different points of consumption.
Drain: This is the escape route for all the hydraulic flow used during the electricity generation process.

In In short, hydroelectric power plants use the force of water falling between two points at different elevations to generate electrical energy. In other words, the entire facility operates by harnessing the force of gravity and the mass of water to the benefit of a series of mechanical elements that absorb this energy potential for subsequent conversion into electrical energy. In this sense, the water retained in the reservoir circulates through the dam’s hydraulic circuits, bridging the difference in level between the two points. This artificial waterfall, which emulates those found in natural waterfalls, allows the liquid to acquire, thanks to the effect of gravity, a speed that is transferred in the form of kinetic energy to the turbines located at the lower point of the infrastructure. Thus, the water circulates through the turbine, which accelerates its rotation, generating mechanical energy that is transferred to the electric generator for conversion into electrical energy.

However, the water leaves the facility and is drained into the lower course of the river without any virulence to the environment. This entire process also obtains an outstanding performance in which almost 90% of the water’s potential energy is used to generate electricity, generating only performance losses in the loads of the hydraulic circuit and in the friction process of the hydroelectric group (turbines).

In this way, we are able to obtain 100% renewable electrical energy, which is among the most positive, given its high level of sustainability and reuse, and which helps reduce the emission of greenhouse gases into the atmosphere. In addition, the water used in the process can be used for domestic consumption or irrigation. This type of technology, with a long useful life, is also of special interest in regulating river flows and preventing floods; a fundamental reason for the construction of the Three Gorges Dam in China, whose energy-producing purpose is combined with preventing a flood like the one that occurred in 1931 and caused millions of victims and deaths.

What types of hydroelectric power plants are there?

Due to their functionalities and locations, today we can distinguish three main types of hydroelectric power plants:

Types of hydroelectric power plants

Flowing water: This is the model that is most dependent on meteorological conditions or the flow of the river it is supplied by; since they do not have a water storage capacity, but rather use circulating water to generate energy. This means that these plants, which are mostly smaller and have a smaller capacity than the rest, cannot adapt to the needs of electrical demand. In their favor is that they do not interrupt the course of the river, minimizing the environmental impact on the surroundings.
Regulation: These are the type of hydroelectric plants that we would all think of if asked. They are based on the storage of different types of water with which to regulate their operation based on the electrical demand at any given time. These are large semi-natural energy batteries with which we are able to meet the energy needs of society, as long as water resources are adequate.
Pumped: These are regulating hydroelectric plants that are based on different levels of reservoirs at superimposed elevations to which water is pumped to generate a continuous circuit of water resources with which to generate energy.

What is the role of hydroelectric power in energy storage?

One of the great characteristics of hydroelectric power is its functionality to provide electrical energy at times of greatest demand thanks to the possibility of converting reservoirs into large energy batteries. This, which was absolutely beneficial until a few decades ago, has grown in importance with the emergence of other renewable technologies whose production flow declines due to changing weather conditions. Thus, the role of hydroelectric power has been reinforced with the arrival of pumping stations that harness surplus energy from photovoltaic or wind installations to channel the water used during the hydroelectric generation process upstream. With this, the wind or photovoltaic energy that is not fed into the grid during generation is used in these hydraulic installations to feed the infrastructure’s upper reservoirs, allowing for the use of this water resource in a renewable manner later on without wasting the wind or photovoltaic energy generated. And although the wind does not always blow in our favor nor does sunlight always shine with the necessary energy, hydroelectric power would serve as a refuge for green energy generation. This is how a reservoir becomes a gigantic battery.

A clear example of the success of this type of technology and its great growth potential can be found in the Spanish Gorona del Viento Hydroelectric Power Plant, located on the island of El Hierro (Canary Islands). This plant, which began operating in 2014, supplies 70% of the total electricity demand of this small Canary Island using a 100% renewable method; even achieving entire days in which 100% of the energy is covered by this method.