What is hydropower and how does it work?
Water is the most widely used renewable energy source worldwide and a technology that continues to grow. It guarantees safety, efficiency, and sustainability. So, what is hydropower, and how does it work?
Water is one of the main sources of life, and also of energy, an inexhaustible energy as long as there is water in rivers, lakes and even the sea. The use of mechanical energy generated by the force of water began thousands of years ago, to move grain mills and water wheels for irrigation or channeling. The generation of electricity using water, which began in the last decades of the 19th century, has expanded rapidly worldwide. One of the reasons for its success is that it has an energy conversion capacity of up to 90 per cent in the latest systems, making it the most efficient renewable energy source.
Hydropower is the main renewable source, accounting for more than half of green energy production and providing around 15% of the world's total energy, making it essential to the decarbonisation strategy. The world's installed capacity for hydroelectric power was 1,416 GW in 2023, on an equal footing with solar energy, which has grown exponentially in recent years. However, hydropower can still produce more and continues to grow with new technologies that increase efficiency and protect water resources.
How do we turn water into energy?
The basic principle of hydroelectric energy production has remained unchanged for practically ever, depending on the kinetic force of water. What changes is how it is captured and harnessed. Some systems utilise the current of a river as it passes, others take advantage of the force and rise of the tides, but the most commonly used are dams, which create a reservoir of water ready to be used according to energy needs. The process that enables this transformation is as follows.
In conventional hydroelectric power stations, the water is usually stored in a reservoir, created by the construction of a dam, at a level much higher than the level at which the power generating units are located. This stored water is collected in a water intake and channelled to the hydroelectric plant through a hydraulic circuit or forced conduit.
Along the way, the water picks up speed due to the drop caused by the difference in elevation, transforming potential energy into kinetic energy.
This flow of moving water reaches the turbine, causing it to rotate at high speed and transforming kinetic energy into mechanical energy which, in turn, is used to turn the generator.
And it is here, in the generator, that the principle of electromagnetism takes place - its movement creates a magnetic field that ‘gives birth’ to electrical energy. The energy produced is conducted to a transformer that raises the voltage, thus preparing the electric current to be routed through kilometres of electrical transmission and distribution lines. As for the water that has passed through the turbine, it is returned to the river, downstream of the dam, and then follows its course.
Hydroelectric power stations usually have several generator sets (turbine + generator) and are an essential aid to balancing the electricity grid, because they can move very quickly from inactivity to maximum production, and vice versa, and can also vary the load very easily.
Pumping increases flexibility
A system that is gaining more and more significance in hydroelectric power is the introduction of the pumping component, a technology present in several of EDP's hydroelectric power stations. Our plants of this type use reversible generator sets. In other words, the groups can work in one direction to produce electricity and in the opposite direction, consuming energy from the grid to lift the water downstream from the dam back up to the upstream reservoir, ensuring more storage for new energy production.
The reservoir of a dam is like an energy storage system, a huge battery that can also be ‘charged’ by pumping water.
Pumping takes place when there is a surplus of energy in the grid, and can also take advantage of other renewable energy sources, such as solar photovoltaics or wind farms, to feed the system. This makes the process even more efficient and increases the flexibility of the electricity system. It's also a way of making better use of an increasingly scarce resource, helping to keep ecosystems protected.
EDP has dams in three countries
There are tens of thousands of dams all over the world, from micro-plants used to power homes and businesses, to large-scale projects that create huge artificial lakes and can feed thousands of people. The world's largest power station, the Three Gorges Dam is in China and has a capacity of 22.5 GW. EDP's Alqueva power station, with 520 MW, stands out mainly for the body of water it has created. The artificial lake of the Portuguese dam covers an area of 250 square kilometres and is the largest in Europe.
EDP has 67 dams in operation in Portugal, Spain and Brazil, totalling an installed capacity of 7.5 GW, which represents 30% of the Group's renewable capacity. Hydropower is a key segment for the company, subject to constant innovation. The greatest example is the hybridisation achieved between the Alqueva hydroelectric power station and the floating solar power station installed on the reservoir of this project, which takes advantage of the existing infrastructure, as well as the same connection point to the grid. The Alqueva floating solar power station was installed following the success of a pilot project at the Alto Rabagão dam.
Hydropower generation and beyond
Hydropower is not limited to dams, but it is the main part of this productive sector. In addition to energy production, hydroelectric power stations fulfil various other needs and support the entire ecosystem around them. Dams serve as water reservoirs for human consumption and irrigation, increase security against periods of drought or flooding, serve as habitats for plants and animals, and enable the introduction of other activities such as fishing, water sports or tourism.
