When it comes to sustainable energy supply, hydroelectric power plants are playing an increasingly important role. They use the mechanical energy of flowing or falling water to generate electricity. But how does a hydroelectric power plant actually work?
Hydroelectric power plants have a long tradition in Germany. They are one of the oldest methods of generating renewable energy. In fact, people have been using the power of water for more than 5,000 years. In the past, water pressure in rivers was used to drive millstones, for example.
Today, hydropower covers more than 16 percent of the world's electricity needs. There are 7,300 hydropower plants in Germany. Together, they have an installed capacity of around 5,600 megawatts. Most hydropower plants are located in Bavaria and Baden-Württemberg. They account for around 80 percent of all German hydropower plants.
How does a hydroelectric power plant work?
Hydroelectric power plants generate electricity using water. The energy of the flowing water – also known as fluid mechanical energy – drives turbines. This creates rotational energy. Generators then use this energy to generate electricity.
The efficiency of hydroelectric power plants is up to 85 percent, which is significantly higher than that of other types of power plants. There are four common types: air-hydro power plants, water storage power plants, pumped storage power plants and tidal power plants.
How run-of-river and storage power plants generate electricity
Run-of-river power plants use the natural flow of a river. The amount of electricity generated depends on the water mass and the head, which is why rivers are often dammed by weirs to increase the height difference and improve efficiency.
Because the bigger the difference, the higher the efficiency. The turbine is driven by a continuous flow of water, which enables constant power production. The generator transforms the energy of the rotational movement into electricity.
At a Storage power plant A dam or a retaining wall stores large amounts of water. This creates reservoirs to store water. Additional water often flows from surrounding rivers into the reservoirs via tunnels. If necessary, the water can be piped to the lower engine house. There it hits a turbine at high pressure and drives a generator.
How pumped storage power plants and tidal power plants work
Pumped storage power plants use excess energy to pump water from a lower basin to an upper one. This stores potential energy. When there is a need for energy, the water is returned to the lower basin. In doing so, it drives turbines that generate electricity. This form of hydroelectric power plant acts as an energy store and stabilizes the power grid. It can also supply large amounts of electricity when needed.
Tidal power plants generate electricity using the tides. The currents set a turbine in motion and drive generators. At low tide the turbines rotate in one direction, at high tide the other.
The disadvantage: Tidal power plants depend on the currents and therefore cannot generate electricity continuously. Traditionally, a dam is part of the construction. This is where the turbines are installed. However, this type of construction only works with a tidal range of around five meters. The difference in height between high and low tide must therefore be correspondingly large.
Alternatively, there are also ocean current power plants. Similar to wind turbines, they have rotors that are located below the water surface. The water current sets them in motion and drives the generators to generate electricity. A large tidal range is not necessary.
Hydroelectric power plants in Germany
In 2020, hydroelectric power plants generated around 3.3 percent of the gross electricity generated in Germany. By comparison, wind energy provided 24 percent in the same period. This means that hydropower plays a rather minor role in Germany.
The amount of electricity produced in a year also depends on rainfall. In recent years, the value has fluctuated between 19 and 29 terawatt hours. That is enough for 800,000 to 1.2 million households in this country.
However, hydroelectric power plants also have some disadvantages: Firstly, the construction of dams and the diversion of rivers can have a significant impact on nature. Fish and other aquatic creatures are particularly affected by this.
In addition, the construction of the plants is expensive and time-consuming. Large projects in particular require considerable investment. Hydroelectric power plants are ultimately always dependent on natural water sources. Dry periods or changing weather conditions can affect electricity production.
Source: https://www.basicthinking.de/blog/2024/08/19/wie-funktioniert-ein-wasserkraftwerk/
