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Water energy: flow becomes electricity
Water energy was already used as a means of propulsion in ancient Rome. Today, hydropower supplies more than half of the electricity from renewable energies worldwide. But how exactly does that work?
Hydropower: This is how hydropower generates electricity
Water energy can be used in many different ways to generate electricity. Most hydroelectric power plants work with turbines. The power of the water propels them so that the water energy is converted into kinetic energy. A connected generator then converts this kinetic energy into electrical energy. Hydroelectric power plants generate electricity in rivers and dams as well as in the sea. The individual power plant types differ greatly from one another.
Hydro energy is therefore one of the most important renewables
If we look at the global share of regenerative energy sources, water energy is far ahead. In 2020, 69.87 exajoules of electricity from renewable energies were consumed worldwide. This corresponds to approximately 19.4 trillion kilowatt-hours. Water energy has a share of 38.16 exajoules, i.e. around 54.6 percent. This means that in 2020 more than half of the electricity consumption from renewable energy sources worldwide will come from hydropower. The role of water energy in the global energy transition is therefore particularly important.
Hydroelectric power plants: water energy is used in so many different ways
Water energy comes in a variety of forms. In order to use the natural currents of the sea to generate electricity, other power plants are required than dams. The following power plant types are among the most important in the world.
Storage power plant
Storage power plants are often built on lakes or reservoirs. The lake's water flows in a controlled manner through turbines to generate electricity. This is often achieved by using a natural slope or one artificially created by dams. Because the water is stored in the lake before its power is used to generate electricity, this type of power plant is called a storage power plant. A special form of this is so-called pumped storage power plants. In this case, pumps are used to refill the water reservoir during off-peak hours. Since only a little electricity is consumed during off-peak periods, excess wind energy, for example, can provide the electricity required for the pumps in a climate-friendly manner. In this way, lakes become important batteries for a stable power supply.
Run-of-river power station
Run-of-river power plants are used to convert the water energy from rivers into electricity. The river water flows through water turbines to generate electricity. In contrast to storage power plants, the head of the water in run-of-river power plants can hardly be increased. Differences in height can only be realized by means of weir systems.
Wave power plant
A wave power plant uses the wave energy of the sea. The principle behind it is sophisticated because air flows through the turbines of such a power plant instead of water. To do this, vertical columns are installed that contains air above the water surface. The ebb and flow of sea waves alternately pushes the air up and pulls it down again. This airflow moves a turbine, which then transmits its movements to a generator to generate electricity.
Tidal power plant
A tidal power plant works in a similar way to a storage power plant on a dam. A dam is also being built here. The difference: the dam for a tidal power plant usually separates a bay from the open sea. The water can only pass through the dam through turbines. Due to the ebb and flow of the tide, the turbines move with both rising and falling water and therefore make optimal use of the water energy of the tides.
Ocean current power plant
The structure of an ocean-current power plant is almost reminiscent of a wind turbine installed upside down. There is a rotor underwater that is moved by the flow energy of the sea. This kinetic energy is then converted into electrical energy by a generator.
Osmosis power plant
In an osmosis power plant, different salinity levels in freshwater and saltwater provide the water energy to generate electricity. The principle sounds complicated at first, but it is very simple. Because nature always wants to create a balance. When salt water and fresh water meet, they mix until the salt content is the same. In osmosis, a membrane that is only permeable on one side acts as a kind of filter: Only the small water molecules can flow through the membrane, and salt molecules are too large for the openings.
So if you equip a tank with such a membrane, fill it with fresh water on one side and salt water on the other side, then water will flow from the freshwater side to the saltwater side to dilute the salt water until it's just as salty as the fresh water on the other side. This increases the pressure on the saltwater side because the membrane is only permeable on one side. And this pressure created by water energy is used in an osmosis power plant to drive a turbine and ultimately generate electricity.