Energy from nature

Hydropower is a classic among renewable energy sources. Its first uses were documented as early as the 4th and 3rd centuries B.C. At RWE, we have been using energy drawn from water to reliably produce electricity for over a century now, thus making an important carbon-free and economical contribution towards energy supply. In addition, hydropower is one of the few renewables technologies that is almost baseload capable and can thus provide climate-friendly electricity 24/7.

There are three main types of hydroelectric power plant: run-of-river power plants, storage power plants and pumped-storage power plants. Run-of-river hydroelectric power plants continuously generate electricity from water flowing down a river. Storage power plants can hold back some of the water and thus respond flexibly to peaks in electricity demand. Pumped-storage power plants pump water up into an upper reservoir when electricity demand is low. At peak demand times, the stored water is released back to the lower reservoir, driving turbines in the process. With their large degree of flexibility, pumped-storage power plants contribute significantly to stability in the electricity system.

And how do run-of-river power plants work?

Run-of-river power plants primarily use the natural water cycle. The feed water flows through a turbine, creating mechanical energy. The rotational motion of a shaft operates a generator that produces electrical power. This process makes use of potential energy that is created by the kinetic energy of the water. The capacity of the hydropower plants depends on the location’s geographic conditions.

Storage hydropower plants

Like run-of-river power plants, power plants with reservoirs utilise the natural downward flow of water to generate electricity. However, unlike run-of-river power plants, the water is collected in a reservoir and released at a later time. Natural lakes or river segments, for example, can be used as reservoirs. Man-made reservoirs can cover energy consumption over days, months or even years. With reservoirs, water that flows in periodically can be used to generate energy constantly and evenly or cover peak demand.

Nature as quick-response electricity storage

Pumped-storage power plants can be started up very quickly due to the technology involved. Therefore, no other power plant type is as quick and flexible as pumped-storage hydroelectric power plants, making these sprinters of energy generation the ideal systems to provide control energy for balancing out fluctuations in generation and demand on the electricity grid. This task is becoming ever more important due to the increasing share of fluctuating feed-in from renewables. Pumped-storage power plants thus ensure security of supply, in particular in the age of renewables.

Since a constant voltage and frequency in the grid is vital for supplying all electrical appliances such as refrigerators and computers with power without damaging them, this is controlled continuously by all large power plants. To this end, particularly the reactive power, the part of the electricity that is necessary to drive electric motors, for example, but is also generated by many applications unintentionally, is monitored and controlled continuously. Pumped-storage power plants are designed in such a way that they can provide reactive power control and thus take care of this element for keeping the voltage stable in the grid when running idly or in “phase-shifter mode”. Since wind turbines or photovoltaics plants can currently only perform limited reactive power control, pumped-storage power plants play a key role in integrating renewables.

The principle behind a pumped-storage power plant is as brilliant as it is simple. When supply exceeds demand, the energy can be stored and then turned into electricity when demand is high. To this end, water from a lower basin is pumped into a higher-level reservoir through a pipeline. At peak demand times or when generation from other sources is low, the water is released back to the lower reservoir through a pipeline via a turbine to generate the required electricity. All this takes place within seconds and the pumped-storage power plant can operate at full capacity, often several hundred megawatts, within a matter of minutes.

RWE’s hydropower portfolio

RWE operates hydropower plants on rivers in Germany, the UK, Portugal and Spain, with a total installed capacity of over 500 megawatts. In Germany alone, our operating team ensures that 77 turbines produce a reliable supply of energy at some 30 locations. In addition to its own 150-MW pumped-storage hydroelectric plant in Herdecke, RWE also holds shares in pumped-storage facilities in the Black Forest and in Luxembourg. Via these shares, RWE has access to 21 pumped-storage machine sets with an installed capacity of more than 2,000 MW.

RWE’s hydropower portfolio forms the backbone of renewables and is very important for us. We are making sure that these long-running and reliable systems continue to be fit for the future”.