In a hydropower station, a turbine converts the kinetic energy of flowing water into mechanical energy. A generator then converts the mechanical into electrical energy. Hydropower allows the power of water in streams and rivers to be used regardless of topographical conditions – from plains to mountain ranges with heads far above 1,000 meters. This wide range of natural conditions requires the use of different, optimised types of power stations.
In a run-of-river power station, the river is dammed slightly using a weir structure upstream of the power plant. The turbines are operated continuously by the inflowing water. The generator converts the power of the flowing water into electrical enery. Energy production depends on the head, the available volume of water and the inflow at a given point in time. Flexible energy production is not possible because there is no storage system for managing the continuous inflow of water.
A pumped storage power station consists of two reservoirs – one higher up, one lower down – and the pumped storage station itself. The water stored in the upper reservoir is used to generate electricity in turbine operation. If there is an energy surplus in the grid (caused, for example, by strong winds), the station switches to pumped operation to pump the water back from the lower reservoir to the upper reservoir, where it is stored for subsequent use. Pumped storage stations thus play an important role in stabilising the power grid. The Kühtai pumped storage station is typical of this type of power station.
In a storage power station, the inflowing water is stored in a natural or man-made lake located above a power station for several hours or even months. The water is drawn off and fed to the machines in the powerhouse for electricity generation as required. The Silz storage station is a typical example of this type.
The water used in hydropower plants mostly originates from vast areas called catchment areas. The natural precipitation in these areas collects in watercourses and flows downhill – some of it directly to the power stations or the water intake structures and reservoirs above the stations. The catchment area as such – the areas above the water intake structures – is in no way affected by the power station.
A water intake is a structure used to draw supply water from a stream. No matter if water is supplied directly to the power station or is fed into a reservoir first, rock, sand, driftwood, leaves and sediment must be removed to prevent operational problems or damage to the subsequent plant sections. The Tyrolean weir, specially developed for Alpine mountain streams, reliably leaves bedload in the stream, thus permitting optimum water drawoff.
In the catchment area of a hydropower plant, water intakes are often far away from the reservoir. Collection works guide the water drawn at the weirs to the reservoir via a system of tunnels or pipes.
A headrace channel is the direct connection from the water intake in a river, stream, lake or reservoir to the powerhouse and on to the outlet channel where the water is returned to the body of water.
In a hydropower station, the turbine and generator are mounted on the same shaft assembly. This combination is called a machine unit.
A generator is a machine for electricity generation that converts mechanical into electrical energy. The generator is connected to a turbine. The kinetic energy of the turbine shaft produces electrical energy in the generator due to the movement of an electrical conductor in a magnetic field.
A turbine is a continuous flow machine that converts the flow of water into a rotary movement. In power stations, turbines are coupled with generators to utilise the rotary motion for electricity generation. The type of turbine chosen depends mainly on the available head and volume of water. The three types of turbines most commonly used today are Pelton, Francis and Kaplan turbines.
The term efficiency describes the ratio of energy output to input in energy conversion processes. In hydropower plants, friction losses occur in the pipelines, hydraulic losses in the turbines, and electrical losses in the generators and transformers. With an efficiency of 90%, hydropower is an extremely efficient way of generating electricity because up to 90% of the energy of water is actually converted into electrical energy.