Hydropower is energy extracted from flowing water. The currents can be found in streams, or created by temperature differences in the world's ocean or as tidal currents. Even artificial streams can be used.
What is commonly used in hydropower is the recovery of the state energy that water has had in its natural cycle through solar-evaporation followed by precipitation in higher-lying land areas. Water from rain or melted snow accumulates in rivers and lakes. When the water from a dust flows down to the turbine, the force defined by the level difference in meters between the water surface in the pond and the bottom of the power plant and the flow of water in cubic meters per second are recovered. The energy is transformed into a water turbine into mechanical energy that drives a generator that generates electrical energy.
Until the mid 1800's, hydroelectric power was used primarily by placing water wheels in racks and falls for driving, for example, mills such as ground grain or as a source of power for hammers and other direct-driven machines. During the 19th century, a rapid development of all more efficient water turbines took place. During the last decades of the 19th century, the electrical transmission also developed, so that the hydroelectric power was able to supply plants and consumers with power at locations far from the power plant itself.
About 85% of Sweden's watercourses are expanded with hydropower. In total there are around 1900 hydroelectric power plants in Sweden, of which approx. 3% fishing routes or bypasses In Sweden there are still no legislation that obliges the developer to build fauna passages.
Water power is adjustable and can be quickly adapted to the changes that occur in the consumption of electricity. The ability to quickly regulate hydroelectric production is an important part of expanding wind power to a greater extent throughout northern Europe.