In ruslovy and dam hydroelectric power stations the pressure of water is created by the dam which is partitioning off the river and raising water level in the river. Thus inevitably some flooding of the valley of the river. In case of a construction of two dams on the same site of the river the area of flooding decreases. On the flat rivers the greatest economically admissible area of flooding limits dam height. Ruslovy and dam hydroelectric power stations build and on the flat rivers abounding in water and on the mountain rivers, in the narrow squeezed valleys.
On hydroelectric power station with a pressure head derivation the conduit is laid with several big longitudinal bias, than at a free-flow derivation. Application of the pressure head bringing derivation is caused by convertibility of the horizon of water in the top byef because of what also the internal pressure of a derivation in use changes.
Use of tidal energy is limited mainly to the high cost of a construction PES, the cost of a construction of PES is nearly 2,5 times more, than usual river hydroelectric power station of the same power. The most important feature of hydroenergy resources in comparison with fuel and energy resources - their continuous renewability. Absence of need for fuel for hydroelectric power station defines low prime cost of the electric power developed on hydroelectric power station. Therefore to a construction of hydroelectric power station, despite considerable specific capital investments and long terms of construction, the great value, especially was attached and attached when it is connected with placement of electrocapacious productions.
The special place among hydroelectric power station is taken by hydroheat-sink power plants (pumped storage power plant) and tidal power plants (PES). The construction of pumped storage power plant is caused by growth of need for peak power in large power systems, as determines the generating power which is required for a covering of peak loadings. Peak power plant — the power plant, part or which all units work when electricity consumption sharply increases in a power supply system for a short time — at dive of loading when electricity consumption sharply increases. Units of peak power plant have to possess high operational maneuverability, ability in a short space of time, sometimes in two three minutes, to develop full capacity and also quickly to stop. Peak power plants can serve in power supply systems usual hydroelectric stations and gas-turbine power plants, and also the thermal power steam-turbine plants adapted for such operating mode.