NOVELTY - An energy accumulation system (1) has at least one reservoir (2) for storing sea water elevated above sea level and located near a sea shore, preferably a sea or ocean coastal line (3), at least one turbine (5) located below the level of the reservoir and mechanically connected to at least one hydroelectric generator (6), and at least one conduit (80) connecting the reservoir to the turbine. The downward flow of sea water from the reservoir through the conduit engages with and rotates the turbine and generator so as to produce electricity.    USE - Energy accumulation system for storing large quantities of potential energy that can be released on demand and converted into electrical energy.    ADVANTAGE - The system is capable of storing large amounts of energy that can be released on demand, preferably within minutes of the request for energy being received, enabling the system to provide power levels that could be substantial by comparison with the entire power peak power requirements for a particular region, as well as provide power levels for durations of one hour or more that is comparable to or longer than typical durations of peaks in power consumption. Using the energy accumulation system with power generation stations such as coal or gas power plants reduces demand on such stations during peak electricity demand times, as well as reduces or moderates increase in installed capacity of the power generation stations so as to reduce cost of electricity generation in the jurisdiction. Using the system also reduces dependence of island regions on imported fossil fuels and allows for increase in number of electricity users that can be supplied with power from existing power generation stations and still meet the peak power demand. The system also facilitates introduction of the greater fraction of energy from renewable sources e.g. wind, into the electrical power grid, making the system clean to operate. The system can be easily constructed at low cost using the natural terrain of an island region. The system also allows for convenient visual inspection of all key system components, and can provide cranking power to restart even unrelated facilities of the users that lose power due to storms or blackouts. The system uses an energy storage medium having higher gravimetric density than the one utilizing fresh water, providing the system with higher energy storage density.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) a sea water reservoir for use in an energy accumulation system;    (2) a method of accumulating energy;    (3) a system comprising the energy accumulation system and a device for supplying energy required for a production process; and    (4) a method for construction of a dam in an energy accumulation system.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of an energy accumulation system.    Energy accumulation system (1)    Reservoir (2)    Sea or ocean coastal line (3)    Turbine (5)    Hydroelectric generator (6)    Conduit (80)