Aimed to balance run-offs from peak-load operation of the Orava HPP, the small hydroelectric power plant was constructed by the Tvrdošín balancing reservoir. The smaller of the turbo-generators has a maximum usable flow of 5 m3 sec-1, i.e. as much as required by the biological flow rate in the Orava river downstream the Orava water work, therefore it is in operation almost continuously. The larger turbo-generators are operated when inflows into the Orava reservoir are higher.
Slovenské elektrárne operates 31 hydroelectric plants. Their combined output is 1,652.7 MW, representing approximately 38.4% of the Company’s total installed capacity. Majority of the installations is located on the Váh River cascade, or the longest river in Slovakia. On average, the hydroelectric sources generate 2,070 MW annually (consumption of pumped storage power stations excluded), or some 11% of the electricity produced by Slovenské elektrárne.
Because of their very variable power output and operational flexibility, hydroelectric plants are capable to satisfy the swiftly changing demands in the daily-load diagram, pairing nicely with the base load supply covered by nuclear power plants. Slovenské elektrárne has 736.6 MW installed in river hydropower plants and 916.4 MW in pumped storage power stations.