Kruonis Pumped Storage Plant (the KPSP) is located near Kruonis, Lithuania, 34 km (21 mi) east of Kaunas. Its main purpose is to provide a spinning reserve of the power system, to regulate the load curve of the power system 24 hours a day. It operates in conjunction with the Kaunas Hydroelectric Power Plant. During periods of low demand, usually at night, Kruonis PSHP is operated in pump mode, and, using cheap surplus energy, raises water from lower - Kaunas reservoir to upper one. The station is designed to have an installed capacity of 1,600 MW but only four 225 MW generators are currently operational (fifth is planned for 2015). With fully filled upper reservoir the plant can generate 900 MW for about 12 hours.