Kruonis pumped storage plant successfully operates in the Baltic region. Initially the plant was built for Ignalina NPP. Nowadays the capacities of renewable energy sources are increasing and it may cause a necessity to improve electrical energy storage options. In a liberalized power market it is up to the owners of RES plants to construct storage solutions. Alternatively, it can be done by enterprises willing to provide balancing and other grid services. Energy storage plants can be classified in large-scale, i.e. those that affect the whole power system, and small-scale - providing services to certain its elements, e.g., particular consumers or generating sources.