The Roncovalgrande Hydroelectric Plant, also known as the Delio Hydroelectric Plant, is located 3 km (2 mi) north of Maccagno in the Province of Varese, Lombardy, Italy. Using the pumped-storage hydroelectric method, the power plant has an installed capacity of 1,016 MW. The power plant was complete in 1971 and the last generator operational in 1973. During construction, the upper reservoir, Lago Delio, was expanded in capacity with two gravity dams; a northern and southern, 28.5 m (94 ft) and 36 m (118 ft) in height, respectively. The lower reservoir, Lago Maggiore, already existed. The power plant itself is located underground in between Delio and Maggiore. To produce electricity, water is released from the upper reservoir to the power plant via two 1,100 m (3,609 ft) long penstocks. At the power plant, eight four-stage Pelton turbine-generators generate electricity. Power generation occurs during periods of high energy demand and when energy demand is low, pumping usually occurs. The pumps are on the same shaft as the Pelton turbines and send water from the lower to the upper reservoir to serve as stored energy. In the future, this water is sent back down to the power station and the process repeats. The difference in elevation between the upper and lower reservoirs affords a hydraulic head of 736.25 m (2,416 ft) and Lago Delio has a usable storage capacity of 10,000,000 m3 (8,107 acre·ft).
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