Initially the power station was to serve as a power accumulator for the nearby Żarnowiec Nuclear Power Plant being constructed in the nearby Kartoszyn. The upper reservoir is one of the largest elements of the power plant. Fully manmade, the reservoir accumulates electrical power in the amount of 3.6 million kWh. The amount of water provides enough power to feed 716 MW to the electrical system for about 5.5 hours. The peak demand for power in the Pomeranian Voivodeship is 600 MW (winter evening peak). Comparing those two values gives a sense of the importance of the Żarnowiec hydro plant as a power source. When drained, the bed of the reservoir would have enough room for 130 football pitches, and replenishing the water in the upper reservoir requires about 6.5 hours.
Water is directed to pump-turbines by four pipelines, each 1,100 m long. Their diameter ranges from 7,100 mm by the inlet chamber and 5,400 mm in the power plant. The maximum water flow through the four pipelines is 700 m3/s, i.e. as much as the annual average flow of water in the Vistula near Warsaw.
The power plant is an over-60-m-high building, two thirds of which is located underground. There, 17 metres below mean sea level, four turbines with 6-metre-diameter rotors propelled by water masses provide power to the hydrogenerator, whose rotor weighs more than 420 tonnes. Installing it required an excavation, which reached 33 m below mean sea level. During construction it was the greatest depression in Poland.
The operation of the station is fully automated, and individual components are launched and turned off remotely from the National Electricity Supply Board in Warsaw. On average, the components operate for about 18,000 hours every year, each turning on twice in a day, which gives a total amount of annual starts of about 3,000. The outlet channel is a manmade construction that connects the power plant to Żarnowieckie Lake. It is 835 m long. It reaches its greatest depth – 13 m – by the power plant, and the width of the bed 250 m to the outlet of Lake Żarnowieckie.
The natural lower reservoir of the power plant is Lake Żarnowieckie. Its total area is 1470 ha, and capacity 121mln m3. Along the entire length of the lake, from south to north, runs the river Piaśnica. From the western side the Struga Bychowska flows into the lake. The greatest depth of the lake is 19.4 m. The level of the water table in the lake changes with the working cycle in the plant, and the difference between the highest and lowest level is about 1 metre.
Autor: P.Syrocki, Starostwo Powiatowe w Wejherowie
Foto: B. Trepiński, Starostwo Powiatowe w Wejherowie